Soil Conservation and Management [2 ed.] 3031303407, 9783031303401

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Humberto Blanco · Rattan Lal

Soil Conservation and Management Second Edition

Soil Conservation and Management

Humberto Blanco • Rattan Lal

Soil Conservation and Management Second Edition

Humberto Blanco University of Nebraska Lincoln, NE, USA

Rattan Lal Ohio State University Columbus, OH, USA

ISBN 978-3-031-30340-1 ISBN 978-3-031-30341-8 https://doi.org/10.1007/978-3-031-30341-8

(eBook)

# The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2008, 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Preface

Management and conservation of soil and water resources are more important now than ever before to meet the high demands for food, fiber, feed, and fuel production and satisfy the needs of an increasing world population. Despite the extensive research and abundant literature on soil and water conservation strategies, concerns of worldwide soil degradation, food insecurity, and environmental pollution remain high. An up-to-date and state-of-the-science textbook, for graduate and undergraduate students with emphasis on soil management to address the serious problems of soil erosion and the attendant environmental pollution is much needed. Managing soils under intensive use and restoring degraded soils are top priorities to a sustained agricultural production while conserving soil and water resources. This book differs from the first edition because it incorporates new concepts and provides an up-to-date review of soil management principles and practices. This edition also incorporates new chapters including cover crops, crop residues, soil water management, nutrient management, perennials in crop rotations, organic amendments (e.g., animal manure, biochar), and others. This textbook differs from other books in that it incorporates detailed discussions of all soil management practices (e.g., no-till systems, cover crops, diversified crop rotations, organic farming, use of perennials in agriculture, crop residues) to address soil erosion, soil physical and chemical problems, C dynamics and sequestration, non-point source pollution (e.g., hypoxia), soil health and resilience, and other relevant topics. This textbook specifically links the soil and water conservation issues with the restorative practices, soil resilience, C sequestration in contrasting scenarios of land use and soil management, and global food security. This textbook also synthesizes current information on a new paradigm of soil management. Being a textbook of global relevance, it links and applies the leading research done in the USA to contrasting scenarios of soil problems in other countries. Soil erosion history and the basic principles of water and wind erosion have been widely discussed in several textbooks. Thus, in this textbook, major attention is given to management rather than to generic factors and processes of erosion.

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This textbook is suitable for undergraduate and graduate students in soil science, agronomy, agricultural engineering, hydrology, and management of natural resources and agricultural ecosystems. It is also of interest to soil conservationists and policymakers to facilitate understanding of principles of soil erosion and implementing strategic measures of soil conservation and management. Lincoln, NE, USA Columbus, OH, USA

Humberto Blanco Rattan Lal

Contents

1

2

Soil and Water Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Why Manage Soil? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Soil Ecosystem Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Why Manage Soil Water? . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Soil Management and Population Growth . . . . . . . . . . . . . . . . 1.5 Agents That Degrade Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5.1 Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5.1.1 Geologic and Accelerated Erosion . . . . . 1.5.1.2 History of Soil Erosion . . . . . . . . . . . . . 1.5.1.3 Water Erosion . . . . . . . . . . . . . . . . . . . . 1.5.1.4 Wind Erosion . . . . . . . . . . . . . . . . . . . . 1.5.1.5 Consequences of Soil Erosion . . . . . . . . 1.5.1.6 On-Site Consequences . . . . . . . . . . . . . . 1.5.1.7 Off-Site Consequences . . . . . . . . . . . . . 1.5.1.8 What Causes Soil Erosion? . . . . . . . . . . 1.5.1.9 Erosion in the USA and the World . . . . . 1.5.1.10 How Much Soil Loss Is Acceptable? . . . 1.5.2 Tillage Erosion and Soil Loss Due to Crop Harvesting . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5.3 Soil Compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5.4 Poor Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5.5 Salinization, Sodification, and Acidification . . . . . . . 1.5.6 Soil Biological Degradation . . . . . . . . . . . . . . . . . . . 1.6 The Need for Soil and Water Management . . . . . . . . . . . . . . . 1.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 1 2 3 4 5 5 5 6 7 7 8 8 8 10 11 12

Water Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.1 Splash Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.2 Interrill Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.3 Rill Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.4 Gully Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

23 23 23 24 25 25

12 14 15 16 16 18 19 21

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2.1.5 Tunnel Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.6 Streambank Erosion . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Processes of Water Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Factors of Water Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Soil Properties Affecting Erodibility . . . . . . . . . . . . . . . . . . . . 2.4.1 Texture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.2 Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.3 Surface Sealing . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.4 Aggregate Properties . . . . . . . . . . . . . . . . . . . . . . . . 2.4.4.1 Stability . . . . . . . . . . . . . . . . . . . . . . . . 2.4.4.2 Wettability . . . . . . . . . . . . . . . . . . . . . . 2.4.5 Antecedent Soil Water Content . . . . . . . . . . . . . . . . 2.4.6 Soil Organic Matter Content . . . . . . . . . . . . . . . . . . 2.4.7 Water Transmission Properties . . . . . . . . . . . . . . . . 2.4.7.1 Water Infiltration . . . . . . . . . . . . . . . . . . 2.4.7.2 Saturated Hydraulic Conductivity . . . . . . 2.5 Measuring Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6 Agents of Water Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.1 Rainfall Erosivity . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.2 Runoff Erosivity . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7 Estimation of Runoff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7.1 Time of Concentration . . . . . . . . . . . . . . . . . . . . . . 2.7.2 Surface Roughness . . . . . . . . . . . . . . . . . . . . . . . . . 2.7.3 Watershed Slope . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7.4 Size of the Watershed . . . . . . . . . . . . . . . . . . . . . . . 2.7.5 Length and Shape of the Channel . . . . . . . . . . . . . . 2.8 Runoff Volume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.9 Characteristics of the Hydrologic Groups . . . . . . . . . . . . . . . . 2.10 Peak Runoff Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.11 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

27 28 28 29 31 31 31 32 32 33 33 34 34 34 34 35 35 37 37 39 40 40 41 41 42 42 43 44 47 48 50

Modeling Water Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Modeling Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Empirical Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Universal Soil Loss Equation . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1 Rainfall and Runoff Erosivity Index . . . . . . . . . . . . . 3.3.2 Soil Erodibility Factor (K) . . . . . . . . . . . . . . . . . . . . 3.3.3 Topographic Factor (LS) . . . . . . . . . . . . . . . . . . . . . 3.3.4 Cover-Management Factor (C) . . . . . . . . . . . . . . . . 3.3.5 Support Practice Factor (P) . . . . . . . . . . . . . . . . . . . 3.4 Modified USLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 Revised USLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6 Soil and Water Assessment Tool . . . . . . . . . . . . . . . . . . . . . . 3.7 Process-Based Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

53 53 54 55 56 57 57 58 58 62 62 63 64

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3.7.1 Water Erosion Prediction Project . . . . . . . . . . . . . . 3.7.2 Ephemeral Gully Erosion Model . . . . . . . . . . . . . . 3.8 Other Water Erosion Models . . . . . . . . . . . . . . . . . . . . . . . . 3.9 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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64 67 68 68 70

4

Wind Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Wind Erosivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Soil Erodibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.1 Texture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.2 Crusts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.3 Dry Aggregate Size Distribution . . . . . . . . . . . . . . . 4.4.4 Aggregate Stability . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.5 Soil Surface Roughness . . . . . . . . . . . . . . . . . . . . . 4.4.6 Soil Water Content . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.7 Wind Affected Area . . . . . . . . . . . . . . . . . . . . . . . . 4.4.8 Surface Cover . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.9 Management-Induced Changes . . . . . . . . . . . . . . . . 4.5 Measuring Wind Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.1 Efficiency of Sediment Samplers . . . . . . . . . . . . . . . 4.5.2 Types of Sediment Samplers . . . . . . . . . . . . . . . . . . 4.5.3 Wind-Tunnel Method . . . . . . . . . . . . . . . . . . . . . . . 4.5.4 Point Measurements . . . . . . . . . . . . . . . . . . . . . . . . 4.5.5 Radionuclide Fallouts . . . . . . . . . . . . . . . . . . . . . . . 4.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

73 73 76 77 79 80 80 81 81 82 82 83 83 84 84 84 85 86 86 86 87 88

5

Wind Erosion Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Wind Erosion Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Wind Erosion Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.1 Erodibility Index (I) . . . . . . . . . . . . . . . . . . . . . . . . 5.2.2 Climatic Factor (C) . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.3 Soil Ridge Roughness Factor (K) . . . . . . . . . . . . . . . 5.2.4 Vegetative Cover Factor (V) . . . . . . . . . . . . . . . . . . 5.3 Revised WEQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.1 Weather Factor (WF) . . . . . . . . . . . . . . . . . . . . . . . 5.3.2 Soil Roughness Factor (K) . . . . . . . . . . . . . . . . . . . 5.3.3 Erodible Fraction (EF) . . . . . . . . . . . . . . . . . . . . . . 5.3.4 Surface Crust Factor . . . . . . . . . . . . . . . . . . . . . . . . 5.3.5 Combined Crop Factors . . . . . . . . . . . . . . . . . . . . . 5.4 Process-Based Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.1 Wind Erosion Prediction System . . . . . . . . . . . . . . . 5.4.2 Other Wind Erosion Models . . . . . . . . . . . . . . . . . .

89 89 90 90 91 91 92 94 95 95 95 96 96 96 97 99

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5.4.2.1

Wind Erosion Stochastic Simulator (WESS) . . . . . . . . . . . . . . . . . . . . . . . 5.4.2.2 Texas Tech Erosion Analysis Model (TEAM) . . . . . . . . . . . . . . . . . . . . . . . 5.4.2.3 Wind Erosion Assessment Model (WEAM) . . . . . . . . . . . . . . . . . . . . . . 5.4.2.4 Wind Erosion and European Light Soils (WEELS) . . . . . . . . . . . . . . . . . . 5.4.2.5 Dust Production Model (DPM) . . . . . . . 5.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

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Tillage Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 Extent of Tillage Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Tillage Erosion Versus Water and Wind Erosion . . . . . . . . . . . 6.3 Factors Affecting Tillage Erosion . . . . . . . . . . . . . . . . . . . . . . 6.3.1 Landform Erodibility . . . . . . . . . . . . . . . . . . . . . . . 6.3.2 Soil Erodibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.3 Tillage Erosivity . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.3.1 Tillage Depth . . . . . . . . . . . . . . . . . . . . 6.3.3.2 Tillage Implement . . . . . . . . . . . . . . . . . 6.3.3.3 Tillage Direction . . . . . . . . . . . . . . . . . . 6.3.3.4 Tillage Speed and Passes . . . . . . . . . . . . 6.4 Tillage Erosion and Soil Properties . . . . . . . . . . . . . . . . . . . . . 6.5 Indicators of Tillage Erosion . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.1 Changes in Surface Elevation . . . . . . . . . . . . . . . . . 6.5.2 Activity of Radionuclides . . . . . . . . . . . . . . . . . . . . 6.5.3 Measurement of Soil Displacement . . . . . . . . . . . . . 6.6 Tillage Erosion and Crop Production . . . . . . . . . . . . . . . . . . . 6.7 Tillage Erosion Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.7.1 Predictive Equations . . . . . . . . . . . . . . . . . . . . . . . . 6.7.2 Computer Models . . . . . . . . . . . . . . . . . . . . . . . . . . 6.7.2.1 Tillage Erosion Prediction (TEP) Model . 6.7.2.2 Water and Tillage Erosion Model (WaTEM) . . . . . . . . . . . . . . . . . . . . . . . 6.7.2.3 Water- and Tillage-Induced Soil Redistribution (SPEROS) . . . . . . . . . . . . 6.8 Management of Tillage Erosion . . . . . . . . . . . . . . . . . . . . . . . 6.8.1 Slope Stabilization . . . . . . . . . . . . . . . . . . . . . . . . . 6.8.2 Management of Tillage Operations . . . . . . . . . . . . . 6.9 Soil Erosion and Crop Harvesting . . . . . . . . . . . . . . . . . . . . . 6.10 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

103 103 105 106 107 107 107 108 108 108 109 109 111 111 111 112 113 113 113 117 117 117 118 118 119 119 120 122 124

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Tillage Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1 Tillage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Tillage Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 Types of Tillage Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4 Conventional Tillage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.1 Crop Residues . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.2 Soil Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.3 Soil Compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5 Conservation Tillage Systems . . . . . . . . . . . . . . . . . . . . . . . . 7.5.1 No-Till Farming . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5.1.1 No-Till in the Americas . . . . . . . . . . . . . 7.5.1.2 No-Till in Europe . . . . . . . . . . . . . . . . . 7.5.1.3 No-Till in Africa and Asia . . . . . . . . . . . 7.5.1.4 No-Till in Australia and New Zealand . . 7.5.1.5 Ecosystem Services from No-Till as Compared with Other Tillage Systems . . . . . . . . . . . . . . . . . . . . . . . . 7.5.1.6 Soil Properties . . . . . . . . . . . . . . . . . . . . 7.5.1.7 Soil Water . . . . . . . . . . . . . . . . . . . . . . 7.5.1.8 Soil Temperature . . . . . . . . . . . . . . . . . . 7.5.1.9 Soil Biota . . . . . . . . . . . . . . . . . . . . . . . 7.5.1.10 Losses of Soil, Water, and Nutrients . . . . 7.5.1.11 Some Challenges in No-Till Management . . . . . . . . . . . . . . . . . . . . . 7.5.1.12 Variable Crop Yields . . . . . . . . . . . . . . . 7.5.1.13 Increased Potential for Leaching and Pollutant Runoff . . . . . . . . . . . . . . . . . . 7.5.1.14 Strategic Tillage . . . . . . . . . . . . . . . . . . 7.5.2 Reduced Tillage . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5.2.1 Mulch Tillage . . . . . . . . . . . . . . . . . . . . 7.5.2.2 Ridge Tillage . . . . . . . . . . . . . . . . . . . . 7.5.2.3 Strip Tillage . . . . . . . . . . . . . . . . . . . . . 7.5.2.4 Vertical Tillage . . . . . . . . . . . . . . . . . . . 7.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

127 127 127 128 130 131 131 132 133 133 135 137 138 138

Cropping Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1 Fallow Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 Monoculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3 Crop Rotations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.1 Soil Properties and Erosion . . . . . . . . . . . . . . . . . . . 8.3.2 Nutrient Input and Cycling . . . . . . . . . . . . . . . . . . . 8.3.3 Pesticide Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.4 Crop Yields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.5 Selection of Crops for Rotations . . . . . . . . . . . . . . .

159 160 161 163 164 165 165 166 166

138 140 141 141 142 143 144 145 146 147 148 149 150 151 152 154 155

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8.4 8.5 8.6 8.7 8.8 8.9 8.10 8.11 8.12 8.13 8.14

Cropping Intensity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Row Crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multiple Cropping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Double Cropping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Relay Cropping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Intercropping or Mixed Cropping . . . . . . . . . . . . . . . . . . . . . . Contour Farming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Strip Cropping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Contour Strip Cropping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Land Equivalent Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Organic Farming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.14.1 Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.14.2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.14.3 Importance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.14.3.1 Erosion and Water Quality . . . . . . . . . . . 8.14.3.2 Soil Properties . . . . . . . . . . . . . . . . . . . . 8.14.3.3 Crop Yields . . . . . . . . . . . . . . . . . . . . . 8.14.4 Organic No-Till Farming . . . . . . . . . . . . . . . . . . . . . 8.15 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

167 167 168 169 170 170 171 172 173 173 174 175 175 176 177 178 179 180 181 182

Crop Residue Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1 Production of Crop Residues . . . . . . . . . . . . . . . . . . . . . . . . . 9.2 Crop Residues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3 Soil Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3.1 Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3.2 Compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3.3 Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3.4 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3.5 Fertility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3.6 Biological Properties . . . . . . . . . . . . . . . . . . . . . . . . 9.4 Wind Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.5 Water Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.6 Crop Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.7 Residue Grazing by Livestock . . . . . . . . . . . . . . . . . . . . . . . . 9.8 Threshold Level of Residue Removal for Expanded Uses . . . . 9.9 Increasing Crop Residue Amount . . . . . . . . . . . . . . . . . . . . . . 9.10 Measurement of Crop Residue Cover . . . . . . . . . . . . . . . . . . . 9.11 Measurement of Crop Residue Amount and Harvest Index . . . . 9.12 Root Biomass Production . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.13 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

185 185 187 187 187 192 193 195 195 196 197 198 199 201 203 204 204 205 205 207 208

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Cover Crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.1 Components of Cropping Systems . . . . . . . . . . . . . . . . . . . . . 10.2 Biomass Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.3 Mixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4 Weed Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.5 Water Erosion and Water Quality . . . . . . . . . . . . . . . . . . . . . . 10.6 Wind Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.7 Soil Compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.8 Soil Structure, Hydraulic Properties, and Temperature . . . . . . . 10.9 Soil Fertility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.9.1 Nutrient Recycling . . . . . . . . . . . . . . . . . . . . . . . . . 10.9.2 Nitrogen Fixation . . . . . . . . . . . . . . . . . . . . . . . . . . 10.10 Soil Carbon and Biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.11 Soil Water Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.12 Crop Yields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.13 Grazing and Harvesting Cover Crops . . . . . . . . . . . . . . . . . . . 10.14 Cover Crops and Crop Residue Removal . . . . . . . . . . . . . . . . 10.15 Goals for Establishing Cover Crops . . . . . . . . . . . . . . . . . . . . 10.16 Management of Cover Crops . . . . . . . . . . . . . . . . . . . . . . . . . 10.17 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

211 212 213 214 215 216 218 219 221 222 222 223 225 226 227 228 229 231 232 233 235

11

Perennial Plants and Soil Management . . . . . . . . . . . . . . . . . . . . . . 11.1 Perennial Plants: Mimicking Nature to Manage Soils . . . . . . . . 11.2 Conservation Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.1 Multi-Functionality of Conservation Buffers . . . . . . . 11.2.2 Riparian Buffer Strips . . . . . . . . . . . . . . . . . . . . . . . 11.2.3 Filter Strips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.4 Grass Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.5 Contour Buffer Strips . . . . . . . . . . . . . . . . . . . . . . . 11.2.6 Grass Waterways . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.7 Field Borders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.8 Windbreaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.9 Intercropping Crops with Trees: Alley Cropping . . . . 11.2.9.1 Benefits of Alley Cropping . . . . . . . . . . 11.2.9.2 Design and Management of Alley Cropping Systems . . . . . . . . . . . . . . . . . 11.3 Growing Dedicated Energy Crops in Marginal Croplands . . . . 11.4 Perennials in Rotation with Food Crops . . . . . . . . . . . . . . . . . 11.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

239 239 240 242 244 246 249 253 254 259 260 264 265

12

267 269 271 272 274

Soil Amendments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 12.1 Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 12.2 Specificity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278

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13

Animal Manure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.3.1 Soil Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.3.2 Soil Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.3.3 Manure Management . . . . . . . . . . . . . . . . . . . . . . . 12.4 Biochar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.4.1 Soil and Crop Benefits of Biochar . . . . . . . . . . . . . . 12.4.2 Soil Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.4.3 Nutrient Cycling . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.4.4 Crop Yields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.4.5 Factors Affecting Biochar Benefits . . . . . . . . . . . . . . 12.5 Soil Conditioners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.6 Polyacrylamides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.6.1 Soil Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.6.2 Water Erosion and Quality . . . . . . . . . . . . . . . . . . . 12.6.3 Crop Production . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.6.4 Factors Affecting Performance of Polyacrylamides . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.6.5 Soil Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . 12.6.6 Polyacrylamide Characteristics . . . . . . . . . . . . . . . . 12.6.7 Soil Management . . . . . . . . . . . . . . . . . . . . . . . . . . 12.6.8 Longevity of Polyacrylamides and Cost-Effectiveness . . . . . . . . . . . . . . . . . . . . . . . . . 12.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

278 279 280 281 283 284 285 285 285 286 287 288 288 290 291

Mechanical Structures and Engineering Techniques . . . . . . . . . . . . 13.1 Types of Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.1.1 Contour Bunds . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.1.2 Silt Fences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.1.3 Surface Mats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.1.4 Lining Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.2 Farm Ponds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.2.1 Groundwater-Fed Ponds . . . . . . . . . . . . . . . . . . . . . 13.2.2 Stream- or Spring-Fed Ponds . . . . . . . . . . . . . . . . . . 13.2.3 Off-Stream Ponds . . . . . . . . . . . . . . . . . . . . . . . . . . 13.2.4 Rain-Fed Ponds . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.2.5 Design and Installation of Ponds . . . . . . . . . . . . . . . 13.3 Terraces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Functions of Terraces . . . . . . . . . . . . . . . . . . . . . . . 13.3.1 13.3.2 Types of Terraces . . . . . . . . . . . . . . . . . . . . . . . . . . 13.3.3 Design of Terraces . . . . . . . . . . . . . . . . . . . . . . . . . 13.3.4 Management and Maintenance of Terraces . . . . . . . . 13.4 Gully Erosion Control Structures . . . . . . . . . . . . . . . . . . . . . . 13.4.1 Types of Gully Erosion Control Structures . . . . . . . . 13.4.1.1 Gabions . . . . . . . . . . . . . . . . . . . . . . . .

299 300 300 300 302 303 304 305 305 305 306 306 309 309 310 313 316 318 320 321

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13.4.1.2 Chute Spillways . . . . . . . . . . . . . . . . . 13.4.1.3 Pipe Spillways . . . . . . . . . . . . . . . . . . 13.4.1.4 Drop Structure . . . . . . . . . . . . . . . . . . 13.4.2 Maintenance of Gully Erosion Control Practices . . . 13.5 Mechanical Structures and Biological Techniques . . . . . . . . . 13.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

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322 323 323 325 325 326 328

Restoration and Management of Degraded Soils . . . . . . . . . . . . . . . 14.1 Management of Degraded Soils . . . . . . . . . . . . . . . . . . . . . . . 14.2 Eroded or Erosion-Prone Soils . . . . . . . . . . . . . . . . . . . . . . . . 14.3 Nutrient-Depleted Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.4 Compacted Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.5 Management of Soil Compaction . . . . . . . . . . . . . . . . . . . . . . 14.5.1 Controlling Traffic . . . . . . . . . . . . . . . . . . . . . . . . . 14.5.2 Adding Organic Amendments . . . . . . . . . . . . . . . . . 14.5.3 Growing Deep-Rooted Crops . . . . . . . . . . . . . . . . . 14.5.4 Subsoiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.5.5 Considering Tillage Passes, Soil Wetness, and Field Equipment . . . . . . . . . . . . . . . . . . . . . . . . 14.5.6 Using One-Time Tillage . . . . . . . . . . . . . . . . . . . . . 14.6 Acid Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.7 Saline, Saline-Sodic, and Sodic Soils . . . . . . . . . . . . . . . . . . . 14.7.1 Causes of Salinization and Sodification . . . . . . . . . . 14.7.2 Impacts of Salinization and Sodification on Soil Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.7.3 Management of Saline and Sodic Soils . . . . . . . . . . . 14.7.3.1 Leaching . . . . . . . . . . . . . . . . . . . . . . . 14.7.3.2 Increasing Soil Water Content . . . . . . . . 14.7.3.3 Use of Salt-Tolerant Crop Varieties . . . . 14.7.4 Use of Salt-Tolerant Trees and Grasses . . . . . . . . . . 14.7.5 Establishment of Drainage Systems . . . . . . . . . . . . . 14.7.6 Tillage Practices: Subsoiling . . . . . . . . . . . . . . . . . . 14.7.7 Addition of Amendments . . . . . . . . . . . . . . . . . . . . 14.7.8 Application of Gypsum . . . . . . . . . . . . . . . . . . . . . . 14.7.9 Other Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . 14.8 Mined Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.8.1 Restoration of Mined Soils . . . . . . . . . . . . . . . . . . . 14.8.2 Restoration Practices . . . . . . . . . . . . . . . . . . . . . . . . 14.8.3 Restoration Indicators . . . . . . . . . . . . . . . . . . . . . . . 14.9 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

331 331 332 334 335 336 337 338 338 339 339 340 341 344 346 346 346 347 349 349 349 349 350 350 350 352 353 354 355 356 357 359

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Soil Fertility Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.1 Management of Essential Nutrients . . . . . . . . . . . . . . . . . . . . . 15.2 Soil Properties and Nutrient Dynamics . . . . . . . . . . . . . . . . . . 15.2.1 Particle-Size Distribution . . . . . . . . . . . . . . . . . . . . . 15.2.2 Specific Surface Area . . . . . . . . . . . . . . . . . . . . . . . 15.2.3 Bulk Density and Porosity . . . . . . . . . . . . . . . . . . . . 15.2.4 Hydraulic Conductivity . . . . . . . . . . . . . . . . . . . . . . 15.2.5 Water Infiltration . . . . . . . . . . . . . . . . . . . . . . . . . . 15.2.6 Aggregate Stability . . . . . . . . . . . . . . . . . . . . . . . . . 15.2.7 Organic Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.2.8 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.2.9 Clay Mineralogy . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.2.10 Cation Exchange Capacity . . . . . . . . . . . . . . . . . . . 15.2.11 Anion Exchange Capacity . . . . . . . . . . . . . . . . . . . . 15.3 Soil–Water–Nutrient–Root Interrelationships . . . . . . . . . . . . . . 15.4 Mobility and Solubility of Nutrients . . . . . . . . . . . . . . . . . . . . 15.5 pH and Base Saturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.6 Buffering Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.7 Nitrogen and Phosphorus Cycles . . . . . . . . . . . . . . . . . . . . . . 15.8 Nutrient Management Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.8.1 Soil Sampling for Nutrient Analysis . . . . . . . . . . . . . 15.8.2 Nutrient Recommendation . . . . . . . . . . . . . . . . . . . . 15.8.3 Nutrient Application . . . . . . . . . . . . . . . . . . . . . . . . 15.9 Precision Agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.10 Managing Soils to Enhance Soil Fertility . . . . . . . . . . . . . . . . 15.11 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

363 363 364 365 365 366 367 367 368 369 371 371 372 374 375 376 378 379 379 382 382 384 385 385 387 387 389

16

Nutrient Erosion and Hypoxia of Aquatic Ecosystems . . . . . . . . . . . 16.1 Water Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.2 Eutrophication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.3 Non-Point Source Pollution and Runoff . . . . . . . . . . . . . . . . . 16.4 Factors Affecting Non-Point Source Pollution . . . . . . . . . . . . . 16.5 Pollutant Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.6 Common Pollutants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.6.1 Sediment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.6.2 Nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phosphorus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.6.3 16.6.4 Animal Manure . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.6.5 Pesticides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.7 Pathways of Pollutant Transport . . . . . . . . . . . . . . . . . . . . . . . 16.7.1 Runoff and Lateral Flow . . . . . . . . . . . . . . . . . . . . . 16.7.2 Leaching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.7.3 Volatilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.8 Hypoxia of Coastal Waters . . . . . . . . . . . . . . . . . . . . . . . . . .

391 391 391 393 394 394 396 396 397 398 399 400 401 401 402 402 403

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Wetlands and Pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.9.1 Degradation of Wetlands . . . . . . . . . . . . . . . . . . . . . 16.9.2 Restoration of Wetlands . . . . . . . . . . . . . . . . . . . . . 16.10 Mitigating Non-Point Source Pollution and Hypoxia . . . . . . . . 16.10.1 Management of Chemical Inputs . . . . . . . . . . . . . . . 16.10.2 Management Practices . . . . . . . . . . . . . . . . . . . . . . 16.11 Models of Non-Point Source Pollution . . . . . . . . . . . . . . . . . . 16.12 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

405 406 407 407 408 408 411 412 413

17

Soil Water Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17.1 Understanding Water Balance . . . . . . . . . . . . . . . . . . . . . . . . 17.2 Water Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17.3 Measurement of Soil Water . . . . . . . . . . . . . . . . . . . . . . . . . . 17.3.1 Water Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17.3.2 Water Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17.4 Soil Properties and Soil Water Dynamics . . . . . . . . . . . . . . . . 17.5 Soil Organic C and Water Retention . . . . . . . . . . . . . . . . . . . . 17.6 Drought Management Strategies . . . . . . . . . . . . . . . . . . . . . . . 17.7 Conservation Tillage and Water Conservation . . . . . . . . . . . . . 17.7.1 Soil Water Content . . . . . . . . . . . . . . . . . . . . . . . . . 17.7.2 Water Infiltration . . . . . . . . . . . . . . . . . . . . . . . . . . 17.7.3 Water Use Efficiency . . . . . . . . . . . . . . . . . . . . . . . 17.8 Cropping Systems and Water Conservation . . . . . . . . . . . . . . . 17.9 Crop Residues and Water Conservation . . . . . . . . . . . . . . . . . 17.10 Terraces and Farm Ponds . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17.11 Conservation Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17.12 Management of Irrigation Water . . . . . . . . . . . . . . . . . . . . . . . 17.12.1 Irrigation Systems . . . . . . . . . . . . . . . . . . . . . . . . . . 17.12.1.1 Surface Irrigation . . . . . . . . . . . . . . . . . 17.12.1.2 Sprinkler Irrigation . . . . . . . . . . . . . . . . 17.12.1.3 Drip Irrigation . . . . . . . . . . . . . . . . . . . . 17.12.2 Impacts of Irrigation on Soil Properties . . . . . . . . . . 17.13 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

417 417 419 420 420 421 422 422 423 425 425 425 426 427 429 430 431 432 435 435 435 436 437 438 439

18

Management of Grazing Lands . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.1 Rangeland Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.2 Pastureland Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.3 Degradation of Grazing Lands . . . . . . . . . . . . . . . . . . . . . . . . 18.3.1 Rangelands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.3.2 Pasturelands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.4 Grazing Impacts on Soil Erosion . . . . . . . . . . . . . . . . . . . . . . 18.5 Grazing and Soil Properties . . . . . . . . . . . . . . . . . . . . . . . . . . 18.5.1 Temperature and Water Content . . . . . . . . . . . . . . .

443 444 445 446 446 446 448 450 450

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18.5.2 Particle-Size Distribution . . . . . . . . . . . . . . . . . . . . . 18.5.3 Structure and Water Infiltration . . . . . . . . . . . . . . . . 18.5.4 Compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.5.5 Organic Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.6 Grazing and Plant Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.7 Benefits of Well-Managed Grazing Lands for Soil Protection and Stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.7.1 Protection of the Soil Surface . . . . . . . . . . . . . . . . . 18.7.2 Stabilization of Soil Matrix . . . . . . . . . . . . . . . . . . . 18.8 Grass Roots and Soil Erodibility . . . . . . . . . . . . . . . . . . . . . . 18.9 Grazing of Conservation Buffers . . . . . . . . . . . . . . . . . . . . . . 18.10 Methods of Grazing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.11 Management of Grazing Lands . . . . . . . . . . . . . . . . . . . . . . . 18.12 Prescribed Fire as a Management Tool . . . . . . . . . . . . . . . . . . 18.13 Resilience and Recovery of Grazed Lands . . . . . . . . . . . . . . . 18.14 Conversion of Grazing Lands to Croplands . . . . . . . . . . . . . . . 18.15 Conversion of Croplands to Permanent Vegetation . . . . . . . . . 18.16 Restoration of Degraded Grazing Lands . . . . . . . . . . . . . . . . . 18.17 Modeling of Grazing Land Management . . . . . . . . . . . . . . . . . 18.18 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

451 451 452 452 453

Soil Management and Carbon Dynamics . . . . . . . . . . . . . . . . . . . . . 19.1 Importance of Soil Organic Carbon . . . . . . . . . . . . . . . . . . . . 19.2 Soil Organic Carbon Balance . . . . . . . . . . . . . . . . . . . . . . . . . 19.3 Soil Erosion and Organic Carbon Dynamics . . . . . . . . . . . . . . 19.3.1 Aggregate Disintegration . . . . . . . . . . . . . . . . . . . . . 19.3.2 Preferential Removal of Carbon . . . . . . . . . . . . . . . . 19.3.3 Redistribution of Carbon Transported by Erosion . . . 19.3.4 Mineralization of Soil Organic Matter . . . . . . . . . . . 19.3.5 Deposition and Burial of Carbon Transported by Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.4 Fate of the Carbon Transported by Erosion . . . . . . . . . . . . . . . 19.5 Carbon Transported by Erosion: Source or Sink for Atmospheric CO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.6 Tillage Erosion and Soil Carbon . . . . . . . . . . . . . . . . . . . . . . . 19.7 Management Practices and Soil Organic Carbon Dynamics . . . 19.7.1 No-Till and Carbon Sequestration . . . . . . . . . . . . . . 19.7.1.1 Stratification of Soil Carbon . . . . . . . . . . 19.7.1.2 Site-Specificity of Carbon Sequestration . . . . . . . . . . . . . . . . . . . . 19.7.2 Intensified Crop Rotations . . . . . . . . . . . . . . . . . . . . 19.7.3 Cover Crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.7.4 Crop Residues . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.7.5 Animal Manure . . . . . . . . . . . . . . . . . . . . . . . . . . .

471 472 472 473 473 474 474 474

453 453 454 455 456 457 459 460 460 461 462 463 464 465 466

474 475 475 477 478 478 479 481 481 482 483 484

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19.7.6 Agroforestry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.7.7 Organic Farming . . . . . . . . . . . . . . . . . . . . . . . . . . 19.7.8 Bioenergy Crops . . . . . . . . . . . . . . . . . . . . . . . . . . 19.7.9 Reclaimed Lands . . . . . . . . . . . . . . . . . . . . . . . . . . 19.7.10 Biochar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.8 Measurement of the Soil Carbon Pool . . . . . . . . . . . . . . . . . . . 19.8.1 Infrared Reflectance Spectroscopy (IRS) . . . . . . . . . 19.8.2 Laser-Induced Breakdown Spectroscopy (LIBS) . . . . 19.8.3 Inelastic Neutron Scattering (INS) . . . . . . . . . . . . . . 19.8.4 Remote Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.9 Soil Management and Carbon Emissions . . . . . . . . . . . . . . . . 19.10 Modeling Soil Carbon Dynamics . . . . . . . . . . . . . . . . . . . . . . 19.11 Soil Management and Carbon Credits . . . . . . . . . . . . . . . . . . . 19.12 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

485 486 486 487 488 489 490 490 491 491 491 493 494 495 497

One Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.1 Soil Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.2 Soil Health Paradigm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.3 One Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.3.1 Plant Heath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.3.2 Animal Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.3.3 Human Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.3.4 Ecosystem Health . . . . . . . . . . . . . . . . . . . . . . . . . . 20.4 Conceptual Definition and Assessment Approaches . . . . . . . . . 20.5 Indicators of Soil Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.5.1 Soil Physical Health . . . . . . . . . . . . . . . . . . . . . . . . 20.5.2 Soil Chemical Health . . . . . . . . . . . . . . . . . . . . . . . 20.5.3 Soil Biological Health . . . . . . . . . . . . . . . . . . . . . . . 20.5.4 Factors and Soil Property Interactions . . . . . . . . . . . 20.5.5 Crop Yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.5.6 Selection of Soil Properties . . . . . . . . . . . . . . . . . . . 20.6 Soil Health Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.6.1 Farmer-Based Soil Health Assessment Approach . . . 20.6.2 Soil Management Assessment Framework (SMAF) . . . . . . . . . . . . . . . . . . . . . . . . 20.6.3 Comprehensive Assessment of Soil Health (CASH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.7 Emerging Assessment Techniques . . . . . . . . . . . . . . . . . . . . . 20.8 Soil Health and Erosion Relationships . . . . . . . . . . . . . . . . . . 20.8.1 Soil Erosion and Profile Depth . . . . . . . . . . . . . . . . 20.8.2 Soil Physical Properties . . . . . . . . . . . . . . . . . . . . . . 20.8.3 Soil Chemical and Biological Properties . . . . . . . . . . 20.9 Managing Soil Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.9.1 Reducing Soil Disturbance . . . . . . . . . . . . . . . . . . .

501 501 502 503 504 504 505 505 506 507 508 508 509 510 511 511 511 513 513 514 514 515 516 516 517 517 517

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20.9.2 Providing Armor . . . . . . . . . . . . . . . . . . . . . . . . . 20.9.3 Intensifying Cropping Systems . . . . . . . . . . . . . . . 20.9.4 Promoting Permanent Vegetative Cover . . . . . . . . . 20.9.5 Integrating Crops with Livestock . . . . . . . . . . . . . . 20.10 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . .

518 518 519 519 520 521

21

Soil Resilience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.1 Concept of Soil Resilience . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2 Importance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3 Classification of Soil Resilience . . . . . . . . . . . . . . . . . . . . . . . 21.4 Soil Disturbance Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.5 Factors that Affect Soil Resilience . . . . . . . . . . . . . . . . . . . . . 21.5.1 Parent Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.5.2 Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.5.3 Biota . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.5.3.1 Flora . . . . . . . . . . . . . . . . . . . . . . . . . . 21.5.3.2 Fauna . . . . . . . . . . . . . . . . . . . . . . . . . . 21.5.4 Anthropogenic Influence . . . . . . . . . . . . . . . . . . . . . 21.5.5 Topography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.5.6 Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.6 Soil Processes and Resilience . . . . . . . . . . . . . . . . . . . . . . . . . 21.7 Resilience of Soil Properties . . . . . . . . . . . . . . . . . . . . . . . . . 21.7.1 Soil Physical Resilience . . . . . . . . . . . . . . . . . . . . . 21.7.2 Soil Chemical and Biological Resilience . . . . . . . . . 21.8 Soil Resilience and Chemical Contamination . . . . . . . . . . . . . 21.9 Measurement of Soil Resilience . . . . . . . . . . . . . . . . . . . . . . . 21.10 Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.11 Managing Soil Resilience . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.12 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

525 525 526 527 529 529 530 531 532 532 532 533 533 533 534 535 536 536 537 537 538 540 541 542

22

Food, Water, and Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.1 Soil as a Centerpiece . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.2 Soils and Water Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.3 Soils and Food Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.3.1 Soil Erosion and Crop Yields . . . . . . . . . . . . . . . . . 22.3.2 Soil Type, Climate, and Crop Type . . . . . . . . . . . . . 22.3.3 Erosion-Induced Changes in Soil Properties . . . . . . . 22.3.3.1 Physical Hindrance . . . . . . . . . . . . . . . . 22.3.3.2 Compaction and Available Water . . . . . . 22.3.3.3 Soil Organic Matter and Nutrient Reserves . . . . . . . . . . . . . . . . . . . . . . . . 22.3.4 Methods of Assessment of Crop Response to Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

545 545 547 547 548 550 551 551 552 552 553

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22.3.4.1 Natural Soil Erosion . . . . . . . . . . . . . . . 22.3.4.2 Artificial Removal of Topsoil . . . . . . . . . 22.3.4.3 Artificial Addition of Topsoil . . . . . . . . . 22.3.5 Modeling Erosion-Yield Relationships . . . . . . . . . . . 22.4 Climate Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.4.1 Climate Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.4.2 Soil Formation and Processes . . . . . . . . . . . . . . . . . 22.4.3 Soil Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.4.3.1 Soil Temperature and Water Content . . . 22.4.3.2 Structural Properties . . . . . . . . . . . . . . . 22.4.3.3 Soil Biology . . . . . . . . . . . . . . . . . . . . . 22.4.3.4 Soil Organic Carbon . . . . . . . . . . . . . . . 22.4.4 Crop Production . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.4.4.1 Positive Effects . . . . . . . . . . . . . . . . . . . 22.4.4.2 Negative Effects . . . . . . . . . . . . . . . . . . 22.5 Modeling of Extreme Weather Impacts . . . . . . . . . . . . . . . . . . 22.6 Adapting to Fluctuating Climates . . . . . . . . . . . . . . . . . . . . . . 22.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

554 554 555 555 556 557 558 560 560 561 561 562 562 563 563 564 565 566 568

The Way Forward . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.1 Strategies for Managing and Conserving Soil and Water . . . . . 23.2 Embracing a Multidisciplinary Approach . . . . . . . . . . . . . . . . 23.3 Policy Imperatives for Managing and Conserving Soil and Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.4 Specific Priorities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.4.1 Securing Food Production . . . . . . . . . . . . . . . . . . . . 23.4.2 Expanding Conservation Agriculture . . . . . . . . . . . . 23.4.3 Managing Crop Residues . . . . . . . . . . . . . . . . . . . . 23.4.4 Adopting Cover Crops . . . . . . . . . . . . . . . . . . . . . . 23.4.5 Establishing Conservation Buffers . . . . . . . . . . . . . . 23.4.6 Integrating Perennials with Crops: Alley Cropping . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.4.7 Managing Tillage Erosion . . . . . . . . . . . . . . . . . . . . 23.4.8 Considering Organic Farming . . . . . . . . . . . . . . . . . 23.4.9 Adding Biochar . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.4.10 Enhancing Soil Health and Resilience . . . . . . . . . . . 23.4.11 Sequestering Soil Carbon . . . . . . . . . . . . . . . . . . . . 23.4.12 Modeling Soil Ecosystem Services . . . . . . . . . . . . . . 23.4.13 Adapting to Extreme Weather Events . . . . . . . . . . . . 23.5 Soil Management and Conservation Challenges . . . . . . . . . . . . 23.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

571 572 573 574 574 574 575 576 577 578 579 580 582 582 583 584 585 586 587 588 589

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Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 591 Appendix A Abbreviations of Some of the Words Frequently Used in the Textbook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 591 Appendix B Common and Scientific Names of Plants Used in the Textbook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595

1

Soil and Water Management

1.1

Why Manage Soil?

Soil is one of the most fundamental and basic resources. Although erroneously dubbed as “dirt” or sometimes perceived as something of insignificant value, humans cannot survive without soil because it is the basis of all terrestrial life. Soil is a non-renewable resource over the human time scale as it can take about 100 years to form 0.5 cm of soil. Productive lands are finite and comprise only about 10% of total land area yet supply food to billions of people. Thus, soil is a vital and precious resource that provides food, feed, fuel, and fiber. It underpins food security, energy security, and environment quality, all essential to human existence. Soil is dynamic and prone to rapid degradation with land misuse. The critical nature of soil to human well-being is often not recognized until food production drops or is jeopardized when soil is severely eroded or degraded to such an extent that it loses its inherent resilience. Soil resilience can be thought of as the “springiness” or ability to rebound after some stressor. Traditionally, soil was considered only a medium for plant growth. Now, along with the increasing concerns of food security, soil is being recognized as a multifunctional system to address energy security, water security, biodiversity, environmental quality, repository for urban/industrial wastes and sink of atmospheric CO2. Thus, widespread degradation of finite soil resources can severely jeopardize global food security and threaten environmental quality. Conserving this finite resource has many agronomic, environmental, and economical benefits. The goal of soil management is to further enhance the multi-functionality of soils to: (1) meet the everincreasing food demand, (2) filter air, (3) purify water, and (4) store C, among others (Table 1.1). If managed properly, soils can deliver multiple services including recycling nutrients, reducing nutrient input costs, holding more water during dry periods, draining rapidly during wet periods, and reducing water, C, and N losses, among others. Enhancing the multi-functionality of soils through innovative management practices is thus a high priority. While factors such as climate, soil texture, and # The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 H. Blanco, R. Lal, Soil Conservation and Management, https://doi.org/10.1007/978-3-031-30341-8_1

1

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1

Soil and Water Management

Table 1.1 Multi-functionality of soils Food security, biodiversity, and urbanization • Food • Fiber • Housing • Recreation • Infrastructure • Waste disposal • Microbial diversity • Preservation of flora and fauna

Water quality • Filtration of pollutants • Purification of water • Retention of sediment and chemicals • Buffering and transformation of chemicals

Carbon and nutrient cycling • Sink of CO2 and CH4 • Carbon sequestration in soil and biota • Reduction of nitrification • Deposition and burial of C-enriched sediment

Production of biofuel feedstocks • Bioenergy crops (e.g., warm season grasses and shortrotation woody crops) • Prairie grasses

topography cannot be fully managed, dynamic soil properties, soil water storage, nutrient availability, soil erosion, and crop production can be manageable. The need to maintain and enhance soil multi-functionality necessitates improved and prudent management of soil for meeting the needs of present and future generations. The extent to which soil stewardship and protection is practiced determines the sustainability of land use, the adequacy of food supply, the quality of air and water resources, and the survival of humankind. Soil conservation has traditionally been discussed in relation to keeping the soil in place for crop production. Now, soil conservation is evaluated in terms of its benefits for increasing crop yields, reducing water pollution, mitigating concentration of greenhouse gases in the atmosphere, and delivering other ecosystem services.

1.2

Soil Ecosystem Services

The multi-functionality of soils can be discussed in terms of soil ecosystem services, which refers to the services that soils provide with direct agronomic, environmental, economic, and societal implications. Soil ecosystem services are grouped into four categories: provisioning, supporting, regulating, and cultural services, which are defined as follows (MEA 2003; Fig. 1.1). One, provisioning services refer to products provided by soils. Two, regulating services are benefits that soils provide by regulating ecosystem processes. Three, supporting services are the benefits that soils provide by supporting the production of all other ecosystem services. Four, cultural services are the non-material benefits from soils. While provisioning services such as food production are well recognized, other services such as regulating, supporting, and cultural services often remain unrecognized. Maintaining, improving, and expanding these services are vital to human existence and preservation of ecosystems. Soils are under increased pressure to deliver multiple outputs including crop production, forage production, biofuel production, forestry, urbanization, and others

SOIL ECOSYSTEM SERVICES

1.3 Why Manage Soil Water?

3

PROVISIONING - Food - Feed - Fiber - Fuel - Water - Genetic resources - Biochemicals REGULATING - Mitigating climatic fluctuations - Filtering water and absorbing pollutants - Reducing soil erosion - Reducing risks of flooding, drought, and heat waves SUPPORTING - Carbon, nutrient, and water cycling - Primary production - Habitat provision - Soil development and formation CULTURAL - Aesthetic - Recreation - Ecotourism - Religious

- Educational - Cultural heritage

Fig. 1.1 Some essential ecosystem services that soil provides (MEA 2003)

(Pereira et al. 2018). Reductions in soil fertility, soil organic C concentration, water holding capacity, soil aggregation, and microbial biomass and biodiversity, and increases in water and wind erosion, topsoil loss, water pollution, and compaction are indicators of degradation and loss of soil ecosystem services. Soil ecosystem services have direct (e.g., marketing of agricultural products) and indirect (e.g., improved wildlife habitat and recreational areas) economic values (Yee et al. 2021). A full recognition of the numerous ecosystem services provided by soils is critical to address global challenges such as food security, energy and freshwater supplies.

1.3

Why Manage Soil Water?

Water is another finite and valuable natural resource. Conserving water is becoming increasingly critical for crop and livestock production. Increase in drought frequency and severity in recent decades on a global scale warrants the consideration that water management is just as critical as soil management. The amount of water that we can conserve depends on management. Agricultural production can positively or negatively affect water quantity (i.e., changes in evapotranspiration) and quality (i.e.,

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water pollution with nutrients), depending on management. While rainfall frequency and intensity may not be manageable, practices including crop residue management, tillage system (e.g., conventional till, no-till, reduced till), cropping system, and others can be managed. For example, residue mulch such as under conservation agriculture can reduce water losses from evaporation by at least 50%. In turn, intensive tillage mixes residues with soil, exposes soil to the atmosphere, and increases water loss. Practices that reduce water evaporation can increase precipitation capture and reduce irrigation water requirements as well as water pumping and energy costs. Improving soil hydraulic properties such as water infiltration and water holding capacity can improve precipitation capture and increase plant available water. Managing water is not only about increasing the ability of the soil to retain water but also about increasing the ability of the soil to release water rapidly after heavy rainstorms and reduce risks of flooding. In wet seasons, some soils are under water or flooded for days or weeks. Developing soils with high water infiltration capacity can reduce risks of flooding, runoff, and off-site transport of pollutants, which negatively affect soil and water quality. For example, flooded soils impede the provision of oxygen, nutrient cycling, soil aggregation, microbial activity, and other processes. Practices to manage and conserve soil water are discussed in more detail in a later chapter.

1.4

Soil Management and Population Growth

It is estimated that the world population will reach 9.5 billion by 2050 and 11 billion by 2100. The rate of increase is country-specific with most of the increase in developing countries. Estimates indicate that the current growth rate is about 78 million people per year. The rapid increase in population means that requirements for food, water, energy, and other basic necessities will increase accordingly. While industrialized countries such as the USA are experiencing slow growth, the rapid population growth in developing countries affects global food production and economy. Population growth will result in increased demand for food, which will put more pressure on soil and water resources, leading to increased soil degradation. Our challenge is to balance food production with soil and environmental quality. Since land is a finite resource, the same piece of land will require increased inputs to produce more food which increases risks for environmental pollution. One must not forget that soils not only affect crop production but also air and water quality as well as plant, animal, and human health. Maintaining and improving “soil quality” and “soil health” will be essential to sustain agriculture and thus support world population.

1.5 Agents That Degrade Soil

1.5

5

Agents That Degrade Soil

Some of the processes that degrade soils include: • • • • • • • • • •

Water erosion Wind erosion Tillage erosion Soil compaction Poor drainage Nutrient depletion Acidification Sodification Salinization Biological degradation

Water and wind erosion are the leading agents of soil degradation. Soil compaction, poor drainage, nutrient depletion, acidification, sodification, salinization, and biological degradation are processes that also degrade soils under specific conditions of management, parent material, climate, terrain, and water. An often overlooked but important pathway of soil redistribution in sloping fields is tillage erosion caused by plowing, which gradually moves soil downslope in plowed fields with adverse on-site effects on crop production similar to water and wind erosion.

1.5.1

Erosion

1.5.1.1 Geologic and Accelerated Erosion Geologic erosion is a normal process of weathering that generally occurs at low rates in all soils as part of the natural soil-forming process. The rate of geologic erosion varies with soil, parent material, climate, and others, but the estimated rate is 1 Mg ha-1 year-1 (Nearing et al. 2017). The wearing away of rocks and formation of soil profiles are processes affected by slow but continuous geologic erosion. It occurs over long geologic time horizons and is not influenced by human activity. Indeed, low rates of erosion are essential to the formation of soil. Soil erosion becomes a major concern when the rate of erosion exceeds a certain threshold level, known as accelerated erosion (Fig. 1.2). This type of erosion is triggered by anthropogenic causes such as intensive plowing, crop residue removal, biomass burning, deforestation, and uncontrolled grazing. Intense climatic fluctuations including increased localized and heavy rainstorms can interact with the above causes and further accelerate risks of soil erosion. Extreme wet and dry (e.g., drought) conditions adversely affect near-surface soil structural quality and make the soil more susceptible to water and wind erosion. Specific discussion on how increasing climatic fluctuations affect soil and water conservation is presented in a later chapter.

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Fig. 1.2 Runoff not only carries water and soil but also nutrients off-site, which reduces soil fertility, crop production, and water quality (Courtesy USDA-NRCS)

1.5.1.2 History of Soil Erosion Accelerated erosion is as old as agriculture. It dates back to the ancient civilizations in Mesopotamia, Greece, Rome, and other regions in the Middle East (Bennett 1939). The collapse of the great ancient civilizations in Mesopotamia along the Tigris-Euphrates Rivers illustrates the consequences of irreversibly degraded lands. Soil erosion has plagued mankind since the beginning of agriculture, but its magnitude and severity have increased during the twentieth century due to changes in implements (e.g., moldboard plow), population increase, mismanagement of cultivated soils, deforestation, overgrazing, and climatic fluctuations (Amundson et al. 2015; Jarrah et al. 2020). Several textbooks discussed the consequences of severe erosion for the demise of ancient civilizations. Indeed, Hugh Hammond Bennett, recognized as the “Father of Soil Conservation” in the USA, described in detail the historical episodes and consequences of severe erosion in his well-known textbook (Bennett 1939). Troeh et al. (2004) also reviewed past and current erosion rates around the world. Knowledge of historic erosion rates is critical to understand the severity and consequences of erosion and develop strategies for effective management of present and future soil erosion. Thus, readers are referred to other textbooks for details on historic rates of erosion. This textbook primarily focuses on processes and strategies for managing soil effectively.

1.5 Agents That Degrade Soil

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1.5.1.3 Water Erosion On a global scale, water erosion is the most severe and extensive type of soil erosion (Fig. 1.2). Land affected by water erosion represents about 50% of the total degraded land, while wind erosion affects about 30% of the total degraded land area. Runoff washes away soil particles from sloping and bare lands, whereas wind blows away loose and detached soil particles from flat and unprotected lands (Jarrah et al. 2020). Water erosion is the dominant form of erosion in humid, sub-humid, and semiarid regions characterized by frequent rainstorms. It is also a problem in arid regions where limited precipitation often occurs in the form of intense storms when the soil is bare and devoid of vegetative cover. One of the most severe types of water erosion is concentrated gully erosion, which can cause severe soil erosion even in a single event of high rainfall intensity. Excessive gully erosion can wash out crops, expose plant roots, and lower the groundwater table while adversely affecting plant growth and landscape stability. Gullying is the major source of sediment and nutrient loss. It causes drastic alterations in landscape aesthetics and removes vast amounts of sediment. Sedimentation at the lower end of fields in depressional sites can bury crops, damage field borders, and pollute water bodies. In mountainous terrain and structurally fragile soils subjected to intense rains, total erosion from gullies can be as high as that from other types of erosion such as rill and interrill erosion. 1.5.1.4 Wind Erosion Wind erosion is a widespread phenomenon (Fig. 1.3). It is a dominant geomorphic force that has reshaped the earth. Most of the material carried by wind consists of silt-sized particles. Deposition of this material, termed “loess,” has developed into very fertile and deep soils. The thickness of most loess deposits ranges from 20 to 30 m, but it can be as thick as 335 m (e.g., Loess Plateau in China). Extensive deposits of loess exist in northeastern China, Midwestern USA, Las Pampas of Argentina, and central Europe. Wind erosion is prominent but not unique to arid regions. Rates of wind erosion increase in the order of: Arid > Semiarid > Dry subhumid > Humid areas. Unlike water, wind has the ability to move soil particles up- and down-slope and can pollute both air and water. While arid lands are more

Fig. 1.3 Wind erosion can cause air pollution (left; Courtesy USDA-NRCS), reduce vegetative cover, and form sand dunes (right; Photo by H. Blanco)

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prone to wind erosion than humid ecosystems, any cultivated soil that is seasonally disturbed can be subject to wind erosion, particularly in windy environments. Wind erosion has intensified in recent years due to frequent droughts and the expansion of agriculture to marginal lands. Wind erosion carries nutrients (e.g., N, P) and contributes to water pollution. Cultivation of poorly structured soils with low soil organic matter content and fertility exacerbates severe wind erosion in arid and semiarid regions. Semiarid and arid regions are most susceptible to degradation by wind erosion because of limited vegetative cover and harsh climate (e.g., low precipitation, strong winds). About 60% of total semiarid and arid area in the world are susceptible to erosion. Rates of soil degradation in semiarid and arid lands are particularly high in developing nations (Borrelli et al. 2017). The “Dust Bowl” in the USA that occurred during the 1930s is an illustration of severe wind erosion when proper soil conservation practices are not implemented (Fig. 1.3).

1.5.1.5 Consequences of Soil Erosion Accelerated soil erosion causes adverse agronomic, ecologic, environmental, and economic effects both on-site and off-site. It not only affects agricultural lands but also the quality of forestlands, pasturelands, and rangelands. Cropland soils are, however, more susceptible to erosion because these soils are often left bare or with little residue cover between cropping seasons. Even during the growing season, row crops are susceptible to soil erosion. The on-site consequences involve primarily the reduction in soil productivity, while the off-site consequences are mostly due to the sediment and chemicals transported away from the source into natural waters by streams and depositional sites by wind. 1.5.1.6 On-Site Consequences The primary on-site effect of erosion is the reduction of topsoil thickness, which results in soil structural degradation, soil compaction, nutrient depletion, loss of soil organic matter, poor seedling emergence, and reduced crop yields (Table 1.2). Erosion not only causes losses of soil but also losses of water and nutrients. Removal of the nutrient-rich topsoil reduces soil fertility and decreases crop yield. Soil erosion reduces the functional capacity of soils to produce crops, filter pollutants, and store C and nutrients. One may argue that, according to the law of conservation of matter, soil losses by erosion in one place are compensated by the gains at another place. The problem is that the eroded soil is often deposited in locations where no crops can be grown. Control and management of soil erosion are important because when the fertile topsoil is eroded away, the remaining soil is less productive with the same level of input. 1.5.1.7 Off-Site Consequences Water and wind erosion preferentially remove the soil layers where most agricultural chemicals (e.g., nutrients, pesticides) are concentrated. Thus, off-site transport of sediment and chemicals causes pollution, sedimentation, and silting of water resources (Figs. 1.2 and 1.3). Sediment transported off-site alters landscape

1.5 Agents That Degrade Soil

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Table 1.2 Implications of increased soil erosion on soil processes, properties, and productivity Physical processes Increase in: • Surface sealing • Crusting • Compaction • Deflocculation • Sand content Decrease in: • Topsoil depth • Soil structural stability • Macroporosity • Plant available water capacity • Water infiltration

Chemical processes Increase in: • Acidification • Salinization • Sodification • Water pollution Decrease in: • Cation exchange capacity • Nutrient storage and cycling • Biogeochemical cycles

Biological processes Increase in: • Organic matter decomposition • Eutrophication • Hypoxia • Emission of greenhouse gases Decrease in: • Biomass production • Soil organic matter content • Nutrient content and cycling • Microbial biomass, activity, and diversity

characteristics, reduces wildlife habitat, and causes economic loss. Erosion also decreases livestock production through a reduction in forage production, damages water reservoirs and protective shelterbelts, and increases tree mortality. Accumulation of eroded materials in alluvial plains causes flooding of downstream croplands and water reservoirs. Soil erosion also contributes to losses of soil C, which can negatively affect soil productivity. Large amounts of C are rapidly oxidized during erosion, exacerbating the release of CO2 and CH4, two greenhouse gasses, to the atmosphere (Table 1.2). The on- and off-site costs of erosion for replenishing lost nutrients, dredging or cleaning up water reservoirs and conveyances, and preventing erosion are very high. Wind erosion causes dust pollution, which changes atmospheric radiation levels and fluxes of energy, reduces visibility, and causes traffic accidents. Dust particles penetrate into buildings, houses, gardens, and water reservoirs and deposit in fields, rivers, lakes, and wells, causing pollution and increasing maintenance costs. Dust storms transport fine inorganic and organic materials, which are distributed across the wind path. Most of the suspended particles are transported off-site and are deposited hundreds or even thousands of kilometers far from the source. Airborne fine particulate matter with diameters of 10 μm (PM10) and 2.5 μm (PM2.5) pose an increasing threat to human and animal health, industrial safety, and food processing plants. Finer particles float in air and are transported at longer distances than coarser particles. Particle size of the deposited eolian material decreases with increasing distance from the source area. A number of changes in soil physical, chemical, and biological processes occur due to accelerated soil erosion (Table 1.2). These processes rarely occur individually but in tandem with one another. For example, compacted soils are more prone to soil structural deterioration (physical process), salinization (chemical process), and reduced microbial activity (biological process) than non-compacted soils. Some processes are more dominant in one soil than in another. For instance, salinization is often more severe in irrigated lands with poor internal drainage than in welldrained soils of favorable structure.

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1.5.1.8 What Causes Soil Erosion? Anthropogenic activities involving intensive cultivation, urbanization, deforestation, overgrazing, and cultivation of steep slopes accelerate soil erosion risks. Land use and management, topography, climate, and social, economic, and political conditions influence soil erosion (Table 1.3). In developing countries, soil erosion is directly linked to poverty level. Resource-poor farmers lack the means to establish conservation practices. Subsistence agriculture forces farmers to use extractive practices on small-size (0.5–2 ha) farms year after year for food production, delaying or completely excluding the adoption of conservation practices that reduce soil erosion risks. Deforestation removes the protective vegetative cover and accelerates soil erosion. Forests provide essential ecosystem services such as soil erosion control, ecosystem stabilization, and moderation of climate and energy fluxes. Forests also provide wood, food, medicines, and many other wood-based products. Excessive logging and clear-cutting, expansion of agriculture to marginal lands, frequent fires, construction of roads and highways, and urbanization are the main causes of denudation. For example, in the Amazon forest, deforestation continues to be a major problem. Forests are disappearing more rapidly in developing countries than in developed countries. Concentrated pasturing of cattle and sheep herds on the same piece of land for too long in livestock farms can lead to repeated trampling, soil displacement during traffic, and overgrazing. Removing or thinning of grass cover by grazing reduces the protective cover and increases soil erosion, particularly on steep slopes or hillsides. Overgrazing reduces soil organic matter content, degrades soil structure, and accelerates water and wind erosion. Trampling by cattle causes soil compaction, reduces root proliferation and growth, and decreases water infiltration rate and drainage. Increases in animal stocking rates result in a corresponding increase in runoff and soil erosion in heavily grazed areas. In wet and clayey soils, compaction and surface runoff from overgrazed lands can increase soil erosion. Increased erosion from pasturelands can also cause siltation and sediment-related pollution of downstream water bodies. In dry regions, animal traffic disintegrates aggregates Table 1.3 Soil erosion causes and associated environmental and societal issues Land use • Deforestation • Overgrazing • Urbanization • Burning and slashing • Mining • Road construction • Forest fires

Cultivation • Excessive plow tillage • Salinization • Residue removal at high rates • Low-biomass producing crops • Shifting cultivation

Climate and topography • Frequent and intense droughts • Steep slopes (water and tillage erosion) • Intense rainstorms • Frequent flooding • Intense windstorms • Flat terrains (wind erosion)

Social and economic conditions • Ineffective conservation policies • Poorly defined land tenure • Lack of incentives and weak institutional support • High population density • Low income

1.5 Agents That Degrade Soil

11

in surface soils and increases soil’s susceptibility to wind erosion. Continuous grazing increases the sand content of the surface soil as the detached fine particles are preferentially removed by flowing water and wind. Light and moderate grazing do not have major negative implications on soil and water conservation, but overgrazing can have large negative impacts. Expansion of agriculture to sloping, low-lying, and marginal lands is a common cause of soil erosion. Intensive agriculture and plowing, wheel traffic, and absence of vegetative cover can negatively affect soil properties. Removal of crop residues for feed, biofuel, and industrial uses reduces the amount of protective cover left on the soil surface below the level adequate to protect the soil against erosion. Intensive cultivation accelerates water runoff and exacerbates soil erosion, which transport nutrients and pesticides off-site, decreasing soil and water quality.

1.5.1.9 Erosion in the USA and the World Estimates indicate that water and wind erosion from croplands in the USA generally decreased from about 1982 to 2007 (Fig. 1.4). However, the same estimates indicate water erosion in the USA has slightly increased since 2007 (Fig. 1.4). The rates of total soil erosion in the USA vary with the region and year. The total amount of soil lost is not easily quantifiable. Erosion is particularly high in the major crop production areas under intensive tillage. For example, topographical surveys indicate that a median historical erosion rate is 1.8 ± 1.2 mm year-1 in the Midwestern USA (Thaler et al. 2021). The problem of soil erosion can be even more severe in the tropics and sub-tropics because of high population pressure and scarcity of prime agricultural lands. The threat of erosion is region-specific. The main hot spots of soil erosion at present are: sub-Saharan Africa, Haiti, China Loess Plateau, the Andean region, the Caribbean, and the lower Himalayas. Erosion rates in these regions easily exceed 20 Mg ha-1 year-1 due to row cropping in marginal soils, sloping lands, and 10 9

Erosion Rate (Mg ha-1)

Fig. 1.4 Total water and wind erosion from croplands in the USA from 1982 to 2017 (USDA 2020)

Water Erosion Wind Erosion

8 7 6 5 4 1982 1987 1992 1997 2002 2007 2012 2017 Year

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mountainous terrain (Borrelli et al. 2017). An example of one of the most erosionaffected regions in the world is Africa. About 75% of the arable land in Africa is affected by erosion. Estimates indicate that for some countries in the region (e.g., Rwanda), mean water erosion rates can be 300 Mg ha-1 year-1 (Karamage et al. 2016). This high erosion rate is primarily due to the presence of croplands with steep slopes (>10%), intense rainstorms, and limited adoption of soil conservation practices. Crops are often grown on the same piece of land year after year, leading to large extractions of nutrients, which typically are not replenished by input of fertilizers and amendments due to the high cost and limited availability of fertilizers. Since new lands for agricultural expansion are limited, as it was traditionally done (e.g., fallows), farmers are now forced to cultivate the same piece of land year after year and crop after crop. Haiti, known as an eroding nation, is another example where soil erosion is very severe due to deforestation. The high rates of soil erosion and declining crop yields have increased problems of food insecurity and environmental degradation. Food production is either decreasing or remaining stagnant in most regions affected by erosion. The readers are referred to Borrelli et al. (2017) for further information on soil erosion rates by country and continent.

1.5.1.10 How Much Soil Loss Is Acceptable? While soil erosion cannot be completely curtailed, excessive erosion must be reduced to a manageable or tolerable level to minimize adverse effects on soil productivity. The magnitude and impacts of soil erosion on productivity depend on soil profile and horizonation, terrain, soil management, and climate characteristics. The estimated average tolerance (T) level of soil erosion used in soil and water conservation planning in the USA is about 11 Mg ha-1 year-1, but this T value varies among soils and often ranges from 2.2 to 11.0 Mg ha-1 year-1 (Troeh et al. 1999). Most of the prime agricultural lands are located on soils with an erosion tolerance level of 11.0 Mg ha-1 year-1. In fact, moderate soil erosion may not adversely affect productivity in well-developed, fertile, high C, and deep soils, but the same amount of erosion may have drastic effects on shallow, degraded, low C, and sloping soils. Thus, critical limits of erosion must be determined for each soil, ecoregion, land use, and farming system. Some argue that the T (tolerance) values may be set too high and that even smaller rates of erosion can severely reduce crop production, depending on topsoil thickness and management systems. Soil erosion gradually removes thin layers of soil of ≤1 mm thickness at a time. Even the removal of 1 mm of soil, while apparently very small, amounts to about 12.5 Mg ha-1, which exceeds the rate of annual soil formation or geologic erosion (about 1 Mg ha-1 year-1). Losses of soil above the natural rate of soil formation can be unsustainable.

1.5.2

Tillage Erosion and Soil Loss Due to Crop Harvesting

Erosion by wind and water has traditionally been recognized as the only major components of total erosion. Tillage erosion and erosion due to root crop harvesting

1.5 Agents That Degrade Soil

13

are often neglected. Yet, the latter pathways of soil loss are also important components of total erosion. For example, tillage erosion is one of the most important soil degradation processes in sloping croplands around the world (Fig. 1.5). Tillage erosion refers to the gradual translocation of soil downslope due to frequent and intensive tillage operations. Tillage, particularly up- and down-slope plowing, can move soil downhill and accumulate eroded soil at the bottom of croplands (Logsdon 2013). Tillage erosion depends on tillage tools. Chisel plowing can move soil near the soil surface, while moldboard plowing can move soil for the whole tillage depth. This process also makes soil more susceptible to water and wind erosion by loosening the soil (Wang et al. 2016). The combined forces of water, wind, and tillage erosion can increase soil loss more than a single erosion force. Tillage erosion accelerates water and wind erosion in sloping fields. Over time, tillage erosion creates a gradient of nutrient distribution along a landscape where soil C and nutrient concentrations decrease from the upper to the bottom portions of the field. Such losses of soil C and nutrients from the upper portions of the field can negatively affect soil productivity and environmental quality. Tillage erosion can cause the denudation of summit and backslope positions of the field, while exposing subsoil layers with low fertility. Tillage erosion can be more severe than water and wind erosion in some croplands depending on the soil slope, precipitation input, residue cover, tillage intensity, equipment size, and soil surface conditions. Even hand-held tillage implements used primarily in developing countries can cause erosion in the long term. Soil loss due to root crop harvesting is another concern (Kuhwald et al. 2022). However, few have studied soil loss due to root crop harvesting. Large amounts of soil attached to the roots can be removed with the harvest of root crops including sugarbeet, carrot, potato, sweet potato, yam, cassava, taro, turnip, and radish, among many others (Fig. 1.5). The soil loss due to root crop harvesting can be particularly large in places where adequate equipment for sorting and washing root crops at the field site is not available. Losses of soil due to crop harvesting can be as much as 20% of the total soil loss and can be as high as 22 Mg ha-1 harvest-1 (Kuhwald et al.

Fig. 1.5 Plowing gradually moves soil downhill (left; Photo by T.E. Schumacher), while root crop harvesting such as carrot harvesting can remove soil attached to the roots (right; Photo by M. Parlak)

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2022). This rate of soil loss due to crop harvesting can be equal to or higher than soil loss due to water and wind erosion. The implications of soil loss due to root crop harvesting to total erosion and nutrient losses deserve consideration. Combined effects of water, wind, and tillage erosion along with soil losses due to root crop harvesting can pose a threat to sustainable agriculture.

1.5.3

Soil Compaction

Soil compaction is another major soil degradation process that occurs due to heavy farm equipment or animal traffic (Pulido-Moncada et al. 2022; Fig. 1.6). The weight and size of field equipment (tractors, harvesters, manure spreaders, and others) have gradually increased since the mid-1900s. For example, the average weight of a tractor has increased from about 3 Mg in the 1940s to about 20 or 45 Mg in the 2010s. Soils are particularly prone to compaction when they are wet. Erratic climatic patterns (e.g., intense rainstorms), changes in planting strategies (e.g., early planting when soil is wet), and increased demands for food production all contribute to soil compaction. Increased soil compaction risks under modern agriculture threaten agricultural productivity as well as environmental quality. Repeated wheel traffic during tillage, planting, harvesting, manuring, and weed and pest control degrades the soil structure and causes surface and subsurface compaction in cultivated soils. Subsurface compaction or compaction just below the depth of tillage occurs when a compacted subsurface horizon of higher bulk density and lower total porosity than the topsoil, known as plow pan, is formed (Glossary of Science Terms 2008). The extent of compaction depends on axle load, tillage methods, and site-specific conditions (e.g., texture and drainage). Soil compaction is particularly challenging in poorly-drained clayey soils with high shrinkswell potential. Soil compaction adversely affects soil properties, specifically water, gas, and heat fluxes. Moderate compaction can enhance water and nutrient uptake, but excessive compaction can restrict root growth, reduce nutrient and water uptake,

Fig. 1.6 Grain cart weighing more than 20 Mg can cause significant soil compaction (left), while grazing cover crops in wet soils can also compact soil (right; Photos by H. Blanco)

1.5 Agents That Degrade Soil

15

and reduce crop yields. Excessive compaction may reduce crop yields by up to 50%, depending on axle loads and soil-specific characteristics (e.g., texture, drainage). Practices that remove the protective residue from the soil surface or intensive tillage can cause a breakdown of surface soil aggregates and increase soil crusting, thereby forming compacted soil layers. Increased soil compaction can have economic and environmental consequences. Mechanical operations to fix soil compaction can be expensive in terms of labor, fuel usage, and emissions of CO2.

1.5.4

Poor Drainage

Poor drainage results from alterations in soil water balance. Poorly-drained soils have excess water, and thus low aeration, which can limit crop establishment and cause environmental problems (Fig. 1.7). Poorly-drained soils are susceptible to occasional flooding. Poor drainage is especially a problem near floodplains or nearly-level soils. Intensive tillage operations, compaction, and use of monocrops can reduce drainage with time due to the degradation of soil properties. Because most of the upland row crops such as corn and soybeans require well-drained soils for growth, artificial drainage (e.g., subsurface tile drains, canals, ditches) is a strategy to remove the water from the root zone and lower the water tables, but establishment and maintenance of such systems can be expensive. Pastures or soils under permanent vegetation can tolerate some occasional flooding. Poorly-drained soils often have high clay content and are susceptible to compaction. These soils can also be subject to N losses such as N2O through denitrification. Poorly-drained soils can also be more susceptible to flooding than well-drained soils. For example, the major floods in the US Midwest in spring 2019 highlight the need to improve soil

Fig. 1.7 Intense rainstorms can cause flooding in poorly-drained soils (Photo by H. Blanco)

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drainage with proper soil management practices to, at least, partly reduce flooding risks.

1.5.5

Salinization, Sodification, and Acidification

Accumulation of water-soluble salts including Ca, Mg, Cl, Na, carbonates, and others near the soil surface results in salinization, while the preferential near-surface accumulation of Na results in sodification. These processes are predominant in regions with low precipitation. Evaporation is responsible for the accumulation of salts near the soil surface. Causes of salinization and sodification include irrigation with water of high salt concentration, poor drainage, low rainfall, high evaporation, and intensive tillage and cropping systems. Salinization can reduce root and plant growth because it increases osmotic pressure, limits nutrient uptake, and induces toxic effects. Excessive concentration of Na deflocculates soil aggregates and reduces soil structural quality, further reducing the water flow through the soil. Increases in soil temperature (heat waves) and reductions in precipitation (droughts) under fluctuating climates can trigger salinization and sodification. These processes can lead to soil desertification, loss of soil fertility, crusting, and low production. This problem is most predominant in arid, semiarid, and sub-humid areas. Acidification occurs when soil pH decreases and is a growing concern under intensive agriculture. Most crops require a soil pH between 6 and 7.5. Excessive acidity can reduce nutrient availability, reduce biological activity, increase deficiency in basic cations, and increase levels of toxic elements such as heavy metals. Excessive application of ammonium-based N fertilizers or acidifying fertilizers, N leaching, continuous cropping, removal of crops, and leaching of basic cations (Ca, Mg, Na, and K) are some of the causes for the rapid acidification in cultivated soils. Acidification is most predominant in regions of high precipitation and clayey soils. Compared with soils under native vegetation, croplands under intensified agriculture and high precipitation are highly susceptible to acidification due to differences in management.

1.5.6

Soil Biological Degradation

Intensive cultivation may not only lead to soil physical and chemical degradation but also to soil biological degradation. The latter is often overlooked in soil management discussions. Yet, soil macro and microorganisms, also known as soil biota, are the biological engine that drive and regulate many soil ecosystem services. Thus, a decrease in the number and activity of microorganisms as well as a reduction in microbial biomass and soil organic matter are key indicators of soil biological degradation. Agricultural management practices that reduce soil organic matter concentration can directly deteriorate soil biological properties. Also, soil pollution and excessive use of inorganic fertilization can adversely affect soil biology (de Graaff et al. 2019). Soil organisms directly contribute to C and nutrient cycling,

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Regulates all biogeochmical cycles Regulates emissions of soil gasses

Controls pests and pathogens

Retains and supplies nutrients

SOIL BIOTA AND ECOSYSTEM SERVICES

Degrades pollutants

Promotes soil aggregation and water infiltration

Reduces soil erosion

Reduces flood and drought risks

Filters and cleans water

Fig. 1.8 Some of the ecosystem services that soil biota provide (Wall et al. 2004; Lehman et al. 2015)

soil aggregation, aeration, water movement, organic matter decomposition, control of pest and diseases, and other vital processes affecting ecosystem functioning (Lehman et al. 2015; Fig. 1.8). For example, soil organisms can bind soil particles into aggregates through the secretion and release of organic compounds. Soil macroorganisms such as earthworms can physically create biochannels to promote water infiltration and transfer of soil C and nutrients in the soil profile. Soil biological processes are directly related to soil erosion. A complex yet a mutual relationship between soil biological properties and soil erosion exists (Orgiazzi and Panagos 2018). For instance, the extent to which soil organisms promote soil aggregation will determine the resistance of the soil to erosion (erodibility) and overall degradation. However, soil biological properties are not often considered when quantifying or estimating soil erosion. This is due to, in part, the complexity of quantifying soil biological properties compared to quantifying physical and chemical properties related to erosion. Yet, incorporation of the biological

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component can allow a better understanding of processes and estimation of soil losses. One of the key strategies to reduce soil degradation is by enhancing soil biological properties. Managing or improving soil suitability as a habitat for soil organisms is one of the main goals of soil management. Enhancing the soil biological environment can also enhance soil’s resistance to degradation for ensuring the delivery of multiple ecosystem services.

1.6

The Need for Soil and Water Management

The above discussion indicates that judicious management of soils is needed and must be a priority. As an example, managing soil is not only about adding the right amount of fertilizers and water to soil but it is also about enhancing the resilience or capacity of the soil to buffer or resist changes. A well-managed soil should be able to provide nutrients when soil fertility is low, retain water during dry periods, and release water during wet periods. As indicated earlier in this chapter, the goal of soil management is to manage and conserve soil to enhance its performance for a sustainable agricultural production. This means that well-managed soils should allow profitable farming while maintaining or improving environmental quality. While managing factors such as climate can be beyond our control, managing soils is within our reach. Since the middle of the twentieth century, considerable progress has been made in developing effective soil management practices through a better understanding of the causes, factors, and processes of soil degradation and the related soil properties. For example, an understanding of the factors determining the magnitude of soil erosion risk has made possible the development and establishment of erosion control practices in many parts of the world. However, despite these technological advances, proper management of soils is still a challenge. Erosion, compaction, salinization, acidification, and biological degradation are still major concerns with a magnitude depending on the region. Reversing or reducing the continued degradation of soils is possible through proper management. As an example, the decreasing trend or stabilization in water and wind erosion rates in the USA since the 1960s is attributed to land stewardship and soil conservation efforts and policies. The Great Depression and the Dust Bowl that occurred during the 1930s stirred interest and promoted research in developing soil conservation practices (e.g., windbreaks and terraces). Soil conservation policies were implemented in the early 1930s. The early policies stressed the importance of keeping the soil in place and were mostly focused on the on-site effects (e.g., crop production) of soil erosion. Since the 1980s, conservation policies have stressed both on- and off-site adverse impacts of soil erosion. A number of USDA programs and initiatives exist that promote a reduction in soil erosion and improvement in water quality and wildlife habitat. The Food Security Act of 1985 created the Conservation Reserve Program (CRP) which rewards landowners and farmers for their land stewardship. The CRP provides technical and financial assistance to producers implementing approved conservation practices on highly erodible cropland. Adoption of conservation tillage such as no-till farming, a practice where crops are grown

1.7 Summary

19

without turning soil, has also contributed in part to better soil management, but much remains to be done. Soil erosion, water pollution, acidification, and losses of other soil ecosystem services remain a major problem. The extent of soil degradation greatly varies with soil type, management, ecoregion, and climatic characteristics. The significant improvements in soil and water management achieved in some regions are not reflected in other regions where soil degradation constitutes a major threat to food security. More formidable strategies of soil management are required to counteract soil degradation based on an integrated agronomic, economic, social, and political approach. Unless farming systems are based on economically feasible and environmentally sound practices of soil management, soil degradation will continue to pose a threat to agricultural and environmental sustainability. It is important to consider that the recent increased climatic fluctuations (intense rainstorms, windstorms, flooding, and drought) further pose a challenge to soil and water management. The increasing climatic fluctuations demand the redesign of existing systems (Blanco-Canqui and Francis 2016). A number of soil conservation practices have been used to manage soils. However, such practices are designed to manage soils for past climates. New scenarios of climatic conditions and reduced soil ecosystem services require that soil management and conservation be a priority. Now, emphasis is shifting toward enhancing soil health through combined management practices that not only keep the soil in place but also increase or maintain soil resilience under increasing climatic fluctuations. Reducing soil loss below T values is not sufficient to enhance soil resilience, mitigate climate fluctuations, and reduce emissions of greenhouse gases. The time has come to go beyond managing soil erosion. Enhancing soil health and resilience is a new paradigm to ensure that soils provide multiple services, known as soil ecosystem services. A new level of improvement is needed to manage soil and water to meet the increasing demands. The following chapters will discuss specific management practices that can enhance soil’s capacity to resist and buffer the above degradative processes.

1.7

Summary

Management of soil and water is essential to address global challenges. Soil is a multi-functional system and delivers multiple ecosystem services. Greater focus on improving soil and management practices is needed to meet the increasing demands for food, fiber, fuel, and feed. The goal of soil management is to improve soil performance for various functions. For example, soil management is not only about food security but also about environmental quality. Soil is the medium that recycles nutrients, buffers water pollutants, and stores C. Enhancing soil ecosystem services and soil security is key to address global challenges. (continued)

20

1

Soil and Water Management

Soil erosion by water, wind, tillage, and root crop harvesting is the primary agent of soil degradation. Other causes of soil degradation include compaction, acidification, salinization, and biological degradation. Deforestation, overgrazing, intensive cultivation, mismanagement of cultivated soils, and urbanization are the main causes of accelerated soil erosion. Soil is eroding at rates faster than it is being formed and thus deserves more attention. While erosion is a global problem, its magnitude is region-specific. Soil erosion has decreased in the USA since the 1960s and ranges from 2.2 to 11 Mg ha1 year-1, but the rate is still higher than the rate of soil formation. The problem of soil erosion in the rest of the world is more severe with erosion rates often above the T values. The hot spots of soil erosion include the sub-Saharan Africa, Haiti, and the China Loess Plateau. Improved management practices must be embraced to improve soil multifunctionality and resilience. Implementation of adequate conservation policies and programs has reduced soil degradation but much more needs to be done. For example, keeping soil in place is not enough. It is also important to restore the health and resilience of soils through novel or improved management practices. Current management practices need to be redesigned or improved to withstand increasing climatic fluctuations such as droughts, intense rainstorms, floods, heat waves, and wind storms. Questions 1. 2. 3. 4. 5. 6. 7. 8.

9. 10.

Describe the four categories of soil ecosystem services. Describe the on-site and off-site impacts of soil erosion. Briefly describe the history of soil erosion around the world. Discuss how the extent of water and wind erosion varies from west to east or north to south in the region where you live. Compare soil losses due to water, wind, and tillage erosion as well as root crop harvesting. What is the T value, and how it is estimated? Do you think T values will vary between fertile and low-fertility soils; sandy and clayey soils; and sloping and flat soils? Discuss your response to each condition. Soil erosion rates in the USA vary between 2.2 and 11.0 Mg ha-1 year-1. Convert these values to mm year-1 assuming that soil bulk density is 1.25 Mg m-3 (1.25 g cm-3). One Megagram (Mg) is equal to 1000 kg. Convert 2.2 and 11.0 Mg ha-1 year-1 to English units in ton/ac if 1 Mg ha-1 = 0.446 US tons per acre. Soil erosion rates, in most soils, in the USA vary between 2.2 and 11.0 Mg ha-1 year-1. Compute the total C (lbs/ac-year) and total N (lbs/ac-year) lost for each rate (2.2 and 11.0 Mg ha-1 year-1) if the sediment contains 1.5% of total C and 0.15% of total N. What is the total cost ($) to replace the N lost if one pound of N costs 65 cents?

References

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11. Four rainstorm events eroded 0.1, 0.3, 0.5, and 1.0 mm of soil, respectively. Convert these values to Mg ha-1 and ton/ac, assuming the soil bulk density of 1.25 Mg m-3. 12. Discuss results from Problem 11 in relation to T values. 13. Discuss why compaction can be a problem in agricultural soils when tillage can readily break and fix compacted layers. 14. What is the new outlook for soil management?

References Amundson R, Berhe AA, Hopmans JW et al (2015) Soil and human security in the 21st century. Sciences 348. https://doi.org/10.1126/science.1261071 Bennett HH (1939) Soil conservation. McGraw-Hill, New York Blanco-Canqui H, Francis CA (2016) Building resilient soils through agroecosystem redesign under fluctuating climatic regimes. J Soil Water Conserv 71:127A–133A Borrelli P, Robinson DA, Fleischer LR, Lugato E, Ballabio C, Alewell C, Meusburger K, Modugno S, Schütt B, Ferro V, Bagarello V, Oost KV, Montanarella L, Panagos P (2017) An assessment of the global impact of 21st century land use change on soil erosion. Nat Commun 8: 2013 de Graaff M, Hornslein N, Throop HL, Kardol P, van Diepen LTA (2019) Chapter One – Effects of agricultural intensification on soil biodiversity and implications for ecosystem functioning: a meta-analysis. Adv Agron 155:1–44 Glossary of Science Terms (2008) Soil Science Society of America. https://www.soils.org/ publications/soils-glossary/ Jarrah M, Mayel S, Tatarko J, Funk R, Kuka K (2020) A review of wind erosion models: data requirements, processes, and validity. Catena 187:104388 Karamage J, Zhang C, Ndayisaba F, Shao H, Kayiranga A (2016) Extent of cropland and related soil erosion risk in Rwanda. Sustainability 8:609. https://doi.org/10.3390/su8070609 Kuhwald M, Busche F, Saggau P, Duttmann R (2022) Is soil loss due to crop harvesting the most disregarded soil erosion process? A review of harvest erosion. Soil Till Ress 215:105213 Lehman RM, Cambardella CA, Stott DE, Acosta-Martinez V, Manter DK, Buyer JS, Maul JE, Smith JL, Collins HP, Halvorson JJ, Kremer RJ, Lundgren JG, Ducey TF, Jin VL, Karlen DL (2015) Understanding and enhancing soil biological health: the solution for reversing soil degradation. Sustainability 7:988–1027 Logsdon SD (2013) Depth dependence of chisel plow tillage erosion. Soil Tillage Res 128:119–124 MEA (2003) Millennium Ecosystem Assessment: a framework for assessment. Island Press, Washington, DC Nearing MA, Xie Y, Liu B, Ye Y (2017) Natural and anthropogenic rates of soil erosion. Int Soil Water Conserv Res 5:77–84 Orgiazzi A, Panagos P (2018) Soil biodiversity and soil erosion: it is time to get married. Adding an earthworm factor to soil erosion modelling. Global Ecol Biogeogr 27:1155–1167 Pereira P, Bogunovic I, Munoz-Rojas M, Brevik E (2018) Soil ecosystem services, sustainability, valuation and management. Curr Opin Environ Sci Health 5:7–13 Pulido-Moncada M, Petersen SO, Munkholm LJ (2022) Soil compaction raises nitrous oxide emissions in managed agroecosystems. A review. Agron Sustainable Dev 42:38 Thaler EA, Larsen IJ, Yu Q (2021) The extent of soil loss across the US Corn Belt. Proc Natl Acad Sci 118:e19223751 Troeh FR, Hobbs JA, Donahue RL (1999) Soil and water conservation. Prentice Hall, New Jersey Troeh FR, Hobbs JA, Donahue RL (2004) Soil and water conservation for productivity and environmental protection, 4th edn. Prentice Hall, New Jersey

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U.S. Department of Agriculture (USDA) (2020) Summary Report: 2017 National Resources Inventory. Natural Resources Conservation Service, Washington, DC, and Center for Survey Statistics and Methodology, Iowa State University, Ames, Iowa Wall DH, Bardgett RD, Covich AP, Snelgrove PVR (2004) The need for understanding how biodiversity and ecosystem functioning affect ecosystem service in soils and sediments. In: Wall DH (ed) Sustaining biodiversity and ecosystem services in soils and sediments, vol 64. Island Press, Washington, DC, pp 1–12 Wang Y, Zhang JH, Zhang ZH, Jia LZ (2016) Impact of tillage erosion on water erosion in a hilly landscape. Sci Total Environ 551:522–532 Yee SH, Paulukonis E, Simmons C, Russell M, Fulford R, Harwell L, Smith LM (2021) Projecting effects of land use change on human well-being through changes in ecosystem services. Ecol Model 440:109358

2

Water Erosion

Water erosion is the wearing away of the soil surface by water from rain, runoff, snowmelt, and irrigation. Rainwater is the main driver of water erosion in the form of runoff. Runoff refers to the movement of water on the soil surface by gravity. It carries soil organic and inorganic particles and deposits them at lower landscape positions. The eroded material can either form a new soil or simply fill streams, lakes, and reservoirs. Water erosion occurs in all soils to varying degrees. Slight erosion is actually beneficial to the formation of soil, but severe or accelerated erosion adversely affects soil and environment. Accelerated erosion refers to soil loss above the tolerable soil loss level. Understanding the mechanisms and magnitude of water erosion is vital to managing and developing erosion control practices. The goal of this chapter is to describe the basic principles of water erosion including types, processes, factors, and causes.

2.1

Types

The main types of soil erosion are: splash, interrill, rill, gully, streambank, and tunnel erosion. Splash and sheet erosion are sometimes known as interrill erosion, but their processes differ. Note that the different types of erosion are interconnected. For example, splash erosion is the precursor of interrill, rill, and gully erosion. Each type of erosion is discussed next.

2.1.1

Splash Erosion

Raindrops falling on the soil surface disperse and splash the soil, displacing particles from their original positions. Splash erosion is caused by the bombardment of the soil surface by impacting raindrops. Processes of splash erosion involve raindrop impact, splash of soil particles, and formation of small craters. The diameter of the craters can be as large as 10 cm in diameter. Raindrops striking the soil surface develop a # The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 H. Blanco, R. Lal, Soil Conservation and Management, https://doi.org/10.1007/978-3-031-30341-8_2

23

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raindrop-soil particle momentum before releasing their energy in the form of splash. These raindrops strike the soil like small bombs forming craters or cavities of contrasting shapes and sizes. The soil displacement by splash erosion can be as high as 1.5 m and exceed 5 m in horizontal distance under windy conditions (Fernandez-Raga et al. 2017).

2.1.2

Interrill Erosion

As soon as runoff starts, rills (small channels) develop. The portion of runoff that flows between rills can cause sheet or interrill erosion (Fig. 2.1). This type of erosion is mostly due to shallow flow. Some particles are carried away in runoff flowing in a thin sheet and some particles concentrate in small rills. Interrill is the most common type of soil erosion. Splash and interrill erosion make up about 70% of total soil erosion and occur simultaneously although splash erosion dominates during the initial process. Interrill erosion is a function of particle detachment, rainfall intensity, slope gradient, and slope length. It is represented as per Eqs. (2.1) and (2.2) (Foster et al. 1982; Huang et al. 1996; Zhang et al. 2014): Di = K i RI 0:22 Sf L - 0:25

Fig. 2.1 A cropland affected by rill and interrill erosion (Courtesy USDA-NRCS)

ð2:1Þ

2.1 Types

25

where Di is the interrill erosion rate (kg m-2 s-1), Ki is rate of interrill erodibility (kg m-2 s-1), R is runoff rate (m s-1), I is rainfall intensity (m s-1), Sf is slope factor, and L is slope length (m). The slope factor is equal to Sf = 1:05 - 0:85 expð- 4 sin θÞ

ð2:2Þ

where θ is slope angle.

2.1.3

Rill Erosion

The term rill erosion refers to the soil erosion that occurs in small channels or rills. Rill erosion occurs due to concentrated rather than shallow flow (Fig. 2.1). Runoff water that concentrates in small channels erodes soil at faster rates than interrill erosion. The force of flow and the soil particles creeping along the rill bed enlarge the rills. Rill erosion is the second most common pathway of soil erosion. The rills are easily obliterated by tillage operations but can cause large quantities of soil loss, especially under intensive rains. Rill erosion is a function of soil erodibility, runoff transport capacity, and hydraulic shear of water flow. Soil erosion occurs mostly through the simultaneous action of interrill and rill erosion in accord with the steadystate sediment equation (Shen et al. 2016) ∂qs = Dr þ Di ∂x

ð2:3Þ

where qs is sediment delivery rate in rills (kg m-1 s-1), x is length of rill (m), Dr is rill detachment rate (kg m-2 s-1), and Di is interrill sediment delivery (kg m-2 s-1).

2.1.4

Gully Erosion

Gully erosion is the soil removal along channels or drainage lines due to concentrated runoff (Fig. 2.2; Troeh et al. 2004). It creates either V- or U-shaped channels. The gullies are linear incision channels of at least 0.3 m width and 0.3 m depth. Gullies are larger channels than rills, which are responsible for rill erosion. Undulating fields cause runoff to concentrate in natural swales as runoff moves downslope in narrow paths in the form of channelized flow (Castillo and Gomez 2016). Continued gully erosion removes entire soil profiles in localized segments of the field. As gullies grow, more sediment is transported away from the field. There are two types of gullies: ephemeral and permanent (Castillo and Gomez 2016). Ephemeral gullies are shallow channels that can be corrected by routine tillage operations. In contrast, permanent gullies are too large to be smoothed by regular tillage or crossed by machinery traffic, requiring expensive measures of reclamation and control. Ephemeral gullies following removal tend to reform in the same points of the field if not controlled. Even if gullies are repaired by tillage, soil is already lost due to the off-site transport of the eroded material.

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Fig. 2.2 Concentrated runoff forms gullies (Courtesy USDA-NRCS). Channels without hydraulic roughness elements erode at faster rates with incoming runoff than those nested with deep plant roots and rocks. Gullies are expanded by steep waterfall at the gully heads, called headcut, and by gradual lateral erosion and sloughing of the gully sides

The shear stress of flowing water (force of flowing water against the channel) and critical shear stress of the soil (soil property that determines detachment by runoff) are two prominent factors affecting gully erosion (Castillo and Gomez 2016). The flow shear stress detaches the channel bed and sides and transports eroded materials. Equation (2.3) also applies to gully erosion when rills are scaled up to larger channels. Grass waterways reduce gully formation, but when the flow shear stress exceeds the critical stress of the soil and plant roots, the vegetative cover fails and shear stress of the flow rapidly increases, enlarging the gullies and increasing erosion. Bare and freshly plowed soils have the lowest critical shear stress and thus are the most susceptible to gully erosion. Critical shear of soil is a function of soil texture, bulk density, clay content, aggregate stability, tillage, plant roots, residue cover, and soil slope. Shear stress of runoff < Critical shear of soil = No gully formation Shear stress of runoff > Critical shear of soil = Gully formation

2.1 Types

27

The widening of an ephemeral gully with successive rainstorms can be expressed as per Eqs. (2.4) and (2.5) (Foster and Lane 1983): ΔW = ½1- expð- t  ÞðW f þ W i Þ

ð2:4Þ

where ΔW is change in channel width, Wf is final channel width under the new storm, Wi is initial channel width, and t is time. t =

t ∂W ∂t i ðW f - W i Þ

ð2:5Þ

is initial rate of change in channel width with respect to the previous where t ∂W ∂t i width. A rapid approximation of the amount of soil eroded by gully erosion is done by measuring the size of the gully (length and area) and correlating it with the bulk density of the reference soil (Foster 1986; Liu et al. 2023). Advanced techniques of mapping gully erosion across large areas involve aerial photographs, remote sensing, geographic information systems (GIS) tools, artificial intelligence, and machine learning algorithms, among others (Liu et al. 2023). Conservation practices such as no-till, reduced tillage, and residue mulch are effective to control rill and interrill erosion but not gully erosion. Permanent grass waterways, terraces, and mechanical structures (e.g., concrete structures, tile) are often used to control gully erosion.

2.1.5

Tunnel Erosion

Tunnel erosion, also known as pipe erosion, is underground soil erosion and common in arid and semiarid lands often affected by alkalinity (high concentration of Na+; Hudson 1995). Soils with highly erodible and sodic B horizons but stable A horizons are prone to tunnel erosion. Runoff in channels, natural cracks, and animal burrows initiate tunnels by infiltrating into and moving through dispersible subsoil layers. The surface of tunnel erosion-affected soils is often stabilized by roots (e.g., grass) intermixed with soil, while the subsoil is relatively loose and easily erodible. The presence of water seepage, lateral flow, and interflow is a sign of tunnel erosion. The tunnels or cavities expand to the point where they no longer support the surface weight, thereby collapsing and forming potholes and gullies. Tunnel erosion changes the geomorphic and hydrologic characteristics of the affected areas. Reclamation procedures include deep ripping, contouring, revegetation with proper fertilization and liming, repacking and consolidation of soil surface, diversion of concentrated runoff, and reduction of runoff ponding. Revegetation should include trees and deeprooted grass species to increase water absorption.

28

2.1.6

2 Water Erosion

Streambank Erosion

Streambank erosion refers to the collapse of banks along streams, creeks, and rivers due to the erosive power of runoff from upland fields (Fig. 2.3; Hudson 1995). Pedestals with fresh vertical cuts along streams are the result of streambank erosion. Intensive cultivation, grazing, and traffic along streams, and the absence of riparian buffers and grass filter strips accelerate streambank erosion. Planting grasses (e.g., native and tall grass species) and trees, establishing engineering structures (e.g., tiles, gabions), mulching stream borders with rocks and woody materials, geotextile fencing, and intercepting/diverting runoff are measures to control streambank erosion.

2.2

Processes of Water Erosion

Water erosion is a complex four-step natural phenomenon, which involves detachment, transport, redistribution, and deposition of soil particles. The processes of erosion act in sequence (Table 2.1). The process of water erosion begins with discrete raindrops impacting the soil surface, then detaching of soil particles, and finally transporting soil particles downstream. Detachment of soil releases fine soil

Fig. 2.3 Corn field severely affected by streambank erosion (Courtesy USDA-NRCS). Saturated soils along streambanks slump readily under concentrated runoff, which causes scouring and undercutting of streambanks and expansion of water courses

2.3 Factors of Water Erosion

29

Table 2.1 Role of the main processes of water erosion Detachment • Soil detachment occurs after the soil adsorbs raindrops and pores are filled with water. • Raindrops loosen and break down aggregates. • Weak aggregates are broken apart first. • Detached fine particles move easily with surface runoff. • When dry, detached soil particles form crusts of low permeability. • Detachment rate decreases with increase in surface vegetative cover.

Transport/redistribution • Detached soil particles are transported in runoff and redistributed. • Smaller particles (e.g., clay) are more readily removed and redistributed than larger (e.g., sand) particles. • The systematic removal of fine particles leaves coarser particles behind. • The selective removal modifies the textural and structural properties of the original soil. • Eroded soils often have coarse-textured surface with exposed subsoil horizons. • Amount of soil transported depends on the soil roughness. • Presence of surface residues and growing vegetation slows runoff.

Deposition • Transported particles deposit in low landscape positions. • Most of the eroded soil material is deposited at the downslope end of the fields. • Placing the deposited material back to its origin can be costly. • Runoff sediment transported off-site can reach downstream water bodies and cause pollution. • Runoff sediment is deposited in deltas along streams. • Texture of eroded material is different from the original material because of the selective transport process.

particles, which form surface seals. These seals plug the open-ended and waterconducting soil pores, reducing water infiltration, and causing runoff. At the microscale level, a single raindrop initiates the whole process of erosion by weakening and dislodging an aggregate, which eventually leads to large-scale soil erosion under intense rainstorms. The erosion processes involve dispersion and removal or redistribution of soil, which define the amount of soil that is eroded, and the last process (deposition) determines the distribution of the eroded material along the landscape. If there were no erosion, there would be no deposition. Thus, detachment of soil particles is the primary process of soil erosion, and, like deposition, occurs at any point of the soil. When erosion starts from the point of raindrop impact, some of the particles in runoff are deposited at short distances, while others are carried over long distances often reaching large bodies of flowing water and the flow velocity decreases.

2.3

Factors of Water Erosion

The major factors controlling water erosion are precipitation, vegetative cover, topography, and soil properties (Table 2.2; Troeh et al. 2004). The interactive effects of these factors determine the magnitude and rate of soil erosion. For example, the longer and steeper the slope, the more erodible the soil, and the greater the transport capacity of runoff under intense rain. The role of vegetation in

30

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Table 2.2 Factors affecting water erosion Climate • Precipitation, humidity, temperature, evapotranspiration, solar radiation, and wind velocity affect water erosion. • Precipitation is the main agent of water erosion. • Amount, intensity, and frequency of precipitation dictate the magnitude of erosion. • Intensity of rain is the most critical factor. • The more intense the rainstorm, the greater the runoff and soil loss. • High air humidity is associated with higher soil water content. • Higher winds increase soil water depletion and reduce water erosion.

Vegetative cover • Vegetative cover reduces erosion by intercepting and adsorbing the erosive energy of raindrops. • Plant morphology (e.g., height of plant and canopy structure) influences the effectiveness of vegetation cover. • Surface cover increases soil roughness, slows runoff velocity, and filters runoff. • Soil detachment increases with a decrease in vegetative cover. • Dense and short growing (e.g., grass) vegetation is more effective at reducing erosion than sparse and tall vegetation.

Topography • Runoff transport capacity increases with increase in slope steepness. • Soil topography determines the velocity at which water runs off the field. • Soils on convex fields are more readily eroded than in concave areas due to interaction with surface creeping of soil by gravity. • Degree, length, and size of slope determine the rate of surface runoff. • Rill, gully, and stream channel erosion are typical to sloping watersheds. • Steeper terrain slopes are prone to mudflow erosion and landslides.

Land use and management • Intensive tillage increases soil erosion compared with no-till. • Intensive tillage followed by crop residue removal further accelerates soil erosion. • Deforestation and forest fires increase erosion risks. • Burning of crops residues and slashing increase erosion risks. • Overgrazing can make the soil susceptible to erosion. • Mining disturbs soil and increases soil erodibility. • Road construction disturbs and induces erosion potential. • Urbanization can cause soil erosion especially during construction.

Soil properties • Texture, organic matter, macroporosity, and water infiltration influence soil erosion. • Antecedent water content determines pore space available for rainwater absorption. • Soil aggregation affects the rate of detachment. • Clay particles are transported more easily than sand particles, but clay particles form stronger and more stable aggregates. • Organic materials stabilize soil. • Compaction reduces soil macroporosity and water infiltration and increases runoff rates.

2.4 Soil Properties Affecting Erodibility

31

preventing soil erosion is well recognized. Surface vegetative cover improves soil resistance to erosion by stabilizing soil structure, providing soil organic matter, and promoting activity of soil macro- and micro-organisms. The effectiveness of vegetative cover depends on plant species, density, age, and root and foliage patterns.

2.4

Soil Properties Affecting Erodibility

Erodibility is the soil’s susceptibility to erosion. It changes over time and space with soil properties (Hudson 1995). Soil texture, soil structure (e.g., macroporosity, aggregate properties), organic matter content, hydraulic properties, and wettability are some of the factors that affect erodibility. Field, plot, and lab studies are used to assess soil erodibility. Erosion indexes such as potential soil erosion divided by the tolerable soil loss value have often been used to estimate soil erodibility (Wischmeier and Smith 1965).

2.4.1

Texture

Sandy soils are less cohesive than clayey soils and thus aggregates with high sand content are more easily detached. However, it is also important to note while wellaggregated clayey soil is more resistant to erosion than coarse-textured soils, once detached, the clay particles readily move with runoff due to their smaller size. Silty soils derived from loess (loamy) parent material are the most erodible soils. Water infiltration increases with an increase in coarse soil particles and decreases with an increase in fine particles. Sandy soils absorb water more rapidly than clayey soils due to more abundant macropores in sandy soils. Thus, sandy soils often produce less runoff than clayey soils. Sandy soils have lower total porosity than clayey soils, but their porosity consists mostly of macropores.

2.4.2

Structure

Soil structure, the architectural arrangement of soil particles, is comprised of pore space, biological entities, and soil aggregates of different size, shape, and stability (Bronick and Lal 2005). The soil’s ability to resist erosion depends on its structure. Soils with poor soil structure are more detachable, unstable, and susceptible to compaction with low water infiltration and high runoff rates. Because soil structure is a qualitative term, parameters such as water infiltration, air permeability, and soil organic matter are measured to assess soil structural development. Assessment of aggregate structural properties is also a useful approach as their properties determine the macroscale structural attributes of the whole soil to withstand erosion. Various techniques exist for characterizing and modeling soil structure (Bronick and Lal 2005). Measuring aggregate size distribution is a common laboratory method for characterizing soil structure. Advanced techniques of soil structure

32

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modeling are designed to capture the heterogeneity of soil structure and relate these quantifications to various processes (e.g., erosion). Techniques focusing on the whole soil combined with aggregate characterization provide more insights into the soil structure dynamics. Among the current techniques are tomography, neural networks, and fractals (Katuwal et al. 2018). Tomography allows the investigation of the interior architectural design of soil and permits the 3D visualization of soil structure (Katuwal et al. 2018). By using this approach, it is possible to examine the geometry and distribution of macropore and micropore networks within the soil, which contribute to air and water flow. The use of neural networks is another approach to look at the soil structural attributes for retaining water, storing organic matter, and resisting erosion. Soil fragmentation during tillage and its susceptibility to soil erosion are governed by the fractal theory. This theory involves the study of the complexity of soil particle arrangement, tortuosity, and abundance of soil pores, which are essential to explain processes of water flow through the soil. Tortuosity can be defined as the ratio of the shortest pathway to the straight-line length (Ghanbarian et al. 2013). The relatively new techniques above can help to quantify soil structural attributes.

2.4.3

Surface Sealing

Surface sealing is a major cause of low water infiltration rate and high runoff and soil loss (Hudson 1995). Surface sealing results from the combined effect of raindrop impact on soil surface and deflocculation of clay particles. Initially, the rainfall impact breaks exposed surfaces of soil aggregates, and disperses clay creating a thin and compact layer of slaked fine particles at the soil surface, known as surface seals. The settled fine particles fill and clog the water-conducting soil pores, significantly decreasing the infiltration rate and increasing surface runoff and soil transport. The process for forming surface seals is complex and depends on the rainfall amount, intensity, runoff rate, soil surface conditions (e.g., residue mulch), soil textural class, vegetative cover, and tillage system. When dry, surface seals form crusts.

2.4.4

Aggregate Properties

An aggregate is created when soil primary particles adhere to each other more strongly than to the neighboring soil particles (Blanco-Canqui and Lal 2004). Aggregate attributes are important to understanding and modeling soil erosion processes—particularly in well-aggregated soils. Soil properties in relation to stability and erodibility are often assessed using large samples rather than structural units or discrete aggregates. Attributes of macro- and micro-aggregates determine the rates of soil detachment by rainfall and runoff. Aggregate structural properties such as stability, strength, density, sorptivity, and wettability affect soil erodibility.

2.4 Soil Properties Affecting Erodibility

33

2.4.4.1 Stability Stability refers to the ability of an aggregate to withstand destructive applied forces (e.g., raindrops; Bronick and Lal 2005). It demonstrates how cohesive forces hold the primary particles together. Soil detachment by rainfall depends on the ability of surface aggregates to resist the disruptive energy of rain. Raindrop energy must overcome the cohesive energy of the aggregate to disintegrate it. Wet-sieving, which involves submergence and oscillation of a group of aggregates, is a common lab technique to assess aggregate stability (Nimmo and Perkins 2002). This method uses a group of aggregates rather than a single aggregate. Tests of aggregate stability on individual aggregates using a simulated raindrop technique account for the heterogeneity of field aggregates and provide additional insights into aggregate dynamics in soil erosion. Aggregate stability is a function of soil texture, soil organic matter content, cation exchange capacity (CEC), presence of cementing agents, tillage and cropping systems, manure application, and residue management. Aggregates from plowed soils are structurally unstable and are dispersed readily by raindrop energies unlike those from undisturbed agricultural systems (e.g., pasture, no-till). Intensive tillage interrupts the natural soil structural development and causes the breakdown of stable aggregates and loss of soil organic matter. Abundant surface residue cover, in interaction with reduced soil disturbance results in stable aggregates. The kinetic energy required to disintegrate aggregates increases with larger-sized stable aggregates (Hudson 1995). Thus, large and stable aggregates are less erodible than small and weak aggregates. Small aggregates are also easily transported in runoff and contribute to higher soil losses. The homogenization and seasonal mixing of the plow layer in tilled soils form weak aggregates, which are easily detached by rain regardless of size. Macro- and micro-aggregates in undisturbed soils are stable and have slow turnover rates due to their high soil organic matter content (Bronick and Lal 2005). 2.4.4.2 Wettability Wettability is the ability of a soil to absorb water. Some soil aggregates exhibit slight water repellency due to the surface coating by soil organic matter-derived exudates and humic substances, which form hydrophobic surface films (Blanco-Canqui 2011; Lowe et al. 2021). Moderate water repellency is beneficial to soil structural stability because it reduces slaking and increases stability of aggregates, but high water repellency can reduce water infiltration and increase runoff rates (Lowe et al. 2021). Slaking refers to breakdown of dry soil aggregates under sudden immersion in water (Blanco-Canqui 2011). Quantity and quality of soil organic matter influence hydrophobicity of aggregates. Mulching and manure application induce some degree of water repellency by increasing soil organic matter content. Soil aggregates under no-till tend to have higher water repellency than those under plow tillage (BlancoCanqui 2011). Techniques for assessing water repellency include water-drop penetration time test, the critical surface tension test, water repellency index, and the contact angle method.

34

2.4.5

2 Water Erosion

Antecedent Soil Water Content

The antecedent water content influences the rate of soil detachment (Ma et al. 2020). The wetter the soil and the less the pore space available for rainwater absorption, the greater the runoff and soil erosion. The role of initial water content on detachment and soil erosion is influenced by rainfall characteristics, soil texture, and soil organic matter content. The influence of antecedent soil water content on runoff is relatively small in compacted soils or when the rain is intense. The kinetic energy of rain required to break soil aggregates apart decreases with lower soil water content. Air-dry aggregates are more dispersible than moist aggregates because rapid wetting of dry aggregates causes a sudden release of heat and entrapped air, resulting in faster disintegration in contrast with moist aggregates.

2.4.6

Soil Organic Matter Content

Soil organic matter is one of the key factors that control the stability of aggregates (Blanco-Canqui et al. 2013). It physically, chemically, and biologically binds primary particles into aggregates. Organic materials supply cementing and binding agents and promote microbial processes responsible for the enmeshment of soil particles into stable aggregates. It is important to understand the types of organic binding agents that intervene in soil aggregation. The organic binding agents comprise temporary, transient, and persistent agents. Temporary agents consist of plant roots, mucilages, mycorrhizal hyphae, bacterial cells, and algae (Tisdall and Oades 1982; Blanco-Canqui and Lal 2004). These agents enmesh the mineral particles and are mainly associated with macro-aggregation. Transient agents consist mainly of polysaccharides and organic mucilages resulting from microbial processes of plant and animal tissues and exudations. Persistent agents include highly decomposed organic materials such as humic compounds, polymers, and polyvalent cations and are associated with microaggregate dynamics. These compounds are inside microaggregates forming clay-humic complexes and chelates. The action of soil organic matter-derived stabilizing agents determines the nature, size, stability, and configuration of aggregates. Plant roots, residue mulching, and manure addition are the main sources of organic matter. Also, minimizing soil disturbance is a strategy to reduce organic matter oxidation and stabilize the soil structure.

2.4.7

Water Transmission Properties

2.4.7.1 Water Infiltration Runoff occurs when the rate of surface water from rain, snowmelt, and irrigation exceeds the water infiltration rate of the soil (Reynolds et al. 2002). Thus, the amount of water infiltrated determines the amount of water lost as runoff. Runoff occurs only after surface water: (1) is absorbed by the soil, (2) fills up the soil pores and surface soil depressions, (3) is stored in surface detention ponds if in place, and

2.5 Measuring Erosion

35

(4) accumulates on the soil surface at a given depth. At the beginning of a rain or irrigation event, most water is absorbed by the soil, but as the soil becomes saturated, a portion of rain fills surface depressions and excess water runs off the field even on land with a gentle slope. During infiltration, the soil layers become wetter over time as the wetting front advances into layers of lower water content as compared with the overlying soil.

2.4.7.2 Saturated Hydraulic Conductivity Saturated hydraulic conductivity (Ksat), defined as the ability of a soil to conduct water under saturated conditions, is an essential parameter that affects runoff, drainage, infiltration, leaching, and overall soil hydrology (Reynolds and Elrick 2002). The higher the Ksat values, the lower the runoff rates. Soil texture and macroporosity are the main parameters that affect Ksat. Clay soils typically have lower Ksat values than sandy soils. For example, the Ksat of claypan soils (clay content >450 g kg-1) in the Midwestern US (covering about 4 million ha) can be as low as 1.83 μm h-1 due to the presence of argillic horizon at depths of 130–460 mm (Blanco-Canqui et al. 2002). Claypan soils often perch water and create lateral flow or interflow during spring when soils remain practically saturated. Runoff rates may be equal to rainfall on clayey soils if Ksat is very low.

2.5

Measuring Erosion

Knowing the amount of soil leaving a field is essential to assess the: • • • • •

Magnitude or severity of erosion Ascertain effects of erosion on soil productivity and water pollution Understand and manage sedimentation in depositional areas Design and establish erosion control practices Develop mathematical models and test their applicability for soil erosion prediction

Soil erosion is often measured on field plots under natural and simulated rainfall (Boardman and Evans 2019). Various types of rainfall simulators exist (Figs. 2.4 and 2.5). Measuring soil erosion requires the consideration of plot size and knowledge of factors that affect data variability. Choice of the plot size and proper replication are ways to minimize measurement variability. Types of erosion plots include: micro, medium or Universal Soil Loss Equation (USLE) plots, and large plots or field-scale or watersheds. The amount of soil lost per unit area varies depending on the plot size. Because large plots capture interrill, rill, and possibly ephemeral gully erosion, they are preferable over microplots to characterize soil erosion. Microplots The size of small plots can vary from 0.05 to about 2 m2. These microplots are frequently used to provide hands-on opportunities to manipulate and understand principles of soil erosion processes and factors under simulated

36

2 Water Erosion

Fig. 2.4 The Swanson type rotating boom rainfall simulator (Swanson 1965; Photo by H. Blanco). The simulator booms are equipped with nozzles positioned at radii of 1.5, 3.0, 4.5, 6.0, and 7.6 m. Booms and nozzles rotate in a circle, and the wetted diameter is about 16 m

rainfall. They allow a detailed study of the physics of erosion under controlled conditions. Microplots are particularly suitable for studying interrill erosion. Medium or USLE plots The size of medium plots is often similar to that of the standard plots (4 × 22.1 m) used for the validation of the USLE model. Many have used the medium plots to collect erosion data and validate the USLE for local conditions. The minimum width should be at least 2 m in order to minimize the effect of plot boundary influence on soil erosion. Large plots or watersheds The size of large plots is at least 100 m2 and is suitable for studying combined processes of rill and interrill erosion. Large plots portray the erosion occurring at large-scale conditions and are used to test one or more hypotheses of the effects of different management scenarios. These plots represent a sample of the landscape and capture different erosional phases. Watersheds equipped with runoff sampling devices are the ideal choice for assessing rill and even ephemeral gully erosion. The long-term and large cultivated watersheds at the North Appalachian Experimental Watersheds in Coshocton, OH, established in the mid-1930s, which are equipped with complete runoff and soil loss monitoring structure for continuous runoff sampling, are an illustration of field-scale plots

2.6 Agents of Water Erosion

37

Fig. 2.5 A portable rainfall simulator with a single nozzle inside an aluminum frame (Miller 1987; Photo by H. Blanco)

(Bonta et al. 2018). Data from field-scale or watershed studies better reflect field conditions compared with those from small or microplots.

2.6

Agents of Water Erosion

Two main agents affecting soil erosion by water are rainfall and runoff erosivity.

2.6.1

Rainfall Erosivity

Rainfall erosivity refers to the intrinsic capacity of rainfall to cause soil erosion (Hudson 1995). Water erosion would not occur if all rains were non-erosive. Since this is hardly the case, knowledge of rainfall erosivity is essential to understand erosional processes, estimate soil erosion rates, and design erosion control practices. Properties affecting erosivity are: amount, intensity, terminal velocity, drop size, and drop size distribution of rain (Table 2.3). Erosivity of rain and its effects differ among climatic regions. The same amount of rain has strikingly different effects on the amount of erosion depending on the intensity and soil surface conditions. Annual distribution of rainfall also influences the erosivity of rain. Rains in temperate

38

2 Water Erosion

Table 2.3 Factors affecting the erosivity of rainfall Amount • More rain means more erosion, depending on rain intensity. • Amount of rain is a function of duration and intensity of rain. • Measurement of the amount of rain is affected by the type, distribution, and installation protocol of the rain gauges. • Height of rain gauges and wind drift affect measurement. • Available data are only point estimates of a large area.

Intensity • Intensity is the amount of rain per unit of time (mm h1 ). • Intensity is normally WEPP > SWAT > Other models (Borrelli et al. 2021).

3.7 Process-Based Models

65

The advantage of WEPP over other erosion models is that it can estimate erosion for single hillslopes (hydrologic units) and the whole watershed which comprises various hillslopes. It simulates soil erosion at different temporal (daily, monthly, annual basis) and spatial (hillslope, small, medium, and large watersheds) scales. It simulates rill and interrill erosion over hillslopes and sediment transport and deposition in channels, and impoundment interactions with surface cover conditions, soil properties, surface roughness, and soil management. The main components of the model are (Flanagan and Nearing 1995; Guo et al. 2021): 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

Weather conditions Winter processes Irrigation practices Infiltration dynamics Overland flow hydraulics Water balance Plant growth Plant residue decomposition Soil parameters Hillslope erosion and deposition Watershed channel hydrology Watershed impoundment component

A brief overview of selected equations used in WEPP is presented below. A detailed description of the WEPP model components is presented by Flanagan and Nearing (1995). The peak intensity of a storm is computed as follows (Nicks et al. 1995) rp = - 2P lnð1- rlÞ

ð3:20Þ

where rp is peak intensity of the precipitation (mm h-1), P is precipitation amount (mm), and rl is gamma distribution of the monthly mean half-hour precipitation amounts. The surface runoff (v) is estimated using the kinematic wave model (Stone 1995), which is based on the continuity equation: ∂h ∂q þ =v ∂t ∂x

ð3:21Þ

q = αhm

ð3:22Þ

and the depth of peak discharge is:

where h is runoff flow depth (m), q is runoff discharge per unit width (m3 m-1 s-1), α is coefficient of depth of runoff discharge, m is depth-discharge exponent, t is time, and x is distance downslope (m).

66

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Modeling Water Erosion

Runoff depth depends on the infiltration rate. The WEPP computes infiltration based on the Green–Ampt model, which uses effective hydraulic conductivity (Keff) and wetting front matric potential as input parameters (Alberts et al. 1995). When measured, Keff is not available, WEPP computes the “baseline” effective hydraulic conductivity (Kb) internally based on: K b = - 0:265 þ 0:0086ð100sandÞ1:8 þ 11:46CEC - 0:75

ð3:23Þ

if the soil clay content is ≤40% and K b = 0:0066eð clay Þ 2:44

ð3:24Þ

if the soil clay content is >40% The WEPP allows for corrections for the effects of temporal variables (e.g., crusting, tillage operations) on Kb. The WEPP predicts soil erosion based on the separate processes of interrill and rill erosion. The movement of sediment in WEPP hillslope model is described by the equation of sediment continuity (Foster et al. 1995) as follows ∂G = Df þ Di ∂x

ð3:25Þ

where G is sediment load (kg s-1 m-1), x is distance downslope of a field (m), Df is rill erosion rate (kg s-1 m-2), and Di is interrill erosion rate (kg s-1 m-2). While Di is always positive, the Df has a positive value for detachment and a negative value for deposition. The rill detachment is computed as per Eq. (3.26) Df = Dc 1-

G Tc

ð3:26Þ

where Dc is detachment capacity by rill runoff (kg s-1 m-2), and Tc is sediment transport capacity (kg s-1 m-1). If the hydraulic shear stress of the rill is higher than the critical shear stress of the soil, Dc is described as per Eq. (3.27) Dc = K r ðτf - τc Þ

ð3:27Þ

where Kr (s m-1) is a rill erodibility parameter, τf is hydraulic flow shear stress, and τc is rill detachment threshold parameter. Rill detachment does not occur when flow shear stress is lower than the critical shear stress of the soil. The net deposition in a rill is computed as per Eq. (3.28) Df =

βV f ðT c- GÞ q

ð3:28Þ

where β is a raindrop-induced turbulence coefficient assumed to be 0.5 for rain and 1.0 for snow melting and furrow irrigation, Vf is effective fall velocity of sediment

3.7 Process-Based Models

67

particles (m s-1), and q is flow discharge (m2 s-1). The sediment transport capacity (Tc) is estimated as 3

T c = kt τ2f

ð3:29Þ

where kt is a transport capacity coefficient (m0.5 s2 kg-0.5). The WEPP model is under continuous improvement and integration with other technological advances (Guo et al. 2021). Now, WEPP is being linked to GIS through the Geo-spatial interface for WEPP (GeoWEPP), which allows the simulations based on digital sources (e.g, internet sources) of readily available geo-spatial information. These links include digital elevation models (DEM), climate data, soil surveys (e.g., USDA-NRCS data), precision farming, and topographical maps using the Arcview software (Renschler 2003). The GIS component allows the selection, manipulation, and parameterization of potential input parameters for the simulations at small- and large-scale land areas of interest. The expansion of traditional WEPP and its combination with GIS adds flexibility to soil erosion modeling. The GeoWEPP is a variant of the traditional WEPP and further development would permit the simulation of distribution, extent, and magnitude of soil erosion at larger spatial scales, and represent an improved approach for land use planning as well as soil and water conservation. The updated version of WEPP can better simulate channel soil detachment, and runoff and sediment yields under different management practices compared with the original WEPP model (Guo et al. 2021).

3.7.2

Ephemeral Gully Erosion Model

The Ephemeral Gully Erosion Model (EGEM) was specifically developed to predict gully formation and erosion based on physical principles of gully bed and side-wall dynamics (Woodward 1999; Foster and Lane 1983). Common erosion models such as USLE, RUSLE, and WEPP do not include direct options for predicting gully erosion. The EGEM considers the dynamic processes of concentrated flow responsible for gully incision and headcut development. The headcut refers to the intense erosion that occurs on a near-vertical step in some streams. The EGEM is one of the few process-based models to predict gully erosion. The EGEM was developed based on the Ephemeral Gully Erosion Estimator (EGEE) (Laflen et al. 1986). The EGEM consists of two major components: hydrology and erosion. The hydrologic component is estimated using the runoff curve number, drainage area, watershed slope and flow depth, peak runoff discharge, and runoff volume. The erosion component is based on the width and depth of ephemeral channels. The EGEM can predict gully erosion for single storms or seasons or crop stage periods. The width of the gullies is computed using regression equations (Foster 1982; Woodward 1999) as

68

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Modeling Water Erosion

W e = 2:66 Q0:56 n0:387 S - 0:16 CS - 0:24

ð3:30Þ

W u = 179 Q0:552 n0:556 S0:199 CS - 0:476

ð3:31Þ

where We is equilibrium channel width (m), Wu is ultimate channel width (m), Q is peak runoff rate (m3 s-1), n is Manning’s roughness coefficient, S is concentrated runoff slope, and CS is critical shear stress (N m-2). The detachment rate in gullies is computed by a modified form of rill erosion equation as follows D = KCð1:3t - τc Þ

ð3:32Þ

where D is detachment rate (g m-2 s-1), KC is channel erodability factor (g s-1 N1 ), t is average shear stress of flowing water (N m-2), and tc is critical shear stress of soil (N m-2).

3.8

Other Water Erosion Models

Other models for predicting soil erosion include the Agricultural Non-point Source Pollution model (AGNPS), Annualized Agricultural Non-Point Source Pollutant Loading (AnnANPSPL), Areal Nonpoint Source Watershed Environment Response Simulation (ANSWERS), EPIC, European Soil Erosion Model (EUROSEM), Groundwater Loading Effects of Agricultural Management Systems (GLEAMS), Limburg Soil Erosion Model (LISEM), Griffith University Erosion System Template (GUEST), and Water and Tillage Erosion Model (WATEM). These models have multi-purpose use and can predict, not only runoff and soil loss, but also nutrient losses. Some models have the ability to simulate subsurface water flow or lateral flow influencing the transport of pollutants. Process-based models such as WEPP, SWAT, and AGNPS are particularly popular to simulate the impact of contrasting scenarios of land use and tillage, and cropping systems on non-point source pollution. Models such as WEPP, LISEM, and EUROSEM simulate soil erosion based on the theory that deposition occurs when the concentration of sediment in runoff water surpasses the runoff transport capacity, whereas GUEST estimates erosion based on the simultaneous transport and deposition processes (Yu 2003).

3.9

Summary

Modeling water and wind erosion is essential to understanding the processes of soil erosion and estimating the rates of soil erosion. The estimates are needed to design and implement erosion control measures. Modeling is also (continued)

3.9 Summary

69

useful for scaling up information from small-scale experiments to larger geographic areas and for estimating soil erosion on a regional and national basis. Empirical- (e.g., USLE) and process-based (e.g., WEPP) erosion models are available for modeling soil erosion. Compared with process-based models, empirical equations such as the USLE require fewer input parameters and are thus more adaptable to scenarios with limited databases. The USLE does not, however, simulate the soil detachment, transport, and deposition processes and is designed to predict soil loss from only small plots. The MUSLE and RUSLE are the results of the ongoing development of the empirical models. The SWAT model is a semi-empirical model based on USLE, MUSLE, and RUSLE theory that is increasingly being used globally to assess management impacts on water quantity, water quality, and related ecosystem services. Process-based models are based on the sediment continuity equation. The WEPP is a common process-based model that estimates erosion for single hillslopes and whole watersheds on temporal (daily, monthly, and annual basis) and spatial (hillslopes and small, medium, and large watersheds) scales. It integrates information on weather conditions, tillage and soil management, soil hydrology, plant growth, soil parameters, erosion and deposition, channel hydrology and erosion processes, and watershed processes. The EGEM is another process-based model, which is designed to predict gully erosion on an event basis. The most used water erosion models are in this order: RUSLE > USLE > WEPP > SWAT > Other models. Current erosion models have some limitations to accurately predict soil erosion. The large database required as input hampers the applicability of some process-based models. Available models are highly variable and sitespecific. Improvement of current models and development of new water erosion models are a research priority. Combining current models with advanced tools, such as remote sensing and GIS, is a promising approach to enhancing the predictive ability of models at different temporal and spatial scales. Questions 1. Estimate the kinetic energy of a rainstorm if the average rainfall amount of 30-min duration is 20 mm of constant intensity. 2. Estimate the average annual soil loss for 300 m field, chisel plow in spring, under corn-soybean rotation in eastern Nebraska. The soil is silt loam (17% coarse and medium sand, 3% very fine sand, 22% clay, and 58% silt) with 3.1% of soil organic matter content and slope of 3.8%. The structure is fine granular and the saturated hydraulic conductivity is 55 mm h-1. Some erosion control practice is used and P factor is 0.5.

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3. Estimate and compare the average annual soil loss for 200 m field of each tillage treatment for a long-term tillage-rotation study at the Rogers Memorial Farm (Lincoln, NE). The soil is a Sharpsburg silty clay loam (fine, smectitic, mesic Typic Argiudoll). The soil texture for the plow layer is 34% clay and 61% silt plus very fine sand. Select tillage treatments are moldboard plow, chisel plow, and no-till under continuous corn. Organic matter content is 3% for no-till, 2.5% for moldboard plow, and 2.65% for chisel plow. The structure is fine granular and the saturated hydraulic conductivity is about 25 mm h-1. The P factor is 0.20. 4. Compare the K-factor value between the equation and the nomograph. 5. How is the C-factor in USLE calculated? 6. What are the differences between an empirical and a physically-based model? 7. Discuss the shortcomings of current models. 8. Explain the reasons as to why empirical models of erosion are more widely used than process-based models. 9. Describe misuses of USLE. 10. How can USLE be validated for soils and cropping systems of the tropics and highlands?

References Alberts EE, Nearing MA, Weltz MA et al (1995) Chapter 7. Soil component. In: Flanagan DC, Nearing MA (eds) USDA-Water Erosion Prediction Project (WEPP). Hillslope profile and watershed model documentation. National Soil Erosion Laboratory (NSERL) Report #10, West Lafayette, IN Alewell C, Borrelli P, Meusburger K, Panagos P (2019) Using the USLE: chances, challenges and limitations of soil erosion modelling. Int Soil Water Conserv Res 7(2019):203–225 Arnold JG, Srinivasan R, Muttiah RS, Williams JR (1998) Large-area hydrologic modeling and assessment: Part I. Model development. J Am Water Resour Assoc 34(1):73–89 Bennett HH (1939) Soil conservation. McGraw-Hill, New York Borrelli P, Alewell C, Alvarez P, Anache JA, Baartman J, Ballabio C, Bezak N, Biddoccu M, Cerdà A, Chalise D, Chen S, Chen W, De Girolamo AM, Gessesse GD, Deumlich D, Diodato N, Efthimiou N, Erpul G, Fiener P, Freppaz M, Gentile F, Gericke A, Haregeweyn N, Hu B, Jeanneau A, Kaffas K, Kiani-Harchegani M, Villuendas IL, Li C, Lombardo L, López-Vicente M, Lucas-Borja ME, Märker M, Matthews F, Miao C, Mikoš M, Modugno S, Möller M, Naipal V, Nearing M, Owusu S, Panday D, Patault E, Patriche CV, Poggio L, Portes R, Quijano L, Rahdari MR, Renima M, Ricci GF, Rodrigo-Comino J, Saia S, Samani AN, Schillaci C, Syrris V, Kim HS, Spinola DN, Oliveira PT, Teng H, Thapa R, Vantas K, Vieira D, Yang JE, Yin S, Zema DA, Zhao G, Panagos P (2021) Soil erosion modelling: a global review and statistical analysis. Sci Total Environ 780:146494 Browning GM, Parish CL, Glass J (1947) A method for determining the use and limitations of rotation and conservation practices in the control of soil erosion in Iowa. J Am Soc Agron 39: 65–73 Flanagan DC, Nearing MA (1995) USDA-Water Erosion Prediction project: Hillslope profile and watershed model documentation Rep 10. USDA-ARS National Soil Erosion Research Laboratory, West Lafayette, IN Foster GR (1982) Modeling the erosion process. In: Haan CT, Johnson HP, Brakensiek DL (eds) Hydrologic modeling of small watersheds. ASAE Monogr 5, St. Joseph, MI, pp 297–380

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Foster GR (2005) Science Documentation: Revised Universal Soil Loss Equation Version 2 (RUSLE2). USDA-Agricultural Research Service, Washington, DC Foster G, Lane L (1983) Erosion by concentrated flow in farm fields. In: Li RM, Lagasse PF (eds) Proceedings of the D.B. Simons Symposium on erosion and sedimentation. Colorado State University, Fort Collins, pp 9.65–9.82 Foster GR, McCool DK, Renard KG et al (1981) Conversion of the universal soil loss equation to SI metric units. J Soil Water Conserv 36:355–359 Foster GR, Flanagan DC, Nearing MA et al (1995) Chapter 11: Hillslope Erosion Component in USDA Water Erosion Prediction Project : Hillslope Profile and Watershed Model Documentation, vol NSERL Report No. 10. In: Flanagan DC, Nearing MA (eds) USDA-ARS National Soil Erosion Research Laboratory Francesconi W, Srinivasan R, Perez-Minana E, Willcock SP, Quintero M (2016) Using the Soil and Water Assessment Tool (SWAT) to model ecosystem services: a systematic review. J Hydrol 535:625–636 Guo T, Srivastava A, Flanagan DC (2021) Improving and calibrating channel erosion simulation in the Water Erosion Prediction Project (WEPP) model. J Environ Manag 291:112616 Laflen JM, Flanagan DC (2013) The development of U.S. soil erosion prediction and modeling. Int Soil Water Conserv Res 1:1–11 Laflen JM, Watson DA, Franti TG (1986) Ephemeral gully erosion. Proceedings of the Fourth Federal Interagency Sedimentation Conference, pp 3.29–3.37 Lal R (1976) Soil erosion on Alfisols in western Nigeria: III. Effects of rainfall characteristics. Geoderma 16:389–401 Musgrave GW (1947) The quantitative evaluation of factors in water erosion: a first approximation. J Soil Water Conserv 2:133–138 Nicks AD, Lane LJ, Gander GA (1995) Weather generator. In: Flanagan DC, Nearing MA (eds) USDA-Water Erosion Prediction Project: Hillslope profile and watershed model documentation. NSERL Report No. 10. USDA-ARS Nat. Soil Erosion Research Lab, West Lafayette, IN Renard KG, Foster GR, Weesies GA et al (1997) Predicting soil erosion by water: a guide to conservation planning with the Revised Universal Soil Loss Equation (RUSLE). Agric Handbook, vol 703. US Gov Print Office, Washington, DC Renschler CS (2003) Designing geo-spatial interfaces to scale process models: the GeoWEPP approach. Hydrol Process 17:1005–1017 Smith DD (1941) Interpretation of soil conservation data for field use. Agr Eng 22:173–175 Stone RJ (1995) Modeling subsurface drainage and surface runoff with WEPP. J Irr Drain Eng ASCE 121:217–218 SWAT (2013) SWAT: Soil and Water Assessment Tool. USDA–ARS, Grassland, Soil & Water Research Laboratory, Temple, TX. http://swat.tamu.edu/. Accessed 12 Aug 2022 USDA-ARS (1997) Revised Universal Soil Loss Equation (RUSLE). Agricultural Handbook, vol 703. US Gov Print Office, Washington, DC Wischmeier WC, Smith DD (1965) Predicting rainfall erosion losses from cropland east of the Rocky Mountains. Agricultural Handbook, vol 282. US Gov Print Office, Washington, DC Wischmeier WH, Smith DD (1978) Predicting rainfall erosion losses: a guide to conservation planning. USDA Agric Handb 537. US Gov Print Office, Washington, DC Woodward DE (1999) Method to predict cropland ephemeral gully erosion. Catena 37:393–399 Yu B (2003) A unified framework for water erosion and deposition equations. Soil Sci Soc Am J 67: 251–257 Zingg AW (1940) Degree and length of land slope as it affects soil loss in runoff. Agr Eng 21:59–64

4

Wind Erosion

Wind erosion, also known as eolian erosion, is a dynamic process by which soil particles are detached and displaced by the erosive forces of the wind. Wind erosion occurs when the force of wind exceeds the threshold level of the soil’s resistance to erosion (Webb et al. 2021). Geological, anthropogenic, and climatic processes control the rate and magnitude of wind erosion (Fig. 4.1). Wind erosion is the result of complex interactions among wind intensity, precipitation, surface roughness, soil texture and aggregation, agricultural activities, vegetation cover, and field size (Borrelli et al. 2017). Abrupt fluctuations in weather patterns can also trigger severe wind erosion events (Duniway et al. 2019). Deforestation and agricultural activities are the main causes of wind erosion. For example, plowed soils with low organic matter content and those intensively grazed and trampled upon are the most susceptible to erosion.

4.1

Processes

Wind detaches and transports soil particles. Transported particles are deposited at some distance from the source as a result of an abrupt change in wind-carrying capacity. The four dominant processes of wind erosion are the same as those of water erosion: detachment, transport, redistribution, and deposition (Table 4.1). The mechanics and modes of soil particle movement are complex. Deposition of suspended particles depends on their size and follows Stoke’s Law where large particles settle down first followed by particles of decreasing size. Smaller particles remain suspended and become atmospheric dust. The three pathways of particle transport are suspension, saltation, and surface creep (Table 4.2; Webb et al. 2021). The mode of transport of soil particles during wind erosion is governed by particle size. Small particles ( μ1 indicates that velocity increases with height above the soil surface. Threshold wind velocity refers to the velocity required to entrain a soil particle. The threshold velocity required to initiate soil movement varies with soil surface and vegetative cover conditions. It increases in concert with an increase in soil particle

Disturbed Soil Undisturbed Soil

Increase in Wind Velocity

79

Increase in Erosion Rate

Increase in Erosion Rate

4.4 Soil Erodibility

Bare Soil Mulched Soil

Increase in Wind Velocity

Fig. 4.4 Erosion risks increase exponentially with an increase in wind velocity. Erosion rates are directly proportional to the amount of exposed and loose erodible material, which is influenced by the level of soil disturbance (left), crusting, crop residue management (right), and soil texture

size. Particles that are fine and loose are transported more easily than coarse particles under the same wind velocity. Greater wind velocity is needed to break away and move particles in undisturbed and surface-covered soils. There are two types of threshold levels: static and dynamic. The static or minimum threshold velocity is the velocity at which the least stable soil particles are detached but are not transported. The dynamic or impact threshold velocity is the velocity at which the detached particles are transported. Soil erosion rates increase exponentially with increases in wind velocity (Fig. 4.4). The rate of erosion by wind is proportional to the cube of the wind velocity above the threshold level.

4.4

Soil Erodibility

The magnitude of wind erosion is a function of soil erodibility, which refers to the ability of surface soil to resist the erosive forces of wind (Webb et al. 2021). Intrinsic soil properties such as texture, structure, and water content in interaction with surface roughness and living and dead vegetative cover define the rate at which the soil is detached and eroded (Bouajila et al. 2022). Any soil that is dry and loose with bare and flat surfaces is susceptible to wind erosion. Dry loose soil material silt > fine sand, decreasing with increase in particle size.

4.4.2

Crusts

The unconsolidated and loose fine soil particles in tilled soils form seals under the influence of rain, which later develop into thin crusts or skins when soil dries out (Zhang et al. 2017). These soil skins have textural and structural properties (e.g., water, air, and heat fluxes, mechanical bonding) completely different from the soil beneath. Crusts are more dense, stable, and resistant to erosion than uncrusted soils. The rate at which crusts are degraded or eroded depends on the magnitude of the abrasive forces of the wind. Crusts temporarily protect the soil beneath until they are either lifted or broken apart by wind past the threshold level of velocity. Soil under the crusts erodes rapidly after wind velocity is beyond the threshold level (Webb et al. 2021). Crust formation and thickness vary from soil to soil as a function of soil physical, biological, and chemical properties, surface roughness, vegetative cover, and raindrop impacts. They even vary within the same soil type. The presence of residue mulch and stable aggregates reduces crust formation. The fraction of soil surface covered by crusts is quantified by methods similar to those used for vegetation cover characterization. While excessive crusting can impede seedling emergence and reduce water infiltration, moderate crusting reduces wind erosion. Wind erosion rates decrease exponentially and linearly with an increase in percentage of crust cover. Erosion rates from crusted soils can be several times lower than those from uncrusted soils, depending on the wind velocity (Zhang et al. 2017). Wind tunnel experiments are used to assess the ability of crust to withstand abrasion by sand particles. Some simple equations developed for estimating wind erosion rates (E) for crusted soils (Li et al. 2004) are: Wind speed = 26 m s - 1 → E = 582:41 × expð- 0:021 × CrustÞ

ð4:4Þ

Wind speed = 18 m s - 1 → E = 41:898 × expð- 0:0147 × CrustÞ

ð4:5Þ

4.4 Soil Erodibility

Wind speed = 10 m s - 1 → E = 3:041 × expð- 0:0048 × CrustÞ

81

ð4:6Þ

where Crust is in %. The fraction of soil that is not erodible (SFcv) because it is covered by crusts or rocks can be estimated as (Zhang et al. 2017): SFcv = ½ð1- SFcr Þðð1- SF84 Þ þ SFcr - SFlos ð1- SVroc Þ þ SVroc

ð4:7Þ

where SFcr is the fraction of the soil surface that is not erodible because it is covered by crusts, SFlos is the fraction of the soil surface that is erodible because it is covered by loose soil, SVroc is the proportion of the soil volume with particle >2.0 mm in diameter, and SF84 is the fraction of the uncrusted surface covered by aggregates 13 million ha. About 60% of the cropland in Brazil is now under no-till (Calegari et al. 2020). In Argentina, Paraguay, and Uruguay, nearly 90% of the cultivated land is under no-till, representing countries with the largest no-till adoption in the world in terms of percentage of cultivated land. In eastern Bolivia, no-till is also becoming popular for growing sorghum, sunflowers, corn, soybeans, wheat, rice, and even cotton. In Mexico, about half a million ha of land is under no-till, which is also expanding to Central American countries. About 69% of the cropland area in South and Central America is under conservation agriculture. Soybeans, corn, oats, lentils, sorghum, wheat, barley, sunflowers, and beans are the main crops grown with a no-till system. In some regions, no-till systems are being integrated with crop rotations and green manure cover crops. About half a million ha of land are under no-till in irrigated rice paddies in the tropics of South America (e.g., Brazil). Reduced production costs are appealing to farmers although large-scale producers have been more receptive to no-till technology. Differences in climate, soil type, cropping systems, crop management (e.g., irrigation), availability of inorganic fertilizers, and others determine the extent to which no-till is adopted in different regions in the Americas and around the globe.

7.5.1.2 No-Till in Europe No-till farming in Europe started in the 1950s. Abundant residues on the soil surface and restrictions on straw burning induced a proliferation of weeds, slowing the rapid expansion of no-till in Europe (Soane et al. 2012). The lower production costs in machinery, fuel, and labor under no-till are attractive to farmers over conventional tillage because any reductions in crop yields under no-till are easily compensated by the reduction in production costs and the improvement in soil and environmental quality. Direct planting without plowing saves time and energy. Despite the many advantages, wide-scale adoption of no-till in Europe is still limited when compared with that in North and South America. Field data on the benefits of no-till farming are also scarce although there has been a renewed interest in no-till farming in recent years. For example, about 10% of cropland in Finland is under no-till (Soane et al. 2012). The success with no-till in Europe, similar to that in other continents, depends on crop residue management, weed control, compaction risks, and appropriate selection of herbicides and no-till drills.

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7.5.1.3 No-Till in Africa and Asia Adoption of no-till technology has also been slow in Africa and Asia (Kassam et al. 2022). For example, cropland area under no-till in Asia is under five million ha, which is only about 2% of global cropland area in no-till (Somasundaram et al. 2020). Pioneering research work in no-till for Africa started in Nigeria in the early 1970s (Lal 1990). Studies in African countries including Nigeria, Kenya, South Africa, Tanzania, Zimbabwe, Liberia, and Ghana show that no-till is being used to grow corn, wheat, cotton, and sorghum. Despite the significant research work, adoption of no-till technology is still limited in these regions. In India, areas under no-till with wheat have increased in recent years, particularly under rice-wheat systems. No-till is also being practiced in Malaysia and Sri Lanka. The limited use of no-till in Africa and Asia is probably attributed to various problems associated with (1) the high cost of importing no-till equipment for mechanized farms, (2) land tenure, (3) harsh climate conditions, (4) knowledge gap, (5) a lack of crop residue mulch, (6) small land holdings (5 years). Water infiltration rates and saturated hydraulic conductivity are often higher under no-till than in plowed soils because of abundant macropores, but such responses can be site-specific (Table 7.4; Skaalsveen et al. 2019). For example, long-term no-till management may (Stone and Schlegel 2010; TerAvest et al. 2015) or may not (Blanco-Canqui et al. 2017) increase water infiltration. No-till can improve water infiltration by increasing the amount of macropores (e.g., earthworm channels, root channels), which remain intact in no-till soils. Residue cover reduces surface sealing of open and continuous macropores, which are major conduits for water flow and gaseous diffusion and transport. Surface residues intercept and retain runoff water and increase the runoff water infiltration opportunity time. The presence of continuous macropores increases the hydraulic conductivity and can offset any reductions in hydraulic conductivity due to compaction. Frequent tillage can, in some cases, increase water infiltration, by loosening soil and creating macropores although those impacts are short-lived as reconsolidation occurs throughout the growing season (Blanco-Canqui et al. 2017). No-till impacts on soil C concentration for the whole soil profile can be mixed or minimal when compared with conventionally tilled soils. No-till often accumulates more C near the soil surface (upper 10 cm) compared with conventional tillage, but no-till does not generally accumulate more C for the whole soil profile due to placement of crop residues on the soil surface (Powlson et al. 2014; Blanco-Canqui 2021). How management systems affect soil C accumulation is discussed later in another chapter. Furthermore, while no-till generally improves soil properties compared with conventionally tilled systems, it may not differ from reduced till. Indeed, the benefits of reduced till to improve soil properties can lie between no-till and conventional tillage. For example, Fernandez et al. (2015) reported water infiltration did not differ

7.5 Conservation Tillage Systems

141

between no-till and strip till (reduced till) in a silt loam (Table 7.4). The limited or no differences in soil response to no-till and reduced till have led to suggestions that reduced till can be a potential option to no-till for cool and clayey soils in temperate regions.

7.5.1.7 Soil Water No-till management also impacts soil water storage. Because of abundant residue cover, no-till soils store more water than bare and plowed soils. Residue mulch reduces evaporation rates, and thus soil water content improves with an increase in residue return rate (Fig. 7.1). The use of no-till technology is often favored in waterlimited regions to conserve soil water. Soils with limited or no residue cover wet and dry quicker than residue-covered no-till soils. No-till farming moderates water balance by reducing runoff, evaporation, and excessive percolation as per the equations below. Δ water storage = Input - Output Δ water storage = Rainfall þ Irrigation þ Capillarity - ðEvaporation þ Runoff þ PercolationÞ

ð7:1Þ ð7:2Þ

A global review found that no-till management can increase plant available water content by an average of 44% relative to conventionally tilled systems (BlancoCanqui and Ruis 2018). Increased organic matter concentration and improved soil structural properties can enable no-till soils to retain more water than tilled soils. However, a number of factors affect no-till potential to improve soil water retention. As an example, the magnitude of increases in water retention varies with the duration of no-till management. Soil hydraulic properties such as water retention can be slower to respond to no-till management than other soil properties such as wet aggregate stability. Also, changes in soil hydraulic properties are often confined to the upper 10 cm depth, particularly in the short term (4%) may be difficult. 5. Maintaining ridges at harvesting and planting can be expensive and labor intensive. 6. Runoff and soil erosion can be higher in ridge tillage as compared with no-till.

7.5.2.3 Strip Tillage This system is also called partial-width tillage and consists of performing tillage in isolated bands while leaving undisturbed strips throughout the field (Fig. 7.11; Fernandez et al. 2015; Laufer and Koch 2017). By doing so, strip tillage combines the benefits of no-till and tillage. Only the strips that will be used as seedbeds are tilled. The strips between the tilled rows are left under no-till with residue cover. Strip tillage loosens the tilled strip, temporarily improves drainage, and reduces soil compaction. Strip tillage can be an alternative to no-till farming in poorly drained and clayey soils. Strip tillage can be an option to no-till in soils (i.e., clayey soils) where no-till has not maintained or improved soils and crop production

Fig. 7.11 Two fields managed under strip tillage (Courtesy USDA-NRCS)

152

7

Tillage Systems

(Fernandez et al. 2015). Some producers prefer strip till over ridge till to increase soil warming in spring. Strip till can be practiced in fall or spring while fertilizing at the same time. If conventional tillage (e.g., chisel plow) > mulch tillage > ridge tillage > strip tillage > vertical tillage > no-till. While vertical tillage can be an option in systems with heavy residue mulch such as no-till, other companion practices to no-till management including partial residue removal, diversification of cropping systems, development of row cleaners, and others that reduce excessive residue accumulation or limit soil disturbance should be first considered before using tillage.

154

7.6

7

Tillage Systems

Summary

Plowing is as old as agriculture itself. The old plows were manual and simple until the introduction of moldboard plows that revolutionized agriculture and increased concerns of soil erosion. Now, a number of tillage systems are available, which can be grouped into two main categories: conventional tillage and conservation tillage. The former refers to practices that invert and mix the soil, whereas the latter refers to practices that reduce or eliminate soil disturbance and leave most of the residue on the soil surface. Conventional tillage includes moldboard plowing, chisel plowing, and other tillage systems that perform primary and secondary tillage operations, breaking up the soil and mixing the residue with the soil. Intensive tillage disturbs and mixes the soil and can negatively affect soil properties. Conventional tillage provides temporary control of compaction and weeds, but it buries the majority of crop residues. Soils without residue mulch are most susceptible to erosion and structural deterioration. Soil erosion rates are generally greater in plowed fields than in no-till fields although runoff and losses of dissolved nutrients between conventional tillage and no-till may not differ in some cases. Conservation tillage includes no-till, mulch tillage, strip tillage, ridge tillage, and vertical tillage. No-till is one of the top soil conservation technologies that causes the least soil disturbance. It is an evolving system and its performance depends on site-specific conditions (e.g., crop, climate, management). No-till management may increase, reduce, or have no effect on crop yields, but it is an effective soil and water conservation practice. It generally improves soil properties relative to conventional tillage. No-till practice, combined with complex, diverse crop rotations and cover crops, is a better strategy than no-till alone for improving soil properties and productivity while addressing the challenges of no-till management. Reduced tillage (e.g., mulch tillage, strip tillage, vertical tillage) can be an alternative to no-till for some conditions where no-till performs poorly. Also, occasional (or one-time) tillage of long-term no-till soils every 5 or 10 years can be employed if other conservation practices cannot address the challenges of no-till technology. Studies have shown that one-time tillage generally has no effects on soil properties, while it may or may not increase crop yields. Economic and environmental concerns should be considered before implementing occasional tillage. Questions 1. Discuss the differences that exist among the conservation tillage systems. 2. Is there any difference between no-till and zero tillage? 3. Describe the mechanisms for runoff reduction under no-till systems.

References

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4. Discuss the constraints for the limited adoption of no-till. 5. Discuss the differences in crop yields among conventional till, no-till, strip till, and other tillage systems. 6. Discuss the economics among the different tillage systems. 7. Discuss the advantages and disadvantages of occasional or one-time tillage. 8. State the companion practices for enhancing no-till performance. 9. Discuss the effects of no-till on runoff, soil loss, and losses of dissolved nutrients. 10. What are the implications of no-till technology for managing non-point source pollution? 11. What are the strategies or alternatives to address the challenges of no-till farming? 12. What is the effect of strip till on soil properties and crop yields as compared with no-till and conventional till? 13. Compare impacts of vertical tillage on soil properties and crop yields with those of other tillage systems based on published literature.

References Abail Z, Whalen JK (2018) Corn residue inputs influence earthworm population dynamics in a no-till corn-soybean rotation. Appl Soil Ecol 127:120–128 Alghamdi RS, Daigh ALM, DeJong-Hughes J, Wick AF (2021) Soil temperature and water contents among vertical tillage, strip tillage, and chisel plowing in the upper Great Plains. Can J Soil Sci 101:596–616 Archer DW, Halvorson AD, Reule CA (2008) Economics of irrigated continuous corn under conventional-till and no-till in northern Colorado. Agron J 100:1166–1172 Bennett HH (1939) Soil conservation. McGraw Hill, New York Blanco-Canqui H, Lal R (2008) Extent of subcritical water repellency in long-term no-till soils. Geoderma 149:171–180 Blanco-Canqui H, Wienhold BJ, Jin VL, Schmer MR, Kibet LC (2017) Long-term tillage impact on soil hydraulic properties. Soil Till Res 170:38–42 Blanco-Canqui H (2021) No-till technology has limited potential to store carbon: how can we enhance such potential? Agric Ecosyst Environ 313:107352 Blanco-Canqui H, Ruis SJ (2018) No-tillage and soil physical environment. Geoderma 326:164– 200 Blanco-Canqui H, Wortmann CW (2020) Does occasional tillage undo the ecosystem services gained with no-till? A review. Soil Tillage Res 198:104534 Butt KR, Shipitalo MJ, Bohlen PJ et al (1999) Long-term trends in earthworm populations of cropped experimental watersheds in Ohio, USA. Pedobiologia 43:713–719 Calegari A et al (2020) No-till farming systems for sustainable agriculture in South America. In: Dang Y, Dalal R, Menzies N (eds) No-till farming systems for sustainable agriculture. Springer, Cham. https://doi.org/10.1007/978-3-030-46409-7_30 Carretta L, Tarolli P, Cardinali A, Nasta P, Romano N, Masin R (2021) Evaluation of runoff and soil erosion under conventional tillage and no-till management: a case study in Northeast Italy. Catena 197:104972 Cornish PS, Tullberg JN, Lemerle D, Flower K (2020) No-till farming systems in Australia. In: Dang Y, Dalal R, Menzies N (eds) No-till farming systems for sustainable agriculture. Springer, Cham. https://doi.org/10.1007/978-3-030-46409-7_29

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CTIC (Conservation Technology Information Center) (2016) Top 10 conservation tillage benefits. http://www.ctic.purdue.edu/resourcedisplay/293/ Dang Y, Balzer A, Crawford M, Rincon-Florez V, Liu H, Melland AR, Antille D, Kodur S, Bell MJ, Whish JPM, Lai Y, Seymour N, Carvalhais LC, Shenk P (2018) Strategic tillage in conservation agricultural systems of North-Eastern Australia: why, where, when and how? Environ Sci Pollut Res 25:1000–1015 Elias D, Wang LX, Jacinthe PA (2018) A meta-analysis of pesticide loss in runoff under conventional tillage and no-till management. Environ Monit Assess 190:79 Fernandez FG, Sorensen BA, Villamil MB (2015) A comparison of soil properties after five years of no-till and strip-till. Agron J 107:1339–1346 Giller KE, Andersson JA, Corbeels M, Kirkegaard J, Mortensen D, Erenstein O, Vanlauwe B (2015) Beyond conservation agriculture. Front. Plant Sci 6:1–14 Glossary of Science Terms (2008) Soil Science Society of America. https://www.soils.org/ publications/soils-glossary/ Jordan D, Stecker JA, CacnioHubbard VN et al (1997) Earthworm activity in no-tillage and conventional tillage systems in Missouri soils: a preliminary study. Soil Biol Biochem 29: 489–491 Kassam A, Friedrich T, Derpsch R, Kienzle J (2015) Overview of the worldwide spread of conservation agriculture. Field Actions Sci Reports 8:1–11 Kassam A, Friedrich T, Derpsch R (2022) Successful experiences and lessons from conservation agriculture worldwide. Agronomy 12:769 Lal R (1990) Soil erosion in the tropics: principles and management. McGraw Hill, New York, p 580 Lal R, Reicosky DC, Hanson JD (2007) Evolution of the plow over 10,000 years and the rationale for no-till farming. Soil Tillage Res 93:1–12 Laufer D, Koch HJ (2017) Growth and yield formation of sugar beet (Beta vulgaris L.) under strip tillage compared to full width tillage on silt loam in Central Europe. Eur J Agron 82:182–190 Liu H, Crawford M, Carvalhais LC, Dang YP, Dennis PG, Schenk PM (2016) Strategic tillage on a Grey vertosol after 15 years of no-till management had no short-term impact on soil properties and agronomic productivity. Geoderma 267:146–155 Mendez MJ, Buschiazzo DE (2015) Soil coverage evolution and wind erosion risk on summer crops under contrasting tillage systems. Aeolian Res 16:117–124 Melland AR, Antille DL, Dang YP (2017) Effects of strategic tillage on short-term erosion, nutrient loss in runoff and greenhouse gas emissions. Soil Res 55:201–214 Melman DA, Kelly C, Schneekloth J, Calderón F, Fonte SJ (2019) Tillage and residue management drive rapid changes in soil macrofauna communities and soil properties in a semiarid cropping system of eastern Colorado. Appl Soil Ecol 143:98–106 Palm C, Blanco-Canqui H, DeClerck F, Gatere L, Grace P (2014) Conservation agriculture and ecosystem services: an overview. Agric Ecosyst Environ 187:87–105 Pittelkow CM, Liang X, Linquist BA et al (2015) Productivity limits and potentials of the principles of conservation agriculture. Nature 517:365–368 Powlson DS, Stirling CM, Jat ML, Gerard BG, Palm CA, Sanchez PA, Cassman KG (2014) Limited potential of no-till agriculture for climate change mitigation. Nat Clim Chang 4:678– 683 Skaalsveen K, Ingram J, Clarke LE (2019) The effect of no-till farming on the soil functions of water purification and retention in North-Western Europe: a literature review. Soil Tillage Res 189:98–109 Smith DR, Warnemuende-Pappas EA (2015) Vertical tillage impacts on water quality derived from rainfall simulations. Soil Tillage Res 153:155–160 Soane BD, Ball BC, Arvidsson J, Basch G, Moreno F, Roger-Estrade J (2012) No-till in northern, western and South-Western Europe: a review of problems and opportunities for crop production and the environment. Soil Till Res 118:66–87

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Somasundaram J, Sinha NK, Dalal RC, Lal R, Mohanty M, Naorem AK, Hati KM, Chaudhary RS, Biswas AK, Patra AK et al (2020) No-till farming and conservation agriculture in South Asia— issues, challenges, prospects and benefits. CRC Crit Rev Plant Sci 39:236–279 Stone LR, Schlegel AJ (2010) Tillage and crop rotation phase effects on soil physical properties in the west-central Great Plains. Agron J 102:483–491 TerAvest D, Carpenter-Boggs L, Thierfelder C, Reganold JP (2015) Crop production and soil water management in conservation agriculture, no-till, and conventional tillage systems in Malawi. Agric Ecosyst Environ 212:285–296 USDA-ERS (Economic Research Service) (2017) National Agricultural Statistics Service Wortmann CS, Drijber RA, Franti TG (2010) One-time tillage of no-till crop land five years posttillage. Agron J 102:1302–1307 Zeng Z, Thoms D, Chen Y, Ma X (2021) Comparison of soil and corn residue cutting performance of different discs used for vertical tillage. Sci Rep 11:2537 Zheng ZHB, Huang H, Liu JX, Yao L, He H (2014) Recent progress and prospects in the development of ridge tillage cultivation technology in China. Soil Tillage Res 142:1–7 Zuber SM, Villamil MB (2016) Meta-analysis approach to assess effect of tillage on microbial biomass and enzyme activities. Soil Biol Biochem 97:176–187 Zhao X, Liu SL, Pu C, Zhang XQ, Xue JF, Ren YX, Zhao XL, Chen F, Lal R, Zhang HL (2017) Crop yields under no-till farming in China: a meta-analysis. Eur J Agron 84:67–75

8

Cropping Systems

A cropping system refers to the type and sequence of crops grown over space and time, the practices using current available technologies, and the components of crop production. Cropping systems have been traditionally structured to maximize crop yields. Now, interest is growing in designing cropping systems that consider not only crop production but also social, economical, and ecological or environmental concerns (Hufnagel et al. 2020; Yang et al. 2020). While there is a continued pressure to produce more food, the negative impacts of some cropping systems on soil and water resources have raised some concerns. Designing socially acceptable, economically profitable, and ecologically and environmentally compatible cropping systems for each ecosystem is a priority. Design and management of cropping systems directly affect soil and water conservation and long-term soil productivity. Indeed, properly designed and managed cropping systems can maintain and improve or restore the productivity of degraded lands. Thus, the overall goal of a cropping system must be to conserve soil and water, sustain crop production, and protect the environment. Management of cropping systems involves management of tillage systems, crops, nutrients, water, crop residues, pests, and other production components to meet the goals of soil conservation and food and feed production. For example, choosing or developing appropriate cropping systems accompanied by precision farming can be strategies to reduce the use of inorganic fertilizers, herbicides, and pesticides, which increase production costs and risks of non-point source pollution. Proper residue management, addition of organic amendments, and adopting cover crops and complex crop rotations are some of the strategies to enhance the performance of cropping systems. The best combination of cropping practices for soil conservation and management must be determined for each soil and region. Some cropping systems include: • Fallow systems • Monoculture • Strip cropping # The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 H. Blanco, R. Lal, Soil Conservation and Management, https://doi.org/10.1007/978-3-031-30341-8_8

159

160

• • • • •

8 Cropping Systems

Multiple cropping Contour strip cropping Crop rotations Relay cropping Organic farming

8.1

Fallow Systems

Fallow systems consist of “leaving land either uncropped and weed-free, or with volunteer vegetation during at least one period when a crop would normally be grown” in order to control weeds, accumulate and store water, regenerate available plant nutrients, and restore soil productivity (Glossary of Science Terms 2008). For example, in the US Great Plains, fallow systems such as winter wheat-fallow or wheat-summer crop-fallow are common (Holman et al. 2021). The fallow period in a winter wheat-fallow system lasts about 15 months from early summer (wheat harvest) to fall (wheat planting) of the following year. The extended fallow period is intended to store and conserve part of rainwater, but soil erosion, loss of soil C, and loss of precipitation via evaporation due to limited residue input are increasing concerns in crop-fallow systems. The practice of fallowing has decreased in recent decades, but it is still used in the Great Plains of North America, Australia, and other regions (Holman et al. 2021; Williams et al. 2022). Fallow systems are either plowed or managed under no-till. Under no-till, fallow fields are treated with chemicals to keep the land free of weeds and pests. Systems based on plowed fallow can be susceptible to wind and water erosion especially in the absence of volunteer or seeded vegetation. Intensive plowing also degrades soil structure, accelerates organic matter decomposition, reduces water infiltration, and adversely affects other soil properties. Tillage of a fallow land can be necessary, in some cases, to manage herbicide-resistant weeds, but its frequency and intensity must be minimized to reduce soil erosion risks (Blanco-Canqui and Wortmann 2020). Intensification of cropping systems with the introduction of conservation tillage (no-till and reduced tillage) and inclusion of double crops, cover crops, and forage or short-season crops during the fallow period has the potential to replace fallow (Williams et al. 2022). This intensification can be economically profitable because it allows more crop production on the same piece of land. Intensification of cropping systems maintains abundant crop residues on the soil surface, reduces evaporation, and increases soil water content in the root zone (Fig. 8.1). Higher return of crop residues in no-till soils with reduced fallow periods can improve macro-aggregation, total soil porosity, soil organic matter, and other soil properties (Williams et al. 2022). The increase in soil pore space can capture more rainwater while the increase in soil organic matter can improve the soil’s capacity to retain water (Lopez et al. 2005). Growing crops instead of bare fallow rotations can provide continuous vegetative cover to soil and to improve soil biological activity and nutrient cycling.

8.2 Monoculture

161

Fig. 8.1 Cropping systems with (left) and without (right) fallow replaced with crops (Photo by H. Blanco)

Research shows intensification of crop-fallow systems results in greater precipitation use efficiency and profitability than systems without crops during fallow. For example, in the central Great Plains, Holman et al. (2018) found growing winter and spring triticale and lentil as forage crops during the fallow period in no-till winter wheat-fallow increased net returns by 26 to 240% as compared with no-till winter wheat-fallow without forage crops. Thus, replacing fallow with forage crops can be a strategy for managing soils and improving farm profitability in crop-fallow systems. In some soils, crop yields from intensively managed no-till cropping systems can be lower than those with fallow systems. However, yields from crops replacing fallow could offset the differences. Intensified no-till cropping systems leaving high amounts of residues can also improve soil properties relative to no-till fallow systems without intensification (Peterson and Westfall 2004). For instance, in the central Great Plains, cover crops (spring lentil, spring pea, and winter and spring triticale) planted during fallow in winter wheat-fallow systems increased soil wet aggregate stability relative to winter wheat-fallow systems without fallow replacement after 5 years of management (Fig. 8.2; Blanco-Canqui et al. 2013). An increase in soil wet aggregate stability is important for reducing soil erosion potential and promoting C, nutrient, and water storage. Intensifying crop-fallow systems by adopting no-till, cover crops, and residue management strategies reduces the need for fallowing. In summary, intensified no-till cropping systems leaving high amounts of residues not only reduce erosion potential but also improve soil properties and farm economics relative to crop-fallow systems without intensification.

8.2

Monoculture

Monoculture refers to a cropping system in which the same crop is grown in the same field on a continuous basis. It is the most common cropping system throughout the world principally in large-scale or industrialized farming. High demands for

8 Cropping Systems

Geometric mean diameter (mm)

162

1.0 a ab

0.8 bc 0.6

ab

b

c

0.4 0.2 0.0 Fallow

Winter Lentil

Spring Lentil

Spring Winter Spring Pea Triticale Triticale

Fig. 8.2 Replacing fallow in winter wheat-fallow systems with cover crops can improve the proportion of water stable soil aggregates expressed as geometric mean weight diameter of wet aggregates (Blanco-Canqui et al. 2013). Bars with different lowercase letters are significantly different (P < 0.05) Table 8.1 Some implications of monocropping Disadvantages • Eliminates crop diversity • Reduces biological diversity • Increases use of inorganic fertilizers and pesticides • Reduces soil productivity • Increases weed invasion, and pest incidence • Reduces soil resilience • Reduces wildlife habitat

Advantages • Allows specialization in a specific crop • Favors large-scale farm/modern operations • Generates large volume of specific farm products and often produces higher profits • Reduces the cost of farm equipment • Makes seed preparation, planting, harvesting relatively simple • Narrows harvesting times • Increases profit due to economy of scale

specific products have spurred large-scale monocropping. The number of main crops in the world is about 15, but only four crops predominate (corn, wheat, rice, and potato; Shinde et al. 2022). Presently, monocrops often occupy marginal and degraded lands worldwide resulting from both the degradation of prime agricultural land and the expansion of monocropping. Monocropping has advantages and disadvantages (Table 8.1). Monocropping makes planting and harvesting relatively easy, but it makes the soil susceptible to weed invasion, and pest and disease infestation (Table 8.1). It requires a periodic application of synthetic chemicals to supply nutrients and combat diseases and can have negative impacts on water quality (Hoss et al. 2018). The magnitude of adverse impacts of monocropping on soil function depends on soil, tillage system, and climate.

8.3 Crop Rotations

8.3

163

Crop Rotations

Crop rotations are systems in which different crops are grown sequentially on the same field in alternate seasons or years. Switching crops in a recurring fashion under a planned sequence contrasts with continuous monoculture. Planting three or more different crops before returning to the original crop constitutes long-term rotation. The larger the number of crops involved in a rotation, the greater the benefits to soil productivity and plant diversity. Crop rotation, depending on the type of rotation, is one of the most desirable strategies to improve soil and water conservation and thus soil productivity. Three main types of rotations exist based on the duration: 1. Monoculture. It is confined to a single crop with no diversity. 2. Short rotation. It is basically a 2-year rotation (e.g., corn-soybean). 3. Extended rotation. It refers to >2-year rotation (e.g., corn-oat-wheat-cloverbarley). Based on the crop and plant species used, crop rotations can be: 1. Annual. It refers mostly to monoculture systems (e.g., corn). 2. Annual-perennial. It includes rotations with row crops and perennials (e.g., cornalfalfa; Fig. 8.3). 3. Diverse. It includes more than three crops (e.g., corn-oats-wheat-soybean).

Fig. 8.3 Corn-alfalfa rotation to conserve soil and improve soil fertility in central Ohio (Photo by H. Blanco)

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Rotating different crops using extended crop rotations is an ecologically viable alternative to monocropping and is relevant to addressing agricultural and environmental concerns. Economic pressures have led to monocropping or short rotations as is the case in the US Corn Belt region where cropping systems are commonly confined to corn-corn-corn and corn-soybean. Monocropping with corn occupies a significant portion of cropped land in the Midwestern USA to meet the demands for animal feed, ethanol production, and human consumption although most corn in this region is used for animal and ethanol production. Agricultural mechanization, large-scale farming, intensive use of fertilizers and pesticides, and high economic returns have all simplified crop rotations and favored short rotations and monocropping. Small-scale farmers without much agricultural mechanization traditionally practiced diversified and extended crop rotations. Now, only 12% of global agricultural land is under rotations with two or three different crops in a sequence (Waha et al. 2020). Some of the benefits of extended crop rotations include (Peterson and Westfall 2004; Hoss et al. 2018): 1. 2. 3. 4. 5. 6. 7.

Improved water quality Improved soil properties Improved soil fertility Increased crop yields Reduced build-up of pests and diseases Improved wildlife habitat Reduced use of chemicals

8.3.1

Soil Properties and Erosion

Impacts of short rotations on soil erosion and soil properties may be similar to those of monocropping (Hoss et al. 2018). In Illinois, after 15 years of management, soil organic C concentration, soil bulk density, and wet aggregate stability did not generally differ between continuous corn and corn-soybean when managed under no-till and conventional tillage (Zuber et al. 2015). Diversified and extended crop rotations with high above- and below-ground biomass-producing forages and crops can reduce soil erosion hazards and improve soil properties (Shah et al. 2021). Rotating row crops over longer time intervals (>2 year) with legumes and perennial grass for hay and pasture is an effective soil conservation practice (Fig. 8.3; Jankauskas et al. 2004). Diversified rotations in association with other soil conservation practices (e.g., buffer strips) can further improve performance of rotations alone. Crop rotations that include deep-rooted legumes also increase water movement in the soil profile. In Minnesota, a study across a wide range of soils with differing texture and drainage conditions showed that saturated hydraulic conductivity under diverse crop rotations including corn-soybean-alfalfa-small grain was higher than that under 2-year corn-soybean rotations (Oquist et al. 2006). The degree of soil

8.3 Crop Rotations

165

property improvement under rotations depends on the amount of residue left after harvest and the root biomass. For example, corn crops leave more residue than soybeans and protect the soil against the erosive energy of raindrops and crusting. Overall, crop rotations that produce significant amounts of biomass can maintain soil properties and reduce erosion compared with those with low biomass input.

8.3.2

Nutrient Input and Cycling

Crops vary in their ability to absorb, maintain, and supply nutrients. While some row crops (e.g., corn) extract and reduce most of the essential nutrients in the soil, rotations with legumes (e.g., soybean, alfalfa) can fix atmospheric N and supply non-synthetic N to succeeding crops, reducing inorganic fertilizer requirements. A review focused on soils with low fertility and declining quality indicated that combining inorganic fertilization, green manuring, and crop residue management with crop rotations consisting of grain legumes increased crop yields and reduced production costs relative to the use of inorganic fertilization and green manuring alone without crop rotations (Agegnehu and Amede 2017). This shows that crop rotations with legumes can be an integral component of nutrient management in agricultural systems to maintain or increase crop yields, particularly in low fertility soils. In essence, extended rotations with legumes and other crops can improve nutrient cycling and storage by (1) supplying nutrients, (2) reducing nutrient loss in runoff, and (3) improving soil biological activity. For example, the beneficial effects of legumes within rotations can persist for two or three years following legume cultivation. Also, including sod- and bunch-grass (e.g., perennials) in rotations can increase soil organic matter concentration because of high above- and below-ground biomass input due to longer growing season. Further, the abundant biomass and deep growth pattern of grass roots absorb nutrients from deeper soil, promote microbial processes, and increase nutrient cycling.

8.3.3

Pesticide Use

The types of insects, nematodes, diseases, and weeds that create infestation are specific to a crop. Thus, rotating crops can interrupt the pest cycles and reduce the use of pesticides (Weisberger et al. 2019). The reduction in the use of pesticides and synthetic fertilizers with extended crop rotations results in lower production costs and less non-point source pollution than with monocrops. The effectiveness of crop rotations for controlling pests depends, however, on the nature and specificity of pests. Rotations are effective measures whenever the pests are (1) specific to a crop and field, (2) not widely spread across crops, and (3) not increasing under the absence of host crops (Osipitan et al. 2018; Weisberger et al. 2019). Crop rotations may not completely eliminate weed populations but can contribute to their reduction. A global review by Weisberger et al. (2019) concluded that

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extended crop rotations can reduce weed density by about 50% but may not significantly reduce weed biomass. The same review found that diversifying crops at crop establishment or planting dates can more effectively suppress weeds than simply increasing the number of crop species. Establishing forage crops, cover crops, or short-season crops and terminating them at main crop planting can be a strategy for diversifying crops around the main crop planting date. Indeed, a review by Osipitan et al. (2018) indicated that late-terminated cover crops can be particularly effective at suppressing early-season weeds without affecting yields of main crops. Overall, extended rotations can be more effective at reducing weed population than short rotations as the latter may not be sufficient to break the insect life cycles.

8.3.4

Crop Yields

One of the direct benefits of crop rotation can be the increase in crop yields. For example, corn grown after soybean often produces higher yields than continuous corn systems (Hoss et al. 2018). The differences in crop yields between monocrops and crop rotations can, however, depend on N fertilization rate. Crop rotations often yield more than monocrops when N fertilization rate is low. Pikul et al. (2005) reported that corn grain yield was 6.1 Mg ha-1 under corn-soybean rotations, 7.3 Mg ha-1 under corn-soybean-wheat-alfalfa-alfalfa rotations, and only 3.83 Mg ha-1 under continuous corn in systems without N fertilization, but corn yield among the three cropping systems did not significantly differ when N fertilization rate was high (260 kg ha -1). Monocrops that maximize crop yields often rely on high application of fertilizers and pesticides. Extended crop rotations can reduce production costs and increase net profits by increasing crop yields and by reducing inputs (e.g., fertilizers, pesticides) relative to short rotations and monocrops. Rotating crops every year also adds diversity to the system and flexibility against price fluctuations. Further, crop rotations adopted in conjunction with no-till agriculture save energy by eliminating tillage and further improve farm economics.

8.3.5

Selection of Crops for Rotations

The selection of crops for a rotation sequence varies with local and regional markets and climate. It depends on the soil type, soil fertility, soil slope, economic and market goals, presence of pests, and livestock type. In the Midwestern USA, two-year corn and soybean rotation has become a popular practice since the 1950s. This relatively new rotation structure has somewhat replaced more diverse rotations which included oats, wheat, and alfalfa. The similarities in farm equipment, cultural operations, growth requirements, labor costs, economic profits, marketing options, and numerous food and industrial uses between corn and soybean have triggered the expansion of the corn-soybean rotation (Zuber et al. 2015).

8.5 Row Crops

167

Crop rotations that include alfalfa, clover, or perennial grasses can be ideal practices to improve soil structure, expand macroporosity, reduce soil compaction, and increase soil organic matter content. Growing perennial crops in rotation with row crops can eliminate tillage and restore soil productivity. Deep-rooted (>1 m) legumes or grass species can loosen relatively compact or impermeable soil horizons, ameliorate plow pan formation, improve soil porosity, promote infiltration rate, and reduce runoff and soil erosion. A proliferation of roots and reduced soil disturbance under perennial crops promote soil aggregate stability and strength (Jankauskas et al. 2004). In essence, multi-species legume and grass species must be incorporated in row crop systems to rejuvenate soil and reduce its erodibility as short crop rotations are not sufficient to reduce soil erosion to tolerable levels in highly erodible soils (Thaler et al. 2021). Also, crop rotations alone cannot address all the declining soil ecosystem services unless used in conjunction with other conservation measures (i.e., no-till, cover crops, conservation buffers).

8.4

Cropping Intensity

Cropping intensity is the ratio of total cropped or harvested land over total cultivated or arable land over a specific period of time. Cropping intensity =

Number of crops Total cropped land = Unit of land Total cultivated land

ð8:1Þ

Cropping intensity refers to the number of crops grown on the same piece of land in a specific time period (e.g., 2 years). Cropping systems that favor intensive cropping produce more biomass and provide higher plant diversity resulting in better soil condition for crop production than less intense systems. Reducing fallow frequencies and planting multiple crops in rotation are examples of intensive cropping. Continuous tillage, extended fallow periods, and reductions in cropping intensity and diversity are practices that lead to soil degradation and reduced productivity.

8.5

Row Crops

Row crops refer to crops grown in parallel rows. These crops are usually profitable, representing a significant portion of world agriculture. Corn, wheat, rice, soybean, cotton, peanuts, sorghum, sugarcane, sugar beets, and sunflowers are all examples of row crops. Soil erosion is a major concern in intensive row cropping systems under plow-tillage systems or when residue production is low. The unprotected wide space between rows exacerbates the risks of rill and gully erosion. Corn and soybean are usually planted in rows spaced 0.76 m apart. Crops grown in narrower spaced rows (1 means that intercropping or strip cropping is better than monocropping, whereas an LER 20 years of management in eastern Nebraska (Blanco-Canqui et al. 2017; Williams et al. 2017). Means with different letters within each row are significantly different (P < 0.05) Soil properties Soil organic matter (%) Particulate organic matter (mg g-1) Mean weight diameter (mm) Soil compactibility (Proctor maximum bulk density, Mg m-3) Cumulative water infiltration (cm) Bulk density (Mg m-3) Saturated hydraulic conductivity (mm h-1) Plant available water content (cm3 cm-3)

Conventional farming 2.9b 6b 1.80b 1.54b 3b ns ns ns

Organic farming 3.4a 10a 2.60a 1.58a 37a

and lakes. Synthetic nutrients and pesticides are soluble and may be rapidly transported in runoff and seepage to surface and ground waters. Elevated concentrations of agrichemicals in coastal waters (hypoxia), such as the Gulf of Mexico, question the long-term sustainability of conventional farming systems. However, application of large amounts of animal manure to organic farms can lead to P enrichment, which could result in significant P losses in runoff and via leaching. Thus, it is important to account for the amount of P applied when applying animal manure to meet the N requirements.

8.14.3.2 Soil Properties Organic farming generally improves soil physical, chemical, and biological properties. For example, an organic farming system receiving animal manure and green manure amendments in eastern Nebraska improved soil properties relative to conventional farming after 20 years of management (Table 8.3; Blanco-Canqui et al. 2017). Organic farming can particularly increase organic matter concentration due to

8.14

Organic Farming

179

the addition of organic amendments (Table 8.3). Organic farming with reduced tillage may improve soil properties more than organic farming with intensive tillage. Frequent and intense tillage in organic farming can break soil aggregates and accelerate soil organic matter decomposition. Biologically bound soil aggregates under organic farming can be less susceptible to disintegration than under conventional farming with limited or no addition of organic amendments. Organic farming also often enhances activity and diversity of soil organisms. Several literature reviews have found that organic farming can increase earthworm population (Moos et al. 2017), microbial biomass (Tully and McAskill 2020), and microbial abundance and activity (Lori et al. 2017), mainly due to the addition of organic amendments. For example, use of reduced till for organic farming can increase earthworm populations more than intensive tillage. The increased earthworm population promotes macroporosity and water infiltration and contributes to C and N cycling. The use of more diverse crops (e.g., cover crops) and fewer tillage operations for weed control can result in overall improvement in earthworm population and other soil properties under organic farming.

8.14.3.3 Crop Yields Crop yields under organic farming are often lower than those under conventional farming systems. A meta-analysis of relative yield performance between organic and conventional farming on a global scale found that yields from organic farming can be 5 to 34% lower than from conventional farming, depending on type of crops, soil type, and management practices (Seufert et al. 2012). While crop yields are normally lower, organic farming may be as profitable as conventional farming because of the higher market price of organic produce. In addition, the reduced crop yields under organic farming may be compensated by gains in improved soil fertility, reduced energy use, enhanced biological diversity, and improved environmental quality. Crop yields can be lower in organic farming, but the use of fertilizers and pesticides is reduced, which can minimize the differences in net benefits between organic farming and conventional farming. Another meta-analysis concluded that environmental benefits from organic farming are larger than crop yield benefits (Smith et al. 2019). Indeed, organic farming can improve the overall soil ecosystem services unlike conventional farming. The yield gap between organic farming and other systems depends on management duration, tillage intensity, and source of organic amendment in organic farming. Reduced crop yields in organic farming are common during the transition from conventional farming to organic farming. It takes three-to-five years for the soil to rebuild its natural fertility and stimulate the regrouping of soil organisms following the cessation of conventional farming (Seufert et al. 2012; Smith et al. 2019). The transition period is often called “learning curve” where yields in organic farming lag behind conventional farming yields. Biological rebuilding of soil fertility is slow but sustainable once achieved. As the number of soil organisms increases over time, the more breakdown of organic materials occurs, increasing nutrient availability to plants. Soil organisms also absorb and retain nutrients in their bodies, reducing risks of nutrient leaching and allowing greater nutrient availability to plants over

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extended periods of time. If proper management practices (e.g., crop types, organic amendments) are employed, yields from organic farming may equal those from conventional farming in some cases. Overall, organic farming is an essential component of food production in a sustainable manner, but the factors that limit crop yields in organic farming should be addressed for site-specific conditions, considering environmental, economic, and social benefits (Seufert et al. 2012). It is important to perform a comprehensive analysis of costs and benefits of conventional and organic farms for a better understanding of both agricultural practices.

8.14.4 Organic No-Till Farming Interest in organic no-till farming has increased in recent decades, particularly among conventional no-till farmers. Conventional no-till producers are interested in transitioning to organic no-till farming while continuing their no-till operations (Halde et al. 2017). Organic no-till farming can be ideal for improving soil properties and productivity compared with the traditional organic farming using tillage because no-till reduces soil disturbance and maintains abundant surface reside cover. However, organic no-till farming has significant challenges, particularly with weed management, although the use of complex rotations with perennials and highbiomass-producing cover crops can address some of the challenges. In a review, Anderson (2015) proposed a complex no-till organic rotation for the US Great Plains with 3 years of alfalfa followed by a 6-year corn-soybean-winter wheat-oat-soybeancorn and then alfalfa and concluded that this complex rotation can reduce weed emergence, improve nutrient cycling and soil properties, and reduce yield losses. Another review of organic no-till systems focused on Eastern Canada concluded that organic no-till systems using cover crops can be viable in the region, but their performance is highly variable (Halde et al. 2017). Transitioning from conventional organic farming with intensive tillage to conservation tillage using no-till or reduced till can be commendable to further enhance soil ecosystem services from organic systems. Including perennial legumes for several years and rolling and crimping of cover crops can be essential components to lessen some of the challenges with organic no-till farming for managing weeds while improving soil properties and enhancing long-term sustainability relative to conventional organic farming. Also, switching to organic no-till farming from conventional organic farming can reduce labor, fuel, and other production costs and improve soil services, but knowledge gaps exist regarding the selection of cover crop species, cover crop termination timing and methods, cropping systems (e.g., perennials), and proper equipment for planting into heavy residue much, among others (VincentCaboud et al. 2019). For example, soils with heavy residue mulch under organic no-till systems can be cooler in spring than in conventional organic farming. Cool temperatures and heavy residue mulch can make adequate soil-seed placement and timely crop planting difficult. Additional long-term research into organic no-till farming for different regions or climatic conditions is needed to develop management recommendations.

8.15

8.15

Summary

181

Summary

Conserving soil and water depends on the design and management of cropping systems and their companion practices. Management of cropping systems involves management of tillage, crops, crop residues, nutrients, pests, and erosion control practices. Cropping systems include fallow systems, monoculture, strip cropping, multiple cropping, contour strip cropping, crop rotations, cover crops, mixed and relay cropping, and organic farming, among others. Well-diversified and high-biomass-producing cropping systems can enhance soil fertility, reduce soil erosion, improve soil properties, promote biological activity, nutrient cycling, soil rejuvenation, and minimize environmental pollution. The selection and design of cropping practices are a function of soil, management, and climate conditions. Crop rotations and organic farming are examples of effective cropping systems for managing soil fertility and weeds, and reducing soil erosion and water pollution. Monocropping allows specialization in a specific crop and the reduction of cultural operations and costs of farm equipment, but it also reduces crop diversity, increases the use of fertilizers and pesticides, and may deteriorate soil properties and reduce crop yields. Crop rotations can consist of single crops, short rotations, and extended rotations. Rotating row crops (e.g., corn, soybean) with legumes and perennial grasses are strategies for managing soil erosion and maintaining soil productivity. Cropping systems that maintain permanent vegetative cover not only control water and wind erosion but also stabilize soil and maintain or improve soil properties. Multicropping, which consists of growing more than one crop per year, can be a strategy to keep the soil covered with vegetation through double cropping, intercropping, relay cropping, and others. In sloping croplands, contour farming and strip cropping can be practices that stabilize soil and reduce soil erosion. Organic farming is a cropping system that eliminates the use of synthetic fertilizers, pesticides, and growth regulators to produce food and fiber. It is an ecological approach designed to improve the soil’s natural fertility and biology. As its name states, organic farming uses organic amendments instead of inorganic fertilizers to supply essential nutrients to plants, while it often uses tillage such as reduced tillage to manage weeds. Organic farming is a promising strategy to reduce excessive use of inorganic fertilizers and promote environmentally friendly cropping systems, while generating profits similar to conventional systems when price premiums for organic produce are high. Organic no-till farming can be an alternative to conventional organic farming although practices to manage weeds and reduce yield losses need further refinement for organic no-till systems.

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Questions 1. Discuss differences among intercropping, contour cropping, and strip cropping in relation to design and erosion control effectiveness. 2. What would be the impacts of corn monocropping for biofuel production on soil erosion and long-term soil productivity? 3. Suggest the type of crop rotations that should be practiced to improve soil ecosystem services. 4. Discuss differences in organic farming practiced before and after the pre-modern era. 5. Discuss the benefits of organic farming on crop yields and soil properties. 6. Discuss how crop-fallow systems can be managed better to conserve soil and water. 7. Describe the differences between organic farming and no-till systems. 8. Compare crop yields between organic farming and conventional farming. 9. Define and discuss the importance of computing the LER. 10. Compare the cropping efficiency of monocropping of corn and soybean with strip cropping with the same crops. Yield of corn was 6 Mg ha-1 and that of soybean was 2.3 Mg ha-1 when monocropped. Under strip cropping, yield of corn increased to 7.5 Mg ha-1 and soybean yield decreased to 2.0 Mg ha-1.

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9

Crop Residue Management

Managing crop residues is of paramount importance for soil and water conservation (Fu et al. 2021). Crop residues include leaves, stalks, cobs, roots, and other plant parts. In other words, crop residues include all that is left in the field after grain harvest. Crop residue is the most common organic input (Fig. 9.1). Maintaining adequate levels of crop residue on the soil surface is essential to the delivery of soil ecosystem services. Crop residues can reduce water and wind erosion, accumulate soil C, maintain or improve soil properties and productivity, and enhance the overall soil health and resilience (Turmel et al. 2015). Further, crop residue mulch is a companion practice to other conservation practices including conservation tillage (e.g., no-till and reduced tillage), crop rotations, cover crops, conservation buffers (e.g., vegetative filter strips, riparian buffers, agroforestry), and others. This chapter discusses the importance of crop residues and mechanisms by which crop residues can affect soil properties and soil ecosystem services (Fig. 9.1).

9.1

Production of Crop Residues

The quantity of crop residue produced varies with crop (Fig. 9.2). For example, on a global scale, the three major residue-producing crops include corn, wheat, and rice. These crops produce about three times more residues than sugarcane, soybean, and barley, and about 25 times more residues than sorghum, millet, oats, and rye (Fig. 9.2). In the USA, corn residue is the most abundant crop residue. Global production of crop residues has generally increased in recent decades. At the same time, demands for crop residues for different competing uses have also increased (Shinde et al. 2022).

# The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 H. Blanco, R. Lal, Soil Conservation and Management, https://doi.org/10.1007/978-3-031-30341-8_9

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186

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Fig. 9.1 Some crops such as corn can produce large amounts of residues. The large amount of crop residue left on the soil surface can be vital for soil and water conservation (Photo by H. Blanco)

1,400

Crop Residue Production (Million Tons)

1,200

1162

1141

1135

1,000

800

600 467 400

353 236

200 88

46

25

23

Millet

Oats

Rye

0 Corn

Wheat

Rice

Sugarcane Soybean

Barley

Sorghum

Fig. 9.2 Global crop residue production by different crops (Shinde et al. 2022)

9.3 Soil Properties

9.2

187

Crop Residues

Crop residues are a precious commodity (Fig. 9.1). They have a value, although sometimes they are misguidedly considered “waste” or “trash.” Crop residues are multifunctional and are used for a number of purposes (Fig. 9.3), but their primary function is to conserve soil and water. The four main competing uses are soil and water conservation, animal feed and bedding, biofuel feedstocks, and industrial raw material (Fig. 9.3). For example, corn residues are often baled for feed or grazed by livestock (Fig. 9.4). Using crop residues for purposes beyond conservation of soil and water requires proper residue management after crop harvest to ensure that sufficient amounts of crop residues remain on the field to support other soil services.

9.3

Soil Properties

Crop residue management directly influences soil aggregation, compaction, water flow and retention, C and nutrient cycling, soil biological activity, and other dynamic processes (Ranaivoson et al. 2017). Crop residues can maintain and improve soil properties not only by protecting the soil surface from erosive impacts of rain and wind but also by interacting with the soil matrix through roots and by increasing soil organic C concentration (Ranaivoson et al. 2017). Crop residues contain 40 to 45% C and thus contribute to soil organic matter maintenance and soil C sequestration, which, in turn, improves soil properties and sustains crop production. However, the magnitude of crop residue impacts on soil depends on soil type, residue amount, tillage and cropping systems, and climate. Changes in residue cover may have greater impacts on properties of silt loams than those of clayey soils because of differences in drainage and residue decomposition rates. Also, tillage and climate affect residue decomposition and the amount of soil organic C accumulation, which, in turn, impacts soil physical, chemical, and biological properties. Management practices such as conservation tillage (e.g., no-till) that leave all or most of the crop residues on the soil surface after harvest can better protect soil relative to other tillage systems.

9.3.1

Structure

Crop residues maintain and improve soil structural properties by covering the soil surface, increasing soil organic C concentration, and improving soil biological activity (Ranaivoson et al. 2017). Crop residues reduce surface sealing, crusting, cracking, and detachment of soil aggregates (Fig. 9.5; Blanco-Canqui and Wortmann 2017). Formation of surface seals, which are thin cemented layers formed when raindrops strike the surface of bare soils, can reduce water infiltration and increase runoff amount. Surface seals develop strong crusts when dry, which restrict seedling emergence, increase risks of water erosion, and reduce water, air, and heat

Crop, Livestock and Biofuel Production • Recycle nutrients • Maintain and increase soil organic matter concentration • Reduce evaporation to conserve water • Moderate soil temperature • Reduce nutrient losses through erosion and leaching • Provide feed for livestock (residues are often baled or grazed by livestock) • Provide biomass for cellulosic biofuel production

Soil Properties

• Improve soil physical properties (aggregate stability, porosity, water infiltration, water retention capacity, and others) • Increase or maintain soil organic C content • Improve soil chemical properties (e.g., cation exchange capacity) • Improve soil biological properties (earthworm population and microbial biomass and activity)

• Reduce wind erosion • Absorb wind energy and mitigate erosive power of winds • Intercept flying, saltating, and creeping soil particles • Reduce dust pollution and particulate matter emissions • Buffer transport of air pollutants • Reduce soil organic matter and nutrient losses with sediment

Wind Erosion and Air Quality

9

Fig. 9.3 Multi-functionality of crop residues in agricultural systems

• Buffer or reduce the erosive impacts of falling raindrops • Intercept and filter runoff • Promote time for rainwater infiltration • Trap sediment and nutrients • Reduce transport of non-point source pollutants • Promote nutrient cycling and thus reduce nutrient leaching and water pollution

Water Erosion and Water Quality

Importance of Crop Residues

188 Crop Residue Management

9.3 Soil Properties

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Fig. 9.4 Crop residue removal for expanded uses reduces the amount of crop residue left on the soil surface (Photo by H. Blanco)

Fig. 9.5 Residues protect soil from cracking, crusting, and surface sealing (Photo by H. Blanco)

190

Physical Mechanisms Crop residues insulate soil surface, intercept erosive raindrops, and moderate freezing-thawing and wetting-drying cycles of surface soil.

9

+

Chemical Mechanisms Crop residues provide organic binding agents (polysaccharides, humic compounds, and mucilages) to bind and glue primary soil particles into stable macroaggregates.

+

Crop Residue Management

Biological Mechanisms Crop residues enhance activity of macro- (e.g., earthworms) and micro-organisms (e.g., fungi), which diffuses or emits organic compounds to form and stabilize aggregates.

=

Stable Soil Aggregates

Fig. 9.6 Main mechanisms responsible for the formation and stabilization of soil aggregates

fluxes (Fig. 9.5). Maintaining a continuous cover with crop residue mulch on the soil surface is essential to reduce formation of surface seals. Soil aggregate stability is one of the most sensitive indicators of soil structural development. Crop residues promote formation of stable aggregates through physical, chemical, and biological mechanisms (Fig. 9.6). One of the main mechanisms by which crop residues increase soil aggregate stability is by increasing soil organic C concentration. Crop residues provide transient, temporary, and persistent organic binding agents to form stable aggregates (Tisdall and Oades 1982). In general, soil aggregate stability linearly increases as soil organic C concentration increases in agricultural soils (Blanco-Canqui et al. 2013). However, crop residues promote soil aggregation not only by increasing soil C concentration but also by improving other soil properties and processes (Fig. 9.6). Soil water repellency is another dynamic soil property that can influence soil aggregation. Slight water repellency in some no-till soils can develop near the soil surface from the accumulation of hydrophobic organic C compounds because of high-crop residue input, biological activity, and little or no soil disturbance. Based on the time needed for a drop of water to penetrate into an aggregate, soil aggregates can exhibit no water repellency (600 s; Blanco-Canqui 2011; GonzalezPenaloza et al. 2012). Organic matter accumulation under crop residues in no-till soils can delay water entry into aggregates by as much as 15% compared to soils without residues. The slight increase in soil water repellency under crop residues can contribute to near-surface soil aggregation because it reduces rapid water entry and release of air from soil aggregates, which causes aggregate slaking or breakdown. Crop residue removal for off-farm uses can reduce soil aggregate stability (Blanco-Canqui et al. 2013). Several reviews of literature have reported that crop residue removal at high rates (>50%) can significantly reduce soil C concentration and soil aggregate stability (Smith et al. 2012; Ruis and Blanco-Canqui 2017). For example, corn residue removal above 50% can rapidly reduce near-surface soil aggregate stability (Table 9.1). High rates of residue removal (>50%) should thus

9.3 Soil Properties

191

Table 9.1 Impact of corn residue removal on wet soil aggregate stability expressed as mean weight diameter of aggregates (MWD) across various soils (aRogovska et al. 2016; bRuis et al. 2017; cSindelar et al. 2019). Means with different letters within the same soil are significantly different (P < 0.05) Duration (year) 4

Soil depth (cm) 0–15

Crop Corn

Tillage system Till

Silty clay loamb

3

0–5

Corn

No-till

Silt loamb

3

0–5

Corn

No-till

Silt loamc

6

0–5

Corn

No-till

Soil texture Loama

Residue removal (%) 0 50 90 0 25 50 75 100 0 25 50 75 100 0 56

MWD (mm) 0.32a 0.29ab 0.28b 1.54a 1.63a 1.55a 1.47ab 1.19b 1.00ab 1.17a 0.91b 0.94ab 0.88b 2.30a 1.85b

be avoided to maintain soil aggregate stability. The effects of residue removal on soil structural properties are, however, highly site specific. In some cases, crop residue removal may not affect soil aggregate stability in the short term (5 year; Klopp and Blanco-Canqui 2022). Also, crop residue removal may have larger and more rapid effects on hydraulic properties in sloping soils than in flat silt loams and clayey soils. Changes in water infiltration rates after crop residue removal or application can be slow in nearly level and fine-textured soils relative to sloping and coarse-textured soils (Blanco-Canqui and Lal 2007). In some soils, the presence of clayey horizons or poorly drained subsoil horizons may influence infiltration more than crop residue cover. Overall, maintenance of appropriate amount of crop residue on the soil surface is critical to reduce evaporation, conserve soil water, and improve related soil properties.

18 15

No Residue Cover

12

50% Residue Cover 100% Residue Cover

Soil Temperature (°C)

9

Freeze Point

6 3 0 -3 -6 -9 -12 -15 -18 Fall

Winter

Spring

Fig. 9.7 Soil temperature response to changes in corn residue cover in late fall, winter, and spring when soil temperature sensors were installed between corn harvest and planting (Kenney et al. 2015)

9.3 Soil Properties

9.3.4

195

Temperature

Soil temperature is a function of the amount of surface residue cover (Fig. 9.7). Thus, changes in surface residue cover can rapidly alter the soil temperature. Crop residue cover affects the overall balance and flow of energy. It has an insulating effect and reduces the abrupt fluctuations of soil water and temperature regimes (Fig. 9.7). It moderates the near-surface radiation energy balance and the dynamics of heat exchange between the soil and the atmosphere. Soils without residue mulch are commonly warmer during the day and cooler during the night than residue-mulched soils. Furthermore, during winter, soils with residues can be warmer than those without residues, while the opposite is true in spring and summer (Fig. 9.7). In the western US Corn Belt, Kenney et al. (2015) reported corn residue cover impacts on soil temperature were less pronounced in winter than in other seasons across rainfed and irrigated no-till continuous corn systems. The study found soils with 100% residue cover were warmer in winter and cooler in spring before corn canopy closure. The reduced soil temperature with increased residue mulch in summer can conserve soil water because it reduces evaporation. Reduced soil water losses in summer under residue mulch can reduce irrigation requirements in water-limited regions. Soil temperature under fields without residues can fluctuate more abruptly than under fields with residues (Fig. 9.7). Also, standing crop residues can trap snow, reduce soil freezing, and increase soil temperature in winter. Crop residue mulch protects soil and moderates soil temperature. Moderating soil temperature or reducing abrupt fluctuations in soil temperature using crop residues is essential to numerous soil and agronomic processes. Crop residue mulch positively affects soil physical, hydrological, chemical, and biological processes, seed germination, plant growth, soil water flow and storage, soil gas fluxes, biological activities, nutrient cycling, and many other soil processes. The amount of crop residue left on the soil surface is correlated with soil temperature as the amount of crop resdiue controls temperature exchange between the soil and the atmosphere (Fig. 9.7). It is also important to note that in cool temperate regions, crop residue mulch can delay seed germination and plant growth due to lower soil temperatures. Crop residue management such as partial removal of residues or use of reduced tillage systems (e.g., strip tillage, vertical tillage) can be strategies to manage excessive cooling of spring soils under heavy residue mulch in cool, temperate regions. Overall, changes in crop residue amount can have more rapid and larger impacts on soil temperature than on other soil properties such as hydraulic properties.

9.3.5

Fertility

Crop residues are a reservoir of essential plant nutrients. For example, crop residues can contain, on average, 42 g kg-1 of total C; 10 g kg-1 of N; 1 g kg-1 of total P, 5 g kg-1 of K; 5 g kg-1 of Ca; 2.4 g kg-1 of Mg; 8 mg kg-1 of B; 7 mg kg-1 of Cu; 196 mg kg-1 of Fe; and 43 mg kg-1 of Mn (Blanco-Canqui and Lal 2009).

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Permanent residue cover is thus important to maintaining soil fertility. Studies have found that crop residue removal can reduce soil organic matter or nutrient pools, particularly in the long term. Crop residue removal can have larger effects on soil C and N than on P and K concentrations. Changes in soil nutrient pools due to residue removal or addition are not often measurable in the short term (2 >1 3–6

9.9

Source Ranaivoson et al. (2017)

Klopp and Blanco-Canqui (2022) Blanco-Canqui and Wortmann (2017) Wilhelm et al. (2007)

Increasing Crop Residue Amount

In soils where crop residue amount or cover is limited and erosion risks are high, the use of the following practices can increase residue retention and accumulation on the soil surface: 1. 2. 3. 4.

No-till and reduced tillage systems to keep crop residues on the soil surface. Crops in rotations that produce large amounts of residue such as corn. Crops that provide a continuous and uniform surface cover such as wheat. Cropping systems that provide continuous surface cover such as cover crop, double-cropping, and perennial crops. 5. Crops that produce residues with high C:N ratio such as corn and wheat to slow decomposition and provide long-lasting protective cover to soil. 6. Irrigated no-till corn to produce large amounts of residues combined with cover crops. 7. When crop residues are removed, planting cover crops or adding other organic amendments after crop residue removal can be an option to offset the potential adverse effects of crop residue removal.

9.10

Measurement of Crop Residue Cover

There are several methods of measuring crop residue cover including line-transect, optical, and remote sensing methods. 1. The line-transect method. This method consists of: • Stretching a 100-foot tape diagonally across the crop rows. • Counting the number of marks at every foot that have residues or a piece of residue under the leading edge when looking directly above the mark.

9.12

Root Biomass Production

205

• Looking straight down to count only the marks that are directly above the residue. • Repeating the process at least three times in different points of the field to obtain a representative estimate of percentage of residue cover for the whole field. The percent residue cover is equal to the average number of marks above residues or a piece of residue. If a 50-foot tape is used, multiply the number of marks by two to compute the percentage of residue cover. 2. The photo comparison method. This method consists of: • Taking photos of the soil surface when looking straight down on the surface. • Avoiding taking photos while looking across the field as bare spots can be missed. • Comparing the appearance of photos with other photos of known percentages of the same type of residue. This method provides only an estimate. A more accurate method consists in analyzing high contrast photographs onto a grid and quantifying the areas in the photo with and without crop residues. 3. Remote sensing method. Remote sensing methods are new tools for estimating the crop residue cover over large areas based on the relationships between residue cover and spectral vegetation indices and reflectance. The remote sensing methods are novel and becoming more appealing to estimate crop residue cover at large scales.

9.11

Measurement of Crop Residue Amount and Harvest Index

Quantification of the total amount of residue produced after harvest is needed for many ecosystem services that crop residues provide. In some cases, crop residues are quantified manually prior to grain harvest. Grain and residues from rows of interest are harvested separately by hand. In cases when residue produced cannot be measured, the residue amount can be estimated using the harvest index (HI). Using corn as an example, the amount of corn residue produced is about the same as the amount of grain produced, which is known as HI. In a normal year, the HI is equal to 0.50. The HI, however, can vary with soil type, cropping system, field variability, and climatic fluctuations from year to year. As a result, HI provides only an estimate. The HI is computed as: HI = Amount of grain/(Amount of residue + Amount of grain).

9.12

Root Biomass Production

Discussions on crop residues normally focus on aboveground biomass production or residues left on the soil surface because such residues can be easily seen. It is important to remember crop residues not only include leaves, stalks, cobs, and other aboveground plant parts but also roots. Root are considered the “hidden half” of the plant and are often overlooked during the quantification of crop residue

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Fig. 9.12 Crop roots hold soil aggregates together and increase organic matter concentration (Photo by H. Blanco)

production (Fig. 9.12). Root biomass production can be 30 to 50% of the total biomass production (Blanco-Canqui et al. 2020). Belowground (root) biomass production can be equally or more important than surface crop residues for maintaining and improving soil ecosystem services. Fibrous roots such as those from cereal crops closely interact with the soil matrix, enmesh and bind soil particles into aggregates, stabilize the soil, and reduce soil erosion. Roots are also key to nutrient, C, and water cycling in the soil. Indeed, roots contribute to soil organic C accumulation more than surface residues. Unlike roots, most surface residues are lost via erosion, rapid decomposition, or removal for off-farm uses. Mazzilli et al. (2015) found belowground biomass can be responsible for 60% to 80% of the total new C in particulate organic matter in the upper 10 cm of soil relative to aboveground biomass. Legume crop (e.g., soybean) roots decompose faster than non-legume crops (e.g., corn) roots and can rapidly contribute to soil fertility and C cycling. Roots can thus play a major role in enhancing soil ecosystem services. Recognizing the importance of crop roots for the maintenance and improvement in soil ecosystem services is key to soil management. While quantification of the amount of surface residues can be relatively simple, quantification of root biomass can be difficult and time-consuming, which may be a reason for the limited characterization of roots. Washing, flotation (hydropneumatic elutriation system), hand picking, image analysis (WinRHIZO), and scanning (X-ray computed tomography) are some of the techniques to quantify root biomass production and root length density (Mehra et al. 2021; Hirte et al. 2021). When root biomass production is low,

9.13

Summary

207

cropping systems that include high-root biomass producing species and deep-rooted crop species in the rotation can be relevant to boost root biomass production and thus soil ecosystem services.

9.13

Summary

Crop residues are one of the most readily available organic inputs to maintain or improve soil ecosystem services. Crop residues are major assets to agricultural soils for reducing runoff and soil erosion, improving soil physical, chemical, and biological properties, and maintaining or improving crop production and environmental quality. Soil erosion decreases exponentially with an increase in residue cover as crop residues intercept raindrops and stabilize the soil surface. Also, crop residues are critical to increasing soil water storage, moderating soil temperature, increasing or maintaining soil organic matter levels, and improving soil fertility. The essentiality of crop residues for managing and conserving soil and water, recycling nutrients (e.g., N, P, K, S, micronutrients), maintaining soil organic matter, and sustaining crop production should not be underestimated. Excessive removal of residues (>50%) for expanded uses, such as biofuel or livestock production, may deteriorate soil properties, reduce soil organic matter concentration, alter water, air, and heat fluxes, accelerate soil erosion, disrupt nutrient cycling, and increase risks of non-point source pollution. The amount of residue that can be removed varies among soil types and management systems, but, in general, about 4 to 5 Mg ha-1 of crop residues are needed to maintain most soil services. Moderate grazing of crop residues has minimal or no negative impacts on soil ecosystem services. Grazing crop residues can thus be part of integrated crop-livestock systems to provide a low-cost feed for livestock production in lean months. Grazing animals return C- and nutrient-enriched manure to soil, which can offset the potential adverse effects of grazing. However, grazing croplands with high stocking rates for extended periods of time or grazing when soils are wet should be avoided to reduce compaction risks and degradation of other soil services. Note grazing and mechanical removal of residues do not remove crop roots, which may be the reason why moderate rates of crop residue removal do not always have negative effects on soil properties and other services. Crop roots, often ignored during typical soil and agronomic measurements, may contribute to the maintenance and improvement of soil services more than aboveground crop residues. Management practices that increase root biomass production and root length within the soil profile can be key to enhancing soil services.

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Questions 1. Define crop residues. 2. What is the impact of (1) leaving crop residues on the soil surface and (2) plowing under the residues on soil ecosystem services? 3. Describe the line-transect method for determining the percentage of residue cover on a given soil. 4. What are the possible reasons for the more rapid impact of removing crop residues on sloping silt loam soils compared with that on clayey soils? 5. Discuss the amount of crop residue needed to maintain each soil ecosystem service. 6. What are the factors that affect the threshold levels of crop residue removal for livestock or biofuel production? 7. What is the difference between leaving residues on the soil surface and burying in the soil in terms of its benefits on soil ecosystem services? 8. Compute the amount of corn grain produced if amount of corn residue produced is 9.5 Mg ha-1. Assume HI equal to 0.52. 9. What are the effects of crop residue grazing on soil properties, erosion, and crop yields? 10. Compare differences between aboveground biomass and belowground biomass production.

References Bagnall DK, Morgan CLS, Cope M et al (2022) Carbon-sensitive pedotransfer functions for plant available water. Soil Sci Soc Am J 86(3):612–629 Blanco-Canqui H (2011) Does no-till farming induce water repellency to soils? Soil Use Manag 27: 2–9 Blanco-Canqui H, Lal R (2007) Soil and crop response to harvesting corn residues for biofuel production. Geoderma 141:355–362 Blanco-Canqui H, Lal R (2009) Corn Stover removal for expanded uses reduces soil fertility and structural stability. Soil Sci Soc Am J 73:418–426 Blanco-Canqui H, Wortmann CS (2017) Crop residue removal and soil erosion by wind. J Soil Water Conserv 72:97A–104A Blanco-Canqui H, Stephenson R, Nelson NO et al (2009) Impacts of crop residue removal as biofuel feedstocks on runoff, sediment, and nutrient losses. J Environ Qual 38:2365–2372 Blanco-Canqui H, Shapiro CA, Wortmann CS, Drijber RA, Mamo M, Shaver TM, Ferguson RB (2013) Soil organic carbon: the value to soil properties. J Soil Water Conserv 68:129A–134A Blanco-Canqui H, Stalker AL, Rasby R, Shaver TM, Drewnoski ME, van Donk S, Kibet LC (2016) Does cattle grazing and baling of corn residue increase water erosion? Soil Sci Soc Am J 80: 168–177 Blanco-Canqui H, Ruis S, Proctor C, Creech C, Drewnoski M, Redfearn D (2020) Harvesting cover crops for biofuel and livestock production: another ecosystem service? Agron J 112:2373–2400 Blanco-Canqui HR, Hassim C, Shapiro PJ, Klopp H (2022) How does no-till affect soil-profile susceptibility to compaction in the long term? Geoderma 425:116016 Carretta L, Tarolli P, Cardinali A, Nasta P, Romano N, Masin R (2021) Evaluation of runoff and soil erosion under conventional tillage and no-till management: a case study in Northeast Italy. Catena 197:104972

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Clark JT, Russell JR, Karlen DL et al (2004) Soil surface property and soybean yield response to corn Stover grazing. Agron J 96:1364–1371 Fryrear DW, Bilbro JD (1998) Mechanics, modeling, and controlling soil erosion by wind. In: Pierce FJ, Frye WW (eds) Advances in soil and water conservation. Ann Arbor Press, Chelsea, MI, pp 39–49 Fu B, Chen L, Huang HY, Qu P, Wei ZG (2021) Impacts of crop residues on soil health: a review. Environ Pollut Bioavail 33:164–173 Gonzalez-Penaloza FA, Cerda A, Zavala LM, Jordan A, Gimenez-Morera A, Arcenegui V (2012) Do conservative agriculture practices increase soil water repellency? A case study in citruscropped soils. Soil Tillage Res 124:233–239 Hirte J, Walder F, Hess J, Büchi L, Colombi T, van der Heijden MG, Mayer J (2021) Enhanced root carbon allocation through organic farming is restricted to topsoils. J Soil Sci 33:141–163 Jin VL, Schmer MR, Wienhold BJ, Stewart CE, Varvel GE, Sindelar AJ et al (2015) Twelve years of Stover removal increases soil erosion potential without impacting yield. Soil Sci Soc Am J 79:1169–1178 Kenney I, Blanco-Canqui H, Presley DR, Rice CW, Janssen K, Olson B (2015) Soil and crop response to Stover removal from rainfed and irrigated corn. GCB Bioenergy 7(2):219–230 Klopp H, Blanco-Canqui H (2022) Implications of crop residue removal on soil physical properties: a review. Soil Sci Soc Am J 86:979–1001 Lehman RM, Ducey TF, Jin VL et al (2014) Soil microbial community response to corn Stover harvesting under rain-fed, no-till conditions at multiple U.S. locations. Bioenergy Res 7:540– 550 Lopez MV, Moret D, Gracia R et al (2003) Tillage effects on barley residue cover during fallow in semiarid Aragon. Soil Till Res 72:53–64 Mazzilli R, Kemanian AR, Ernst OR, Jackson RB, Piñeiro G (2015) Greater humification of belowground than aboveground biomass carbon into particulate soil organic matter in no-till corn and soybean crops. Soil Biol Biochem 85:22–30 Mehra P, Kumar P, Bolan N, Desbiolles J, Orgill S, Denton MD (2021) Changes in soil-pores and wheat root geometry due to strategic tillage in a no-tillage cropping system. Soil Res 59:83–96 Minasny B, McBratney AB (2018) Limited effect of organic matter on soil available water capacity. Eur J Soil Sci 69:39–47 Rakkar KM, Blanco-Canqui H (2018) Grazing of crop residues: impacts on soils and crop production. Agric Ecosyst Environ 258:71–90 Ranaivoson L, Naudin K, Ripoche A, Affholder F, Rabeharisoa L, Corbeels M (2017) Agroecological functions of crop residues under conservation agriculture. A review. Agron Sustain Dev 37 Redfearn D, Parsons J, Drewnoski M, Schmer M, Mitchell R, McDonald J, Farney J, Smart A (2019) Assessing the value of grazed corn residue for crop and cattle producers. Agric Environ Lett 4:180066 Reichert JM, Brandt AA, Rodrigues MF, Reinert DJ, Braida JA (2016) Load dissipation by corn residue on tilled soil in laboratory and field-wheeling conditions. J Food Sci Agric 96:2705– 2714 Rogovska N, Laird DA, Karlen DL (2016) Corn and soil response to biochar application and Stover harvest. Field Crop Res 187:96–106 Ruis S, Blanco-Canqui H (2017) Cover crops could offset crop residue removal effects on soil carbon and other properties: a review. Agron J 109:1785–1805 Ruis S, Blanco-Canqui H, Ferguson RB, Jasa P, Slater G (2017) Can cover crop use allow increased levels of corn residue removal for biofuel in irrigated and rainfed systems? Bioenergy Res 10: 992–1004 Schmer SMR, Brown RM, Jin VL, Mitchell RB, Redfearn DD (2017) Corn residue use by livestock in the United States. Agric Environ Lett 2:160043

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Shinde R, Shahi DK, Mahapatra P, Singh CS, Naik SK, Thombare N, Singh AK (2022) Management of crop residues with special reference to the on-farm utilization methods: a review. Ind Crop Prod 181:114772 Sindelar M, Blanco-Canqui H, Virginia J, Ferguson R (2019) Cover crops and corn residue removal: impacts on soil hydraulic properties and their relationships with carbon. Soil Sci Soc Am J 83:221–231 Smith WN, Grant BB, Campbell CA, McConkey BG, Desjardins RL, Kröbel R, Malhi SS (2012) Crop residue removal effects on soil carbon: measured and inter-model comparisons. Agric Ecosyst Environ 161:27–38 Stalker LA, Blanco-Canqui H, Gigax JA et al (2015) Corn residue stocking rate affects cattle performance but not subsequent grain yield. J Anim Sci. https://doi.org/10.2527/jas.2015-9259 Stewart CE, Roosendaal DL, Sindelar A, Pruessner E, Jin VL, Schmer MR (2019) Does No-tillage mitigate stover removal in irrigated continuous corn? A multi-location assessment. Soil Sci Soc Am J 83:733–742 Sulc RM, Franzluebbers AJ (2014) Exploring integrated crop-livestock systems in different ecoregions of the United States. Eur J Agron 57:21–30 Tisdall JM, Oades JM (1982) Organic matter and water stable aggregates in soils. J Soil Sci 33:141– 163 Turmel MS, Speratti A, Baudron F, Verhulst N, Govaerts B (2015) Crop residue management and soil health: a systems analysis. Agric Syst 134:6–16 Wilhelm WW, Johnson JMF, Karlen D, Lightle D (2007) Corn stover to sustain soil organic carbon further constrains biomass supply. Agron J 99:1665–1667 Wortmann CS, Shapiro CA, Schmer M (2016) Residue harvest effects on irrigated, no-till corn yield and nitrogen response. Agron J 108:384–390

Cover Crops

10

Cover crops are “close-growing crops that provide soil protection, seeding protection, and soil improvement between periods of normal crop production or between trees in orchards and vines in vineyards” (Fig. 10.1; Glossary of Science Terms 2008). When cover crops are plowed into the soil, they are referred to as green manure crops. The use of cover crops is an ancient practice and dates back to the ancient civilizations in Greece, Rome, China, and others (Groff 2015). Management and roles of cover crops have, however, changed over time. In the past, cover crops were normally plowed under as green manures to improve soil fertility. Currently, cover crops are being promoted as an important companion practice to no-till, reduced tillage, and other conservation practices designed to enhance soil ecosystem services including reduction in soil erosion, improvement in quality of soil and water resources, and maintenance of soil productivity. The new approach is to use cover crops with no-till systems to enhance no-till performance. Tilling cover crops into the soil can accelerate nutrient release due to enhanced residue mineralization and can reduce the benefits of cover crops for conserving soil and water. It is important to note that cover crops were designed to cover and protect the soil as their name states. However, cover crops are grown not only to conserve soil and water but also to provide forage for livestock and cellulosic biomass for biofuel production. Cover crops are thus considered multifunctional conservation practices for enhancing soil ecosystem services (Blanco-Canqui et al. 2015). The numerous soil ecosystem services that cover crops can provide include: • • • • • • • •

Protecting soil against water and wind erosion Improving soil physical, chemical, and biological properties Enhancing soil fertility Suppressing weeds Fixing atmospheric N Sequestering atmospheric C Increasing or sustaining crop yields Recycling nutrients

# The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 H. Blanco, R. Lal, Soil Conservation and Management, https://doi.org/10.1007/978-3-031-30341-8_10

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Fig. 10.1 Rye as a cover crop for corn-soybean rotation in the eastern USA (Photo by H. Blanco)

• Preventing nutrient leaching • Reducing insect pests • Providing biomass for expanded uses (e.g., livestock production)

10.1

Components of Cropping Systems

Cover crops can be an effective conservation practice to manage and conserve soil in agricultural lands (Fig. 10.1). Cover crops should be established in a way that is best suited to a specific land and cropping system to benefit the soil and sustain crop yields. Cropping systems can more closely mimic nature when cover crops are added because the cropland will be covered by growing plants all year round with main crops during the in-season and cover crops during the off-season. Thus, cover crops can be an integral component of cropping systems. A well-structured system with cover crops and rotations can halt or restore declining soil ecosystem services. Cover crops can be interseeded into growing main crops or planted after crop harvest (Blanco-Canqui et al. 2017). Broadcasting and drilling are techniques to interseed cover crops into standing crops (Noland et al. 2018). Cover crops are often drilled if planted after crop harvest. Cover crops are annual crops with species including grasses, legumes, brassicas, and others (Ruis et al. 2019). Some common cover crops used in rotations in temperate and tropical regions are listed in Table 10.1. In temperate regions, winter annuals (e.g., winter rye) are the most common cover crops in typical corn and soybean rotations. Summer annuals are also used, depending on the growing season of main crops. Summer cover crops can

10.2

Biomass Production

213

Table 10.1 Some common cover crop species in temperate and tropical regions (Magdoff and Van Es 2021; Ruis et al. 2019) Temperate regions • Rye • Oats • Winter wheat • Annual ryegrass • Triticale • Winter barley • Radish • Red clover • Rapeseed

• Turnip • Canola • Crimson clover • Winter pea • Hairy vetch • Cowpea • Sunn hemp • Buckwheat • Sorghum sudangrass

Tropical regions • Sunn hemp • Guinea grass • Butterfly pea • Jack bean • Faba bean • Pigeon pea • Velvet bean • Lablab • Cowpea

• Mung bean • Sunflower • Pearl Millet • Buckwheat • Signal grass • Sorghum sudangrass • Sesbania sp.

particularly fit systems when main crops are harvested in summer such as winter wheat. Converting monocropping practices such as corn to complex and diverse rotations involving cover crops is a relatively new paradigm for managing soil erosion, improving soil properties, and enhancing nutrient cycling and soil C sequestration. For example, legume cover crops when used in rotations can enhance soil fertility and increase soil productivity while providing other soil services. Also, when used synergistically, cover crops in conjunction with crop rotations can reduce the incidence of insects, weeds, and diseases and accentuate sustainability and profitability. In other words, cover crops can enhance performance of current crop rotations. In soils with high levels of residual N, grass cover crops can benefit more and grow better than legumes, while the opposite can be true in soils with low levels of residual N as legumes can fix their own N from the atmosphere.

10.2

Biomass Production

Perhaps the most important factor that determines the ability of cover crops to maintain and improve soil ecosystem services is cover crop biomass production. The greater the amount of biomass input with cover crops, the greater the potential of cover crops to protect soil against erosion, improve soil properties, enhance soil fertility (e.g., legumes), suppress weeds, and provide other services. Some estimates suggest at least 1 Mg ha-1 of cover crop biomass can be needed to significantly detect changes in soil services (Koehler-Cole et al. 2020). The optimum amount of cover crop biomass to suppress weeds can be around 4 to 5 Mg ha-1 (Finney et al. 2017). Adding cover crops to a cropping system increases the total amount of residue produced by the system on an annual basis. Cover crops not only add aboveground residues but also belowground residues (roots). Cover crop belowground biomass production can be at least 30% of the cover crop aboveground biomass production (Blanco-Canqui et al. 2020).

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According to a global review, cover crops can produce, on average, 3.37 ± 2.96 Mg ha-1 of aboveground biomass with rye, sorghum, sunn hemp, and millet as the top biomass producing cover crops (Ruis et al. 2019). The same review found that cover crops can produce similar amounts of biomass in humid regions (>750 precipitation) and in regions with precipitation Runoff > Dissolved nutrients in runoff. This indicates cover crops can be most effective at reducing sediment loss and least effective at reducing transport of dissolved nutrients in runoff. Also, cover crops can release nutrients from their tissues (e.g., brassicas) after termination due to rapid residue decomposition and abrupt freeze–thaw cycles and contribute to water pollution especially in cool temperate regions (Liu et al. 2019). The limited effectiveness of cover crops for reducing dissolved reactive nutrients in runoff underscores the need for a site-specific assessment of cover crop performance and proper fertilizer management for managing water quality.

10.6

Wind Erosion

Similar to water erosion control, cover crops can be a strategy to reduce losses of soil and nutrients by wind. Cover crops can mitigate wind erosion by (1) providing a protective surface cover, (2) holding the soil in place through their roots, and (3) improving soil properties. Well-established cover crops provide surface cover during critical periods of the year when wind erosion risks are high. Growing a cover crop also stabilizes soil aggregates and reduces soil detachment. Stable and large aggregates cannot be easily carried by the wind. Furthermore, the presence of cover crops increases surface tortuosity, reducing saltation and surface creeping of soil particles during wind erosion. Cover crops should be planted between crop rows perpendicular to the dominant wind direction to provide physical barriers against the blowing wind. A small decrease in wind speed by cover crops can result in significant reductions in wind erosion rates (Blanco-Canqui et al. 2013). Cover crops combined with no-till practices are the most effective means for controlling wind erosion. Cover crops of small grains planted in the spring or the fall are suitable practices to control wind erosion. Cover crops increase dry soil aggregate stability, which increases the soil’s resistance against wind erosion. Soils under cover crops have larger dry aggregates whereas plots without cover crops have smaller dry aggregates, which are more susceptible to wind erosion (Blanco-Canqui et al. 2013). In a semiarid region, replacement of fallow in winter wheat-fallow systems with winter triticale, lentil, pea, and spring lentil reduced the wind erodible fraction (5 year) studies are, however, needed to determine the effects of harvesting and grazing cover crops on soil properties and crop production in the long term for different soil types and climates.

10.14 Cover Crops and Crop Residue Removal Removal of crop residues for livestock and biofuel production at high rates (>50%) can accelerate soil erosion, reduce soil organic C concentration, disrupt nutrient cycling, and increase risks of non-point source pollution as discussed in the previous chapter. Addition of cover crops to no-till systems after residue removal can be an option to alleviate the adverse impacts of residue removal (Fig. 10.7). Cover crops

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Fig. 10.7 Winter rye cover crop aerially interseeded before corn residue harvest in the western US Corn Belt (Photo by H. Blanco)

can add aboveground and belowground biomass after crop residue removal. Synergies between crop residue removal and cover crops can allow sustainable management of crop residues for expanded uses. A modeling study indicated that cover crops can increase the total amount of crop residue harvested and potentially increase economic returns for producers (Pratt et al. 2014). Crop residue removal removes C. Addition of cover crops can replace C lost with crop residue removal provided cover crops produce an equivalent amount of C (Fig. 10.7). In the short term, cover crops may not, however, accumulate soil C after crop residue removal. In Michigan, when crop residue was removed, winter rye cover crop did not increase soil C concentration compared with non-cover crop plots after 3 years in a corn-soybean rotation (Fronning et al. 2008). In the long term, cover crops can, however, increase soil organic C pools (Blanco-Canqui et al. 2011). Addition of cover crops after crop residue removal can be particularly effective at reducing wind erosion risks because cover crops provide protective surface cover and improve near-surface soil structural properties.

10.15

Goals for Establishing Cover Crops

231

10.15 Goals for Establishing Cover Crops Prior to the adoption of cover crops, one must identify the specific goal for the cover crop use. Simply establishing cover crops because some other producers are planting cover crops may not deliver the intended benefits unless this question is fully answered: Why do I need or want cover crops in my field? A field can differ from other fields in terms of soil type, cropping system, initial soil fertility, management history, and other site-specific characteristics. Some of the goals for adopting cover crops in a given field can be: 1. Management of water and wind erosion. Cover crops with high biomass production such as winter cereal grains or summer cover crops are effective at reducing soil water and wind erosion. In order to obtain dense stands, cover crop seeding rates may need to be high (> 50 kg ha-1). 2. Management of soil compaction. If reduction of soil compaction or improvement in drainage is a goal, cover crop species (e.g., radishes and turnips) with tap roots may break compacted layers and increase water infiltration. Grass and legume cover crops can also alleviate soil compaction, but their benefits may not be measurable in the short term. In general, cover crops improve soil resistance against compaction with time. For example, cover crop-induced increase in soil organic C can reduce susceptibility to compaction. 3. Soil fertility. Nitrogen build-up is often one of the main goals. Legume cover crops fix N from the air and provide N to the next crops. Also, non-legume cover crops such as grasses can contribute to nutrient use efficiency by scavenging nutrients and reducing nutrient leaching. In addition, cover crops can increase soil organic matter concentration, which improves soil fertility and productivity. 4. Forage and feedstock production. High-biomass producing cover crops such as winter rye can produce significant amount of biomass for expanded uses such as livestock and biofuel production. Cover crops planted in late summer or early fall can especially produce abundant biomass relative to cover crops planted late in fall. 5. Weed suppression. Reducing herbicide use through the use of cover crops is one of the main reasons for adopting cover crops in croplands. High-biomass producing cover crops can compete with weeds, suppress weeds, and thus reduce the amount of herbicides needed. 6. Soil carbon sequestration and offsetting gaseous emissions. Extending the growing period of cover crops can result in increased cover crop biomass production. Increasing biomass production directly captures atmospheric C via photosynthesis and sequesters C in the soil. 7. Other goals. Additional goals include improvement in wildlife habitat (e.g., pollinators, birds, beneficial insects) and landscape aesthetics. Adding cover crops to current cropping systems can halt the declining wildlife habitat and diversity in croplands.

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10.16 Management of Cover Crops Management of cover crops is crucial to harnessing the benefits from cover crops. Because cover crop biomass production will determine the magnitude to which cover crops can enhance soil ecosystem services, developing or identifying management strategies to produce sufficient biomass from year to year is essential. Some of the management practices that affect cover crop performance include: 1. Timing of planting and termination of cover crops. Terminating cover crops late, for instance, can increase biomass production relative to early termination, but there is trade-off between late and early termination. While late-terminated cover crops produce more biomass, it can lead to water depletion, nutrient immobilization, and potential reduction in subsequent crop yields, depending on year and growth stage of the cover crop. In turn, early-terminated cover crops produce low biomass amounts, but it can minimize water depletion and favor rapid cover crop decomposition and nutrient release due to low C:N ratio of early-terminated cover crops. Minimizing water depletion is particularly important in water-limited regions. 2. Selection of cover crop species. In general, grass cover crops are the top options for soil erosion control, weed control, and C sequestration, whereas legume cover crops are the top choice for soil fertility and productivity improvement. It is important to consider the context-specific needs and goals to select the appropriate species. For example, a mix of grasses and legumes can be an option to produce forage with high quality for grazing cover crops. 3. Seeding rate. Cover crop biomass production generally increases with an increase in seeding rate up to an optimum level. Seeding rate of cover crops often ranges from 50 to 100 kg ha-1. Higher seeding rates can increase biomass production but increases production costs. 4. Fertilization and irrigation. Unlike main crops, cover crops are not often fertilized nor irrigated. However, fertilization at low rates and one or two irrigation events can be options in low fertility soils and water-limited-regions for an optimum establishment and growth of cover crops. 5. Planting method. Broadcasting and drilling are two methods of planting cover crops. Research shows that, under the same seeding rate, the drilling method often produces more biomass than broadcasting due to better soil-seed contact under drilling. 6. Tillage system. Combining cover crops with no-till is the best cover crop management strategy. Adding cover crops to no-till cropping systems can enhance no-till performance for conserving soil, improving soil properties, and sustaining crop production relative to no-till alone. Tilling cover crops as a green manure enhances organic matter decomposition and rapid nutrient release but can reduce benefits from cover crops such as soil erosion control. Leaving cover crop mulch on the soil surface not only protects the soil from erosion but also suppresses weeds and accumulates soil C.

10.17

Summary

233

7. Years under cover crops. The benefits of cover crops are often seen in the long term (>5 years). Well-established cover crops can rapidly and effectively suppress weeds and control erosion, but improvement in soil properties with cover crops is often realized in the long term. 8. Cropping system. Cropping systems that produce low biomass (e.g., cropfallow, soybeans, potatoes) are the top candidate systems for cover crop adoption. Cover crops can provide aboveground and belowground biomass input to enhance the performance of existing low-biomass producing cropping systems to deliver multiple soil ecosystem services. 9. Growing season. Cover crops established in late summer and early fall commonly produce more biomass and thus provide better surface protection in fall and spring than those planted in mid or late fall and terminated in early spring crops. A surface cover of about 50% during winter and spring would provide significant protection to soil and improve soil properties compared with fields without cover crops. 10. Climate. Cover crops can provide more benefits in water-limited regions with high soil erosion risks, low soil C levels, and low fertility soils than in regions with fertile and productive soils. However, in water-limited regions, cover crops can reduce soil water needed for the next crop in years with precipitation below normal.

10.17 Summary

Cover crops are a reemerging strategy considered to maintain or enhance soil ecosystem services. High-biomass producing cover crops can provide a number of services. They can protect soil from water and wind erosion, improve soil physical, chemical, and biological properties, enhance soil fertility, suppress weeds, increase soil organic matter content, improve soil biodiversity, and provide biomass for livestock, among other benefits. Cover crops can also improve water quality by reducing soil erosion and improving nutrient use efficiency although their benefits for reducing concentration of dissolved nutrients in runoff can be limited. Grass cover crops scavenge nutrients (e.g., N) and reduce leaching, while legume cover crops fix N from the air and reduce inorganic N fertilizer requirements. Legume cover crops can increase crop yields, especially in systems with low inorganic fertilizer application. An additional ecosystem service of cover crops is grazing and harvesting of biomass. Moderate grazing of cover crops can provide valuable forage to livestock while still maintaining the intended benefits from cover crops. Moderate grazing and harvesting (cutting height above 10 cm) do not often adversely affect soil properties and crop yields. Purchase of seeds, planting, (continued)

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termination, and other management operations increase costs of cover crops. These costs can be offset by reducing the N fertilizer requirements (e.g., legumes) for the main crops, grazing of cover crops, harvesting cover crops, and improving other soil ecosystem services. Identification of a goal is critical before adopting cover crops. Goals for the establishment of cover crops include soil compaction management, weed management, improvement in soil fertility, soil erosion control, soil C sequestration, and soil health improvement. However, proper management of cover crops cannot be overemphasized to meet such goals. Planting and termination times, cover crop biomass production, cover crop species, seeding rate, planting method, tillage systems, years after introduction, climate, and others will determine the success of cover crops. For example, low-biomass producing cover crops cannot deliver the expected benefits. Also, in water-limited regions, cover crops may reduce crop yields by depleting water when precipitation is low. Further, cover crop impacts on some soil properties can be variable, particularly in the short term (< 5 years). Identification or development of site-specific management strategies is needed to obtain positive agronomic, environmental, and economic impacts from cover crops. Questions 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

Describe the multi-functionality of cover crops. What is the difference between green manure and cover crops? What is the effect of cover crops on subsequent crop yields? How do cover crop mixes compare with single species in their impacts on soil ecosystem services? What is the effect of cover crop on soil water management and conservation? What are the management strategies to reduce water use by cover crops for the following crop? Discuss the main goals for the use of cover crops. Discuss how differences in C:N ratio affect nutrient release from cover crops. What are the mechanisms by which cover crops reduce soil compaction risks? Discuss the effects of cover crops on soil physical properties. Do cover crops reduce water pollution and improve water quality? Describe the effects of cover crop grazing and harvesting on subsequent crop yields and soil properties. Explain the process of soil C accumulation by cover cropping.

References

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Perennial Plants and Soil Management

11.1

11

Perennial Plants: Mimicking Nature to Manage Soils

The expansion of croplands has reduced the amount of land grown under perennial plants globally. For example, in the US Midwest, cultivation of food crops has reduced the area under tall grass prairie to 10 m) buffer strips are required in steeper slopes for reducing the same amount of sediment as in gentle slopes. 4. Companion management. Buffer strips perform better when combined with other conservation practices. For example, residue management and the use of cover crops improve the effectiveness of buffers. Some types of conservation buffers include: 1. 2. 3. 4. 5. 6.

Riparian buffers Filter strips Grass barriers Prairie strips Grassed waterways Field borders

11.2.2 Riparian Buffer Strips Riparian buffer strips are wide strips of a permanent mixture of woody and herbaceous vegetation planted along agricultural fields designed to mitigate sediment and nutrient flow to streams (Bu et al. 2016; Fig. 11.2). Riparian buffers are used in both agricultural and urban soils alongside streams to control sediment transport (Fig. 11.2). Riparian buffers are more widely used than other buffer strips. These buffers consist of grasses, trees, shrubs, or a combination of these plant species. Wide riparian buffers (>10 m) comprised of native plant species filter sediments and benefit wildlife habitat more than narrower grass strips (Cole et al. 2020). The effectiveness of woody buffers for sediment reduction is mostly due to improved infiltration rate as sparse woody trees may not significantly filter sediment from runoff (Table 11.2). Riparian buffers may fail to reduce N and P export under large amounts of runoff as compared with grass strips. Tree buffers established in Table 11.2 Runoff, sediment, and nutrient trapping ability of riparian buffers in eastern China (Bu et al. 2016). Means with the same letter within each column are not significantly different (P < 0.05) Treatment Cropland without riparian buffer Cropland with riparian buffer (grass +557 poplar trees per ha) Cropland with riparian buffer (grass +769 poplar trees per ha) Cropland with riparian buffer (grass +1346 poplar trees per ha)

Runoff (mm) 580a 284c

Sediment (Mg ha-1) 3.12a 0.66d

Total N (kg ha-1) 3.21a 1.36c

Total P (kg ha-1) 0.56a 0.19c

269c

0.52c

1.20bc

0.17bc

233b

0.30b

0.93b

0.11b

11.2

Conservation Buffers

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Table 11.3 Effectiveness of woody buffer strips for reducing losses of nutrients (Aguiar et al. 2015). Means with the same letter within each column are not significantly different (P < 0.05) Treatment Woody

Shrub

Grasses

Width 12 36 60 12 36 60 12 36 60

Total N (kg ha-1) 23.6a 2.55b 0.03c 25.0a 11.4b 6.9c 32a 30.3b 16.1c

Nitrate (mg L-1) 13.8a 2.3b 0.008c 23a 15.3b 7.9c 31.9a 25.1b 19.2c

Total P (μg L-1) 13.9a 1.7b 0.03c 18.8 13.8b 4.0c 23.4a 23.5a 15.1b

combination with upstream grass strips perform better than buffers with trees alone. The effectiveness of riparian buffer strips depends on the density of vegetation, width of the buffer strip, nutrient load, upstream management system, topography, and climate. For example, the effectiveness of riparian buffer strips for the reduction of runoff and losses of sediment and nutrients increases as the number of trees within the strips increases (Table 11.2). Similarly, the effectiveness of riparian buffer strips increases as the width of the strips increases. In southeastern Brazil, the effectiveness of woody buffer strips for reducing losses of total N, nitrates, and phosphates from no-till corn-soybean fields increased as the width of strips increased (12, 36, and 60 m), and the 60-m buffer strip nearly (99.9%) reduced all nutrient losses (Table 11.3; Aguiar et al. 2015). However, riparian buffers can become saturated with nutrients from upstream sources, which can reduce their ability to act as a nutrient sink (Cole et al. 2020). Thus, the effectiveness of riparian buffer strips depends on how the upstream sediment or nutrient source areas are managed. Riparian buffers should be considered as a companion to other conservation practices to reduce non-point source pollution and deliver other soil ecosystem services. While it is well recognized that riparian buffer strips can reduce losses of sediment and nutrients (Blanco-Canqui 2018), the new approach is that riparian buffers must not only reduce soil erosion and control transport of pollutants but also provide ancillary benefits including social and economic considerations (e.g., recreation, timber harvesting, C credits, wildlife habitat credits). Indeed, a review discussed that riparian buffer strips can provide multiple soil ecosystem services (Cole et al. 2020). For instance, the establishment of fast-growing trees for fiber and biofuel production is a practical option in some agro-ecosystems to enhance net income from riparian buffer strips while still protecting the watercourses. Controlled harvesting of trees such as poplar can be economically profitable (Blanco-Canqui 2016; Hussain et al. 2020). Some forest riparian sites can benefit from moderate thinning and coppicing, depending on the forest species and growth stage. Threshold levels for harvesting forest buffers without negatively affecting the functionality for erosion sediment

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control must be developed. Riparian buffers can also provide additional sources of income from the C credits and CRP (Conservation Reserve Program). Traditionally, riparian buffers have been managed for water quality improvement rather than for C storage. Now, there is more emphasis on managing riparian buffers and other buffer strips for sequestering C in the soil (Blanco-Canqui 2016). Expanding these benefits can promote different management scenarios for riparian buffers that can enhance net income from conservation management while improving soil and water quality. The diversified use of buffers demands careful planning and management of riparian systems.

11.2.3 Filter Strips Vegetative filter strips are areas of grass or other permanent herbaceous vegetation planted between agricultural fields and streams designed to reduce losses of sediment, nutrients, and other pollutants in runoff (Fig. 11.3). These strips often consist of sod-forming grass. The filter strips are a useful conservation practice to reduce water pollution from sediment, nutrients, heavy metals, and pesticides from agricultural fields. Filter strips can be as effective as riparian buffer strips for reducing losses of sediment and sediment-associated nutrients in runoff. The effectiveness of filter strips can increase exponentially as the width of the strip below the sediment source area increases (Fig. 11.4a-b). A study comparing different widths of tall fescue filter strips found that 9-m wide strips reduced sediment loss by up to 90%, while narrower strips had lower effectiveness

Fig. 11.3 Tall fescue filter strip established between a waterway and cropland (Courtesy USDANRCS). Buffers are ecotones of the adjoining terrestrial and aquatic landscapes as they integrate fluxes of energy, matter, and living species

11.2

Conservation Buffers

247

2.1

2.1

A

-1

Sediment (Mg ha )

1.8

Filter Strip

1.5 y = 2.23exp(

1.2

-0.26x

Filter Strip + Barrier

1.5 )

1.2

2

r = 0.98

0.9

0.9

0.6

0.6

0.3

0.3

0.0

0.0 0

B

1.8

2 4 6 8 10 Distance from field edge (m)

y = 0.89exp(

-0.19x

)

2

r = 0.99

0

10 2 4 6 8 Distance from field edge (m)

Fig. 11.4 Sediment mass decreases with an increase in the width of tall fescue alone and in combination with switchgrass barriers (After Blanco-Canqui et al. 2004)

(Fig. 11.4a). Most of the sediment and nutrients are trapped within the first few meters (2 to 3 m) of filter strips from the field boundary (Fig. 11.3). Filter strips are more effective at reducing sediment losses when combined with barriers of warmseason grasses than tall fescue filter strip alone (Fig. 11.4b; Blanco-Canqui et al. 2004). Also, filter strips can reduce sediment loss more than nutrient loss. The main mechanism by which filter strips reduce runoff and thus sediment loss is through increasing water infiltration and improving related soil properties (Table 11.1). Example 11.1 Estimate the sediment trapping efficiency (STE) at 1 m below field edge for the filter strip systems in Fig. 11.4 assuming that the incoming sediment mass is 8.5 Mg ha-1 for both buffer systems. In addition, determine the amount of sediment left in runoff at the 6 m grass strip. (1). Sediment Trapping Efficiency Tall fescue alone: STE = 1-

Exiting 1:72 × 100 = 1× 100 = 79:8% Entering 8:5

Tall fescue plus Grass Barrier: STE = 1-

0:72 × 100 = 91:5% 8:5

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(2). Amount of Sediment Left in Runoff at the 6 m Grass Strip Tall fescue alone: y = 2:23 exp ð - 0:26xÞ Trapping = 2:23 expð - 0:26 × 6Þ = 0:47 Mg ha - 1 Tall fescue plus Grass Barrier: y = 0:89 expð - 0:19xÞ Trapping = 0:89 expð - 0:19 × 6Þ = 0:28 Mg ha - 1 The filter strips are effective to slow runoff, expand runoff flow area, and trap sediments and nutrients if: 1. 2. 3. 4.

Incoming runoff flow is uniform and laminar Runoff rate is relatively small Filter strips are wide enough (>10 m) Filter strips are not inundated by runoff

In cool temperate regions, filter strips often consist of cool-season grasses including tall fescue, Kentucky bluegrass, orchard grass, and smooth bromegrass. The cool-season grasses develop extensive and deep root systems allowing drought resistance and vigorous growth in early spring and late fall (USDA-NRCS 1997a) when erosion and runoff are highest. The most common species used in filter strips for erosion control in temperate regions is tall fescue. In subtropical and temperate climates, Bermudagrass and other warm-season perennial species can be used. • Tall fescue. It is a perennial cool-season grass and reaches about 1 m in height (USDA-NRCS 1997a). As a bunchgrass, it tends to form tight and dense sod. It produces short rhizomes that develop into sod-type growth. Tall fescue is best adapted to the parts of the USA with hot and humid summers (Midwest, Mid-Atlantic, and Southeast). It is well adapted to a wide range of soils but grows best on clay soils, damp pastures, and wet environments. Tall fescue tolerates drought, surviving dry periods in a dormant state. It is more resistant to low temperatures and can remain green later into the winter than other coolseason grasses. It is a high yielding grass used widely for forage for late fall and winter grazing. Some varieties of tall fescue that have endophyte infestation could cause health problems in animals such as decreased forage intake, growth, and milk production. • Bermudagrass. It is a warm-season, sod-forming, and perennial grass with deep and fibrous roots. Bermudagrass is best suited to erosion control in subtropical and tropical climates with 600 mm to 2500 mm of annual precipitation and grows in many parts of the world. In the USA, it is mainly grown in Southern and Midwestern states. It withstands occasional drought periods but requires

11.2

Conservation Buffers

249

irrigation in arid climates. Bermudagrass grows well on a wide range of soils from clayey to sandy and can tolerate acidity and alkalinity and moderate waterlogging although it grows best in well-drained soils. • Kentucky bluegrass. It has a sod-forming ability and is well suited for soil erosion control especially when combined with other grass species. It can grow well in loamy or clayey soils with a pH between 5 and 7. Bluegrass reaches about 0.60 m in height, has a fibrous root system, and resists overgrazing. It is mostly grown in North Central and Northeastern USA with temperatures below 24 °C and is an ideal species for permanent pastures and erosion control. • Orchard grass. It grows in clumps and forms sod. It is a leafy grass with a fibrous and extensive root system. It can grow in a wide range of temperate ecosystems. Orchard grass starts growing in early spring and flowers in late spring. Compared with Kentucky bluegrass, its root system is more extensive and deeper. Thus, it is more resistant to drought. The optimum daytime temperature for growth of orchard grass is about 21 °C, which is slightly lower than for smooth bromegrass or tall fescue. • Smooth bromegrass. It is a long-leafed perennial species of about 1 m in height. It is one of the most useful cool-season grasses for hay, pasture, silage, and ground cover. It has been used for erosion control around ditches, waterways, and gullies. It grows better on well-drained silt or clay loam soils. Because of its deep and extensive root system, smooth bromegrass is relatively resistant to drought.

11.2.4 Grass Barriers Grass barriers, also called grass hedges, are narrow (0.75 to 1.2 m) strips of dense, tall, and stiff-stemmed perennial grass established perpendicular to the field slope within croplands for soil erosion control (Fig. 11.5; USDA-NRCS 1997b). Grass barriers differ from other grass strips because they are planted to grasses with stiff and robust stems, adapted to local soil types and climates and are commonly planted to native warm-season grass species. Barriers can be used in combination with no-till and reduced-tillage cropping systems. They are normally established on the field’s contour in parallel rows at short intervals (0.3 m, and thus sediment is mainly trapped because of runoff retardation (Blanco-Canqui et al. 2004). The more time the backwater remains ponded above the barriers, the more sediment with smaller particle size is deposited. Stoke’s law states that the settling velocity is proportional to the square of the particle diameter. Runoff ponding retains about 90% of particles coarser than 0.125 mm and about 20% of particles Kaolinite > Fine sand in accord with the specific surface of soil materials. Presence of ions at differing concentrations can alter the PAM sorption ability of clay minerals. Soils with abundant divalent cations such as Ca2+ and Mg+2 are more effective in PAM sorption than soils with monovalent cations such as Na+. Size, internal structure, and electrostatic charge of clay minerals explain differences in PAM sorption by soil surface. Salt content of the soil solution or irrigation water is an important factor affecting PAM performance because an increase in salt content decreases the amount of water adsorbed by PAM molecules. Organic matter reduces the PAM adsorption rates significantly because of the reduction of sorption sites and increase of electrostatic repulsion between the soil particles. Polyacrylamides can either increase or decrease water infiltration depending on soil textural characteristics. In soils dominated by clay or silt, application of PAM commonly increases water infiltration rate, thereby reducing runoff and soil erosion. The improvement of water infiltration in fine-textured soils by PAM is caused by the increased flocculation, decreased aggregate detachment and clogging of pores, and increased surface-connected macropores. In sandy soils, conversely, PAM slows water infiltration and improves soil water retention. The viscosity of water increases rapidly with additions of PAM, which causes reduction in water infiltration. Reduction of infiltration in sandy soils means less irrigation and thus reduction in irrigation costs. The PAM-induced increases in soil water retention capacity in sandy soils can be beneficial to crop growth through an increase in the amount of water available because the low water retention capacity and excessive deep percolation reduce the efficiency of water and fertilizer use by plants in coarse-textured soils. The crosslinked PAMs swell up to 100 to 1000 times their dry weight by absorbing water (Sivapalan 2006). One gram of cross-linked PAM can absorb 10 to 1000 mL of water depending on the PAM and soil characteristics. Soil water retention capacity by cross-linked PAMs increases between 20 and 50% with an increase in PAM additions in sandy soils.

12.6.6 Polyacrylamide Characteristics There are a variety of PAM formulations with different molecular weights, ionic charges, and forms which determine the PAM effectiveness (Mulualem et al. 2021). Formulations of PAM include dry granular beads, blocks, powders, and liquid or emulsion. The negative charge density of PAM varies between 2 and 30% with a typical value of 18% (Sojka et al. 2004). The dry forms have about 80% of active ingredient by weight while the emulsions have 30 or 50% (Holliman et al. 2005). The soil stabilization is a function of molecular weight and degree of hydrolysis of PAM. The higher the molecular weight and the lower the degree of hydrolysis, the greater the soil aggregate stabilization. Sprayed PAM may control soil erosion better

294

12

Soil Amendments

than dry applied PAM in the early stages following the onset of rains because of rapid interaction of emulsions with soil. The two common forms of PAM include (1) water-soluble and (2) non-watersoluble or cross-linked PAMs (Holliman et al. 2005). The water-soluble PAMs are also called “linear” and “non-crosslinked” and are commonly used for erosion control. Although cross-linked or non-linear PAMs are insoluble in water, they can adsorb significant amounts of water, a property that makes them likely amendments for improving the water retention capacity of sandy soils. The development of cross-linked polymers has increased use of polymers for increasing water retention in coarse-textured soils. A high rate of PAM application does not necessarily increase PAM effectiveness. Initial applications of PAM can reduce soil erosion more than subsequent heavy applications.

12.6.7 Soil Management Combining PAM with other soil erosion control practices can be a better option than PAM alone for controlling soil erosion. Some practices include applying PAM in combination with crop residue mulch, geotextile fabric covers, gypsum, lime, and biochar. Applying PAM in conjunction with other practices also makes the use of PAM more adaptable to diverse soil types and climatic conditions. For example, applying crop residue mulch to PAM-treated soils can double the reductions in soil erosion compared to PAM alone (Bjorneberg et al. 2000). Indeed, applications of PAM at low rates ( Loam or Silt loam soils > Clayey soils. A larger amount of soil organic C may be required to increase available water in clayey soils than in soils with low clay concentrations. Indeed, a global meta-analysis of published studies found that an increase in organic C in soil has only a small effect on available water (Minasny and McBratney 2018). The meta-analysis found that a 1% increase in soil C mass increased water content at field capacity by 1.61 mm and at wilting point by 0.17 mm per 100 mm of soil, and increased available water by 1.16 mm per 100 mm of soil. Bagnall et al. (2022) developed new pedotransfer functions using data from 124 long-term research sites across the USA, Canada, and Mexico and found that a 1% increase in soil C mass increased available water content by 3 mm in non-calcareous soils per 100 mm of soil and 1.2 mm in calcareous soils per 100 mm of soil across all soil textural classes. Soil organic matter content may not only increase soil water retention but also improve other soil properties such as aggregate stability and specific surface area. It can stimulate the activity of soil organisms such as earthworms and termites, which create water-conducting biopores to improve water infiltration. Soil organic C may also induce slight hydrophobic properties (Blanco-Canqui 2011), which increases aggregate stability and enhances macroporosity. Changes in soil organic C concentration affect porosity by altering both bulk density and particle density although the impact of soil organic C on particle density is smaller than on bulk density. Particle density often decreases when soil organic C concentration increases. The decrease in soil bulk and particle densities can positively affect soil porosity and soil water retention characteristics.

17.6

Drought Management Strategies

Drought is a period of time, commonly one or more growing seasons, where soil water is below levels to sustain optimum crop production and replace transpired water. Persistent and recurrent droughts can hinder crop production, particularly in non-irrigated systems (Crockett and Westerling 2018; Moravec et al. 2021). It can also affect livestock production due to poor forage or pasture production. For example, in 2012, about 80% of the contiguous USA was designated as abnormally dry, 62% as moderate drought, and 33% as severe to extreme drought. The 2012 drought could be similar in intensity and extent to the drought events in the 1930s (Dust Bowl) and 1950s. The lack of rain results in drought, but poor soil management practices can further accelerate the consequences or the intensity of drought. For example, tillage can quickly dry soil to the depth of tillage. A tilled soil has lower water content than a soil that was not tilled before or during the drought. Assume that a silty clay loam has a volumetric water content of 35% at field capacity and 18% at permanent wilting point. In this case, the surface soil to a depth of 20 cm contains 7 cm of water at field capacity and 3.6 cm at permanent wilting point. When this soil is tilled, most of the

424

17 Soil Water Management

3.6 cm of soil water at permanent wilting point will be lost through evaporation. A rain event after the drought will have to replenish the 3.6 cm first before there is sufficient available water for plants to absorb. This is just an example of why prolonged drought coupled with improper soil management can have large negative impacts. Losses of water beyond the permanent wilting point can delay recovery from droughts. Improved soil water management strategies can enhance soil resilience against the impacts of drought events. The impact of drought can decrease with an increase in the soil’s ability to capture and retain rainwater for future crop use. Soil captures and retains more water if it remains covered with residues and has high soil organic matter content. Thus, adopting practices that leave residues on the soil surface and increase soil organic matter content combined with reduced soil disturbance improves soil resilience against drought. Management practices that increase surface residue cover not only increase water infiltration but also reduce evaporation. Among the potential management strategies to combat the impacts of drought include: 1. 2. 3. 4.

Conservation tillage and residue mulch cover to reduce evaporation Conservation buffers to reduce water losses through runoff and increased winds Diversified and intensified cropping systems or complex rotations Contour farming, strip cropping, terraces, and water harvesting to divert and reduce runoff 5. Cover crops to increase water infiltration and reduce evaporation, particularly in regions with higher precipitation input 6. Development of drought-tolerant crops through genetic improvement 7. Selection of water-efficient cropping systems combined with reduced transpiration The adverse impacts of drought on crop production can be managed if drought periods can be predicted for the growing season. Short-term weather forecasts may not be very useful for agriculture. Increased climate fluctuations underscore the need to develop models to predict drought and precipitation events for at least 4 months in advance. For example, in semiarid regions such as the Great Plains, decisions on the use of intensified cropping systems and cover crops in place of crop-fallow systems may depend on future precipitation. Measurement of soil water at the time of planting is a useful approach to estimating crop performance (Hansen et al. 2012). Available water at planting is positively correlated with crop yields. Forecasts based on the El Niño-southern oscillation indexes may be promising to estimate future precipitation (Nielsen et al. 2010). At present, data on available soil water at planting and historic weather records can help producers to make decisions about crop production until more sophisticated models are developed (Hansen et al. 2012).

17.7

17.7

Conservation Tillage and Water Conservation

425

Conservation Tillage and Water Conservation

Adoption of conservation tillage such as no-till is an alternative to intensive tillage in rainfed and irrigated crop production systems (Peng et al. 2020). Conservation tillage can contribute to maximizing water capture and minimizing soil water loss through runoff and evaporation. Water efficient management systems should use no-till, leave residues on the soil surface, and improve soil properties that absorb and retain water in the soil. Indeed, no-till management can increase crop yields in semiarid regions by improving water storage when compared with tilled systems. Timing and type of tillage, crop choice, planting and harvesting date, use of organic amendments and inorganic fertilizers coupled with conservation tillage dictate water losses and gains. Increased soil water storage with conservation tillage can reduce irrigation requirements.

17.7.1 Soil Water Content Conservation tillage increases soil water storage. Soil water content generally is greater under conservation tillage such as no-till than under conventional tillage (Peng et al. 2020). No-till stores more water because it reduces evaporation if it has sufficient residue cover left on the soil surface. Conventional till disturbs and exposes soil to the atmosphere and increases evaporation. The potential of no-till for increasing soil water storage is particularly beneficial in semiarid regions compared with humid regions. No-till management can minimize the adverse effects of droughts. In summer, no-till soils with residues left on the soil surface have lower soil surface temperatures than conventional till soils. The reduced soil temperature under no-till soils results in lower water evaporation than under plowed soils. Benefits of no-till are more apparent in dry than in wet years. If crop residues are removed, the benefits of no-till management for storing soil water can rapidly decrease.

17.7.2 Water Infiltration Tilled soils often have higher water infiltration immediately after tillage compared with no-till, but the water stored in plowed soils is rapidly lost through evaporation. Plowing or disking several times per year to control weeds exposes soil to the atmosphere. Soil exposure during the hottest months of the year in combination with increased winds accelerates water losses through evaporation and rapid desiccation unlike no-till management. No-till management often increases water infiltration over conventional till, depending on soil type, management, and climate. Benefits of no-till for improving water infiltration can be more apparent in the long term as soil rebounds from previous intensive tillage. A global review found that no-till management can increase water infiltration by 17–86% and plant available water by 44% compared with conventional till (BlancoCanqui and Ruis 2018). The greater water infiltration in no-till can thus translate into

426

17 Soil Water Management

greater water availability for crop use. In some soils, however, particularly in soils with a high percentage of clay, no-till may have similar or lower infiltration rates than conventional till due to soil consolidation and increased compaction near the surface layers of no-till soils. For instance, in eastern Nebraska, water infiltration was lower in no-till than in conventional tillage after 35 yr on a silty clay loam (BlancoCanqui et al. 2017). Soil consolidation could reduce water infiltration in no-till systems compared with tilled systems, especially in fine-textured soils in temperate regions. Tilled soils often have more voids and are less consolidated compared with no-till systems due to frequent and intensive disturbance.

17.7.3 Water Use Efficiency Water use efficiency (WUE) refers to the units of crop produced per unit of water used. A number of relationships exist to quantify water use efficiency. Peterson and Westfall (2004) used Eq. (17.3), while other researchers have used Eq. (17.4) to compute WUE. WUE ð%Þ =

Crop Yield × 100 Precipitation þ Soil Water Used by Crops WUE ð%Þ =

Crop Yield × 100 Evapotranspiration

ð17:3Þ ð17:4Þ

Precipitation storage efficiency (PSE) is another parameter used to estimate the amount of precipitation that is captured and stored in the soil during a given period of time. PSE ð%Þ = =

ΔSWC P

SWC2 - SWC1 × 100 Precipitation between SWC1 and SWC2 measurements

ð17:5Þ

where ΔSWC is the change in soil water content in the soil profile during the fallow period or growing season. The SWC1 is soil water content at the beginning and SWC2 is soil water content at the end of the fallow period or growing season. No-till management generally increases water use efficiency over conventional till. Such an increase in water use efficiency can result in increased crop yield compared with conventional till, particularly in semiarid regions (Pittelkow et al. 2015). It is important to clarify that the magnitude at which no-till increases precipitation storage efficiency depends on differences in precipitation input, soil type, cropping system, and site-specific management. In regions with limited precipitation input, such as in the US Great Plains, approximately 75% of annual precipitation falls between April and September when temperature and evaporation are the highest (Peterson and Westfall 2004). High winds, high temperature, and low

17.8

Cropping Systems and Water Conservation

427

Precipitation Storage Efficiency (%)

60 Conventional Tillage No-tillage

50

*

*

40 ns

† ns **

30 20

** *

ns

*

10 0

1996-1997 1997-1998 1998-1999 1999-2000 2000-2001 2001-2002 2002-2003 2003-2004 2004-2005 2005-2006

Fig. 17.2 No-till and conventional tillage effects on precipitation storage efficiency during the entire fallow period under wheat-fallow in eastern Colorado. (* significant at the 0.05 probability level; ns, non-significant; ** significant at the 0.01 probability level; { significant at the 0.10 probability level; Nielsen and Vigil 2010)

humidity during these months can rapidly reduce precipitation storage efficiency. Precipitation storage efficiency is high if precipitation falls during winter months when temperature and evaporation rates are low. Thus, precipitation storage efficiency during fallow in crop-fallow systems in the central US Great Plains is low. Even no-till management may not capture and store a large percentage of precipitation under crop-fallow systems. Nielsen and Vigil (2010) found that only 20% of precipitation was stored in conventional till and only 35% in no-till during the 16-month fallow in wheat-fallow systems (Fig. 17.2). On sandy clay loam, silty clay loam, and clay loam in Oklahoma in the Southern US Great Plains, differences in precipitation storage efficiency between no-till and conventional till for continuous wheat did not differ (Patrignani et al. 2012). The same study found that only 11% of precipitation was stored under both tillage systems in three out of four site-years, which indicated that about 90% of precipitation was lost through evaporation in that region. These studies suggest that crop-fallow or monocultures are not efficient at storing large amounts of precipitation regardless of the tillage system. As discussed next, improved cropping systems are needed to increase the ability of no-till to capture more precipitation and use it more efficiently.

17.8

Cropping Systems and Water Conservation

Intensification and diversification of cropping systems can be strategies to more efficiently capture precipitation and use the extra precipitation. For example, the fallow period, which lasts about 16 months in wheat-fallow rotation in the central US Great Plains, is intended to store soil water for the subsequent wheat phase. However, the fallow phase has low water storage capacity as it only stores about 20–30% of precipitation. Also, the use of fallow is also often at the expense of soil C

428

17 Soil Water Management

16

0.60

12 10 8 ab

6 4

b

b

b

2

Volumetric Water Content (mm 3 mm -3)

Cumulative Water Infiltration (cm)

14

0.65 a

0.55 0.50 0.45 0.40 0.35

Continuous wheat

0.30

Wheat-sorghum-fallow Continuous sorghum

0.25

Sorghum-fallow 0.20

0

Wheat-fallow

0.15 WW

WSF

SS

WF

SF

0.1

1 10 100 Soil Water Potential (-kPa)

1000

10000

Fig. 17.3 Cumulative water infiltration (left) and soil water characteristics curve showing the relationship between water content and matric potential (right) for five cropping systems including continuous wheat (WW), wheat-sorghum-fallow (WSF), continuous sorghum (SS), wheat-fallow (WF), and sorghum-fallow (SF) after 33 yr of management under no-till in the central Great Plains. Bars followed by the same letters are not significantly different (P < 0.05). Error bars are the least significant differences to compare treatments by soil water potential (Blanco-Canqui et al. 2010a)

losses and wind erosion due to lack of residue input during fallow and reduced frequency of a growing crop (Blanco-Canqui et al. 2010a). Because the amount of water stored decreases with an increase in the length of the fallow period, reducing the length of fallow periods and using soil water soon after a precipitation event can be strategies to increase precipitation use efficiency. In a silty clay loam in the central Great Plains, water infiltration and soil water retention under five cropping systems increased with a reduction in fallow period frequency after 33 yr under no-till management (Fig. 17.3; Blanco-Canqui et al. 2010a). Wheatsorghum-fallow and continuous wheat retained 10–16% more water than sorghumfallow between 0 and - 3 kPa matric potentials in no-till. No-till soils without fallow increased cumulative water infiltration more than rotations with fallow because the soil surface remained covered with residues. Increases in water infiltration and water retention are also due to better aggregation and greater soil organic C accumulation under cropping systems without fallow. Intensification of cropping systems coupled with no-till enhances the potential of no-till soils to improve soil physical properties responsible for water capture and storage. Improved management practices such as diversified cropping systems use water more efficiently. In the southern Great Plains (Kansas, Oklahoma, and Texas) with >600 mm annual precipitation, no-till diversified cropping systems with five crop rotations including winter wheat, corn, sunflower, grain sorghum, and soybean resulted in more efficient use of precipitation compared with conventional till continuous wheat (Patrignani et al. 2019).

17.9

Crop Residues and Water Conservation

429

Intensification and diversification of cropping systems can also increase soil productivity, build or restore soil C, and protect soil from water and wind erosion (Peterson and Westfall 2004). Most importantly, it can maximize precipitation capture, minimize losses of water in runoff, and increase water use efficiency. A study from the central US Great Plains reported that the amount of precipitation stored was 10–35% between July and September, 50–85% between September and May, and negative (-4.5%) between May and September for fallow period under no-till wheat-fallow systems (Peterson and Westfall 2004). This rainfall distribution indicates that, in this region, only about 30% of precipitation falls when wheat is growing and the remainder falls during the fallow period in wheat-fallow systems. Thus, including forage crops or cover crops after wheat harvest until wheat planting can be a strategy to use the remaining 70% of precipitation and increase precipitation use efficiency during fallow.

17.9

Crop Residues and Water Conservation

The increased amount of residue left after harvest on the soil surface is the main reason for greater soil water use efficiency under no-till. Particularly in semiarid regions, the presence of surface residue reduces soil desiccation and is critical to maintaining soil properties. Crop residue mulch and soil surface conditions dictate the rainfall partitioning between infiltration and runoff (Blanco-Canqui et al. 2016). When rain falls on bare soil, it rapidly detaches soil aggregates, induces surface sealing, and clogs soil pores, increasing runoff. In turn, when rain falls on residuemulched soil, soil aggregates and surface-connected macropores under the residues often remain stable, which increases rainwater infiltration and reduces runoff. Soil water content is probably the most sensitive parameter to changes in crop residue cover. For instance, soil water content increased with the increase in the amount of corn stover (Kenney et al. 2015). Soils lose water as soon as the protective residue cover is removed. Crop residue mulch improves soil water content because it increases water infiltration rate, and reduces runoff, evaporation, and abrupt fluctuations in soil surface temperature. The amount of residue retained on the soil surface determines the degree of soil surface insulation. Residue-mulched soils are cooler in summer and warmer in winter and thus have lower evaporation losses in summer than unmulched soils. The higher temperature in soils without residues accelerates evaporation and reduces available water storage. Near-surface temperature in no-till soils with residues can be 3–5 °C lower than no-till soils without residues in summer. Mean soil temperature in summer can increase by about 5 °C when crop residues are completely removed. Crop residue cover alters the radiation balance. Light-colored residue cover has high albedo, which can reflect the incoming solar radiation at the soil surface. Residue mulch cover also promotes the activity of soil organisms (e.g., earthworms) and protects soil surface-connected earthworm channels, which increase water infiltration rate (Shipitalo and Butt 1999). In Ohio, corn stover

430

17 Soil Water Management

Infiltration Rate (cm min -1)

2.1

2.1 Silt loam (10% slope)

1.8

Rate of Stover Removal 0%

1.5

Clay loam (< 1% slope)

1.8 1.5

25%

1.2

1.2

50% 75%

0.9

0.9

100%

0.6

0.6

0.3

0.3

0.0

0.0 0

30

60

90 120 Time (min)

150

180

0

30

60

90 120 Time (min)

150

180

Fig. 17.4 Relationship between corn stover removal and water infiltration rate for two contrasting soils in Ohio (Blanco-Canqui et al. 2007). Error bars are the least significant differences to compare differences among treatment by time (P < 0.05)

removal reduced water infiltration rates on sloping and nearly level silt loams but had no significant effects on clay loam (Fig. 17.4; Blanco-Canqui et al. 2007). The extent to which crop residues affect water infiltration can depend on tillage, soil texture, terrain, drainage, cropping system, amount of residue left after harvest, and climate (Rakkar and Blanco-Canqui 2018). Residue mulch may not increase water infiltration if 1) a compacted or poorly drained subsoil horizon is present beneath the residue mulch and 2) there are no abundant earthworms in the soil. Also, in some soils, the stratified surface layer of soil organic matter under mulched soils may impart slight water-repellent or hydrophobic properties and may reduce water infiltration rate (Blanco-Canqui 2011). Tilling crop residues into the soil can reduce the benefits of crop residues on soil water content. The greater the amount of residues on the soil surface, the higher the soil water content. Standing stubble and residue left on the soil surface also trap snow (Fig. 17.5). Crop residue mulch increases the soil surface roughness and enhances the snow accumulation or trapping as compared to soils with little or no residue cover. Residue mulch cover can reduce soil freezing and accelerate early spring thawing as compared with residue removal.

17.10 Terraces and Farm Ponds As discussed earlier under mechanical structures, terraces can conserve water by slowing runoff velocity, retaining runoff water, and increasing water infiltration (Deng et al. 2021). Terraces reduce the slope length, which, in turn, reduces the opportunity for runoff to increase its velocity, transport capacity, and energy. Terraces provide more benefits to water conservation when integrated with no-till, cover crops, and other biological practices. Constructing rainfed ponds on farms is also a viable strategy to capture and conserve water. Rainfed ponds capture water

17.11

Conservation Buffers

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Fig. 17.5 Soils with abundant wheat straw trap snow and increase soil water content (Photo by H. Blanco)

from croplands that may otherwise be lost as runoff. The amount of water stored in ponds can be used for crop and livestock production. The amount of water collected depends, however, on the amount of precipitation and runoff. Capturing water in ponds during wet years can be highly valuable to support crop and livestock production in subsequent dry years.

17.11 Conservation Buffers Conservation buffers such as grass barriers, windbreaks, vegetative filter strips, and others planted on the contour in croplands are effective for water conservation (Blanco-Canqui 2018). These strips of vegetation can capture precipitation, intercept runoff, and store water in the soil. Buffers improve water infiltration and reduce runoff volume by increasing soil organic matter concentration, reducing bulk density, and increasing aggregate stability, macroporosity, and hydraulic conductivity. Buffers consisting of tree and grass species with deep or extensive roots can promote rapid water flow and drainage through the whole soil profile. For instance, in a claypan soil in Missouri, 4.5-m wide agroforestry buffers and grass buffers planted at 36.5 m intervals within corn-soybean systems increased water infiltration and saturated hydraulic conductivity after more than 10 yr of establishment (Sahin et al. 2016). The agroforestry buffers consisted of redtop, brome, birdsfoot trefoil, pin oak, swamp white oak, and bur oak, while grass buffers consisted of redtop, brome, and birdsfoot trefoil (Sahin et al. 2016). Conservation buffers can also reduce runoff and conserve water by reducing slope length and steepness. Wide buffers across sloping soils develop miniterraces above them with time as eroded soil from the upper portions accumulates. Buffers

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can thus act like terraces. The terracing effect of buffers can slow runoff, increase time for water infiltration, and increase groundwater recharge. Surface cover also alters the soil–water relations by reducing excessive evaporation. The magnitude of improvement in water infiltration and reductions in runoff depends on differences in buffer species, buffer management, and climate (BlancoCanqui 2018). Buffers with a dense vegetation can be more effective than sparse vegetation to reduce runoff and store water. The effectiveness of conservation buffers for capturing precipitation is greater the more each buffer resembles the natural system (e.g., prairie). Buffers are best used as companion practices to other management practices to conserve water. For example, because no-till systems may not completely eliminate runoff, conservation buffers can be companion practices to improve the ability of no-till to reduce runoff.

17.12 Management of Irrigation Water Irrigated land area is about 308 Mha worldwide (USDA-ERS 2022; De Wrachien et al. 2021). Table 17.2 lists the top 10 countries based on the percentage of irrigated area. India, China, and the USA are the top three countries with the most irrigated land in the world. Irrigation water management is becoming more critical than ever before under frequent droughts and variable precipitation input. Cultivated area under irrigation has been steadily increasing globally (De Wrachien et al. 2021). In the USA, crops based on irrigation amount can be in this order: Corn > Soybean > Hay and alfalfa > Orchards > Cotton (USDA-ERS 2022). About 45% of food is produced under irrigated land worldwide. For example, in Nebraska, a leading state in irrigation in the USA due to the relatively high abundance of groundwater resources, about 3.5 Mha of the cropped land is irrigated (Table 17.3). Seventy percent of the irrigated land in Nebraska is under corn and about 20% is under soybean. Declining groundwater levels, competition for water, increased pumping, and losses of water (e.g., evaporation, runoff) are increasing Table 17.2 Irrigated agricultural land in the world (De Wrachien et al. 2021)

Country India China USA Pakistan Iran Indonesia Mexico Thailand Brazil Turkey Others Total

Irrigated area (Mha) 70 70 23 18 8 7 7 6 5 5 89 308

Percent of total land irrigated 22.7 22.7 7.6 5.8 2.6 2.3 2.3 1.9 1.6 1.6 28.9

17.12

Management of Irrigation Water

Table 17.3 Percent of all irrigated agricultural land in the USA (USDA-ERS 2022)

States Nebraska California Arkansas Texas Idaho Colorado Kansas Montana Mississippi Washington Oregon Wyoming Missouri Florida Georgia Louisiana Utah Arizona Nevada Michigan All other States

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Percent of land irrigated 14.8 13.5 8.4 7.5 5.9 4.8 4.3 3.6 3.1 2.9 2.9 2.7 2.6 2.6 2.2 2.1 1.9 1.6 1.4 1.2 10.1

concerns. Regulating the amount of irrigation water applied while maximizing water use efficiency for producing higher yields per unit of water applied is becoming increasingly important, particularly in arid and semiarid regions with limited water supplies. The need for wise management of water resources for agricultural sustainability cannot be overemphasized. Optimization of water use efficiency and protection of water quality are high priorities. Irrigation increases or maintains crop yields, but the excessive application of irrigation water can cause runoff and nitrate leaching. Leaching of nutrients into groundwater can be high, especially in highly permeable soils. Both the amount of irrigation water and the amount of inorganic fertilizers must be optimized to reduce concerns about water pollution. Irrigation scheduling is one of the strategies to manage water. Strategies such as deficit irrigation can be alternatives to full irrigation (Chai et al. 2016). Deficit irrigation, also known as limited irrigation, refers to the partial supply of water requirements, while full irrigation refers to the supply of entire requirements of irrigation. Water requirements for a given crop refer to the depth of water per unit soil area needed to meet the water loss from evapotranspiration assuming that soil conditions and plant growth factors are nonrestrictive for plant growth. If irrigation is supplied during critical periods of plant growth, deficit irrigation can maximize water use efficiency and may not significantly reduce crop yields compared with full irrigation. In the central US Great Plains, increased concerns over decreased water levels of the Ogallala Aquifer are prompting the

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implementation of limited or deficit irrigation to reduce excessive water use (Rudnick et al. 2019). Deficit irrigation may become more common in the future over full irrigation under continued decline in water supplies and concerns of environmental quality. To manage irrigation water, it is important to understand the soil–water–plant– atmosphere continuum. Plant characteristics (e.g., height, rooting depth, seasonal water use, and transpiration potential), soil characteristics (e.g., texture, structure, water retention, compacted layers, and drainage), quality and quantity of water, and climatic factors (e.g., precipitation, temperature, wind speed, solar radiation, and air humidity) will influence the development of effective irrigation systems. It is also essential to determine when to irrigate and how much water to apply. Applying the right amount of water at the right place and time not only improves irrigation efficiency but also optimizes crop production. Three main strategies exist to determine when to irrigate a field: 1. Plant indicators. Visual observations and measurement of leaf color, leaf temperature, and other leaf characteristics are direct plant indicators to determine when to irrigate. 2. Soil indicators. Measurement of current soil volumetric water content and knowledge of water content at a permanent wilting point for a specific soil can help to determine when to irrigate and how much water to apply. Instruments such as tensiometers can also be used. Coarse or medium-textured soils are often irrigated when the tensiometer reading is around 40 centibars and fine-textured soils when around 50 centibars. 3. Water balance equation. This strategy is based on Eq. (17.1), which accounts for gains and losses of water. The amount of irrigation water required varies with precipitation amount and evapotranspiration rates. For example, in Nebraska, irrigation water requirements gradually decrease from west to east due to an increase in precipitation input from west to east. Sharma and Irmak (2012) determined that the supplemental water requirements for corn decreased from 575 mm in western Nebraska to 150 mm in eastern Nebraska. Quantification of actual evapotranspiration and irrigation water requirements for major production areas and fields is important to use water more efficiently and maintain water quality. Quantitative knowledge of precipitation and actual evapotranspiration combined with reduced tillage systems, improved cropping systems (intensified and diversified systems), drought-tolerant varieties, and deficit irrigation can lead to better allocation and conservation of water resources. Reducing irrigation water application or growing plants in a slightly moisture-stressed condition can reduce excessive water application. Soil management practices that conserve water can also conserve energy and improve irrigation efficiency. Practices such as conservation tillage, intensified cropping systems, cover crops, and residue management can minimize runoff and increase rainwater infiltration so that less irrigation water can be used. Also, the

17.12

Management of Irrigation Water

435

application of animal manure at optimum rates can improve soil physical and hydraulic properties responsible for precipitation capture and retention.

17.12.1 Irrigation Systems The main types of irrigation include flood, furrow, sprinkler, drip surface, and drip subsurface. These irrigation systems can be classified as gravity systems (e.g., flood, furrow) when water moves through gravity only or pressurized systems (e.g., sprinkler, drip) when water is applied under pressure via pipes. The choice of irrigation type depends on the installation cost, water availability, soil slope, soil texture, and crop water requirements, among others. Pressurized systems have higher water use efficieny and have lower water losses through evaporation, deep percolation, and runoff but are more expensive than gravity systems. In the past three decades, most gravity systems have been converted to pressurized systems.

17.12.1.1 Surface Irrigation Surface irrigation is the oldest irrigation type and uses groundwater or water diverted from rivers or streams. Water use with surface irrigation, which includes furrow and flood irrigation, is not, however, as efficient as other irrigation systems. The water use efficiency for surface irrigation is about 60%. Also, surface irrigation can cause more deep percolation and leaching than sprinkler irrigation or drip irrigation systems. Further, water can be lost through evaporation and runoff at the end of the rows. The advantages of surface irrigation over sprinkler irrigation are low initial installation costs and reduced pumping costs. Application of soil conditioners and use of surge irrigation can increase efficiency in furrow irrigation (Albalasmeh et al. 2021). Polyacrylamides (PAMs), polymers with high molecular weights, are soil conditioners used in furrow irrigation. Polyacrylamides form thin and porous films on the soil surface, flocculate suspended sediment, and reduce turbidity in water flow during irrigation. About 20–60 kg ha-1 of PAM are often mixed in irrigation water to reduce erosion. Surge irrigation is a potential strategy to manage irrigation runoff in furrow irrigation. It consists of applying water intermittently (e.g., 20 minutes or longer) to irrigation furrows unlike continuous flow. The intermittent application reduces deep percolation. When water application stops in surge irrigation, water infiltrates into the furrow, closes macropores, and develops surface seals. When reapplied, water will surge rapidly and reach the furrow end faster than with continuous flow. A surge valve is used to control the intermittent flow. Surge irrigation performance depends on soil texture and furrow slope. If the field slope is steep and the soil texture is fine or high in clay content, surge irrigation may be, however, no better than continuous flow. 17.12.1.2 Sprinkler Irrigation Sprinkler irrigation includes center-pivot and lateral-move systems although centerpivot irrigation is more common. Sprinkler irrigation systems consist of a number of

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17 Soil Water Management

Fig. 17.6 A sprinkler irrigation system in the central US Great Plains (Photo by H. Blanco)

pipes mounted on wheels (Fig. 17.6). They are commonly 400 m long and irrigate approximately 50 ha in a circular pattern. Sprinkler irrigation is becoming increasingly popular globally to improve water use efficiency. For example, in Nebraska, 70% of the irrigated land uses sprinkler irrigation, while only 30% uses furrow irrigation. Still, improvements are being made to increase the efficiency of sprinkler systems. Center-pivot systems often spray water from 2 or 3 m high, which causes losses of water through evaporation. Improved center-pivot systems spray water at lower heights through drop sprinklers, which reduce evaporation.

17.12.1.3 Drip Irrigation Drip or subsurface irrigation applies water directly to the root zone through plastic pipes (e.g., dripline). It is also known as trickle irrigation. The driplines have emitters spaced 20–60 cm along the dripline. The soil depth to which driplines are installed depends on the rooting depth of the crop. Driplines for corn are installed at about 30–45 cm soil depth. The amount of water delivered by drip irrigation depends mainly on the dripline diameter and spacing, emitter spacing and diameter, and pressure applied. Drip irrigation is part of localized irrigation that saves water and fertilizers, but it requires more investment in equipment than other irrigation systems. Although still not widely used, drip irrigation is the most efficient irrigation system under proper installation and management. It has about 90% efficiency. However, the initial cost of investment for drip irrigation is high. It can be about four times higher than for furrow irrigation and two times higher than for sprinkler irrigation system. The drip irrigation system can compete economically with sprinkler irrigation if longevity of the pipes increases.

Management of Irrigation Water

437

10

20

8

16 a

6

a

b b b

4

a

ab ab

a

Soil Organic C (g kg-1)

Biomass Production (Mg ha-1yr-1)

17.12

ab

0 to 5 cm ab

b

12

5 to 10 cm 8 10 to 20 cm 4

2

0

0 0

100 200 300 400 Depth of Irrigation Water (mm)

0

400 100 200 300 Depth of Irrigation Water (mm)

Fig. 17.7 Effect of irrigation on crop residue production (left) and soil organic C (right) for three soil depths on a silt loam in the central US Great Plains (Blanco-Canqui et al. 2010b). Means followed by the same letter are not significantly different (P < 0.05)

17.12.2 Impacts of Irrigation on Soil Properties Irrigation increases grain and biomass production (Fig. 17.7). The increase in biomass production can positively affect C accumulation in no-till intensive cropping systems (Fig. 17.7). Impacts of irrigation on C balance in the soil are the result of two opposite mechanisms. While irrigation can increase C accumulation in the soil by increasing biomass production, it can reduce C accumulation in the soil by accelerating soil organic matter decomposition through increased soil water content and biological activity. Periodic rewetting of soil can favor biological processes in the soil and increase the rapid mineralization of soil organic matter, reducing soil organic C accumulation. Gains in soil C by irrigation may be variable. Across two deficit sprinkler irrigation experiments in western Kansas (Garden City and Tribune), application of irrigation water at 66, 86, 117, 152, 182, and 217 mm at Garden City and at 127, 254, and 381 mm in Tribune for 5 and 8 years, respectively, increased soil organic C concentration and soil aggregate stability in the 0- to 10-cm depth compared to no irrigation in no-till systems (Blanco-Canqui et al. 2010b). The increase in soil organic C concentration and improvement in soil structural properties are attributed to the greater biomass C input due to irrigation. Irrigation may increase soil C concentration by increasing biomass C input, but it may also increase CO2 emissions through energy needed for pumping water. Emissions of CO2 from pumping water under full irrigation can be, on average, 0.20 Mg C ha-1 yr-1 (Follett 2001). In some soils, application of high amounts of irrigation water may reduce C stratification in no-till soils and distribute C in the form of dissolved C in the soil profile, particularly in long-term irrigated fields.

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17.13 Summary

An understanding of water balance is necessary to develop practices to conserve water and combat the consequences of drought. Rainfall, irrigation, and snowmelt represent gains in soil water storage, whereas runoff, evapotranspiration, and deep percolation represent losses in soil water. Some of the soil properties that affect soil water dynamics include texture, structure (aggregate stability, macroporosity, etc.), water retention capacity, and soil organic C concentration. Measurement of soil water content and water potential is essential to determine when to irrigate and how much water to apply. Management practices such as conservation tillage, intensified cropping systems, cover crops, development of drought-tolerant cropping systems, and residue cover can increase water use efficiency and precipitation storage efficiency. Practices that improve soil properties and increase organic C concentration can contribute to increased plant available water content although the extent to which changes in soil organic C increase plant available water content is a function of soil texture. Residue management influences changes in soil water content and temperature. Residue removal can greatly reduce soil water content, alter soil temperature, and reduce snow cover thickness. Maintaining permanent vegetative and residue cover and reducing intensive tillage enhance the ability of no-till systems to use water more efficiently. Application of irrigation water at the right amount, time, and place can conserve valuable water resource and energy and reduce risks of water pollution (hypoxia). It is important to understand the relationships among soil, plant, water, and atmosphere to manage soil water and irrigation practices. Improvement in irrigation strategies (e.g., deficit irrigation) to apply water during critical periods of the growing season can improve water use efficiency when coupled with other water conservation practices such as conservation tillage (e.g., no-till). Questions 1. Describe soil water balance. 2. Explain the difference between water use efficiency and precipitation storage efficiency. 3. Discuss the specific practices that can improve water use efficiency in waterlimited regions. 4. Does an increase in soil organic matter concentration increase plant available water? Show case studies. 5. Discuss how soil aggregate stability and macroporosity can contribute to water retention.

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6. Explain the methods to determine soil water content at field capacity, permanent wilting point, and plant available water. 7. Do cover crops reduce plant available water? Explain. 8. How does soil texture affect the impacts of soil management practices on water retention? 9. Explain the impacts of no-till management on soil water in high and low precipitation regions. 10. Discuss the different methods of irrigation and their water use efficiency.

References Albalasmeh AA, Hamdan EH, Gharaibeh MA, Hanandeh AE (2021) Improving aggregate stability and hydraulic properties of Sandy loam soil by applying polyacrylamide polymer. Soil Tillage Res 206:104821 Albert JS, Destouni G, Duke-Sylvester SM et al (2021) Scientists’ warning to humanity on the freshwater biodiversity crisis. Ambio 50:85–94 Bagnall DK, Cristine LS, Morgan GM, Bean DL et al (2022) Selecting soil hydraulic properties as indicators of soil health: Measurement response to management and site characteristics. Soil Sci Soc Am J 86:1206–1226 Blanco-Canqui H (2011) Does no-till farming induce water repellency to soils? Soil Use Manag 27: 2–9 Blanco-Canqui H (2018) Conservation grass hedges and soil health parameters. In: Reicosky D (ed) Managing soil health for sustainable agriculture Volume 2: Monitoring and management. Burleigh Dodds Science Publishing, Cambridge Blanco-Canqui H, Ruis SJ (2018) No-tillage and soil physical environment. Geoderma 326:164– 200 Blanco-Canqui H, Lal R, Owens LB et al (2007) Soil hydraulic properties influenced by corn stover removal from no-till corn in Ohio. Soil Tillage Res 92:144–155 Blanco-Canqui H, Stone LR, Stahlman PW (2010a) Soil response to long-term cropping systems on an Argiustoll in the central Great Plains. Soil Sci Soc Am J 74:602–611 Blanco-Canqui H, Klocke NL, Schlegel AJ et al (2010b) Impacts of deficit irrigation on carbon sequestration and soil physical properties in no-till. Soil Sci Soc Am J 74:1301–1309 Blanco-Canqui H, Stalker AL, Rasby R, Shaver TM, Drewnoski ME, van Donk S, Kibet LC (2016) Does cattle grazing and baling of corn residue cause runoff losses of sediment, carbon, and nutrients? Soil Sci Soc Am J 80:168–177 Blanco-Canqui H, Wienhold BJ, Jin VL, Schmer MR, Kibet LC (2017) Long-term tillage impact on soil hydraulic properties. Soil Tillage Res 170:38–42 Chai Q, Gan Y, Zhao C et al (2016) Regulated deficit irrigation for crop production under drought stress. A review. Agron Sustain Dev 36:3 Crockett JL, Westerling AL (2018) Greater temperature and precipitation extremes intensify western us droughts, wildfire severity, and Sierra Nevada tree mortality. J Clim 31:341–354 De Wrachien D, Bart S, Mudlagiri BG (2021) Impacts of population growth and climate change on food production and irrigation and drainage needs: A world-wide view. Irrig Drain 70:981–995 Deng C, Zhang G, Liu Y, Nie X, Li Z, Liu J, Zhu D (2021) Advantages and disadvantages of terracing: a comprehensive review. Int Soil Water Conserv Res 9:344–359 Follett RF (2001) Soil management concepts and carbon sequestration in cropland soils. Soil Tillage Res 61:77–92 Grillakis MG (2019) Increase in severe and extreme soil moisture droughts for Europe under climate change. Sci Total Environ 660:1245–1255

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Hansen NC, Allen BL, Baumhardt RL et al (2012) Research achievements and adoption of no-till, dryland cropping in the semi-arid U.S. Great Plains. Field Crop Res 132:196–203 IUCNN (International Union for Conservation of Nature and Natural Resources) (2003). http:// www.iucnredlist.org/ Kargas G, Soulis KX (2019) Performance evaluation of a recently developed soil water content, dielectric permittivity, and bulk electrical conductivity electromagnetic sensor. Agric Water Manag 213:568–579 Kenney I, Blanco-Canqui H, Presley DR, Rice CW, Janssen K, Olson B (2015) Soil and crop response to stover removal from rainfed and irrigated corn. Glob Change Biol Bioenergy 7:219– 230 Minasny B, McBratney AB (2018) Limited effect of organic matter on soil available water capacity. Eur J Soil Sci 69:39–47 Moravec V, Markonis Y, Rakovec O, Svoboda M, Trnka M, Kumar R, Hanel M (2021) Europe under multi-year droughts: how severe was the 2014–2018 drought period? Environ Res Lett 16(3):034062 Nielsen DC, Vigil MF (2010) Precipitation storage efficiency during fallow in wheat-fallow systems. Agron J 102:537–543 Nielsen DC, Halvorson AD, Vigil MF (2010) Critical precipitation period for dryland maize production. Field Crops Res 118:259–263 Patrignani A, Godsey CB, Ochsner TE et al (2012) Soil water dynamics of conventional and no-till wheat in the southern Great Plains. Soil Sci Soc Am J 76:1768–1775 Patrignani A, Godsey CB, Ochsner TE (2019) No-till diversified cropping systems for efficient allocation of precipitation in the Southern Great Plains. Agrosyst Geosci Environ 2(1):1–8 Peng ZK, Wang LL, Xie JH, Li LL, Coulter JA, Zhang RZ, Luo ZZ, Cai LQ, Carberry P, Whitbread A (2020) Conservation tillage increases yield and precipitation use efficiency of wheat on the semi-arid Loess Plateau of China. Agric Water Manag 231:106024 Pereira LS, Paredes P, Jovanovic N (2020) Soil water balance models for determining crop water and irrigation requirements and irrigation scheduling focusing on the FAO56 method and the dual Kc approach. Agricult Water Manag 241:106357 Peterson GA, Westfall DG (2004) Managing precipitation use in sustainable dryland agroecosystems. Ann Appl Biol 144:127–138 Pittelkow CM, Linquist BA, Lundy ME, Liang X, van Groenigen J, Lee J, van Gestel N, Six J, Venterea RT, van Kessel C (2015) When does no-till yield more? A global meta-analysis. Field Crop Res 183:156–168 Rakkar KM, Blanco-Canqui H (2018) Grazing of crop residues: Impacts on soils and crop production. Agric Ecosyst Environ 258:71–90 Rudnick DR, Djaman K, Irmak S (2015) Performance analysis of capacitance and electrical resistance-type soil moisture sensors in a silt loam soil. Trans ASABE 58:649–665 Rudnick DR, Irmak S, West C, Chávez JL, Kisekka I, Marek TH, Schneekloth JP, McCallister DM, Sharma V, Djaman K et al (2019) Deficit irrigation management of maize in the High Plains Aquifer region: A review. J Am Water Resour Assoc 55:38–55 Sahin H, Anderson SH, Udawatta RP (2016) Water infiltration and soil water content in claypan soils influenced by agroforestry and grass buffers compared to row crop management. Agrofor Syst 90:839–860 Schlaepfer DR, Bradford JB, Lauenroth WK, Munson SM, Tietjen B, Hall SA, Wilson SD, Duniway MC, Jia G, Pyke DA, Lkhagva A, Jamiyansharav K (2017) Climate change reduces extent of temperate drylands and intensifies drought in deep soils. Nat Commun 8:14196 Sharma V, Irmak S (2012) Mapping spatially interpolated precipitation, reference evapotranspiration, actual crop evapotranspiration, and net irrigation requirements in Nebraska: Part II. Actual crop evapotranspiration and net irrigation requirements. Trans ASABE 55:923–936

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Shipitalo MJ, Butt KR (1999) Occupancy and geometrical properties of Lumbricus terrestris L-burrows affecting infiltration. Pedobiologia 43:782–794 Singh J, Lo T, Rudnick DR, Irmak S, Blanco-Canqui H (2019) Quantifying and correcting for clay content effects on soil water measurement by reflectometers. Agric Water Manag 216:390–399 Tsutsui H, Sawada Y, Onuma K, Ito H, Koike T (2021) Drought monitoring over West Africa based on an ecohydrological simulation (2003–2018). Hydrology 8:155 USDA-ERS (United States Department of Agriculture-Economic Research Service). (2022) Irrigation & water use. https://www.ers.usda.gov/topics/farm-practices-management/irrigation-wateruse/

Management of Grazing Lands

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A grazing land is defined as a land unit consisting mostly of herbaceous and shrub vegetation where animals graze (Fig. 18.1). While it primarily consists of herbaceous vegetation, it can include some savannas, woodlands, shrublands, and others. In this chapter, grasslands, pasturelands, meadows, and rangelands are all considered an integral component of grazing lands. Grazing lands occupy about 30% of terrestrial area and provide multiple soil ecosystem services (Zhou et al. 2017). Some of the most extensive grazing lands include the savannas of Africa and Australia, the Himalayas in South Asia, the Cerrado in Brazil, the Pampas in Argentina, the Great Plains in the USA, the steppes of Central Asia, the Chaco and Altiplano in South America, and other regions (Suttie et al. 2005; Zhou et al. 2017; Kemp et al. 2018). Grazing lands differ in their management, plant species composition, and distribution. Depending on their life cycle duration, plant species used for grazing can be annuals if they complete their life cycle in ≤1 yr, biennial if they complete in 2 years, and perennials if they live ≥2 yr. Annuals typically reproduce by seed and can grow at different times of the year (Carey et al. 2017). For example, summer annuals germinate in spring and die before winter, whereas winter annuals germinate in fall and complete their life cycle in the summer of the following year. Biennials are not as common as annuals or perennials. They concentrate growth in their root systems in the first year, and aboveground vegetative and reproductive growth in the second. Perennials can consist of sod- or bunch-type grasses and forbs, which grow vigorously in spring or summer and remain dormant in winter. Based on their response to grazing and environment, grasses are decreasers if they are adversely affected by excessive grazing, increasers if their production increases after grazing, and invaders if the vegetation has no forage value and impedes the proliferation of high-value forages (Magandana et al. 2021). Richness in plant species under grazing depends on the grazing intensity, ecosystem, and climate. Grazing lands can be grouped into two main categories: rangelands and pasturelands.

# The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 H. Blanco, R. Lal, Soil Conservation and Management, https://doi.org/10.1007/978-3-031-30341-8_18

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Fig. 18.1 Grazing lands in the US Midwest (Courtesy USDA-NRCS)

Fig. 18.2 Rangelands in the US Great Plains (Photo by N. Jones, University of Nebraska)

18.1

Rangeland Systems

Rangelands may consist of natural grasslands, pasturelands, shrublands, meadows, tundras, coastal marshes, and savannas (Fig. 18.2). These are complex and diverse ecosystems predominated by native grasses, grass-like vegetation, forbs, and shrubs growing in either natural or recreated lands under different scenarios of grazing and management (Sainnemekh et al. 2022). Rangelands are more complex than pasturelands and comprise a host of natural systems (e.g., woodlands, savanna). These lands are often not suited for cropping and forest management. In the western USA, the region predominated by range farming, rangelands are mainly comprised

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Pastureland Systems

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of pasturelands with scattered shrubs and trees. Rangelands deliver a number of soil ecosystem services including animal grazing, firewood production, C sequestration, recreation, landscape scenery, wildlife habitat, and ecotourism. While, traditionally, rangelands have been primarily used for livestock production, there is now an increasing recognition about their importance for sequestering C, improving wildlife habitat, soil hydrology, and water quality, and supporting tourism and other ecosystem services.

18.2

Pastureland Systems

Pasturelands consist of single grass species, native multi-grass species, and grasslegume mixtures (Fig. 18.1). Pasturelands that consist mostly of grasses, known as “grasslands”, are one of the largest ecosystems in the world (Suttie et al. 2005; Zhou et al. 2017). They are distributed across a wide range of ecosystems differing in plant species and grazing pressures. Natural pasturelands are rich in flora with about 10,000 grass species worldwide although only about 150 species are cultivated (Suttie et al. 2005). Pasturelands fit between desert and forest lands and extend across landscapes with sufficient water to grow grasses. Grasslands and meadows are considered part of pasturelands. • Grasslands are lands predominantly covered by grass vegetation with 70%) and diverse perennial grasses can reduce runoff to negligible levels (Descheemaeker et al. 2006). Management of grazing lands determines the rate of erosion from these lands. For example, runoff from soils under continuous grazing is higher than from those under rotational systems due to limited vegetative cover under continuous grazing. A study using 15 watersheds with 3–8% slopes in Arkansas found that continuous grazing increased sediment delivery to downstream waters compared with rotational grazing after 12 yr of management (Table 18.1; Pilon et al. 2017). Rotational grazing can be a potential management practice to manage soil erosion from grazing lands. Increased soil erosion can also increase losses of nutrients from grazing lands and adversely affect water quality. In southern Alberta, Canada, a 3-yr study on pasturelands with 2–7% slopes found that cattle trails in grazed pastures decreased time to runoff and increased runoff and mass loads of total suspended solids from 57 to 85%, NH4- from 31 to 90%, and dissolved reactive P from 30 to 92% in runoff relative to non-trafficked areas (Miller et al. 2017). Reducing cattle traffic or stocking rates in grazing lands can reduce runoff and losses of sediment and nutrients. Surface soil and landscape characteristics are also important determinants of runoff and soil erosion. Overgrazed steep soils (>5%) are more susceptible to runoff and soil erosion than lowland pastures (Tufekcioglu et al. 2013). During rainy seasons, animals tend to concentrate on the upper landscape positions, which can increase the risks of soil erosion. On steep terrains (18–37% slope) in Canada, snow melt runoff volume was higher by a factor of 118 from intensively grazed watersheds under tall fescue compared to ungrazed watersheds over 11 runoff events (Chanasyk et al. 2003). The impact of overgrazing on soil erosion is even larger in desert or semidesert grazing lands with ephemeral grasses and scattered shrubs (Podwojewski et al. 2002). In arid regions, trampling breaks soil crusts and aggregates and pulverizes the soil surface, causing the loss of fine particles through wind erosion. In semiarid regions in northern Mexico and southwestern USA, overgrazing has caused the replacement of pasturelands by shrublands (Ludwig and Tongway 2002). While shrubs are important components of many grazing lands for providing shade and

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shelter, excessive invasion and replacement of grass alter the ecosystem and increase water and wind erosion. In southern New Mexico, semiarid shrublands had greater losses (50.5 vs. 8.5 mm) of runoff than neighboring pasturelands (Schlesinger et al. 2000). There are numerous other examples of excessive grazing and its adverse effects on accelerated soil erosion worldwide.

18.5

Grazing and Soil Properties

Moderate grazing of pasturelands and rangelands can have minimal or no negative effects on soil properties, but overgrazing or continuous grazing can adversely impact soil properties (Table 18.2). Frequent trampling or animal traffic under continuous grazing can loosen, homogenize, and pulverize the soil surface, degrading near-surface soil properties. Trampling often increases soil compaction risks and thus reduces macroporosity and water infiltration (Pilon et al. 2017). The extent of changes in soil properties depends on the stocking rate, topography, management, and vegetative cover, among others (Follett et al. 2020). Changes in soil properties due to grazing can be small under proper grazing management.

18.5.1 Temperature and Water Content A significant decrease in surface vegetative cover (canopy cover) can increase abrupt fluctuations in soil temperature and evaporation. Overgrazed systems with patches of bare soils have lower water content and higher daytime temperatures than grass-or litter-covered soils. In a Eurasian steppe, heavy grazing increased soil temperature by an average of 2.6 °C in the 10 cm soil depth during summer and reduced soil water storage compared with ungrazed systems (Yan et al. 2018). Bare soils warm up Table 18.2 Impacts of grazing on selected soil properties based on case studies (1 dos Santos et al. 2022; 2 Follett et al. 2020; 3 Gilmullina et al. 2020; 4 Pilon et al. 2017). Means with different lowercase letters are significantly different. ns = not significant

Management 1

Degraded pasture Moderate grazing 2 Grazed 2 Ungrazed 3 Mowing 3 Grazing 1

4

Continuous grazing Rotational grazing 2 Grazed 2 Ungrazed 4

4

Continuous grazing Rotational grazing

4

Findings Soil organic C %) 1.6b 3.3a ns ns 2.1a 1.5b Bulk density (g cm-3) ns ns ns ns Penetration resistance (MPa) 3.5a 2.8b

18.5

Grazing and Soil Properties

451

and cool faster than those with a dense vegetative cover. Overgrazed soils typically undergo greater fluctuations in surface temperature. Thus, overgrazing increases evapotranspiration and modifies soil microclimate. Alteration of soil water content and temperature regimes directly influences soil respiration, microbial processes, and other dynamic soil processes.

18.5.2 Particle-Size Distribution The hoof action of animals breaks aggregates, detaches primary soil particles, pulverizes the soil, and increases soil susceptibility to wind and water erosion. Detached small soil particles are easily transported by wind and water erosion. As a result, heavily grazed soils have higher sand content and lower clay content (Fig. 18.5). In some excessively grazed soils, loss of topsoil by erosion may also expose subsoil layers with high clay content (e.g., claypan soils), which modifies the original surface soil texture. A decrease in silt and clay content can reduce the ability of the soil to hold water and nutrients. Indeed, soil with high sand content and low clay content can be more susceptible to nitrate leaching than soils with high clay content.

18.5.3 Structure and Water Infiltration Excessive grazing in conjunction with the trampling effect can degrade soil structure by reducing aggregate stability, pore-size distribution, macroporosity, total porosity, and water infiltration rate. Reduced vegetative cover exposes the soil surface, increasing surface sealing and crusting, and reducing the proportion of open-ended macropores (e.g., earthworm burrows, root channels). Mixing and remoulding of wet soils with animal trampling can deteriorate the stability of soil aggregates. Wellaggregated soils are porous and have high water infiltration rates, but their perturbation increases runoff risks. In the tallgrass prairie region of Oklahoma, the water 100 a 80 Percent

Fig. 18.5 Heavy grazing can change soil particle-size distribution in the long term (Neff et al. 2005). Bars with different letters within the same particle-size fraction are significantly different (P < 0.05)

b

Ungrazed

Grazed

60 40 a

20

b a

b

0 Sand

Silt

Clay

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infiltration rate was 28.5 cm d-1 for ungrazed pasture, 7 cm d-1 for light grazing, 5 cm d-1 for moderate stocking, and 5 cm d-1 for heavy grazing (Daniel et al. 2022). Thus, an increase in grazing intensity can directly reduce water infiltration rates. The decreased water infiltration may not only increase runoff potential but also reduce soil water storage. The reduction in water infiltration with grazing can be particularly large in clayey soils. Decrease in surface vegetative cover and increase in trampling change the pattern of water and air fluxes.

18.5.4 Compaction Compaction, consolidation, and puddling are the main processes set in motion by excessive grazing thereby altering soil physical quality. Compaction refers to the compression of unsaturated soils, whereas consolidation refers to the compression of saturated soils (Drewry 2006). Puddling, which refers to soil deformation by plastic flow when perturbed under saturated conditions, can increase compaction in paddocks with wet soils (e.g., spring) and large livestock concentration. Wet soils have low strength and are rapidly pugged by grazing animals. The magnitude of compaction depends on the management of grazing lands. Select case studies in Table 18.2 show that grazing may not increase soil bulk density but may increase penetration resistance. Rotational or moderate grazing can have minimal impacts on soil compaction. The type of grazing animal can influence compaction risks. For example, cattle may compact soil more than sheep due to differences in body mass, but sheep hoof action often pulverizes dry soil and disturbs and mixes wet soil more than cattle. Low stocking rates and use of rotational systems can be strategies to reduce compaction.

18.5.5 Organic Matter Grazing may or may not reduce soil organic matter concentration, depending on grazing intensity (Table 18.2). Excessive grazing reduces vegetative cover and can deplete soil organic matter, especially in arid and semiarid regions, but moderate grazing can maintain or even increase soil organic matter concentration via manure input. Manure contains more than 15% of C. The increased soil organic matter concentration can promote plant growth, enhance species diversity, and improve soil structural and hydraulic properties. Soil organic matter provides essential nutrients, binds soil particles into aggregates, and enhances microbial activity. Also, high soil organic matter concentration and abundant root biomass of grazing lands can buffer against the compactive forces. However, a decrease in soil organic matter concentration due to excessive grazing can increase soil erodibility and reduce soil fertility and productivity of grazing lands.

18.7

18.6

Benefits of Well-Managed Grazing Lands for Soil Protection and Stabilization

453

Grazing and Plant Growth

While moderate grazing is beneficial to plant development, excessive grazing jeopardizes plant regrowth and reduces yields of hay or forage. Excessive grazing and trampling degrade vegetative cover structure and alter its dynamics by directly altering the plant morphological characteristics (Kemp et al. 2018). It reduces the height and density of plants and amount of coarse litter cover (Fig. 18.6). Excessive grazing progressively degrades vegetative cover and its effects are greater on annuals than on perennials due to differences in biomass quantity and plant resilience. Denudation and sharp discontinuities in vegetation are typical in heavily grazed hilly terrains (Bondi et al. 2021). Reduction in pasture production and plant diversity can reduce livestock production. Damaged plants cannot recover quickly and are often replaced by poorer species. Soils and vegetation of arid and semiarid regions are the most susceptible to desertification by overgrazing (Kemp et al. 2018).

18.7

Benefits of Well-Managed Grazing Lands for Soil Protection and Stabilization

Well-managed pasturelands and rangelands which have dense stands, thick surface litter, and abundant network of fibrous roots can reduce splash by impacting raindrops and increase rain infiltration, thereby reducing runoff and soil erosion. Growing grasses reduce runoff and soil erosion by two interrelated mechanisms, protection of the soil surface by vegetative cover and stabilization of soil matrix.

18.7.1 Protection of the Soil Surface The aboveground biomass intercepts raindrops and incoming runoff, reduces the velocity and transport capacity of runoff, spreads and ponds runoff, and increases

Plant Height

Fig. 18.6 Direct effects of grazing on vegetative cover

Animal Units per Hectare

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water infiltration opportunity time (Blanco-Canqui 2018). Grass density, stem stiffness, and height are important factors that determine the resistance vegetation to erosion. Manning’s coefficient of roughness increases while turbulent runoff flow or Reynolds’s number decreases with an increase in vegetative cover (Mishra et al. 2006). The lower the roughness coefficient value, the lower the ability of grass to resist runoff flow and soil erosion. The root system is as important, if not more than, as the aboveground biomass for controlling soil erosion. While the aboveground biomass protects the soil from the erosive impact of raindrops, the belowground biomass (roots) holds the soil in place. In heavily grazed systems, roots play an important role in reducing soil erosion as the effectiveness of aboveground biomass cover for controlling soil erosion is diminished by grazing. Much attention has been paid to the effects of surface vegetative cover on soil erosion while the vital functions of belowground biomass in soil erosion have been somewhat neglected.

18.7.2 Stabilization of Soil Matrix The belowground biomass of grasses under well-managed grazing lands can stabilize the soil and reduce soil erodibility (De Baets et al. 2006). Grass roots interact with the soil matrix, stabilize sloping soils, and reinforce soil resistance to erosion. The higher the density and longer the roots, the lower the aggregate detachment and slaking. For example, a dense network of roots under well-managed grazing lands can prevent scouring and development of head-cuts under concentrated runoff. Most grasses have fibrous and fine roots with diameters ranging between 0.15 and 0.24 mm, forming a dense natural mesh. Roots of grasses are more effective than those of crops because roots under natural vegetation remain less disturbed, have a longer growing period, and penetrate deeper into the subsoil. Intrinsic characteristics of roots (e.g., diameter, density, hair, length, age) control soil aggregation. Grass roots promote the assemblage of soil particles into stable aggregates through physical, biological, and chemical bonding mechanisms, as follows (De Baets et al. 2006): 1. Physical binding refers to the mechanical enmeshment of soil particles by roots. 2. Biological binding occurs when root-derived organic binding agents such as exudates and glue-like compounds infiltrate and stick the soil particles together. 3. Chemical binding refers to the reaction of root-derived substances along with inorganic compounds. Grass roots reduce soil erosion by: 1. Increasing water infiltration, permeability, and drainage 2. Breaking up compact layers (e.g., hardpan, claypan, plow pan) 3. Enmeshing soil particles and forming stable aggregates

18.8

Grass Roots and Soil Erodibility

455

4. Developing biochannels and increasing soil macroporosity 5. Increasing soil organic matter content and microbial processes Management of aboveground biomass is important for maintaining a dense and stable root system. Overgrazed and short-growing vegetation has lower hydraulic resistance to concentrated overland flow than tall grasses with stiff stems (BlancoCanqui 2018). When the aboveground biomass is overcome by accelerated erosion (e.g., concentrated flow), grass roots become major constituents of the system against the formation of rills and ephemeral gullies. The combined effects of aboveground and belowground biomass further reduce erosion and improve soil properties.

18.8

Grass Roots and Soil Erodibility

Soil erosion decreases exponentially with an increase in grass root density. Several empirical equations have been developed relating grass root density and length to soil erodibility (Alberts et al. 1995; Mamo and Bubenzer 2001; De Baets et al. 2006). Some of these relations are listed below: Y = a × expðk × RDÞ

ð18:1Þ

Krlr = expð- 3:5 × lr Þ

ð18:2Þ

Kr dr = expð- 2:2 × dr Þ

ð18:3Þ

RSD = expð- 1:14RDÞ

ð18:4Þ

RSD = expð- 0:0062RLDÞ

ð18:5Þ

RSD =

RD - 1:76 1:59 þ RD - 1:76

Kr = 0:0017 þ 0:0024 × clay - 0:0088 × OM -

ð18:6Þ

0:00088 × ρb - 0:00048 1000

× root

ð18:7Þ Kr = 42:66 × expð- 0:323 × RLDÞ

ð18:8Þ

Ki = 3:55 × expð- 0:71 × RTM Þ

ð18:9Þ

Ki = 3:62 × expð- 0:029 × RTLÞ

ð18:10Þ

where Y is soil erodibility, a and k are constants, RD is root density (kg m-3), Kr is rill erodibility (s m-1), lr is mass (kg m-2) of living roots, dr is mass (kg m-2) of dead roots, RSD is relative soil detachment rate (0 to 1), RLD is root length density (km m-3), clay is clay content (0 to 1), OM is soil organic matter content (0–1), ρb is soil bulk density (kg m-3), root is total root mass (kg m-2), Ki is interrill erodibility

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parameter of the soil (kg s m-4), RTM is dead root mass (kg m-2), and RTL is dead root length (kg m-2). These equations must be evaluated and validated on a sitespecific basis. Understanding the critical shear stress levels of vegetation in relation to the onset of interrill and rill erosion is vital to the sustainable management of grazing lands. Standing vegetation provides higher friction and greater hydraulic resistance to runoff than if it is submerged. Reduction of vegetation height and stem density by grazing results in reduced friction and increased mean flow velocity. Formation of gullies depends directly on the critical shear stress of the grassroots, whereas interrill flow depends mostly on soil surface conditions and aboveground biomass cover. Flow velocities (V ) (m s-1) in pastureland depressions can be estimated using the modified form of Manning’s equation as follows (Haan et al. 1994): 2

V=

1

R3 S2 xn

ð18:11Þ

where R is hydraulic radius of the grass channel (cm), S is slope of channel (cm cm-1), and xn is adjusted form of roughness coefficient. Whenever the velocity of runoff exceeds the critical shear velocity of grass, the vegetation fails under concentrated runoff. Additional approaches to estimate the sediment trapping efficiency and filtering capacity of different grass species are described in detail by Haan et al. (1994).

18.9

Grazing of Conservation Buffers

Conservation buffers such as filter strips, grass barriers, riparian buffers, and others established within or around croplands are useful conservation measures that reduce soil erosion and the transport of pollutants to streams, rivers, and lakes. These buffers can be multi-functional under proper management (Blanco-Canqui 2018). Wellmanaged conservation buffers can provide forage for livestock and feedstock for biofuel while reducing soil erosion, improving water quality, and providing other services. Moderate grazing of conservation buffers may not diminish the ability of buffers to filter and trap sediment and degrade sediment-bound chemicals (Pilon et al. 2018). However, excessive grazing and the attendant animal trampling can reduce the height and density of grass species, critical shear stress of the grass, hydraulic resistance to runoff, and sediment filtering capacity of conservation buffers. In a riparian meadow in northern Colorado, cattle grazing reduced grass stem density by 40%, the aboveground biomass by 61%, and the sediment trapping efficiency by 13% (Mceldowney et al. 2002). Reduction of grass buffer density can reduce the tortuosity of rills or small channels and induces the formation of concentrated flow channels. Perennial warm-season grasses, such as switchgrass and Indiangrass can be a potential source of forage during months of low biomass production or when cool-

18.10

Methods of Grazing

457

season grasses are dormant (Trosanyi et al. 2009). Moderate grazing of conservation buffers can compensate for the land taken out for growing buffers and thus improve farm economics. Well-managed conservation buffers which produce abundant biomass can be grazed or hayed under proper cutting heights (10 cm cutting height) or grazed and harvested every other year. Overgrazing of buffers can be damaging due to high biomass removal and trampling. Buffers with dense and rough surfaces are important to intercept and pond runoff water and promote infiltration.

18.10 Methods of Grazing There are a number of methods of grazing based on the specific characteristics of each pastureland, ecosystem, and climate regime (Follett et al. 2020; GomezCasanovas et al. 2021). Pastureland management falls primarily within two grazing techniques: continuous and controlled stocking. • Continuous stocking refers to the unlimited access by animals to pastureland during a specified or unlimited period of time. This technique is simple and inexpensive, but it can adversely impact pastureland and soil productivity. • Controlled stocking, sometimes referred to as controlled grazing, unlike continuous stocking is a method that controls what and when animals graze on a specific piece of pastureland for optimizing pastureland production and sustainability. This technique matches up the number of animals with grass condition or growth by balancing animal requirements with grass and supplements. The remaining ungrazed pasture is harvested as hay or silage. Grazing lands under controlled stocking can use one or more grazing techniques within the same grazing system. Some of the specific techniques of controlled stocking include the following (Johnson 2003; Troeh et al. 2004): 1. Rotational grazing. Rotational grazing provides the greatest benefit because animals are shifted from one paddock to another during the grazing period following a systematic schedule (Fig. 18.7). This grazing method is advantageous over continuous grazing because it optimizes forage production. Parameters such as the height of plant before and after grazing are a simple approach to determining grazing regimes based on plant morphology and animal stocking (Carlassare and Karsten 2002). Recommendations on the height of grazing depend on the height and morphology of plant species. Animal intake increases with an increase in plant height because of increased availability and accessibility. Current recommendations of grazing heights for tall grasses vary between 18 and 30 cm before grazing and between 5 and 7.5 cm after grazing, depending on local soil and climate conditions. 2. Alternate stocking. It refers to repeated and successive grazing in two enclosed fields or paddocks.

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Management of Grazing Lands

Fig. 18.7 Rotating sheep from one cell to another is a strategy to manage grazing lands (Courtesy USDA-NRCS)

3. Deferred grazing. It consists of delaying the grazing period within a specific unit of pastureland in order to harvest seeds or allow grass species to reach their full potential of growth. This system is important because it allows grazing during times when grass is scarce. It can also be rotated among the different fields within the pastureland. 4. Intermittent grazing. It is a system in which grazing is allowed at non-systematic intervals. It consists of removing stock for short periods of time (days or weeks) to reduce soil deterioration and overgrazing. 5. Mixed grazing. In this system one or two more animal species are allowed to graze on the same unit of pastureland. Cattle, sheep, or mixed cattle and sheep are examples of this system. Animals are normally selective and differ in their consumption habits and grass species preference. 6. Ration or strip grazing. In this system, animals are confined to a definite piece of pastureland to obtain their daily fodder allowance. 7. Seasonal grazing. This system allows grazing on the same piece of land only during specific seasons of the year. 8. Sequence grazing. It refers to the successive grazing of one or two more pieces of land with different types of grass species or forages. This system is beneficial because grass species differ in their composition, quality, and age, providing diverse benefits to animals.

18.11

Management of Grazing Lands

459

18.11 Management of Grazing Lands The goal of grassland agriculture is not only to produce forage for livestock production but also to conserve soil and water and provide other soil ecosystem services. It aims to achieve a desired outcome by managing all the major components such as soil attributes, plant species, and animals. The ultimate objective is to enhance the productivity of grazing lands, which is measured in terms of forage quality and quantity per unit of land. This depends on grazing pressure or the number of animals per unit of land. Rotational or controlled grazing is a first choice to enhance sustained production. Rangeland management involves the protection, improvement, and rehabilitation of rangeland resources in order to obtain optimum production while conserving soil and water, and improving biological diversity. Restoring degraded rangelands requires intensive planning and adoption of improved practices. Restoration of grazing lands seldom rests on a single practice. The factors affecting management of pasturelands and rangelands include: • • • • • • • • • •

Type of animal and stocking rate Grazing systems Grassland/rangeland size and production potential Pasture/forage quality and quantify Climate (e.g., temperature, rainfall distribution) Cultural-socio-economic characteristics Incentives and conservation programs Soil and landscape characteristics Mechanization/modernization Grass species and distribution

Grazing of rangelands and pasturelands is one of the oldest practices in the world and it does not necessarily reduce the potential of plant species under proper management (Follett et al. 2020). Indeed, moderate defoliation increases the net production of rangeland species by strengthening the stems and improving plant resilience to perturbations. Thus, prudent grazing is beneficial to maintaining an active ecosystem service and animal production. Rotational grazing is particularly effective at enhancing forage production and improving water quality. Grazing duration, plant physiological characteristics, and climate are critical factors that determine stress. In some ecosystems, grazing increases the diversity of plants and reduces invasion by other species (Altesor et al. 2006). The hoof action can allow the spreading of seeds to maintain a diverse proportion of plant species. Finally, grazing is the source of all animal-derived products essential to human consumption. Animals constitute an integral component of the ecosystem because they recycle organic materials along with N and P compounds through manure input. Deposition of dung materials improves soil physical, chemical, and biological properties in localized spots in the field. Animal manure can contain as many as one billion organisms per gram of manure, which enhance soil microbial processes, soil

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aggregation, and nutrient recycling. For example, cattle manure reduces soil bulk density and increases plant available water (Blanco-Canqui et al. 2015). Excessive input of animal manure can be a source of water pollution, but proper management of manure can reduce the off-site movement of pollutants while improving soil properties and ecosystem quality. Controlled stocking coupled with manure input is essential to reduce soil erosion, enhance soil biological activity, and promote C dynamics.

18.12 Prescribed Fire as a Management Tool The use of controlled and well-timed fire, known as prescribed fire, is an important strategy to manage grazing lands. The impact of prescribed burning on vegetation and soil ecosystem services is a function of the intensity and frequency of the fire. Prescribed burning of vegetation stimulates regrowth, removes invasive species, and often increases grass production. Grasses growing on burned lands can be more palatable, thereby attracting more animals than unburned grasses. Timely burning also reduces weed incidence, disease infestations, and wildfire incidence. A review discussed that prescribed fires could adversely affect physical and biological properties but the soil effects depend on fire intensity and type, vegetation characteristics, soil type, burn season, and frequency (Alcañiz et al. 2018). The same review indicated that prescribed fire effects on soils can be less pronounced than the effect of wildfires due to the lower fire intensity under prescribed fires. Burned soils under prescribed fires often recover rapidly after disturbance. While untimely burning increases risks of soil erosion because it leaves bare areas, seasonal burning at the right time can increase vegetation regrowth and the quality and distribution of grass. Burning grasses is done in mid-spring when plants are just greening up and when soils are moist enough to permit rapid regrowth.

18.13 Resilience and Recovery of Grazed Lands Plant species vary greatly in their resilience, tolerance, and competitivity under grazing pressures (Volaire et al. 2014). Identification, knowledge, and development of phenotypic plant species tolerant to grazing for each rangeland ecosystem are important strategies to maintain an equilibrium between plant species and grazing. Grazed plants must have morphological and physiological characteristics to compete with neighboring plants in the community. Some plant species survive under drought and large fluctuations in soil temperature. Stress attenuation also involves the ability of degraded rangelands to allow rapid growth from seeds and resistance of plants to adverse environmental conditions. Avoidance and Tolerance Two main characteristics that enable a plant to resist and survive following perturbations are avoidance and tolerance (Volaire et al. 2014). Avoidance refers to the ability of a plant to reduce defoliation by producing

18.14

Conversion of Grazing Lands to Croplands

461

biochemical compounds in interaction with its morphological characteristics, while tolerance refers to the ability of a plant to regrow after grazing due to its specific physiological characteristics. Removal of stress (e.g., overgrazing) leads to a gradual recovery in forage production, species diversity, and plant population. Resilience Versus Ecological Zones Grazing lands in sub-humid, humid, and temperate regions are more resilient than those in arid and semiarid regions. Limited water, reduced soil development, steep landscapes, limited grass biodiversity, and extreme weather conditions in arid regions are among the factors that contribute to greater degradation and non-equilibrium conditions of grazing lands (Koch et al. 2015). Pastureland ecosystems are highly sensitive to harsh and variable climate conditions (e.g., drought). Two dynamic components of grazing lands are biotic (vegetative cover) and abiotic (soil) entities. Both components are sensitive to mismanagement and can be degraded rapidly. The difference is that the biotic component is highly resilient and recovers as fast as it is overgrazed or burned unlike the abiotic component, which requires a longer span of time (decades or centuries) to recover following degradation. Rate of Recovery Removal of stress or overgrazing allows a rapid recovery. The amount of time needed for a system to recover is site-specific. Some degraded grazing lands can recover within 1 year after exclusion but others require longer (>2 yr) periods of time. On a clay loam soil with high soil organic content in New Zealand, excessively sheep-grazed pastures produced higher sediment and nutrient concentrations in runoff than ungrazed pastures, but differences at 6 weeks following cessation of grazing were not significant, indicating a rapid recovery after heavy grazing was eliminated (Elliott and Carlson 2004). Intensity of grazing, vegetation and soil type, topography, and climate influence the rate of recovery. Threshold Levels of Recovery There is a threshold level of resilience, beyond which a grazed land cannot recover to its original state. Some systems do not recover to their initial condition because of hysteresis resulting from reduced plant available water and nutrient levels. Hysteresis Hysteresis refers to the degree to which the restoration path is a reversal of the degradation path (Collins et al. 2021). The pattern to which degraded grazing lands recover tends to be commonly lower than that of degradation unless the degree of degradation prior to restoration was only slight.

18.14 Conversion of Grazing Lands to Croplands Conversion of grazing lands into croplands can adversely affect soil properties with an extent depending on time after conversion, tillage system, cropping system, and climate. Conversion of grazing lands can have the most adverse impact on fragile

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Table 18.3 Changes in soil properties following conversion of pasturelands to croplands (Shukla et al. 2003; Blanco-Canqui et al. 2005). Means followed by the same letter within the same row are not significantly different (P < 0.05) Soil Property Water content at -0.3 bar (mm3 mm-3) Bulk density (Mg m-3) Cone index (MPa) Water stable aggregates (%) Organic C (Mg ha-1)

Pastureland 0.3a 1.2a 0.4a 85a 30a

Cropland 0.2b 1.4b 0.7b 35b 20b

and mountainous pastureland ecosystems. Also, changes in soil properties after conversion may not occur in the first year but can be significant in the following years. For instance, in the western US Corn Belt, conversion of grassland to cropland had no effect on soil bulk density, soil organic C, and wet aggregate stability after the first year, but it increased soil bulk density from 1.30 to 1.36 g cm-3 in the second year (Lai et al. 2022). Conversion of grazing lands into croplands may have a more rapid effect on greenhouse gas fluxes due to soil disturbance than on other soil properties. The same study by Lai et al. (2022) found that grassland conversion to crops increased CO2 fluxes by 45–63% but had little or no effect on CH4 and N2O fluxes in the first 2 years after conversion. In the long term, tilling of former grazing lands on an annual basis can alter natural soil structure by breaking biologically bound aggregates and accelerating the decomposition of soil organic matter (Table 18.3). Reduction in soil organic matter concentration further accelerates aggregate breakdown as soil aggregate stability is positively correlated with organic matter content. The reduction in aggregate stability not only increases risks of water and wind erosion but reduces soil fertility and degrades environmental quality. Organic matter concentration and soil particle fine fraction ( No-till > Plow tillage.

18.15 Conversion of Croplands to Permanent Vegetation Conversion of croplands to grazing lands or native perennial grasses is an option to halt water and wind erosion and restores soil properties with time to a degree similar to those under natural conditions (Zhang et al. 2013). Soil type and resilience, length of time after conversion, biomass production, and plant species determine the rate at

18.16

Restoration of Degraded Grazing Lands

463

which the soil recovers. High biomass-producing and deep-rooted plant species develop biopores, improve aggregate stability, enhance water movement in the soil, and increase organic matter (Yuan et al. 2006). Conservation programs, such as the CRP in the USA, require the conversion of degraded agricultural lands into permanent grasslands or native prairie grasses to stabilize erodible soils and improve soil quality. Conversion of erodible croplands to grasslands can restore the soil ecosystem services lost with intensive cultivation.

18.16 Restoration of Degraded Grazing Lands Climate, landscape characteristics, livestock number, management, degree of degradation, and other factors determine the time needed for the recovery of degraded grazing lands (Table 18.4). Knowledge of compaction level, degree of erosion, organic matter level, and extent of changes in other soil properties along with the knowledge about vegetation availability and resilience, and animal stocking rates affect the measures needed to restore grazing lands. Some of the specific measures to restore degraded grazed lands include (Klaus et al. 2018; Gomez-Casanovas et al. 2021): 1. Establishment of rotational grazing, shifting the animals from paddock to paddock and backfencing fields to account for the spatial heterogeneity of fields and differences in grass production from year to year. 2. Regulation of the stocking rate and distribution of livestock. 3. Increase of the length of rotational grazing to allow the regrowth of grass and increase the grazing area to reduce stocking density. 4. Temporary closure of degraded areas to allow recovery. 5. Restoration with native and perennial grass species rather than with shortgrowing grass species as native species are more environmentally desirable. 6. Establishment of conservation buffers and construction of streambanks and ponds. Table 18.4 Biotic and abiotic factors influencing grass reestablishment in degraded ecosystems Soil and Climate • Topography • Plant available water content • Compaction • Salinization • Drought and flooding risks

Management • Harvesting • Mechanization • Invasive species • Fertilization • Drainage systems • Fires • Overgrazing

Livestock • Stocking rates • Forage preferences • Trampling potential

Vegetation • Type • Diversity • Availability • Resilience • Adaptability

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7. Construction of stream paths or livestock crossings and establishing drainage systems to reduce pugging and compaction. The greater the animal traffic, the greater the soil deterioration and grass damage. 8. Reseeding of degraded areas with non-invasive grass and legume species. 9. Use of supplements with hay or silage as an alternative to grazing in wet soils. 10. Installation of backfence paddocks to prevent backtracking over the grazed areas which may cause further pugging and reductions in plant growth. 11. Grazing when grass is sufficiently mature or tall (10 to 15 cm). Animals do not walk over large distances when grasses are tall, which can reduce trampling and pugging. 12. Improvement of paths of access to drinking water locations and isolation of sensitive or eroded areas. 13. Fertilization with N when soil is not waterlogged to reduce N losses while maintaining proper levels of other nutrients. 14. Controlled application of animal manure and compliance with the conservation or pastureland management programs. Emerging technologies such as precision agriculture are promising to better manage grazing lands, enhance their productivity, and reduce any adverse environmental impacts. For example, the use of soil sensors, grass growth monitoring sensors, biomass production mapping, remote sensing, satellite imagery, machine learning, UAV technology, and devices for tracking animal movement, health, and feed consumption can help with the proper management of grazing lands (Higgins et al. 2019; Morais et al. 2021). Testing and embracing emerging technologies will be critical to ensure sustainable management of grazing lands.

18.17 Modeling of Grazing Land Management Assessment and management of grazing lands using traditional approaches are often difficult. Models can allow the integration of all complex and interrelated components of the ecosystem. The use of models is a new paradigm for an optimum management of grazing lands. van Oijen et al. (2020) suggested a roadmap to employ biogeochemical and ecological models to mechanistically understand the processes affecting the functioning of grazing lands. Coupling ecological models, which account for biodiversity among plant species, with biogeochemical models, which account for biogeochemical processes at the plant community level, can be a promising approach to assess the resilience of grazing lands against droughts, low fertility, and other stresses. Modeling approaches and remote sensing can be useful tools to characterize and manage the various scenarios of pastureland and rangeland management. For example, GIS can integrate data on plant species, soil type and slope, extent and age of rangelands to assess biomass productivity and soil degradation problems. Modeling approaches also permit anticipation of future trends in management. High-resolution images with differing spectral bands and radiation features have been used to

18.18

Summary

465

estimate plant height, canopy structure, bare soil patches, soil roughness, and soil erodibility (van Oijen et al. 2020). Further, hydrologic models in combination with GIS and satellite images have been used to assess the impacts of converting grazing lands to agricultural and urban areas on runoff rates and flash floods and water quality in northern Mexico and southwestern USA (Miller et al. 2002). Soil erosion models are important decision tools because they predict the likelihood of runoff and soil loss rates by incorporating parameters of surface vegetative cover. For example, the C-factor in RUSLE simulates the relative effects of decreasing grass or forage cover by grazing and burning on soil erosion. The C-factor also integrates information on canopy grass cover, root biomass, soil surface cover or litter, soil roughness, soil water content, and previous land use. Models can allow the assessment of the following (van Oijen et al. 2020): 1. Potential of grazing lands to produce forage and support livestock requirements over time. 2. Performance of past, present, and future management systems. 3. Performance of management systems, and new improved forage production systems. 4. Impacts of grazing on soil and water quality, wildlife habitat, biodiversity, and overall environmental quality.

18.18 Summary

Grazing lands including pasturelands, grasslands, meadows, and rangelands provide numerous ecosystem services. Pasturelands comprise single or native grass species and forbs known as “grasslands,” which cover about 30% of the Earth’s terrestrial ecosystem. Pasturelands can conserve soil and water and improve environmental quality by reducing water and wind erosion, sinking pollutants, sequestering C, and buffering the whole ecosystem. Rangelands are more complex ecosystems than pasturelands consisting of native grasses, grass-like vegetation, forbs, shrubs, and woods. Rangelands are often not cultivated and animal stocking rates are lower than those in pasturelands. Pasture and rangelands are affected by intensive cultivation, intensive grazing, fires, road constructions, and introduction of invasive plant species. The capacity of these lands to provide ecosystem services is declining due to degradation and fragmentation. Intensive grazing or overgrazing can cause soil erosion, reduce soil organic matter concentration, and deteriorate soil’s physical, chemical, and biological properties. In turn, well-managed grazing (continued)

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lands protect the soil surface, stabilize soil matrix, reduce runoff and soil erosion, and maintain soil physical, biological, and chemical properties. There are two main methods of grazing: continuous and controlled stocking. Unlike continuous grazing, controlled stocking is a strategy to reduce the degradation of grazing lands. Controlled stocking includes alternate stocking, deferred grazing, intermittent grazing, mixed grazing, strip grazing, rotational stocking, seasonal grazing, and sequence grazing. Recovering degraded grazing lands can take time and depend on grazing intensity, topography, management, type of livestock, and vegetation. The use of models, remote sensing, and GIS tools can allow monitoring the performance of past, present, and future management of grazing lands under different scenarios of management and climatic conditions. Questions 1. Determine if vegetation along a 6% slope pastureland channel under tall fescue fails under concentrated flow. The runoff flow depth, which varies during the rainstorm event, is 0.1, 0.25, 0.5, and 1 m. The rigidity constant (MEI) is 30 while the channel hydraulic radius is 3 m. 2. Calculate the friction factor of the grass in Prob. 1 if the height of ungrazed is 0.5 m and 0.1 when grazed. 3. Compute the runoff flow velocity if Manning’s coefficient of roughness for the vegetation is 0.06. 4. Discuss the difference between pasturelands and rangelands in terms of the magnitude of soil erosion. 5. Discuss differences among set-stocking, continuous stocking, and rotational stocking. 6. Discuss how modeling can contribute to the better management of pasturelands and rangelands. 7. Explain the potential of grasslands for providing feedstocks for producing biofuel. 8. How does Manning’s roughness coefficient change with overgrazing? 9. Describe the strategies for managing degraded pasturelands. 10. Explain the mechanisms by which plant roots reduce runoff and soil erosion.

References Alberts EE, Nearing MA, Weltz MA et al (1995) Chapter 7. Soil component. In: Flanagan DC, Nearing MA (eds) USDA-Water Erosion Prediction Project (WEPP). Hillslope profile and watershed model documentation. National Soil Erosion Laboratory (NSERL) Report #10, West Lafayette, Indiana Alcañiz M, Outeiro L, Francos M, Úbeda X (2018) Effects of prescribed fires on soil properties: A review. Sci Total Environ 613–614:944–957

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Altesor A, Piñeiro G, Lezama F et al (2006) Ecosystem changes associated with grazing in subhumid south American grasslands. J Veg Sci 17:323–332 Blanco-Canqui H (2018) Conservation grass hedges and soil health parameters. In: Reicosky D (ed) Managing soil health for sustainable agriculture volume 2: Monitoring and management. Burleigh Dodds Science Publishing, Cambridge Blanco-Canqui H, Lal R, Owens LB et al (2005) Strength properties and organic carbon of soils in the North Appalachian Region. Soil Sci Soc Am J 69:663–673 Blanco-Canqui H, Hergert GW, Nielsen RA (2015) Cattle manure application reduces soil's susceptibility to compaction and increases water retention after 71 years. Soil Sci Soc Am J 79:212–223 Bondi G, O’Sullivan L, Fenton O, Creamer R, Marongiu I, Wall DP (2021) Trafficking intensity index for soil compaction management in grasslands. Soil Use Manag 37:504–518 Carey CJ, Blankinship JC, Eviner VT, Malmstrom CM, Hart SC (2017) Invasive plants decrease microbial capacity to nitrify and denitrify compared to native California grassland communities. Biol Invasions 19:2941–2957 Carlassare M, Karsten HD (2002) Species contribution to seasonal productivity of a mixed pasture under two sward grazing height regimes. Agron J 94:840–850 Chanasyk DS, Mapfumo E, Willms W (2003) Quantification and simulation of surface runoff from fescue grassland watersheds. Agric Water Manag 59:137–153 Collins SL, Nippert JB, Blair JM, Briggs JM, Blackmore P, Ratajczak Z (2021) Fire frequency, state change and hysteresis in tallgrass prairie. Ecol Lett 24:636–647 Daniel JA, Potter K, Altom W, Aljoe H, Stevens R (2022) Long-term grazing density impacts on soil compaction. Trans ASAE 45:1911–1915 De Baets S, Poesen J, Gyssels G et al (2006) Effects of grass roots on the erodibility of topsoils during concentrated flow. Geomorphology 76:54–67 Descheemaeker K, Nyssen J, Poesen J et al (2006) Runoff on slopes with restoring vegetation: A case study from the Tigray highlands, Ethiopia. J Hydrol 331:219–241 dos Santos JV, Bento LR, Bresolin JD, Mitsuyuki MC, Oliveira PP, Pezzopane JC, Bernardi AC, Mendes IC, Martin-Neto L (2022) The long-term effects of intensive grazing and silvopastoral systems on soil physicochemical properties, enzymatic activity, and microbial biomass. Catena 219:106619 Drewry JJ (2006) Natural recovery of soil physical properties from treading damage of pastoral soils in New Zealand and Australia: a review. Agric Ecosyst Environ 114:159–169 Elliott AH, Carlson WT (2004) Effects of sheep grazing episodes on sediment and nutrient loss in overland flow. Aust J Soil Res 42:213–220 Follett RF, Stewart CE, Bradford J, Pruessner EG, Sims PL, Vigil M (2020) Long-term pasture management impacts on eolian sand soils in the southern mixed-grass prairie. Quat Int 565:84– 93 Gilmullina A, Rumpel C, Blagodatskaya E, Chabbi A (2020) Management of grasslands by mowing versus grazing impacts on soil organic matter quality and microbial functioning. Appl Soil Ecol 156:103701 Gomez-Casanovas N, Blanc-Betes E, Moore CE, Bernacchi CJ, Kantola I, DeLucia EH (2021) A review of transformative strategies for climate mitigation by grasslands. Sci Total Environ 799: 149466 Haan CT, Barfield BJ, Hayes JC (1994) Design hydrology and sedimentology for small catchments. Academic, California Higgins S, Schellberg J, Bailey JS (2019) Improving productivity and increasing the efficiency of soil nutrient management on grassland farms in the UK and Ireland using precision agriculture technology. Eur J Agron 106:67–74 Johnson K (2003) Terminology for grazing lands and grazing animals. Purdue Univ Agron Extension. http://www.agry.purdue.edu/ext/forages/rotational/index.html. Cited 14 March 2008

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Kemp DR, Han G, Hou F, Hou X, Li Z, Sun Y, Wang Z, Wu J, Zhang X, Zhang Y, Gong X (2018) Sustainable management of Chinese grasslands-issues and knowledge. Front Agric Sci Eng 5:9– 23 Klaus VH, Schäfer D, Prati D, Busch V, Hamer U, Hoever CJ, Hölzel N (2018) Effects of mowing, grazing and fertilization on soil seed banks in temperate grasslands in Central Europe. Agric. Ecosyst Environ 256:211–217 Koch B, Edwards PJ, Blanckenhorn WU, Walter T, Hofer G (2015) Shrub encroachment affects the diversity of plants, butterflies, and grasshoppers on two Swiss subalpine pastures. Arct Antarct Alp Res 47:345–357 Lai L, Yilmaz T, Kumar S, Fennell A, Gonzalez Hernandez JL (2022) Influences of grassland to cropland conversion on select soil properties, microbiome and agricultural emissions. Soil Res 60:561–579 Ludwig JA, Tongway DJ (2002) Clearing savannas for use as rangelands in Queensland: altered landscapes and water-erosion processes. Rangel J 24:83–95 Magandana TP, Hassen A, Tesfamariam EH (2021) Annual net primary productivity of different functional groups as affected by different intensities of rainfall reduction in the semi-arid grasslands of the Gauteng province in South Africa. Agronomy 11:730 Mamo M, Bubenzer GD (2001) Detachment rate, soil erodibility and soil strength as influenced by living plant roots: Part I Laboratory study. Am Soc Agric Eng 44:1167–1174 Mceldowney RR, Flenniken M, Frasier GW et al (2002) Sediment movement and filtration in a riparian meadow following cattle use. J Range Manag 56:367–373 Miller SN, Kepner WG, Mehaffey MH et al (2002) Integrating landscape assessment and hydrologic modeling for land cover change analysis. J Am Water Res Assoc 38:915–929 Miller JJ, Curtis T, Chanasyk DS, Willms WD (2017) Influence of cattle trails on runoff quantity and quality. J Environ Qual 46:348–355 Mishra PK, Neelkanth JK, Maheswara Babu B et al (2006) Effectiveness of Bermuda grass as vegetative cover in grassed waterway: a simulated study. J Irrig Drain Eng 132:288–292 Morais TG, Teixeira RFM, Figueiredo M, Domingos T (2021) The use of machine learning methods to estimate aboveground biomass of grasslands: a review. Ecol Indic 130:108081 Neff JC, Reynolds RL, Belnap J et al (2005) Multi-decadal impacts of grazing on soil physical and biogeochemical properties in Southeast Utah. Ecol Appl 15:87–95 Pilon C, Moore PA, Pote DH, Pennington JH, Martin JW, Brauer DK, Raper RL, Dabney SM, Lee J (2017) Long-term effects of grazing management and buffer strips on soil erosion from pastures. J Environ Qual 46:364–363 Pilon C, Moore PA, Pote DH, Martin JW, Owens PR, Ashworth AJ, Miller DM, DeLaune PB (2018) Grazing management and buffer strip impact on nitrogen runoff from pastures fertilized with poultry litter. J Environ Qual 48:297–304 Podwojewski P, Poulenard J, Zambrana T et al (2002) Overgrazing effects on vegetation cover and properties of volcanic ash soil in the paramo of Llangahua and La Esperanza (Tungurahua, Ecuador). Soil Use Manag 18:45–55 Pulido M, Schnabel S, Contador JFL, Lozano-Parra J, Gómez-Gutiérrez A (2017) Selecting indicators for assessing soil quality and degradation in rangelands of Extremadura (SW Spain). Ecol Indic 74:49–61 Sainnemekh S, Barrio IC, Densambuu B, Bestelmeyer B, Aradóttir ÁL (2022) Rangeland degradation in Mongolia: a systematic review of the evidence. J Arid Environ 196:104654 Schlesinger WH, Ward TJ, Anderson J (2000) Nutrient losses in runoff from grassland and shrubland habitats in southern New Mexico: II field plots. Biogeochem 49:69–86 Shukla MK, Lal R, Owens LB et al (2003) Land use and management impacts on structure and infiltration characteristics of soils in the North Appalachian region of Ohio. Soil Sci 168:167– 177 Suttie JM, Reynolds SG, Batello C (2005) Grasslands in the world. FAO Plant production and protection Series. No. 34, Rome, Italy Troeh FR, Hobbs JA, Donahue RL (2004) Soil and water conservation. Prentice Hall, New Jersey

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Trosanyi ZK, Fieldsend AF, Wolf DD (2009) Yield and canopy characteristics of switchgrass (Panicum virgatum L.) as influenced by cutting management. Biomass Bioenergy 33:442–448 Tufekcioglu M, Schultz RC, Zaimes GN, Isenhart TM, Tufekcioglu A (2013) Riparian grazing impacts on streambank erosion and phosphorus loss via surface runoff. J Am Water Resour Assoc 49:103–113. https://doi.org/10.1111/jawr.12004 van Oijen M, Barcza Z, Confalonieri R, Korhonen P, Kröel-Dulay G, Lellei-Kovács E, Louarn G, Louault F, Martin R, Moulin T, Movedi E, Picon-Cochard C, Rolinski S, Viovy N, Wirth SB, Bellocchi G (2020) Incorporating biodiversity into biogeochemistry models to improve prediction of ecosystem services in temperate grasslands: review and roadmap. Agronomy 10:1–24 Volaire F, Barkaoui K, Norton M (2014) Designing resilient and sustainable grasslands for a drier future: adaptive strategies, functional traits and biotic interactions. Eur J Agron 52:81–89. https://doi.org/10.1016/j.eja.2013.10.002 White RP, Murray S, Rohweder M (2000) Pilot analysis of global ecosystems: grassland ecosystems. World Resources Institute, Washington, DC, p 89 Yan Y, Yan R, Chen J, Xin X, Eldridge DJ, Shao C, Wang X, Lv S, Jin D, Chen J, Guo Z, Chen B, Xu L (2018) Grazing modulates soil temperature and moisture in a Eurasian steppe. Agric For Meteorol 262(2018):157–165 Yuan Y, Bingner RL, Theurer FD (2006) Subsurface flow component for AnnAGNPS. Applied Eng Agric 22:231–241 Zhang ZH, Li XY, Jiang ZY et al (2013) Changes in some soil properties induced by re-conversion of cropland into grassland in the semiarid steppe zone of Inner Mongolia, China. Plant Soil 373: 89–106 Zhang Q, Buyantuev A, Fang X et al (2020) Ecology and sustainability of the inner Mongolian grassland: looking back and moving forward. Landsc Ecol 35:2413–2432 Zhou Q, Daryanto S, Xin Z, Liu Z, Liu M, Cui X, Wang L (2017) Soil phosphorus budget in global grasslands and implications for management. J Arid Environ 144:224–235

Soil Management and Carbon Dynamics

19

The subject of soil management and conservation is traditionally discussed in relation to erosion control, soil water conservation, soil fertility, and crop production. However, because of the continued depletion of the soil organic C pool in both agricultural and non-agricultural soils, enhanced enrichment of atmospheric greenhouse gases (e.g., CO2, N2O, CH4), potential of trading of C credits, and the adverse consequences of soil C loss on long-term soil productivity, the subject of terrestrial C dynamics and soil C restoration is a critical soil management issue. The total soil organic C pool is a sizable component of the terrestrial C pool and its dynamics strongly influence the global C cycle and soil ecosystem services. More C is stored in the soil than in terrestrial biomass or the atmosphere. However, conversion of natural ecosystems to agricultural lands has caused the depletion of the soil organic C pool across the globe. Specifically, agricultural lands have lost 30–50% of the original C due to intensive tillage, crop residue removal and burning, and extractive farming practices (Haddaway et al. 2017; Lal 2022). A goal of soil management is to restore and manage the C pool by increasing the input of biomass C through the adoption of innovative practices including conservation tillage practices (e.g., no-till), use of cover crops, and use of organic amendments (e.g., animal manure, biochar). It is important to note that adopting management practices that reduce soil erosion and maintain soil fertility and productivity can also be effective at enhancing the soil C pool. Soil management practices that promote photosynthesis of CO2 and conversion of aboveground and belowground biomass into the soil organic C pool can restore the lost C. Losses of soil organic C result in gains in the atmospheric abundance of CO2 and CH4. Thus, increasing gains and reducing losses of soil C through the adoption of recommended management practices are strategies that can promote C sequestration in the soil. Soils can be a natural sink of atmospheric C under proper management.

# The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 H. Blanco, R. Lal, Soil Conservation and Management, https://doi.org/10.1007/978-3-031-30341-8_19

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19.1

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Soil Management and Carbon Dynamics

Importance of Soil Organic Carbon

The soil organic C pool is an indispensable natural resource. It is the main component of soil organic matter (58% of soil organic matter is C), which moderates all physical, chemical, and biological soil processes and properties. Its depletion not only exacerbates soil erosion but also diminishes other soil ecosystem services. Restoring and maintaining soil C pools are central to the maintenance and delivery of soil ecosystem services from agricultural lands. Soil organic matter conserves soil and water by stabilizing aggregates and decreasing erodibility, improving water infiltration, and reducing the amount and rate of overland flow (Blanco-Canqui et al. 2013). It improves water quality by adsorbing and filtering pollutants (e.g., pesticides), which prevents toxic compounds from leaving the source area and polluting downstream natural waters.

19.2

Soil Organic Carbon Balance

Organic Amendments

C Emissions

Biomass C

Soil Organic C Pool

LATERAL TRANSFER

Leaching

VERTICAL TRANSFERS

The soil organic C budget is estimated by computing the difference between inputs and outputs of C (Fig. 19.1). Inputs and outputs of C consist of vertical and lateral components. The main vertical inputs include biomass C and C-enriched amendments while the main vertical outputs include C emissions and leaching (Fig. 19.1). The lateral components consist of C removed by water, wind, tillage and crop harvest erosion. Vertical fluxes of C are often larger than lateral fluxes. For instance, lateral C flux by water and tillage erosion can be small on nearly level landscapes, but it can be large due to wind erosion. The magnitude of C fluxes is

Fig. 19.1 Gains and losses of soil organic C

Soil Erosion and Deposition

19.3

Soil Erosion and Organic Carbon Dynamics

473

difficult to quantify because it is influenced by a series of complex and interactive factors such as soil management, landscape characteristics, and climate. A simple model of organic C balance in the soil can be: Δ Soil C = Input - Output = Initial C þ C Input - C Eroded - C Leached - Mineralization

ð19:1Þ

where Initial C is the antecedent soil organic C pool and Mineralization is the decomposition of soil organic matter. Leaching of C occurs in the form of dissolved C. Some of the C leached is precipitated in the subsoil and can be transported into aquatic systems.

19.3

Soil Erosion and Organic Carbon Dynamics

Soil erosion alters the fluxes of soil C because it removes and redistributes the C-enriched sediment and accelerates the process of mineralization (e.g., C emissions; de Nijs and Cammeraat 2020). Each process of soil erosion including detachment, transport, distribution, and deposition affects soil C dynamics (Lal 2022). The process of C removal is set in motion when the raindrops impact or strike the soil surface and disperse soil aggregates. Similar to water erosion, wind erosion removes C in arid and semiarid regions. Indeed, soil organic C is removed by wind more than by water in dry regions (Chappell et al. 2019). The amount of C removed by water and wind erosion depends on the magnitude of sediment removal. Surface cover conditions, soil properties, and degree of soil organic matter decomposition are some of the factors that affect the magnitude of C removal. For example, soil and C losses are higher from conventionally tilled soils than from no-till soils with residue mulch. Because of the deposition of C in the bottom perimeter of fields and continued removal of soil from the upper positions of the landscape, soil organic C concentration decreases in convex positions and increases in the concave or footslope landscape positions (de Nijs and Cammeraat 2020). The eroded soil and associated C differ in their characteristics from those of the original or uneroded soil as sediment in depositional areas often contains fine organic and clay particles. There are six specific processes by which erosion alters C dynamics. These processes are briefly described below:

19.3.1 Aggregate Disintegration Aggregate breakdown is the very first process by which erosion initiates losses of C at an eroding site. Erosive forces such as raindrop impact and the shearing force of runoff and wind disrupt, disperse, and slake aggregates. Soil dispersion exposes C found inside macro- and micro-aggregates to microbial attack (Sapkota and White 2019). Thus, the process of C release by erosion is initiated when soil aggregates are

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disintegrated by erosive forces. The systematic reduction in size of secondary soil particles with erosion concomitantly results in a gradual release of more occluded C. The released C is prone to losses via C emissions, erosion, and microbial decomposition. The process opposite to disintegration, which is aggregation, promotes encapsulation of soil C and thus C sequestration.

19.3.2 Preferential Removal of Carbon Soil C along with disintegrated aggregates and primary particles is readily transported by water and wind. Erosion is a selective process. Because of the low density of the soil organic matter, C-enriched soil particles are more easily removed by water and wind than compact inorganic particles. Also, lighter inorganic particles such as clay are transported longer distances than heavier particles. Further, soil organic matter associated with clay particles is also lost. Another factor by which soil organic C is preferentially removed by water and wind is its location within the soil profile. The organic C is mostly concentrated in the upper few centimeters of the soil surface, which is the region of active perturbation by erosional processes.

19.3.3 Redistribution of Carbon Transported by Erosion The C removed by erosional processes is redistributed all over the landscape. Some of it is deposited in field depressions or transported off-site to rivers, lakes, and eventually to oceans. Depositional areas normally have a greater concentration of soil organic C than the eroding or convex sites of the landscape. Land topography, degree of erosion, and site-specific soil characteristics define the magnitude of C removal by erosional processes and the distance to which the soil C is transported.

19.3.4 Mineralization of Soil Organic Matter The soil organic matter transported by erosion comprises primarily the labile C pool, which is rapidly oxidized (Fig. 19.2). While the labile C in uneroded soils is also susceptible to rapid decomposition, erosion accelerates this process by shifting and mixing the soil, disintegrating the aggregates, and altering temperature and moisture regimes. Significant mineralization of C occurs at all stages of soil erosion. The C emissions are highly variable among the different erosion phases, which impedes an accurate quantification of the net emissions from eroding landscapes.

19.3.5 Deposition and Burial of Carbon Transported by Erosion The soil organic matter at the depositional sites is subject to rapid anaerobic decomposition (e.g., methanogenesis, mineralization), causing loses of CO2, CH4,

19.5

Carbon Transported by Erosion: Source or Sink for Atmospheric CO2

475

C Emissions C Emissions

Eroded C Deposition

Eroded

C Emissions

C Deposition Eroded C Deposition River Fig. 19.2 Dynamics of soil organic C during erosion

and N2O (denitrification) gases (de Nijs and Cammeraat 2020). The soil organic matter deposited in the upper 20 cm of the soil can be rapidly mineralized. Emissions of C from the depositional areas can be higher than at the eroding sites because the eroded sediment is enriched with soil organic C (Sapkota and White 2019). Some of the eroded soil organic matter buried in deeper layers may not, however, decompose easily, which can favor long-term C sequestration. Also, a portion of the buried C forms stable compounds (e.g., calciferous compounds) and initiates re-aggregation with low rates of mineralization.

19.4

Fate of the Carbon Transported by Erosion

The fate of eroded C is rather complex and uncertain. A simple model to estimate the fate of eroded C can be (de Nijs and Cammeraat 2020; Lal 2022): Soil C = Initial Soil C - ðCi þ C t þ C d þ C a Þ þ ðCb þ C ba Þ

ð19:2Þ

where Ci is amount of C oxidized in situ, Ct is C oxidized during transport, Cd is C oxidized in depositional zones, Ca is C oxidized in aquatic systems, Cb is C buried in depositional zones, and Cba is C buried in aquatic systems. The major uncertainty lies with the amount of C emitted during erosion. Some estimates show that most of the C transported by erosion is redistributed along the landscape (Fig. 19.3), but about 20% of C transported by erosion is emitted as CO2.

19.5

Carbon Transported by Erosion: Source or Sink for Atmospheric CO2

There are two main processes affecting the distribution of C transported by erosion (Fig. 19.4; de Nijs and Cammeraat 2020): 1. Soil C transported by erosion can be a source of atmospheric C loss due to the following. One, soil organic matter transported by erosion at long distances can

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FATE OF ERODED CARBON

Transported to the ocean =10% (~ 0.2 Gt)

Emitted to the atmosphere=20% to 30% (~ 1 Gt yr -1)

Redistributed over the landscape = 60% to 70% (~ 0.8 to 1.2 Gt)

Fig. 19.3 Distribution of C transported by erosion

1. Soil aggregate detachment 2. Release of labile C 3. Long distance transport of labile C 4. Losses of C at the eroded site

1. Deep burial of eroded C 2. Short distance transport of C 3. Re-aggregation and occlusion of C 4. Rapid C sequestration at the eroded site

Fig. 19.4 Processes of soil C gains and losses during C erosion (de Nijs and Cammeraat 2020; Lal 2022)

be oxidized during transport and deposition because it consists primarily of labile organic matter fractions. Two, the soil organic C lost by erosion is not easily replaced. Erosion reduces biomass production at the eroding site and thus input of new C, which is crucial to replacing the C transported by erosion. Eroded soils have shallow topsoil layers with limited amounts of plant-available water and nutrients required for plant growth. Continued erosion causes a downward spiral of reduction in the soil organic C pool. Biomass C input may replenish the C transported by erosion in slightly and moderately eroded soils, but it is likely to be insufficient to match large losses of C in severely eroded soils. 2. Erosion can be a sink of atmospheric CO2 and a potential means for long-term C sequestration due to the following. First, deep burial of C transported by erosion with sediments at lower landscape positions can reduce C oxidation and C losses. Second, short-distance transport and deposition of C can promote re-aggregation of soil and C sequestration within newly formed soil aggregates. Third, C lost at the eroded site can be replaced by increased biomass production when proper soil

19.6

Tillage Erosion and Soil Carbon

477

management practices are adopted. Estimates indicate that soil erosion can be a sink of about 26% of C transported by erosion in agricultural soils, which means that most eroded C can be lost from the soil (Van Oost et al. 2007). The contrasting processes above warrant further research and clarification of whether soil erosion is a sink or source of atmospheric CO2. Reliable data on C export and deposition by all forms of erosion including water, wind, tillage, and crops are needed to refine our understanding. It is, however, clear that the C lost from sloping landscape positions may not be readily replaced as highly eroded sites often produce lower amounts of biomass than non-eroded sites, especially when innovative soil C management practices are not embraced. The continued erosion would result in increasingly lower biomass C input into the system. Thus, it is considered that C losses can be greater than C gains during moderate to severe erosion (Fig. 19.4). Quantification of C mineralization during transport and at the depositional sites is further needed to understand the erosion-induced dynamics in soil C cycle.

19.6

Tillage Erosion and Soil Carbon

Dynamics of C need to be discussed not only in regard to water and wind erosion but also in relation to tillage erosion. Tillage erosion can cause the redistribution of C along cultivated landscapes similar in magnitude to that caused by water and wind erosion (Zhao et al. 2018). Tracers such as 137Cs and 210Pb resulting from the fallout of radionuclides can be used for tracking C redistributed by tillage over the landscape. The main difference between tillage erosion and other types of erosion is that C transported by tillage erosion is mostly accumulated in the lower portion of the fields until water and wind erosion intervene. Combined forces of tillage, water, and wind erosion cause off-site transport of C. Frequent tillage loosens and moves the soil downslope and predisposes soil C to removal by water and wind. Tillage erosion reduces C concentration in the upper field positions and increases C concentration in the lower positions (Fig. 19.5). For example, in China, on a hilly cropland with 13.5% slope, tillage erosion caused redistribution of C, reducing soil C concentration in the upper slope positions and increasing C concentration in the lower positions (Nie et al. 2019). The soil C concentration was 0.45% at the upper positions, 0.58% at the middle positions and 0.73% at the lower positions (Nie et al. 2019). Tillage erosion can also bury soil and thus C (Van Oost et al. 2005). The buried C can have important implications to long-term C sequestration in sloping cultivated lands (Nie et al. 2019). Carbon residence time can increase with the burial of C. A significant portion of C transported with tillage is easily mineralized and emitted into the atmosphere. Thus, tillage erosion can be a net source of C. Tillage erosion also exposes subsoil horizons with a low concentration of C as the original topsoil is moved downslope where it accumulates to form stratified C-enriched soil deposits. Exposed subsoil horizons on shoulder slopes normally

19

Fig. 19.5 Redistribution of C by tillage erosion in cultivated sloping fields

Soil Management and Carbon Dynamics

Soil Organic Carbon Pool

478

Summit Backslope Footslope LANDSCAPE POSITION

have higher clay content and lower soil organic C concentration due to intensive tillage. Tillage erosion translocates all forms of organic matter, unlike water and wind erosion which is a selective process and mostly removes fine lighter particles.

19.7

Management Practices and Soil Organic Carbon Dynamics

Increasing soil organic C concentration through improved soil management practices is key to controlling soil erosion and maintaining soil productivity and other ecosystem services. As indicated earlier, improved soil management practices can increase soil C storage and reduce C emissions while reducing runoff and soil loss, conserving water, sustaining crop production, and delivering other services. Developing or refining current soil management practices to accomplish multiple goals is thus a priority. How some management practices affect soil organic C pool is summarized below.

19.7.1 No-Till and Carbon Sequestration Intensive tillage practices disturb soil and cause rapid oxidation of soil organic matter, thereby increasing the flux of C to the atmosphere. It is estimated that as much as 40% of soil organic C in cropland soils has been depleted by intensive tillage in temperate regions. The percentage of soil C loss can be even higher (about 60%) in tropical soils (Lal 2004). As a result, no-till management is considered a promising alternative to intensive tillage for reducing and restoring C as an ancillary benefit from no-till management. No-till management can promote C accumulation by reducing soil disturbance and leaving crop residues on the soil surface. No-till management often accumulates more C near the soil surface (1% C), and 3) precipitation input is low, such as in

19.7

Management Practices and Soil Organic Carbon Dynamics

483

24

Soil Organic Carbon (g kg-1)

0- to 7.5-cm soil depth 21

7.5- to 15-cm soil depth

15

a a

18 b

12

a

a

a

9 6 3 0 No Cover Crop

Late Maturing Soybean Cover Crop

Sunn Hemp Cover Crop

Fig. 19.7 Summer cover crops and their impacts on soil C accumulation under winter-wheat and grain sorghum rotation in the eastern US Great Plains (Blanco-Canqui et al. 2011). Bars followed by the same letter within the same soil depth are not significantly different (P < 0.05)

water-limited regions. Increasing cover crop biomass production is key if the goal is to sequester C with cover crops. Increasing the growing window time for cover crops by planting cover crops early (in summer or early fall) and terminating them late in fall or the following spring can be strategies to increase biomass production. A study in the eastern US Great Plains reported that summer cover crops planted after winterwheat in no-till winter-wheat and grain sorghum rotation accumulated soil C but such accumulation was significant only in the upper 7.5 cm of the soil after 15 yr of cover crop management (Fig. 19.7; Blanco-Canqui et al. 2011). Site-specific management of cover crops is critical for soil C accumulation and improvement in other ecosystem services from cover crops.

19.7.4 Crop Residues Leaving crop residues on the soil surface increases soil organic C stocks near the soil surface while reducing soil erosion. Crop residues contain about 45% C. Tilling residues into the soil accelerates its decomposition through bringing the residues in direct contact with soil organisms. Soil texture, drainage, tillage, and climate influence the residue decomposition rates. Response of soil organic C to residue management can be slow in clayey and cool soils due to reduced crop residue decomposition. No-till soils with high residue input such as continuous corn can accumulate more soil organic C than no-till soils with low residue input (e.g., cornsoybean rotation; Blanco-Canqui et al. 2014). Soybean residues have lower C:N ratio than corn residues and are thus easily decomposed. Quantity and quality of

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residue inputs in interaction with soil texture defines the accumulation, turnover, and retention of C. Because crop residue has a high concentration of C, high rates of residue removal (>50%) for expanded uses such as livestock or biofuel production can reduce soil organic C stocks under excessive residue removal. In a review of 14 crop residue removal experiments in Canada and the Midwestern USA, Smith et al. (2012) discussed that crop residue removal can reduce soil C stocks in the upper 20 cm of the soil, especially under high rates of residue removal in the long term relative to no removal. High rates of crop residue removal can reduce soil organic C stocks by: 1) directly removing C with crop residues, 2) increasing soil erosion and thus C losses, and 3) degrading soil properties (e.g., aggregation) essential for C protection and sequestration.

19.7.5 Animal Manure Animal manure application increases soil organic C concentration because it contains more than 10% C. For example, manured no-till soils have significantly higher soil organic C pools than no-till soils without manure (Fig. 19.8). The soil organic matter in manure entering the soil is initially in the labile form and then transferred into mineral-associated soil C pool. Soil organic C concentration increases with an increase in rate of addition of manure although changes in soil organic C concentration at high rates of addition may be small (Blanco-Canqui et al. 2015). Manure application enhances the formation and stabilization of aggregates and can promote long-term C storage. It increases both the particulate organic matter Fig. 19.8 Depth distribution of soil organic C for no-till continuous corn with and without manure in a sloping silt loam in the eastern US Corn Belt (Blanco-Canqui et al. 2005)

-1

Soil Organic Carbon (Mg ha ) 60 0 20 40 0

Soil Depth (cm)

5 10 15 20 SD 25 No-till with manure No-till without manure 30

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Management Practices and Soil Organic Carbon Dynamics

485

and mineral-associated soil organic C concentration in macroaggregates. Manure application can also reduce runoff and soil losses by stabilizing aggregates and increasing water infiltration. Further, the increase in soil organic C concentration can enhance the ability of the soil to retain plant-available water (Blanco-Canqui et al. 2015). Figure 19.8 shows that gains in soil C with manure addition to no-till soils can be observed at deeper depths (> 10 cm) than no-till without manure. Thus, since gains in soil organic C in typical no-till soils are often confined to the upper 10 cm of soil surface due to residue stratification, no-till in combination with animal manure can be a strategy to increase soil organic C pool in deeper soil layers. The improved soil properties with manure can be a reason for the increased soil C accumulation at deeper soil depths. Manure application at recommended rates can be vital to increase soil organic C stocks in agricultural lands while reducing the excessive build-up of nutrients (e.g., P) and P losses in runoff.

19.7.6 Agroforestry Agroforestry systems, which refer to the integration of crops with trees and shrubs, can play an important role in increasing soil organic C storage and reducing net emissions of greenhouse gases. Because of their rapid growth and abundant aboveground and belowground biomass, trees in an agroforestry system have the ability to increase and stabilize the soil organic C pool. Agroforestry practices can recapture some of the soil organic C that was lost with land clearing and biomass burning. Enhanced soil organic C sequestration by agroforestry systems can be a tradeoff for the land taken out of production for establishing agroforestry trees and/or shrubs. A global review found that the transition from row crops to agroforestry systems can increase soil organic C stock by 26% in the 0–15 cm, 40% in the 0–30 cm, and 34% in the 0–100 cm soil depths (De Stefano and Jacobson 2018). The soil organic C storage rates vary across regions, depending on the type of agroforestry practice, management, and climate (Table 19.2). Most of the estimates of soil organic C storage by agroforestry systems are for tropical regions where C accumulation rates range between 1.5 and 3.5 Mg ha-1 yr-1 (Montagnini and Nair 2004). For example, a meta-analysis for China reported that agroforestry systems can store soil C between 0.23 and 0.92 Mg ha-1 yr-1 (Hübner et al. 2021). The estimated annual C accumulation under various agroforestry systems in the USA by 2025 is about 74 Tg of C for alley cropping, 9 for silvopasture, 4 for windbreaks, 2 for forest farming, and 1.5 for riparian buffers (Montagnini and Nair 2004). At present, the amount of soil organic C stored by agroforestry systems cannot be accurately quantified because of the lack of: 1) information on the land area under agroforestry systems around the world and 2) a complete understanding of aboveground and belowground biomass C input from trees and shrubs. Differences in tree species, age of species, management, agroforestry practice, ecosystem, and climate affect the amount of soil C sequestered under agroforestry systems. For instance, fertilization, irrigation, and weed and pest control in agroforestry systems generally

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favor soil organic C storage but pruning or thinning may reduce increases in soil organic C storage, particularly in sparse stands. Trees and shrubs with dense root systems can have a high capability for belowground C enrichment. Deforestation of natural forest is one of the major causes of soil C loss. It can reduce soil C stocks by as much as 70% (Assefa et al. 2017). The amount of soil organic C regained by the reintroduction of agroforestry practices can help but may not equal that lost in the clearing of primary forests. Thus, long-term agroforestry systems with mixed plant species can be more effective for soil organic C storage than systems with single species. Managing the stands carefully is critical to soil organic C storage in agroforestry systems. Harvesting of trees, particularly in short rotation stands, can reduce the potential of agroforestry systems to store C.

19.7.7 Organic Farming Organic farming with extended crop rotations and annual additions of green and animal manure can increase soil organic C stocks compared with conventionally farmed soils. Organic farming can sequester, on average, 0.45 Mg C ha-1 yr-1 (Table 19.2). Green and animal manure application, a common practice in organic farming, not only increases C storage but also improves soil fertility and biological activity. Addition of animal manure combined with legume-based crop rotations (e.g., alfalfa) can increase soil organic C storage, especially in conjunction with reduced tillage and complex crop rotations. Also, recycled urban waste products or composted and uncomposted local organic amendments, which are rich in organic matter and nutrients, can be used. While losses of soil organic C as CO2 emissions can be higher in organic farming than in conventional farming from the abundant addition of animal manure and intensive tillage for weed control, the annual addition of C-enriched amendments can result in overall C accumulation. A case study in eastern Nebraska found that organic cropping systems accumulated soil C at 0.16 Mg ha-1 yr-1 with cattle manure and 0.18 Mg ha-1 yr-1 with alfalfa green manure in the 0–15 cm depth after >20 yr of management (Blanco-Canqui et al. 2017). Because intensive tillage such as moldboard plowing can reduce the potential of organic farming to increase soil organic C stocks, organic farming with no-till and reduced tillage can be a useful strategy to enhance soil C sink capacity. However, complete weed control can be a challenge with organic no-till farming (Halde et al. 2017). In summary, organic cropping systems receiving organic amendments can sequester C more than conventional farming.

19.7.8 Bioenergy Crops Bioenergy crops, such as perennial warm season grasses and short-rotation woody perennials, conserve water and soil while increasing soil organic C and reducing C emissions. Perennial species can sequester between 0.6 and 3.0 Mg C ha-1 yr-1 in

19.7

Management Practices and Soil Organic Carbon Dynamics

487

the soil compared to fields without perennials (Table 19.2). The capacity of perennial species such as switchgrass to sequester C can be higher than most other management systems (Table 19.2). Herbaceous and woody species can enhance C storage in deeper layers because of their high root biomass and deep root system. When warmseason grasses (e.g., switchgrass) are cut, the height of cut should be ≥10 cm to maintain proper surface cover. In conjunction with some of the aboveground biomass returned after harvest, the belowground biomass enhances soil organic C pools more than growing short-statured grasses and row crops. The magnitude of increases in soil organic C stock can be variable, depending on perennial species, management, and climate. The soil organic C storage by bioenergy crops is generally high and rapid in soils with low antecedent soil organic C pool. Growing warm-season grasses can be particularly feasible in marginal soils to sequestering C while reducing the competition for land with row crops. Switchgrass, one common warm season grass, has been traditionally used as grass barriers or buffers for soil and water conservation. Thus, perennial plant species can be multifunctional systems in that they not only sequester C but also conserve soil and water, improve wildlife habitat, and provide biomass livestock and biofuel production.

19.7.9 Reclaimed Lands Reclamation of degraded soils can be a viable pathway to sequester soil C in addition to that sequestered in productive lands. Degraded soils are potential C sinks because their C levels are commonly below saturation. For instance, drastic land disturbance during mining operations causes losses of soil C due to rapid soil organic matter decomposition. Soil disturbance also reduces aggregation and microbial biomass and activity responsible soil organic C sequestration and protection in the soil. Adoption of improved soil management practices can restore degraded soils and enhance C sequestration. The most common practices to restore and enhance soil C sequestration in degraded include: 1) addition of manure and other organic amendments, 2) use of no-till and reduced till with crop residue mulch, 3) establishment of conservation buffers, 4) establishment of pasture, and 5) forestation. Revegetation is the main path for C accretion in reclaimed minesoils. What has been lost as CO2 has to be replaced with C input through aboveground and belowground biomass input provided that C input is higher than C losses. A review found that the rate of soil C sequestration in minesoils ranges from 0.1 to 3.1 Mg ha-1 y-1 when converted to grasses and 0.7 to 4 Mg ha- 1 yr-1 when converted to forests (Shrestha and Lal 2006). Soil C sequestration in minesoils increases with time (Fig. 19.9a) following reclamation until a new equilibrium is reached (Fig. 19.9b). Soil structure development during reclamation mediates C sequestration. Revegetation with high-biomassproducing plant species can increase C storage and improve related soil properties. In some reclaimed soils, rates of soil organic C storage may not only reach those of unmined sites but may surpass the original soil C levels, depending on management and vegetation type (e.g., high-biomass-producing plants). The soil C sequestration

488

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Soil Management and Carbon Dynamics

60

A

B

-1

Organic Carbon (Mg ha )

50 40 30 20 10

Reclaimed with Pasture Reclaimed with Forest

0 0

10 20 Years under Reclamation

30

Years under Reclamation

Fig. 19.9 Measured (a) and estimated (b) soil C stocks in reclaimed minesoils with time (Akala and Lal 2001)

potential in reclaimed soils depends on the amount of aboveground and belowground biomass input.

19.7.10 Biochar Biochar is a by-product of pyrolysis of organic materials (e.g., wood, grasses, crop residues, animal manure) at high temperatures but low oxygen levels. The concentration of C in biochar ranges from 25 to 95% and most of the biochar C is considered stable. Thus, mixing biochar with soil can be one of the top strategies to rapidly sequester C in agricultural lands (Liu et al. 2016). Biochar C residence in the soil can range from 2000 to 100,000 years (Lehmann and Joseph 2015). Because biomass production needed to produce biochar directly removes atmospheric C via photosynthesis, biochar as a by-product can contribute to the removal of atmospheric C and subsequent sequestration of stable C. Thus, incorporating biochar into the soil can be a viable option for storing C in soil while improving other ecosystem services (El-Naggar et al. 2019). For example, the application of nutrientenriched biochar such as manure biochar can improve soil fertility and increase crop yields, while biochar with a low concentration of essential nutrients (e.g., N) such as wood or crop residue biochar can be effective at retaining nutrients and improving nutrient use efficiency by reducing nutrient losses. Slash-and-burn agriculture produces large amounts of greenhouse gases. Replacing slash-and-burn with slash-and-biochar can annually reduce net emissions

19.8

Measurement of the Soil Carbon Pool

489

of C while improving soil fertility and thus reducing the use of fertilizers (El-Naggar et al. 2019). As a classic example, in Brazil, a number of human-made sites called “black earth” (terra petra) exist along the Amazon River where buried charcoal below the soil surface thousands of years ago restored degraded ecosystems into highly productive lands, enhancing a long-term C storage (Lehmann and Joseph 2015). The frequent and extensive fires in historical times caused the formation of relic charcoal which persist for long periods of time. While the total soil C concentration decreases due to the rapid turnover of soil organic C, biochar C persists due to its high stability and can increase the total amount of stable C concentration in the soil. Biochar potential to sequester C can, however, depend on a number of factors. Not all biochars are the same. Carbon concentration in biochar vary, depending on biochar application amount, biochar feedstock (e.g., wood vs. manure), pyrolysis temperature (e.g., low vs. high), and others. For example, an increase in pyrolysis temperature can increase the concentration of stable C and reduce the concentration of labile C. Biochar properties affect the stability of C and the release of nutrients (El-Naggar et al. 2019). Laboratory or greenhouse studies often show greater benefits from biochar than field studies mainly due to the high amounts of biochar (> 50 Mg ha-1) used in controlled environments. Application of large amounts of biochar may not be practical or economical under field conditions. Additional longterm studies in the field are necessary to determine the optimum levels of biochar application to sequester C and improve other soil ecosystem services under different management scenarios and climates.

19.8

Measurement of the Soil Carbon Pool

The soil organic C concentration needs to be accurately quantified to build reliable C inventories and assess the dynamics of terrestrial C. Wet digestion (Walkley–Black) and dry combustion are common laboratory techniques used to measure the C concentration in soil samples. Several emerging field and laboratory methods are available to determine soil C stocks. The conventional methods of C analysis such as wet digestion and dry combustion involve soil disturbance and require extensive soil sampling and sample preparation for analysis. Spectroscopic methods can measure soil C stocks either in the field or laboratory. Multispectral and/or hyperspectral sensors can be mounted on aircrafts or unmanned aerial vehicles (UAVs) to measure soil C although the accuracy and precision of current sensors can be relatively low (Nayak et al. 2019). At the ecosystem level, eddy-covariance and life-cycle analysis approaches can be used for the estimation of soil C (Nayak et al. 2019; Zhou et al. 2021). Some of the spectroscopic methods include visible and near-infrared (VNIR), shortwave infrared (SWIR), and mid-infrared (MIR), Laser-induced Breakdown Spectroscopy (LIBS), and Inelastic Neutron Scattering (INS) (Gehl and Rice 2007). Upon further improvement, these methods are expected to reduce the intensive sampling and preparation, provide a rapid analysis of C, and allow the in situ determination of C.

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Soil Management and Carbon Dynamics

19.8.1 Infrared Reflectance Spectroscopy (IRS) Infrared reflectance spectroscopy (IRS) including VNIR (440–1100 nm), SWIR (1100–2500 nm), and MIR (2500–25,000 nm) methods is an emerging technique that can be used for the estimation of soil organic C concentration under lab or in situ conditions (Brunet et al. 2007; Nayak et al. 2019). The IRS methods have been used to predict C concentration based on the reflectance signal of soil C. Each atom in the soil has a specific reflective property in the visible or near-infrared zone (between 800 and 2500 nm of wavelength). Since C is mixed with the soil, its specific signature cannot be completely isolated. Thus, calibration of the reflectance signal with measured C is essential to the use of IRS. A drawback of the IRS approach is the need of preparing soil samples and using homogeneous sets of soils for improving accuracy. Ground soil samples (0.2 mm) provide more accurate estimates of C than unground samples. Accuracy is also improved when soil samples are separated and analyzed by textural differences. Statistical parameters such as the partial least-squares (PLS) analysis, principal component analysis (PCA), and pedotransfer functions (PTFs) are being used to improve the calibration between the infrared spectra and measured C with variable outcomes. The IRS portable devices can be used in the field to estimate soil C. The IRS sensors can be mounted on UAVs or helicopters to estimate soil C at large scales. Different levels of accuracy have been obtained with these devices, which thus warrants further evaluation, calibration, and improvement (Nayak et al. 2019). Corrections for water content, surface roughness, bulk density, gravel content, clay content and mineralogy, and other soil properties are needed to reduce their interference with the spectra. Accurate estimation of soil C using the different IRS methods requires site-specific calibration of the methods.

19.8.2 Laser-Induced Breakdown Spectroscopy (LIBS) This method is based on atomic emission spectroscopy and consists of focusing a laser pulse on a small intact soil core, collecting light emitted by the sample in a spectrograph and detector, and relating the light intensity to the total C measured using conventional techniques. This method is still under development, but it shows promise to detect C concentration within 300 mg of error with an accuracy of 3–14% (Cremers et al. 2001; Nayak et al. 2019). It is rapid because it provides a reading in Summer > Fall > Winter. The C emissions are measured using open and closed chamber methods based either on mass balance or gas diffusion theory. Automated sensors are becoming popular for rapid in situ measurement of C emissions. Automated gas chambers such as the LICOR 8100A equipped with a CO2 detector can allow measurement of CO2 on a continuous basis or at pre-defined time intervals (Fig. 19.10). Data collected with the automated gas chambers can be used to compute daily, seasonal, annual, and cumulative CO2 fluxes. The closed chamber method is the simplest and most commonly used technique and consists in measuring the continuously accumulating C emissions from the soil inside a static or non-static chamber (Fig. 19.11). A closed chamber consists of a bottom chamber and a lid where the bottom portion is inserted into the soil. The chamber covered with the lid allows the accumulation of gas inside the chamber during sample collection over a specific period of time (e.g., 0–20, 20–40, 40–60 min). The daily flux of C in g m-2 day-1 is computed as

19.10

Modeling Soil Carbon Dynamics

493

Fig. 19.11 The closed chamber method consists of a gas sampling chamber made of PVC with a bottom section (30 cm long × 15 cm diameter) inserted into the ground, and a lid equipped with a gas sampling port (Photo by H. Blanco). Air samples withdrawn from the chamber are stored in evacuated vials for the soil gas (e.g., CO2, CH4) analyses

Flux =

ΔC Δt

V k A

ð19:3Þ

-3 where ΔC min-1), V is Δt is the rate of gas accumulation inside the chamber (g cm 3 chamber volume (cm ), A is chamber area including the bottom and headspace (m2), and k is time conversion factor (Jacinthe et al. 2002).

19.10 Modeling Soil Carbon Dynamics Measurement of changes in C pools for each soil is expensive. Modeling is a useful approach for estimating the impacts of soil management on soil C dynamics. Carbon models can estimate gains in C storage under various management scenarios. Some of the soil C models include the Daily Time-Step version of CENTURY (DAYCENT), Rothamsted Carbon (RothC), DeNitrification-DeComposition (DNDC), Environmental Policy Integrated Climate (EPIC), Carbon Sequestration (CQESTR), and Ecosystem (ECOSYS). The DAYCENT, RothC, and DNDC are the most widely used C models (Sulman et al. 2018). Some of these models such as DAYCENT and DNDC can also predict greenhouse gas fluxes and N cycling. The ability of models to simulate C dynamics is a function of how well the input parameters reflect the soil management. Some of the input data required for C models include climate (rainfall, potential evapotranspiration, air temperature), soil texture (clay content), decomposition rate of plant material, soil surface condition (bare or covered with residues or vegetation), crop residue input, and application of organic amendments. Soil C models simulate C cycling, turnover of soil organic C,

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and total C accumulation. Properties of soils should be measured over time and space for a detailed modeling of C storage and fluxes in no-till soils as soil processes and properties change with time within and among soils. The C distribution in soils due to tillage erosion can also be modeled. The SPEROS-C is one of the models to estimate the effect of tillage erosion on C distribution over a hillslope (Quijano et al. 2017). This model simulates lateral and vertical translocations of C with soil. Pedotransfer functions (PTFs) and principal component analysis (PCA) are useful tools for studying site-specific relationships between C concentrations and other soil properties. Data on soil properties from long-term experiments are potential input parameters for process-based models and PTFs to predict the ability of improved management practices to enhance C concentration and stocks. The ecosystem C budget can be modeled on local, regional, and global scales. Also, the C budgets developed at smaller or local scales for trading C credits can be eventually applied to regional and global scales. Carbon budget models have been used for estimating annual C fluxes at different scales. In the US Midwest, using seven cropland eddy-covariance sites across 293 counties in Illinois, Indiana, and Iowa, Zhou et al. (2021) simulated C fluxes, net ecosystem carbon exchange, ecosystem gross primary production, ecosystem respiration, leaf area index, and dynamic plant C allocation processes, and then estimated C budget for croplands on a regional scale with the ECOSYST model. The ecosystem C budget should be estimated based on aboveground biomass (e.g., land cover type, detritus material, canopy cover, crop residues) and belowground biomass (e.g., root biomass, root respiration), crop yields, rates of decomposition of organic matter, and measured C fluxes.

19.11 Soil Management and Carbon Credits Increase in soil organic C stocks through the use of innovative soil management practices not only improves soil ecosystem services but is also a tradable commodity and has an economic value. Farmers adopting improved soil management practices can market the generated C units to industries or companies that are currently emitting C. Thus, trading C credits through C sequestration in the soil can provide additional income to farmers. Using no-till combined with residue mulching, intensifying cropping systems, growing permanent vegetation, and other strategies that increase aboveground and belowground biomass input into the soil can sequester C and create opportunities for C trading. Practices that remove atmospheric C via photosynthesis, reduce rapid C mineralization, reduce losses of soil C (e.g., C emissions, erosion), and sequester C in the soil can be potential biological practices. The trading system and price for C credits are still developing, but regional pilot programs to market C have emerged (Oldfield et al. 2022). It is expected that trading C credits across the globe will become important once price regulations and trading policies are further refined. For example, a C-market pilot program in Australia

19.12

Summary

495

found adoption of improved soil management practices for 5 yr led to increased C sequestration across 10 farms which were contracted in C trading (Badgery et al. 2021). The management practices that contracted in the pilot program were: 1) reduced tillage cropping (control); 2) reduced tillage cropping with organic amendments (e.g., biosolids or compost); 3) conversion from cropping land to permanent pasture; and 4) conversion from cropping land to permanent pasture with organic amendments. Soils under pasture had greater C stocks (1.2 vs. 0.28 Mg ha-1 yr-1) than those under reduced tillage cropping, while soils with organic amendments had greater C stocks than those without amendments (1.14 vs 0.78 Mg ha-1 yr-1) in the 0–30 cm depth. This case study shows identification and adoption of proper soil management practices are critical if C sequestration is a goal. It will be important to monitor the amount of C sequestered with time (years or decades) after management adoption. For example, rates of soil C sequestration can be larger in the short term than in the longer term as soil becomes saturated with C over time. Also, soils with initially low soil C concentration can offer more opportunities for soil C sequestration than high C soils. Collection of an appropriate number of soil samples, whole soil-profile sampling, determination of soil bulk density to compute data on equivalent soil mass, and use of reliable C measurement methods before and after imposition of soil management practices which are contracted in a C trading program are key for an accurate inventory of soil C gains and losses. Furthermore, modeling soil C dynamics and stocks can be a tool to determine whether a system is losing or gaining C after croplands are enrolled in C trading programs. Furthermore, payments for soil C sequestration can be particularly prudent if the C accumulated via improved soil management practices such as no-till and cover crops is really sequestered or permanent, especially when these practices appear to accumulate C only near the soil surface. Assessment and monitoring of C permanence or stability after the adoption of management practices are critical to discern the amount of C sequestered, which is important for the development of C credit trading systems.

19.12 Summary

Soil organic C is an essential component of the terrestrial C pool. More C is stored in the soil than in the terrestrial biomass or the atmosphere. Intensive tillage and limited crop residue input can deplete the soil organic C concentration and increase the atmospheric C concentration. Soil erosion by water, wind, and tillage is one of the pathways of C loss. Soil aggregate disintegration and dispersion, preferential removal of C, redistribution of eroded C, and (continued)

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mineralization of eroded C are some of the mechanisms by which soil C is lost. The eroded C consists mostly of labile organic fractions which are thus prone to rapid mineralization. While some of the eroded C is buried in depositional areas and protected from rapid decomposition, some of the eroded C is lost as C emissions during transit. The fate of eroded C is complex, but accelerated soil erosion is most likely a source rather than sink of C. Soil C is central to the delivery of soil ecosystem services. Soil organic C not only reduces soil erodibility but also maintains crop production, filters and adsorbs point- and non-point-source pollutants, and provides other essential services. Thus, soil C lost through anthropogenic activities should be brought back to where it belongs (soil). No-till farming combined with cover crops, intensified crop rotations, perennials, organic amendments (e.g., animal manure, biochar), and other practices can be a strategy to promote C storage in degraded soils. No-till systems with a limited amount of aboveground and belowground biomass input can have limited potential to restore the soil C lost. Under current no-till systems, increases in soil C stocks are mostly confined to the upper 10 or 20 cm of the soil profile due to surface crop residue mulching. The total C stock between no-till and tilled systems for the whole soil profile does not often differ. The existing no-till systems were not specifically designed to restore soil C. If sequestering soil C with no-till is a goal, then current no-till systems need enhancement. The gains in soil C with the enhanced C management systems can be tradable. The stored C has an economic value. The more C is stored in the soil, the greater the opportunities for trading C units. The C trading system is developing and it is expected to become relevant to conserve soil and restore and manage C in the near future. New methods are emerging for rapid measurement of soil organic C concentration under field (in situ) conditions based on atomic emission spectroscopy, infrared reflectance spectroscopy, remote sensing, and ecosystem C budgeting. The field methods are being refined in their resolution to accurately estimate changes in C concentration. Sensitive methods are much needed particularly to detect small changes in soil C concentration under field conditions. Modeling is a useful companion to direct C measurement techniques to estimate soil C storage and extrapolate information across a large geographic spectrum under different soil management scenarios and climates. Questions 1. Explain in detail the mechanisms by which soil organic C reduces soil erosion. 2. Discuss the specific processes by which intensive tillage reduces soil organic C concentration.

References

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3. Explain differences in the mechanisms of C removal among water, wind, and tillage erosion. Provide estimates of the amount of C transported by each component. 4. Discuss the fate of C transported by erosion and provide quantitative estimates of the main pathways of fate. 5. Compare the new methods of C analyses with the conventional methods. 6. Discuss the mechanisms by which no-till farming would store more C in the soil. 7. A soil has a bulk density of 1.3 Mg m-3 and 2.5% of organic C concentration at a soil depth of 10 cm. Estimate the amount of C stored in Mg ha-1, Mg km-2, and g kg-1. How would one estimate the C pool on a volume basis if data on bulk density are unavailable.? 8. Calculate the C sequestration rate for a soil under alley cropping systems with 2-m wide hedgerows and 8-m wide alleys for an 80 m wide × 122 m long field. Soil bulk density is 1.45 Mg m-3 within alleys and 1.1 Mg m-3 within hedgerows, while C concentration is 25 g kg-1 within alleys and 36 g kg-1 within hedgerows. 9. Calculate the C sequestration rate for the same soil in the previous problem under silvopasture. Trees within silvopasture are established in four 8-m wide rows and 30-m apart. Soil bulk density is 0.90 Mg m-3 under the trees and 1.1 Mg m-3 under pasture, while C concentration is 65 g kg-1 under trees and 31 g kg-1 under pasture. 10. Concentrations of CO2 samples were determined using the 0.15 m diameter × 0.30 m high closed soil chamber technique at random points across a 100 × 200 m long field under forest farming. Calculate the emissions of CO2 in g ha-1 day-1 if the average concentration of CO2 in ppm was 350.

References Akala VA, Lal R (2001) Soil organic carbon pools and sequestration rates in reclaimed minesoils in Ohio. J Environ Qual 30:2098–2104 Assefa D, Rewald B, Sandén H, Rosinger C, Abiyu A, Yitaferu B, Godbold DL (2017) Deforestation and land use strongly effect soil organic carbon and nitrogen stock in Northwest Ethiopia. Catena 153:89–99 Badgery W, Murphy B, Cowie A, Orgill S, Rawson A, Simmons A, Crean J (2021) Soil carbon market-based instrument pilot – the sequestration of soil organic carbon for the purpose of obtaining carbon credits. Soil Res 59:12. https://doi.org/10.1071/SR19331 Baker JM, Ochsner TE, Venterea RT et al (2007) Tillage and soil carbon sequestration-what do we really know? Agric Ecosyst Environ 118:1–5 Blanco-Canqui H (2021) No-till technology has limited potential to store carbon: how can we enhance such potential? Agric Ecosyst Environ 313:107352 Blanco-Canqui H (2022) Cover crops and carbon sequestration: Lessons from US studies. Soil Sci Soc Am J 86:501–519 Blanco-Canqui H, Lal R (2007) Soil and crop response harvesting corn residues for biofuel production. Geoderma 141:355–362 Blanco-Canqui H, Lal R (2008) No-tillage and soil-profile carbon sequestration: An on-farm assessment. Soil Sci Soc Am J 72:693–701

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Blanco-Canqui H, Wortmann CW (2020) Does occasional tillage undo the ecosystem services gained with no-till? A review. Soil Tillage Res 198:104534 Blanco-Canqui H, Lal R, Owens LB et al (2005) Strength properties and organic carbon of soils in the North Appalachian Region. Soil Sci Soc Am J 69:663–673 Blanco-Canqui H, Mikha MM, Presley DR, Claassen MM (2011) Addition of cover crops enhances no-till potential for improving soil physical properties. Soil Sci Soc Am J 75:1471–1482 Blanco-Canqui H, Shapiro CA, Wortmann CS, Drijber RA, Mamo M, Shaver TM, Ferguson RB (2013) Soil organic carbon: the value to soil properties. J Soil Water Conserv 68:129A–134A Blanco-Canqui H, Ferguson RB, Shapiro CA, Drijber RA, Walters DT (2014) Does inorganic nitrogen fertilization improve soil aggregation? Insights from long-term tillage experiments. J Environ Qual 43:995–1003 Blanco-Canqui H, Hergert GW, Nielsen RA (2015) Cattle manure application reduces soil's susceptibility to compaction and increases water retention after 71 years. Soil Sci Soc Am J 79:212–223 Blanco-Canqui H, Francis CA, Galusha TD (2017) Does organic farming accumulate carbon in deeper soil profiles in the long term? Geoderma 288:213–221 Brunet D, Barthes BG, Chotte JL et al (2007) Determination of carbon and nitrogen contents in Alfisols, Oxisols and Ultisols from Africa and Brazil using NIRS analysis: effects of sample grinding and set heterogeneity. Geoderma 139:106–117 Campbell CA, Janzen HH, Paustian K, Gregorich EG, Sherrod L, Liang BC, Zentner RP (2005) Carbon storage in soils of the north American Great Plains: effect of cropping frequency. Agron J 97:349–363 Chappell A, Webb NP, Leys JF, Waters CM, Orgill S, Eyres MJ (2019) Minimising soil organic carbon erosion by wind is critical for land degradation neutrality. Environ Sci Pol 2019(93): 43–52 Cremers DA, Ebinger MH, Breshears DD et al (2001) Measuring total soil carbon with laserinduced breakdown spectroscopy (LIBS). J Environ Qual 30:2202–2206 Dang YP, Balzer A, Crawford M, Rincon-Florez V, Liu H, Melland AR, Antille D, Kodur S, Bell MJ, Whish JPM, Lai Y, Seymour N, Costa Carvalhais L, Schenk P (2018) Strategic tillage in conservation agricultural systems of North-Eastern Australia: why, where, when and how? Environ Sci Pollut R 25:1000–1015 de Nijs EA, Cammeraat ELH (2020) The stability and fate of soil organic carbon during the transport phase of soil erosion. Earth Sci Rev 201. https://doi.org/10.1016/j.earscirev.2019. 103067 De Stefano A, Jacobson MG (2018) Soil carbon sequestration in agroforestry systems: a metaanalysis. Agrofor Syst 92:285–299 El-Naggar A, Lee SS, Rinklebe J, Farooq M, Song H, Sarmah AK, Zimmerman AR, Ahmad M, Shaheen SM, Ok YS (2019) Application of biochar to low fertility soils: a review of current status, and future prospects. Geoderma 337:536–554 Feng Q, An C, Chen Z, Wang Z (2020) Can deep tillage enhance carbon sequestration in soils? A meta-analysis towards GHG mitigation and sustainable agricultural management. Renew Sust Energ Rev 133:110293 Florence AM, McGuire AM (2020) Do diverse cover crop mixtures perform better than monocultures? A systematic review. Agron J 112:3513–3534 Fu X, Wang J, Sainju UM, Liu W (2017) Soil carbon fractions in response to long-term crop rotations in the loess plateau of China. Soil Sci Soc Am J 81:503–513 Gattinger A, Muller A, Haeni M, Skinner C, Fliessbach A, Buchmann N, Mader P, Stolze M, Smith P, Scialabba NE-H, Niggli U (2012) Enhanced top soil carbon stocks under organic farming. Proc Natl Acad Sci 109:18226–18231 Gehl RJ, Rice CW (2007) Emerging technologies for in situ measurement of soil carbon. Clim Chang 80:43–54

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Govaerts B, Verhulst N, Castellanos-Navarrete A, Sayre KD, Dixon J, Dendooven L (2009) Conservation agriculture and soil carbon sequestration; between myth and farmer reality. Crit Rev Plant Sci 28:97–122 Haddaway NR, Kedlund K, Jackson LE, Kätterer T, Lugato E, Thomsen IK, Jørgensen HB, Isberg P-E (2017) How does tillage intensity affect soil organic carbon? A systematic review. Environ Evid 6:30 Halde C, Gagné S, Charles A, Lawley Y (2017) Organic no-till systems in eastern Canada: a review. Agriculture 7:36 Hübner R, Kühnel A, Lu J, Dettmann H, Wang W, Wiesmeier M (2021) Soil carbon sequestration by agroforestry systems in China: a meta-analysis. Agric Ecosyst Environ 315:107437 Jacinthe PA, Lal R, Kimble JM (2002) Carbon budget and seasonal carbon dioxide emission from a central Ohio Luvisol as influenced by wheat residue amendment. Soil Tillage Res 67:147–157 Lal R (2004) Soil carbon sequestration impacts on global climate change and food security. Science 304:1623–1627 Lal R (2022) Fate of soil carbon transported by erosional processes. Appl Sci 12:48 Lehmann J, Joseph S (2015) Biochar for environmental management: science, technology and implementation. Sci. Technol, Biochar for Environmental Management. https://doi.org/10. 4324/9780203762264 Lemus R, Lal R (2005) Bioenergy crops and carbon sequestration. Crit Rev Plant Sci 24:1–21 Liu S, Zhang Y, Zong Y, Hu Z, Wu S, Zhou J, Jin Y, Zou J (2016) Response of soil carbon dioxide fluxes, soil organic carbon and microbial biomass carbon to biochar amendment: a metaanalysis. GCB Bioenergy 8:392–406 Luo ZK, Wang EL, Sun OJ (2010) Can no-tillage stimulate carbon sequestration in agricultural soils? A meta-analysis of paired experiments. Agric Ecosyt Environ 139:1–2 McClelland SC, Paustian K, Schipanksi ME (2021) Management of cover crops in temperate climates influences soil organic carbon stocks - a meta-analysis. Ecol Appl 31:e02278 Montagnini F, Nair PKR (2004) Carbon sequestration: An underexploited environmental benefit of agroforestry systems. Agrofor Syst 61:281–295 Nayak AK, Rahman MM, Naidu R, Dhal B, Swain CK, Nayak AD, Tripathi R, Shahid M, Islam MR, Pathak H (2019) Current and emerging methodologies for estimating carbon sequestration in agricultural soils: a review. Sci Total Environ 665:890–912 Nie X, Zhang H, Su Y (2019) Soil carbon and nitrogen fraction dynamics affected by tillage erosion. Sci Rep 9:16601 Novara A, Sarno M, Gristina L (2021) No till soil organic carbon sequestration could be overestimated when slope effect is not considered. Sci Total Environ 757:143758 Oldfield EE, Eagle AJ, Rubin RL et al (2022) Crediting agricultural soil carbon sequestration. Science 375(6586):1222–1225 Poeplau C, Don A (2015) Carbon sequestration in agricultural soils via cultivation of cover crops – a meta-analysis. Agric Ecosyst Environ 220:33–41 Powlson DS, Stirling CM, Jat ML, Gerard BG, Palm CA, Sanchez PA, Cassman KG (2014) Limited potential of no-till agriculture for climate change mitigation. Nat Clim Chang 4:678– 683 Quijano L, Van Oost K, Nadeu E, Gaspar L, Navas A (2017) Modelling the effect of land management changes on soil organic carbon stocks in a Mediterranean cultivated field. Land Degrad Dev 28:515–523 Reicosky DC, Archer DW (2007) Moldboard plow tillage depth and short-term carbon dioxide release. Soil Tillage Res 94:109–121 Ruis SJ, Blanco-Canqui H, Jasa P, Jin VL (2022) No-till farming and greenhouse gas fluxes: insights from literature and experimental data. Soil Tillage Res 220:105359 Sapkota Y, White J (2019) Marsh edge erosion and associated carbon dynamics in coastal Louisiana; a proxy for future wetland- dominated coastline world-wide. Estuar Coast Shelf Sci 226:106289

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Sherrod LA, Peterson GA, Westfall DG, Ahuja LR (2003) Cropping intensity enhances soil organic carbon and nitrogen in a no-till agroecosystem. Soil Sci Soc Am J 67:1533–1543 Shrestha RK, Lal R (2006) Ecosystem carbon budgeting and soil carbon sequestration in reclaimed mine soil. Environ Int 32:781–796 Smith WN, Grant BB, Campbell CA, McConkey BG, Desjardins RL, Kröbel R, Malhi SS (2012) Crop residue removal effects on soil carbon: measured and inter-model comparisons. Agric Ecosyst Environ 161:27–38 Sulman BN, Moore JAM, Abramoff R et al (2018) Multiple models and experiments underscore large uncertainty in soil carbon dynamics. Biogeochemistry 141:109–123 Van Oost K, Govers G, Quine TA, Heckrath G, Olesen JE, De Gryze S, Merckx R (2005) Landscape-scale modeling of carbon cycling under the impact of soil redistribution: the role of tillage erosion. Glob Biogeochem Cycles 19:1733–1739 Van Oost K, Quine TA, Govers et al (2007) The impact of agricultural soil erosion on the global carbon cycle. Science 318:626–629 West TO, Post WM (2002) Soil organic carbon sequestration rates by tillage and crop rotation: a global data analysis. Soil Sci Soc Am J 66:1930–1946 Wielopolski L, Chatterjee A, Mitra S, Lal R (2011) In situ determination of soil carbon pool by inelastic neutron scattering: comparison with dry combustion. Geoderma 160:394–399 Yakubova G, Kavetskiy A, Prior SA, Torbert HA (2017) Applying Monte-Carlo simulations to optimize an inelastic neutron scattering system for soil carbon analysis. Appl Radiat Isot 128: 237–248 Zhao P, Li S, Wang E, Chen X, Deng J, Zhao Y (2018) Tillage erosion and its effect on spatial variations of soil organic carbon in the black soil region of China. Soil Tillage Res 178:72–81 Zhou W, Guan K, Peng B, Tang J, Jin Z, Jiang C, Grant R, Mezbahuddin S (2021) Quantifying carbon budget, crop yields and their responses to environmental variability using the ecosys model for U.S. midwestern agroecosystems. Agric For Meteorol 307:108521

One Health

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Soil Health

Soil is a living, dynamic, complex, and three-dimensional media that supports life. It is a vibrant living entity that not only produces food, feed, fuel, and fiber but absorbs, retains, filters, and purifies water, moderates water, heat, and gas fluxes, and promotes C and nutrient cycling, among many other services. As soil is continuously and dynamically changing, so is its potential to provide services. Rapid changes in water, heat, and gas fluxes and organic matter decomposition within the soil are examples of the dynamic nature of soil. The increased recognition of the soil as an essential system that supports plants, animals, humans, and overall ecosystem functioning resulted in the emergence of conceptual paradigms in the early 1970s known as soil quality (Mausel 1971) and in the late 1990s known as soil health (Doran et al. 1996). Soil quality refers to the “capacity of a soil to function within ecosystem boundaries to sustain biological productivity, maintain environmental quality, and promote plant and animal health” (Glossary of Science Terms 2008), while soil health is the “continued capacity of the soil to function as a living system that sustains plants, animals, and humans” (Doran et al. 1996). The soil quality concept is a precursor of the soil health concept. Soil health is a broader term than the soil quality concept. While some use both soil quality and soil health concepts interchangeably, differences exist. Soil quality is considered similar to water quality and air quality. It is the intrinsic ability of the soil to perform a specific task or function. Soil quality term does not specifically consider soil as a living entity and, as defined, it may be analogous to the quality of an inactive material (e.g., quality of a piece of metal). However, soil health considers soil as a vibrant and living system designed to deliver multiple services to society known as soil ecosystem services (provisioning, regulating, supporting, cultural, and recreation; Fig. 20.1). As discussed earlier in the book, some of the specific soil services include:

# The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 H. Blanco, R. Lal, Soil Conservation and Management, https://doi.org/10.1007/978-3-031-30341-8_20

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SOIL HEALTH

The intrinsic capacity of the soil to function

The actual or continued capacity of the soil to function as a living system

One Health

SOIL ECOSYSTEM SERVICES

The multiple agronomic, environmental, economic, and social services that soils provide

Fig. 20.1 Interconnectedness of soil quality and health with soil ecosystem services

• • • • • • •

Agronomic productivity Storage and sequestration of C Nutrient recycling Storage and purification of water and air Energy exchange Wildlife habitat and biodiversity Reduction and moderation of greenhouse gas fluxes

20.2

Soil Health Paradigm

The concept of soil health stemmed from an innovative perspective that attempts to define how a soil functions and what practices can be used to halt soil degradation and restore, maintain, improve, and enhance the potential of the soil to continue delivering services (Fig. 20.1; Bonfante et al. 2020). The concept of soil health merges traditional concepts of soil taxonomy or soil science with soil ecosystem services to address growing concerns about the depletion of natural resources, nonpoint source pollution, and climatic fluctuations, among many others. Present and future needs of food production and environmental protection depend on how healthy the soil is and how it responds to external and internal stresses (e.g., climatic fluctuations) as a living entity. Introduction of the soil health concept represents an innovative paradigm in soil science with broad implications. The evolving concept of soil health complements soil science research and makes the traditional concepts of soil management more practical. Soil health is a potential educational tool for soil conservationists, extension specialists, land managers, farmers, and policymakers to better manage soil resources. Emergence of the soil health concept is particularly important in a time when soil degradation, soil C depletion, non-point source pollution, and decreased biodiversity are among major global concerns. The modern term “soil health,” which was introduced first for soils in temperate zones (Doran et al. 1996; Lehmann et al. 2020), has practical global implications, especially in regions where deforestation, food insecurity, poverty, and soil degradation are main concerns (Lal et al. 2021). Unlike in temperate zones where non-point source pollution is one of the main

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environmental problems, in tropical regions, such as is the case in Africa, an acute problem is nutrient depletion which in conjunction with soil degradation threatens agricultural production and biodiversity. Soil health attempts to integrate inherent and dynamic soil properties as influenced by management based on threshold values of soil properties. Using this approach, data on soil properties can be converted into simple but useful indexes based on the present knowledge and experience to better assess soil performance than traditional approaches. It is an emerging management tool that can elucidate how a specific practice influences soil behavior or how the soil responds to management over time. The soil health concept could change the way soil is managed provided that appropriate soil health indexes are further developed based on sound scientific principles. Emphasis on soil health can help in evaluating early signs of soil degradation as well as designing measures of restoration. The basic understanding of soil properties and processes through practical and theoretical indexes can be a new approach to better manage soil resources.

20.3

One Health

The soil health concept is now linked with the “One Health” concept, which considers that soil health is interdisciplinary and intrinsically connected with plant, animal, human, and overall ecosystem health (Fig. 20.2; Keith et al. 2016; Lehmann et al. 2020). This concept underscores that a decline in the health of soil can directly

Soil Health

Ecosystem Health

Plant Health ONE HEALTH

Human Health

Animal Health

Fig. 20.2 Interconnectedness among soil, plant, animal, human, and ecosystem health converge into One Health

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impact the health of other entities (e.g., plants, animals, humans). Linkages and interconnectedness among soil, human, animal, plant, and ecosystem health are increasingly being recognized, yet are still underestimated (Lal et al. 2021). An unhealthy soil such as acidic, contaminated, or low organic matter soil may not support an optimum production of crops and forages, which can adversely affect the health of animals and humans. Soil health within the One Health concept encompasses the multi-functionality of soil to meet the increasing demands from a growing world population. It refers to the need to maintain the long-term sustainability of the soil not only for food, fuel, fiber, and feed production but also the overall health of the planet.

20.3.1 Plant Heath Soil health and plant health are mutually interrelated (Lal et al. 2021). A healthy soil recycles water and nutrients and supports plant production. In turn, abundant plant production maintains or improves the health of soils via aboveground and belowground biomass input. Managing soil health goes beyond adding the right amount of fertilizers, irrigation water, and other external inputs for plant production. It is about restoring, maintaining, and improving the capacity of a living system (soil) to store, recycle, and supply essential nutrients and water to plants. Intensive tillage, reduced crop residue input, and other short-sighted anthropogenic activities have reduced soil organic matter concentration and rooting depth (e.g., plow pan), and adversely affected other essential soil properties critical to crop and biomass production. Restoring and improving soil physical, biological, and chemical properties by adopting practices that increase soil organic matter are strategies to maintain and improve the health of soils for continued plant production.

20.3.2 Animal Health Soil health is obviously critical to animal health through plant production. A healthy soil results in healthy plants and thus healthy animals (Lehmann et al. 2020). Animal health can differ among pastures due to differences in forage quality and quantity (Takahashi et al. 2018). Degraded or low-fertility soils often produce sparse vegetation and low quantities of biomass, adversely affecting animal production and health. Healthy soils promote healthy grasslands, rangelands, and croplands for the production of pastures, crop residues, and cover crops for livestock production. Livestock management can also affect soil health. For example, overgrazing can negatively impact soil health by compacting soil, reducing soil organic matter concentration, and degrading other soil properties. Overgrazing not only affects soil health but also overall animal health in the long term by reducing plant productivity. Grazing at recommended stocking rates can maintain soil health and thus plant health. A study in the UK showed that a systematic interaction exists among soil health, livestock grazing, and environment in which increased soil

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organic matter stock equates to increased animal performance and reduced nutrient losses (Takahashi et al. 2018). Well-managed livestock production systems can maintain or improve soil health by adding organic matter as manure, which can enhance soil biological activity and nutrient cycling. Also, soil animals such as earthworms can also promote soil health by burrowing and creating macropores for improved water, heat, and gas fluxes, and promoting C and nutrient cycling. Managing soil, plant, and animal health as one entity within the concept of One Health is needed to ensure agricultural sustainability and planetary health.

20.3.3 Human Health Human health depends on the quality or nutritional value of food crops and animal products, which, in turn, depends on the health of soils. Healthy soils with high soil organic matter concentration can produce crops with high nutritional value (Lehmann et al. 2020). Also, soils with high biodiversity can promote nutrient cycling and nutrient availability for plant production. How soil affects human health depends on the management of soils. While healthy soils can benefit the well-being and health of humans, degraded soils can have negative impacts on human health (Lal et al. 2021). For instance, soils that contain pollutants including pesticides, heavy metals, pathogens, and others can pose a threat to human health. Plant roots can adsorb contaminants from polluted soils, which accumulates in grains, forage, and other edible plant portions. Further, excessive use of fertilizers and pesticides for crop production can lead to losses of chemicals and non-point source pollution of water sources, which directly affects the quality of drinking water. Appropriate nutrient and pesticide management for crop production is critical to reduce losses of chemicals and reduce any harmful off-site effects. The use of cover crops and conservation buffers can be some of the measures to improve the capacity of the soil to reduce nutrient runoff and leaching and maintain water quality for animal and human consumption.

20.3.4 Ecosystem Health Ecosystem health refers to the capacity of an ecosystem to deliver all essential ecosystem services. It is a broad concept that reflects the intrinsic connection among soils, plants, animals, humans, and environment (Keith et al. 2016). Ecosystem health thus directly depends on the health of soils. Specifically, soils contribute to ecosystem health by filtering water, reducing water and air pollution, sequestering C, recycling nutrients, supporting plant production, promoting biodiversity, and providing other services. Soils can also contribute to ecosystem adaptation to fluctuating climates including droughts, heat waves, floods, and other extremes. Proper management of soil can improve or enhance the resilience of

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ecosystems to extreme events. Managing ecosystem health is about managing soil health. For example, adding large amounts of animal manure and inorganic fertilizers to provide nutrients for crop production can increase risks of non-point source pollution of water. Managing soil health in a way that balances the delivery of all ecosystem services is increasingly important.

20.4

Conceptual Definition and Assessment Approaches

Conceptual definition of soil health is still in its infancy. Some may question the concept of soil health due to the challenges of defining soil health, unlike human health which has well-established parameters for assessment (Lehmann et al. 2020). Soil health is not directly quantifiable, which makes the concept somewhat elusive with no clear goal of judgment. Unlike pure substances such as water and air, a soil is a complex three-phase system because it consists of a mixture of water, air, and organic and inorganic materials in addition to living organisms. Theoretical concepts and assessment techniques of soil health need to be further refined. At this point, the definition of soil health varies depending on the views and the background of individuals. Some may associate soil health with crop productivity, similar to soil quality, which is the capacity of a soil to produce a plant or sequence of plants under a given management system. Soil health has greater connotation than soil quality and is associated with ecosystem health, sustainability, and productivity, among others. Soil health refers to the capacity of a soil to buffer anthropogenic perturbations, maintain productivity, degrade pollutants, protect watersheds, and improve water and air quality. This is certainly a complex and multifunctional concept. Soils are complex systems due to their heterogeneity, site-specificity, and ecosystem services they provide. A healthy soil not only produces high-quality crops and forages but also protects the environment. These contrasting but simultaneous functions of soil make the development of standard indicators difficult. The complexity associated with soil health concept is, however, an opportunity for soil health research and development of robust assessment approaches. Standards and guidelines for a rigorous scientific evaluation of soil health are under development. Quantitative standards, threshold values of soil properties, and practical guidelines of soil health evaluation need to be developed and tested across a wide range of soils and management conditions. The use of some of the soil health assessment approaches, which are simplistic (e.g., scoreboard approach), subjective (e.g., interviewee bias), and reductionist (e.g., few soil properties) should be avoided. Simplistic approaches could undermine the scientific method of the discipline of soil science as some argued in the past (Sojka and Upchurch 1999). Some of the current scoring functions of soil health indicators emphasize only on positive weights and not negative impacts. For example, earthworm population can be weighted positively for a healthy soil in regards to improved nutrient cycling, macroporosity, water infiltration, and drainage while disregarding that preferential or

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by-pass flow of chemicals through earthworm burrows, which can lead to groundwater pollution in soils with abundant earthworms (Yu et al. 2019). The indicators of soil health need to be tested against scientific soundness, applicability across a range of soil ecosystems and management objectives, and reliability (Bremer and Ellert 2004; Lehmann et al. 2020). Indicators should be relatively simple to be understood by users, yet complex enough to account for all the interactive factors defining soil services. A relevant indicator of soil health is the one that soil scientists can quantify but farmers can also relate to production and land stewardship and potentially assess such indicator by using standard approaches. To make the soil health more adaptable to a wide range of management and soil systems across the world, additional soil health research accompanied by standard tools and methods is necessary.

20.5

Indicators of Soil Health

Because soil health cannot be measured directly, it is estimated from “indicators” that affect one or more simultaneous functions. A soil health indicator is a measurable soil property, which influences the capacity of a soil to function as a living entity for a specific purpose (Lal et al. 2021). Thus, soil health evaluation relies on the measurement of soil physical, chemical, and biological properties. A full understanding of changes in soil health requires a comprehensive assessment of all soil properties. Measuring only select soil properties can provide an incomplete story. Also, selecting only the more easily measurable soil properties and less expensive measurements may introduce biases to soil health assessment. Challenges exist with the assessment of soil health based on the soil physical, chemical, and biological properties. Soil properties are measurable but are site- and purpose-specific. Also, most soil properties vary over time and space. For example, some soil properties may not be sensitive to change in land use and management in the short term. Further, these indicators are not independent but strongly interrelated. Thus, the dynamic nature of most soil properties requires a detailed monitoring of the indicators for different objectives. Emphasis is often placed on the selection of minimum data sets of soil properties (indicators) for soil health assessment. Emphasizing only on a few indicators can be, however, shortsighted as it is analogous to simply performing only a few laboratory tests to diagnose a potentially serious illness in a person. If soil health is considered analogous to human health, then an in-depth or “full panel” exam is required. Further, such exam should be performed not only once but on a regular basis (e.g., after a crop rotation cycle). Rapid tests of soil health in agricultural lands have mainly focused on changes in soil fertility levels. Expanded methods integrating information on all soil properties can refine our understanding of soil health changes.

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20.5.1 Soil Physical Health Changes in soil profile characteristics and soil structural, hydraulic, and thermal properties are indicators of changes in soil physical health (Table 20.1). For example, a change in soil depth due to erosion is a major indicator of soil health as it affects nutrient and water storage and crop production. Changes in soil strength (e.g., crusting, cracking, cone index, bulk density) parameters indicate the degree of soil compactness. An increase in soil compaction can reduce water infiltration, increase runoff risks, and restrict root development. Likewise, changes in soil aggregate size, strength, and stability are important determinants of soil structural health and the ability of soil to resist erosional processes. Aggregate stability, for example, portrays the soil response to detachment under raindrop and runoff forces. It also determines macroporosity and microporosity critical for water, air, and heat flow within the soil. Information on soil hydraulic properties including water movement and retention is critical to evaluate the partitioning of rainwater into runoff and infiltration, drainage, leaching of solutes, and groundwater recharge. Soil health changes over time and hardly remains static as soil physical and other properties change with time. Periodic monitoring of dynamic soil physical properties is important to determining the change in soil health over time. Some of the dynamic physical properties include crust depth, cracking properties (depth, width), bulk density, wet aggregate stability, pore-size distribution, field water content, water infiltration, air-field porosity, and soil temperature.

20.5.2 Soil Chemical Health A number of soil chemical properties exist to evaluate changes in soil chemical health (Table 20.2). A change in soil organic matter concentration is a common indicator of soil chemical health because of the significant effect of organic matter on other soil properties. For instance, an increase in soil organic matter concentration Table. 20.1 Indicators of soil physical health Soil Profile Characteristics • Profile depth • Degree of erosion • Root zone depth • Horizonation • Sand, silt, and clay content • Clay mineralogy

Soil Structure • Crust depth • Extent of cracking • Cone index or penetration resistance • Shear strength • Bulk density • Wet aggregate stability • Dry aggregate stability • Pore-size distribution

Dynamics of Water, Air, and Heat Flux • Soil sorptivity • Water infiltration • Saturated hydraulic conductivity • Unsaturated hydraulic conductivity • Water content at field capacity (-0.1 to -0.33 bar) • Water content at field capacity (-15 bars) • Plant available water • Air permeability • Soil temperature and thermal conductivity

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Table 20.2 Indicators of soil chemical health Soil Chemical Characteristics • Soil organic matter concentration • Soil organic C concentration • Labile organic matter concentration (e.g., particulate organic matter) • Active C concentration • Macronutrient (e.g., N, P, K) and micronutrient concentrations • pH

• Electrical conductivity • Sodium adsorption ratio • Cation exchange capacity (Ca2+, Mg2+, K+, and Na+) • Base saturation • Toxicity (Al3+and Mn2+) • Concentration of heavy metals

can promote soil aggregation, which in turn, can promote soil macroporosity, and biological activity. Evaluation of different soil organic matter fractions is needed to better understand changes in organic matter and thus soil health. For example, it is considered that labile organic matter concentration such as particulate organic matter can change more rapidly than total organic matter concentration. Routine soil chemical analysis often focuses more on macronutrient and micronutrient concentrations and less on other chemical properties. An analysis of all chemical properties can provide an improved understanding to soil chemical health. Specifically, knowledge of concentration of heavy metals and toxic elements in degraded environments can be useful to evaluate potential adverse effects of soil properties on animal and human health. Also, soil pH, Na adsorption ratio, EC, and others are essential to evaluate soil acidity, salinity, and sodicity.

20.5.3 Soil Biological Health Traditionally, soil properties have been characterized in this order: Chemical properties > Physical properties > Biological properties. As result, current soil health characterization includes more chemical and physical properties than biological properties (Lehmann et al. 2020). Also, standard methods of analysis for chemical and physical properties are more developed than those for biological properties. Further, threshold levels or optimum ranges are better known for soil chemical properties (e.g., organic matter, nutrient concentrations, pH, CEC) than for biological properties. Suitable indicators of soil health and measurement methods for soil biological properties such as biomass, abundance, and diversity of microorganisms need refinement. Table 20.3 lists some biological properties as indicators of soil biological health. Abundance of soil macroorganisms and microorganisms is a key indicator of soil biological health. For example, presence of earthworms reflects a healthy soil. Earthworms ingest crop and process residues, release essential nutrients, and favor microbial processes, soil aggregation, and water and air movement through the soil profile. Changes in microbial population and activity due to shifts in management (e.g., no-till, residue return) are also vital indicators of soil health. The limited knowledge of the role of some biological properties in essential ecosystem services

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Table 20.3 Indicators of soil biological health Soil Biological Characteristics • Soil gas fluxes (e.g., CO2, N2O) • Macro-organisms (e.g., earthworms) • Micro-organisms (e.g., nematodes, protozoa) • Soil protein • Microbial biomass • Microbial biomass C and N • Soil enzymes (e.g., β-glucosidase, phosphomonoesterase, arylsulfatase)

• Soil phospholipid fatty acid (PLFA) profile • Soil fatty acid methyl ester (FAME) profile • Soil microbial genomics • Soil microbial community structure • Soil microbial DNA extraction and sequencing • Pathogens and parasites

such as crop production and water quality makes appreciation of soil biological properties difficult. The high cost of analysis of some biological properties can also limit the characterization of soil biological properties. Integration of biological properties into the potential indicators of soil health is further needed.

20.5.4 Factors and Soil Property Interactions A comprehensive assessment of soil health requires an integrated approach by accounting for microscale (e.g., management) and macroscale (e.g., climate) factors. Soil health is affected by management in interaction with soil type, topography, vegetation, and climate (Nayak et al. 2019; Diaz-Gonzalez et al. 2022). Inherent differences in soil forming factors and anthropogenic interventions determine differences in soil health. Indeed, soil health is the product of an integrated influence of intrinsic and extrinsic factors. It cannot be fully determined unless all major factors that affect soil formation and land attributes are considered. As the soil series and individual soils differ within and among fields, watersheds, and regional levels, so does soil health among soil types and landscape units. External attributes of the landscape (e.g., soil slope, surface geomorphology) are closely related to internal soil attributes (e.g., chemical properties) which influence soil health. For example, changes in soil slope and alterations in landforms due to removal and deposition of soil caused by soil erosion are the dynamic indicators of soil health. Also, soil health characterization warrants the assessment of all macroscale (i.e., properties of the bulk soil) and microscale (e.g., soil aggregate properties) soil attributes. For example, in well-aggregated soils, properties of discrete aggregates can be more responsive to management than those of the bulk soil and are perhaps better indicators of soil health. Integration of macroscale and microscale soil properties is needed to better understand changes in soil health. The soil physical, chemical, and biological indicators are interdependent and interact to determine the health of a soil. For example, soil structural properties are significantly correlated with organic matter concentration. Thus, soil health indexing should emerge from a unique balance and interaction of all soil properties and processes. Indeed, correlated soil properties do not respond independently to

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management change but in interaction with other properties. Single soil properties used as indicators do not account for the many dynamic interacting factors and processes. Multiple soil series within local and regional scales and high variability in soil properties even within a single soil series hinder the selection of a unique set of soil health indicators.

20.5.5 Crop Yield Crop yield is probably the most sensitive indicator of soil health (Bonfante et al. 2020). Crop yield is an integrator of soil physical, chemical, and biological properties. Degraded soils have low fertility and productivity and thus low crop yields. It is important to note that while an improvement in soil properties may not directly increase crop yields, soil properties can indirectly affect crop yields. Also, while an improvement in soil properties may not always increase crop yields, it can contribute to sustained crop production and other essential soil ecosystem services. For example, increased soil aggregate stability can indirectly contribute to crop production by reducing soil erosion risks and reducing losses of soil organic matter and nutrients with sediment. In turn, an increase in plant available water can directly affect crop establishment and yields. Differences in crop yields within the same field such as among summit, backslope, and footslope positions can be due to differences in soil properties.

20.5.6 Selection of Soil Properties Establishing a minimum data set representing the total data set is needed a specific function of soil is sought. The selection of soil properties of interest depends on the goal or ecosystem service (Lehmann et al. 2020). Focusing only on a minimum data set can also reduce costs and redundancy of soil property measurements. However, even when selecting a few soil properties for a specific purpose, the interrelationship among soil properties and complexity of the system should be considered. Some of the select soil properties that need to be included when assessing a specific function of soil are suggested in Table 20.4.

20.6

Soil Health Index

A number of indexes of soil health have been developed. Among such indexes include farmer-based approaches, soil health card, Solvita tests, Haney test, Soil Management Assessment Framework (SMAF), comprehensive assessment of soil health (CASH), Soil Health Assessment Protocol and Evaluation (SHAPE), and Soil Health Calculator (USDA-ARS 2019). All these indexes need further refinement and validation based on scientific evidence and field experiments. A universal and quantitative soil health index is lacking at this point. No index has yet transformed

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Table 20.4 Suggested soil properties to assess the health of soils for some soil ecosystem services Ecosystem Service Soil C storage

Water quality

Water quantity

Crop production

Human and animal health

Soil Properties for the Minimum Dataset • Particle-size distribution • Depth • Bulk density • CO2 and CH4 fluxes • Water content • Temperature • Air-filled porosity • Total soil organic C concentration • Labile organic C concentration • Particle-size distribution • Nutrient concentration • Organic matter concentration • Wet aggregate stability • Porosity • Earthworm population • Runoff and concentration of dissolved nutrients • Sediment and sediment-associated nutrients • Particle-size distribution • Water infiltration • Hydraulic conductivity • Pore-size distribution • Volumetric water content at field capacity (-0.1 to -0.33 bar) • Volumetric water content at permanent wilting point (-15 bars) • Plant available water • Particle-size distribution • Organic matter concentration • Concentration of macro- and micro-nutrients • Phospholipids fatty acids • Enzyme activity • Porosity • Wet aggregate stability • Pathogens • Heavy metals • Pathogens • Heavy metals • Toxins • Pesticides • Hormones • Parasites

all soil physical, chemical, and biological properties as soil health indicators into one index. Integrating all soil health indicators and their dynamic interactions into a single numerical value or score is currently a challenge. Soil health is specific to each ecosystem service. Thus, specific indexes should be developed for representative soils and each ecosystem service accounting for the interactive nature of complex and numerous soil physical, chemical, and biological properties. For example, the use of single indicators, such as organic matter concentration, is not sufficient to evaluate the response of soils to changes, particularly in

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soils with reduced effective depth. Further research and knowledge are required to develop indexes and theoretical models for soil health evaluation. Selection of representative indicators requires the use of advanced statistical tools (e.g., multivariate analyses) and modeling approaches to account for the significant correlations or complex interactions among dynamic and static soil properties. Multivariate statistical and canonical discriminate analyses are tools to identify relevant parameters for soil health assessment (Diaz-Gonzalez et al. 2022). Principal component analysis (PCA), a multivariate statistical approach, is a common tool to select representative minimum data sets of soil properties. The PCA groups soil variables in one or various principal components (PCs) according to the importance and affinity of variables while reducing the dimension of the original data set without losing the overall information of the data set (Andrews et al. 2004). Simple correlations and pedotransfer functions are potential tools to relate independent to dependent variables. The pedotransfer functions have been used to predict a range of dynamic soil properties (e.g., hydraulic properties) and crop yields from readily available soil datasets in relation to soil health. Simulation models (e.g., hydrological models) are also useful to soil health evaluation in that they model highly complex indicators.

20.6.1 Farmer-Based Soil Health Assessment Approach Early soil health indexing was based mainly on simple scoring functions and qualitative approximations. It often involved farmer participation. The Wisconsin Soil Health Scoreboard (WSHS) is an example of soil health evaluations from farmer-based surveys (Romig et al. 1995). The WSHS uses scores ranging from 0 to 4 where 0 is for the least favorable values of soil property and 4 is for the optimum values. The WSHS integrates soil surface characteristics (i.e, surface residue cover, degree of erosion, ease of tillage, surface crusting and cracking), soil profile attributes (e.g., topsoil depth, drainage, depth of A horizon), soil properties (e.g., earthworm population, soil structure development, soil color, compaction level, water infiltration, water retention, soil fertility level, degree of decomposition of organic residues, hardness, soil texture, aeration, biological activity), and soil qualitative indices (e.g., feel, smell).

20.6.2 Soil Management Assessment Framework (SMAF) An advance in soil health indexing is the development of soil management assessment framework (SMAF; Andrews et al. 2004; Karlen et al. 2019). The SMAF is the result of the ongoing research on soil health indexing, and it is thus still under development. It is a computer-based program with specific codes and algorithms in Excel spreadsheets. Case studies have shown that SMAF is promising to examine and monitor soil health across different soils, climates, land uses, and management conditions (Karlen et al. 2019). The overall approach of the SMAF involves defining

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the management goals, obtaining data on soil properties, and selecting, interpreting, and scoring indicators to compute the soil health index (SHI). The three main steps of SMAF are selection, interpretation, and integration of indicators. Based on the estimated scores, a single numeric value, known as SHI, is computed using Eq. (20.1) (Andrews et al. 2004): SHI =

n i = 1 Si

n

× 10

ð20:1Þ

where Si is score of soil health obtained from the scoring curves and n is the number of indicators in the minimum data set. These SHI values are used to: (1) monitor changes in soil health over time for the same soil and (2) compare soils within the same management practice. The SHI simplifies the parameters by providing scores and is a promising assessment tool to reorient soil management and implement corrective measures when necessary.

20.6.3 Comprehensive Assessment of Soil Health (CASH) The Comprehensive Assessment of Soil Health (CASH) is an evolution of the SMAF approach (Moebius-Clune et al. 2016; Karlen et al. 2019). This approach initially used data from the northeastern USA for soil health assessment. The CASH is being expanded to other regions using large-scale soil health databases and advances in data analysis tools (Moebius-Clune et al. 2016; Karlen et al. 2019). Soil profile information, microbial community structure data, soil respiration, soil protein, sensitivity analysis, and development of new algorithms and scoring curves are some of the recent additions to CASH (Karlen et al. 2019). The SMAF and CASH are promising indexes for integrating soil physical, chemical, and biological properties. Upon further refinement, these indexes offer promise to evaluate how long-term management practices affect soil health and provide recommendations to producers and other users.

20.7

Emerging Assessment Techniques

Advanced techniques are emerging to monitor changes in soil properties and thus soil health. These techniques included sensors, precision agriculture, machine learning, random forest, artificial neural networks, deep learning models, internet of things, and other interactive tools (Grunwald 2022; Rejeb et al. 2022). For example, sensor technologies can allow the characterization of soil properties under in situ conditions at different spatial scales as an alternative to traditional techniques, which are laborious and time-consuming (e.g., intense soil sampling, sample preparation, analyses). Soil sensors can monitor changes in water content, temperature, and electrical conductivity in real time using wireless networks. Also, multispectral and/or hyperspectral sensors (near- and mid-infrared energy) using unmanned aerial vehicles (UAVs) can be used to measure soil C under field

20.8

Soil Health and Erosion Relationships

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conditions (Nayak et al. 2019). Drones or UAVs are changing the way agriculture is practiced. The use of UAV technology can save costs, improve efficiency, and increase farm profits (Rejeb et al. 2022). Use of robotics and electronics can also allow the measurement of soil properties at small scales. Remote sensing can generate large volumes of soil and crop data in a short period of time and provide spatial information on soil properties across larger scales. Artificial intelligence via machine learning and deep learning, which consists in training powerful computers to process data and make decisions based on experience like a human brain, offer opportunities to translate and analyze soil information from remote sensing (Grunwald 2022). Deep learning algorithms can train artificial neurons to identify trends and then classify soil information for the desired output (Grunwald 2022). A review by Diaz-Gonzalez et al. (2022) discussed that machine learning to process remote sensing data, UAVs, and satellite platforms can be used to estimate soil indicators. Also, models can be used for estimating soil properties based on artificial intelligence tools. Remote sensing approaches have been used for fertilizer management (N, P, K), and estimation of soil organic matter concentration and crop yields (Kasampalis et al. 2018). Expanding the use of remote sensing to all soil properties beyond soil fertility management can be valuable (Jha et al. 2019). However, the accuracy of the emerging tools needs further improvement for field measurements. For example, site calibration and validation can improve the accuracy of soil sensors. The resolution of the estimated soil properties can be particularly low at larger scales. Also, the use of remote sensing data still has some limitations including difficulty with managing large amounts of data, computational (e.g., high memory) needs and costs, technical knowledge, among others (Odebiri et al. 2021). Advanced techniques that are user-friendly, quick, and inexpensive can be important tools to monitor changes in soil properties and health. Technologies for the automation of agriculture are emerging, but further improvement is needed for large-scale use of these technologies.

20.8

Soil Health and Erosion Relationships

Increased soil erosion by water, wind, and tillage is one of the greatest challenges to maintaining the health of soils. Soil health and erosion are strongly interrelated. Accelerated erosion directly degrades the indicators of soil health such as the soil profile depth and soil physical, chemical, and biological properties. For example, accelerated erosion rapidly reduces soil organic matter concentration, which influences the health of the rest of soil properties. Further, an eroded soil is more susceptible to erosion due to lower biomass production and more unfavorable soil properties than a non-eroded soil, creating a downward spiral of soil degradation.

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20.8.1 Soil Erosion and Profile Depth Thickness of the topsoil and the total soil profile depth are indicators of soil health for crop production and other ecosystem services. Thickness of topsoil horizons decreases linearly with increase in soil erosion, decreasing the total depth of soil profile. Soil erosion truncates the upper horizons and exposes subsurface horizons which result in immediate losses of organic matter and nutrients and deterioration of near-surface soil physical properties. Severe erosion can completely remove the Ap (plow layer) horizons (Thaler et al. 2021). The adverse effects of erosion on soils with shallow surface layer may be irreversible. Surface soil is a medium that partitions the rainfall into different hydrologic components and controls surface runoff. Thus, losses of topsoil diminish the soil’s ability to retain water and nutrients. Exposed subsurface horizons often have higher runoff and soil erosion risks because of reduced soil structural development and low organic matter concentrations. Soil aggregates bound by organic matter are more porous and stable than those bound by clay. Erosion reduces the effective soil depth, which is the depth between soil surface and the root-restrictive subsoil horizons. Most of the important soil processes occur within the effective rooting depth, and thus any reduction in its depth has negative effects not only on soil properties but most importantly on crop production.

20.8.2 Soil Physical Properties Erosion exposes subsurface horizons with different properties from the non-eroded topsoil. The exposed horizons have adverse and often fragile structural properties. Eroded soils are prone to surface sealing and crust formation under raindrop impacts, reducing water infiltration and affecting soil structural formation. Exposed subsurface horizons can have higher clay content, especially in soils with Bt (argillic) horizons, and are prone to cracking. Soil erosion alters soil texture by exposing subsurface layers of different texture and by preferentially removing fine soil particles. Erosion is a selective process in that small primary and secondary particles along organic matter are more rapidly transported by runoff water than large particles. Bulk density and penetration resistance can increase with an increase in topsoil removal (Larney et al. 2016). Soil erosion often increases bulk density and decreases plant available water, water infiltration rate, and hydraulic conductivity because of a decrease in macroporosity in lower horizons. Decrease in saturated hydraulic conductivity increases soil loss and runoff (Blanco-Canqui et al. 2004). The magnitude of changes in soil properties with erosion varies among soils. In soils with high organic matter concentrations and deep horizons, moderate soil losses may not significantly change soil properties. Changes in soil properties by erosion are typically slow and may pass unnoticed until the system reaches a severely degraded or an irreversible stage.

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Managing Soil Health

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20.8.3 Soil Chemical and Biological Properties Erosion by water and wind not only alters soil physical properties but also changes soil chemical and biological properties. Loss of organic matter by erosion is the major cause of soil degradation. Soil organic matter is vital to sustain desirable soil physical, chemical, and biological health of the soil. Soil organic matter concentration and biological activity near the surface decrease with an increase in soil erosion in sloping fields (Larney et al. 2016). Soil erosion displaces organic matter-enriched sediment off-site, degrading soil properties at the eroded sites. An eroded soil is chemically and biologically degraded because soil erosion alters essential chemical and biological processes including nutrient cycling, biological processes, decomposition of organic matter, acidification, transformation, volatilization, and eutrophication. Essential nutrients and electrolytes normally bound to clay particles are transported off-site with eroded materials. Eroded soils are low in fertility and require large inputs of chemicals to compensate for the losses of nutrients. Degradation of soil chemical and biological properties affects soil structural development and resilience of the whole soil.

20.9

Managing Soil Health

Maintaining or improving soil health through appropriate land use and soil management systems for sustained crop production and environmental protection is a high priority. Management practices used for restoring degraded soils and improving soil resilience are recommended practices for managing soil health. Biological practices that reduce soil erosion can also improve soil health and productivity. Soil health mainly depends on land use and tillage management. At least five principles exist to manage soil health including:

20.9.1 Reducing Soil Disturbance Reducing tillage intensity is the first step to restore, maintain, and improve soil health. Avoiding tillage (e.g., no-till) or minimizing tillage intensity leaves most crop residues on the soil surface, thereby reducing residue decomposition and allowing the permanence of abundant crop residue cover. Intensive tillage degrades soil properties and thus soil health. Frequent soil disturbance breaks down soil aggregates, increases organic matter decomposition, reduces earthworm population, and increases soil gas fluxes, soil’s susceptibility to compaction, and soil erosion risks, among other adverse impacts. The adverse impacts of tillage systems on soil health can be in this order: moldboard plow > chisel plow > disk tillage > ridge tillage > mulch tillage = vertical tillage = strip tillage > no-till. Moldboard plow, which is the most intensive tillage, degrades soil properties the most, whereas no-till disturbs the soil the least. The impacts of reduced or minimum tillage on soil health are generally between

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no-till and moldboard plow. Overall, reducing the number of tillage passes or using no-till should be preferred over intensive tillage to maintain or improve soil health.

20.9.2 Providing Armor Crop residues provide armor to soil. They improve soil physical, chemical, and biological properties by increasing soil organic C concentration and providing surface protective cover. Crop residues are probably the most abundant organic amendment to improve soil properties. The permanence of residues on the soil surface protects the soil from water and wind erosion, reduces evaporation, conserves water, reduces abrupt fluctuations in soil temperature, improves nearsurface soil properties, increases soil C accumulation, and enhances soil biological activity (Turmel et al. 2015). Similarly, abundant belowground biomass (root) production can hold the soil together, reduce soil erodibility, increase soil C accumulation, and support biological activity. Crop residues can provide long-lasting benefits to soil when combined with no-till or reduced till. Intensive tillage buries crop residues, accelerates residue decomposition, and rapidly reduces benefits from residues. Competing uses of crop residues such as livestock or biofuel production can reduce the amount of residue left on the soil surface. Balancing or reducing excessive crop residue removal (e.g., excessive baling, overgrazing) is important to leave sufficient residue cover. Establishing threshold levels of crop residue removal is required for different soils and climates when residues are removed for off-farm uses.

20.9.3 Intensifying Cropping Systems Intensifying cropping systems with high-biomass-producing crops is a strategy to increase quantity and quality of biomass production to improve the indicators of soil health. Incorporating perennials in current rotations can improve the potential of simplified or short crop rotations to further stabilize soil, promote soil-root interactions, and maintain or improve soil health. In three different soils in the Midwest USA, crop rotations which included 3 yr. of forage crops had the highest soil health index, while continuous corn had the lowest (Karlen et al. 2006). Systems with diverse plant species, similar to plant diversity in native prairies, can restore degraded soils relative to annual monocrops or cropping systems with limited crop residue input. Diverse and high-biomass-producing plant species may not only maintain soil health but also provide other ecosystem services including improved weed management, disease and pest control, and nutrient cycling. Understanding the benefits from different annual and perennial crops (e.g., grasses, legumes) is critical to design cropping systems that can restore, maintain, and improve soil health.

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Managing Soil Health

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20.9.4 Promoting Permanent Vegetative Cover Continuous presence of living plants is probably the most important factor to maintain soil health in agricultural systems. Growing plants protect the soil surface and stabilize slopes, improving soil properties and other ecosystem services. Permanent cover with growing vegetation can promote soil aggregation, C accumulation, improve water, air, and heat exchange, and provide energy source to soil organisms. Live plants are better than crop residues because they continually use C from the atmosphere to accumulate C in the soil, which is essential for the improvement in soil physical, chemical, and biological properties. Growing perennials can be ideal as perennials actively grow for longer periods of the growing season than annual crops. Double cropping, relay cropping, and growing forage or cover crops between main crop harvest and planting can be options to maintain a vegetative cover all year round. For example, cover crops have reemerged as a potential practice to intensify current simplified cropping systems while maintaining much-needed permanent cover when main crops are absent. Global reviews have found that cover crops generally improve soil physical (Blanco-Canqui and Ruis 2020), chemical (Sharma et al. 2018), and biological properties (Kim et al. 2020) relative to fields without cover crops. Cover crops can especially improve soil biological properties such as soil microbial abundance, activity, and diversity (Kim et al. 2020). However, performance of cover crops depends on biomass production. Increasing biomass production via improved cover crop management practices can enhance cover crop ability to improve soil properties. Planting cover crops during fallow in crop-fallow systems (winter wheat-fallow) with extended fallow periods of about 14 months can be an opportunity to increase biomass production in semiarid regions. In some cases, terminating cover crops late at main crop planting or after crop planting can result in increased biomass production. In general, cover crop management is key to observe any benefits from cover crops for improving soil health.

20.9.5 Integrating Crops with Livestock Integrating crops with livestock is another opportunity to improve soil health. Particularly in industrialized countries, livestock production is often separated from crop production. This separation, while important for short-term economic goals, may not be conducive to sustained management of agricultural systems in the long term (Schomberg et al. 2021; Kelly et al. 2021). A mutual relationship exists between livestock and crop production. Crops via residue or forage production support livestock production while livestock can maintain or improve soil health via input of C- and nutrient-enriched manure. Livestock integration with crops enhances soil C and nutrient cycling and reduces C and nutrient ratios (Rakkar and Blanco-Canqui 2018). For instance, livestock consume crop residues or forages with high C:N ratio and return organic material (manure) with low C:N ratio. The reduction in C:N ratio of organic materials is

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critical to improve or enhance soil fertility and productivity while reducing excessive reliance on inorganic fertilizers and risks of water pollution. Animal manure not only provides essential nutrients (e.g., N, P, S) and increases crop yields but also increases soil organic C, biological activity, and plant available water, reduces soil compactibility, and promotes overall soil health (Blanco-Canqui et al. 2015). Grazing crop residues and cover crops can be strategies to integrate livestock with crops (Blanco-Canqui et al. 2020). In general, crop residue grazing (Rakkar and Blanco-Canqui 2018) and cover crop grazing (Kelly et al. 2021) do not adversely affect soil properties. While overgrazing has negative impacts on soil health, moderate grazing can leave sufficient residue to protect soil and maintain soil health. Grazing animals return manure which can offset the amount of nutrient removed with crop residues and cover crops. Studies found that even when grazing removes about 90% of cover crop biomass, damage to soil and subsequent crop yields can still be minimal (Blanco-Canqui et al. 2020). Grazing when soil is frozen or dry is recommended to reduce risks of excessive compaction (Schomberg et al. 2021). Developing a balanced cropping system that supports both livestock production and soil health is important to promote overall ecosystem health.

20.10 Summary

Soil health refers to the ability of the soil to perform a specific service as a living system. The soil health concept has a widespread application in relation to the management of natural resources, water and air quality, adaptation to fluctuating climates, and overall health of the planet. Soil health was initially associated with soil productivity and plant health but now it has emerged as a concept interconnected with animal, human, and ecosystem health within the “One Health” concept. A healthy soil has a high productivity, buffers anthropogenic perturbations, filters and degrades pollutants, improves wildlife habitat, stores C, reduces greenhouse gas fluxes, and provides other essential ecosystem services. Soil health is a broad approach that attempts to integrate all inherent and dynamic soil properties and processes. The theoretical definition of soil health and its parameters of evaluation require further refinement. Standards and guidelines for a rigorous quantification of soil health are still under development. The complexity of the soil system, unlike pure substances such as water and air, limits the development of a solid framework of soil health indexing. Yet, the soil health concept is a promise to better manage soil resources once sensitive indicators that affect one or more simultaneous functions are identified. Soil physical, chemical, and biological attributes are used as indicators of soil health. The interactions among these soil properties determine the health of a soil. (continued)

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Emerging techniques such as remote sensing, machine learning, spectroscopic methods, soil sensors, and others offer promise to evaluate soil properties under field conditions at larger scales. Also, advanced statistical tools (e.g., multivariate analyses) and modeling approaches can be used to identify indicators of soil health for different soils and management scenarios. The soil management assessment framework (SMAF) and comprehensive assessment of soil health (CASH) are recent advances in soil health indexing based on computer codes and algorithms. Overall, restoring, maintaining, and improving soil health involve a number of steps including reducing tillage or adopting no-till, protecting soil surface with crop residues and growing vegetation, adding forage or cover crops during fallow periods, intensifying cropping systems, and integrating crops with livestock. Questions 1. Establish theoretical differences between soil quality and soil health. 2. Identify the most important indicators of soil health and discuss reasons for their selection. 3. Discuss how soil health is related to soil ecosystem services. 4. The soil bulk density of an eroded field decreased from 1.40 to 1.1 Mg m-3. Explain the possible mechanisms for the decrease in bulk density. 5. Discuss the two relevant soil health indexes (SMAF and CASH). 6. Discuss management practices that can be used to maintain or improve soil health. 7. Discuss the different technological advances to monitor changes in soil properties under field conditions at local and regional scales. 8. Explain how soil erosion affects soil physical, chemical, and biological properties. 9. Discuss how crop and livestock integration can maintain or improve soil health. 10. Define the “One Health” concept.

References Andrews SS, Karlen DL, Cambardella CA (2004) The soil management assessment framework: a quantitative soil quality evaluation method. Soil Sci Soc Am J 68:1945–1962 Blanco-Canqui H, Ruis S (2020) Cover crops and soil physical properties. Soil Sci Soc Am J 84(5): 1527–1576 Blanco-Canqui H, Gantzer CJ, Anderson SH et al (2004) Tillage and crop influences on physical properties for an Epiaqualf. Soil Sci Soc Am J 68:567–576 Blanco-Canqui H, Hergert GW, Nielsen RA (2015) Cattle manure application reduces soil's susceptibility to compaction and increases water retention after 71 years. Soil Sci Soc Am J 79:212–223 Blanco-Canqui H, Drewnoski M, Redfearn D, Parsons J, Lesoing G, Tyler W (2020) Does cover crop grazing damage soils and reduce crop yields? Agrosystems Geosciences Environ 3:e20102

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Bonfante A, Basile A, Bouma J (2020) Targeting the soil quality and soil health concepts when aiming for the United Nations sustainable development goals and the EU green Deal. Soil 6: 453–466 Bremer E, Ellert K (2004) Soil quality indicators: a review with implications for agricultural ecosystems in Alberta. Symbio Ag Consulting Lethbridge, Alberta, Canada http://www1 agricgovabca/$department/deptdocsnsf/all/aesa8681/$FILE/sqi_review_finalpdf Cited 14 March 2008 Diaz-Gonzalez FA, Vuelvas J, Correa CA, Vallejo VE, Patino D (2022) Machine learning and remote sensing techniques applied to estimate soil indicators – review. Ecol Indic 135:108517 Doran JW, Sarrantonio M, Liebig MA (1996) Soil health and sustainability. Adv Agron 56:1–54 Glossary of Science Terms (2008) Soil Science Society of America. https://www.soils.org/ publications/soils-glossary/ Grunwald S (2022) Artificial intelligence and soil carbon modeling demystified: power, potentials, and perils. Carbon Footprints 1:5 Jha K, Doshi A, Patel P, Shah M (2019) A comprehensive review on automation in agriculture using artificial intelligence. Artif Intell Agric 2:1–12 Karlen DL, Hurley EG, Andrews SS et al (2006) Crop rotation effects on soil quality at three northern corn/soybean belt locations. Agron J 98:484–495 Karlen DL, Veum SK, Sudduth K, Obrycki JF, Nunes MR (2019) Soil health assessment: past accomplishments, current activities, and future opportunities. Soil Till Res 195:104365 Kasampalis D, Alexandridis T, Deva C, Challinor A, Moshou D, Zalidis G (2018) Contribution of remote sensing on crop models: a review. J Imaging 4:52 Keith AM, Schmidt O, McMahon BJ (2016) Soil stewardship as a nexus between ecosystem services and one health. Ecosyst Serv 17:40–42 Kelly C, Schipanski ME, Tucker A, Trujillo W, Holman JD, Obour AK, Johnson SK, Brummer JE, Haag L, Fonte SJ (2021) Dryland cover crop soil health benefits are maintained with grazing in the U.S. high and Central Plains. Agric Ecosyst Environ 313:107358 Kim N, Zabaloy MC, Guan K, Villamil MB (2020) Do cover crops benefit soil microbiome? A meta-analysis of current research. Soil Biol Biochem 142:107701 Lal R, Bouma J, Brevik E, Dawson L, Field DJ, Glaser B, Hatano R, Hartemink AE et al (2021) Soils and sustainable development goals of the United Nations: an International Union of Soil Sciences perspective. Geoderma Reg 25:e00398 Larney FJ, Li LL, Janzen H, Angers DA, Olson BM (2016) Soil quality attributes, soil resilience, and legacy effects following topsoil removal and one-time amendments. Can J Soil Sci 96:177– 190 Lehmann J, Bossio DA, Kögel-Knabner I, Rillig MC (2020) The concept and future prospects of soil health. Nat Rev Earth Environ 1:544–553 Mausel PW (1971) Soil quality in Illinois—an example of a soils geography resource analysis. Prof Geogr 23:127–136 Moebius-Clune BN, Moebius-Clune DJ, Gugino BK, Idowu OJ, Schindelbeck RRR, Ristow AJ, van Es HM, Thies JE, Shayler HA, McBride MB, Wolfe DW, Abawi GS (2016) Comprehensive assessment of soil health: the cornell framework manual, 3.1 edn. Cornell University, Geneva, NY Nayak AK, Rahman MM, Naidu R, Dhal B, Swain CK, Nayak AD, Tripathi R, Shahid M, Islam MR, Pathak H (2019) Current and emerging methodologies for estimating carbon sequestration in agricultural soils: a review. Sci Total Environ 665:890–912 Odebiri O, Odindi J, Mutanga O (2021) Basic and deep learning models in remote sensing of soil organic carbon estimation: a brief review. Int J Appl Earth Obs Geoinf 102:102389 Rakkar MK, Blanco-Canqui H (2018) Grazing of crop residues: impacts on soils and crop production. Agric Ecosyst Environ 258:71–90 Rejeb A, Abdollahi A, Rejeb K, Treiblmaier H (2022) Drones in agriculture: a review and bibliometric analysis. Comput. Electron. Agric. 198:107017

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Soil Resilience

21

Soils are dynamic and subject to numerous degradative processes (e.g., erosion, compaction, salinization, acidification). Most of all, climatic fluctuations including frequent droughts, floods, and heat waves, intense rainstorms, and other extremes are the leading stressors of soil (Smith et al. 2022). No soil is free of degradation unless properly managed or adjusted to navigate the persistent degradative processes (Hirsch et al. 2017). The ability of a soil to continue provisioning all vital ecosystem services in spite of the degradative processes is of paramount importance to ecosystem health (Ludwig et al. 2018). This inherent characteristic of a soil is termed as soil resilience.

21.1

Concept of Soil Resilience

Soil resilience refers to the intrinsic ability of a soil to recover from degradation and return to a new equilibrium similar to the antecedent state. Soil resilience is the ability of the system to recover its “functional and structural integrity” (Seybold et al. 1999; Ludwig et al. 2018). Functional integrity is the capacity of the soil to moderate and improve dynamic functions (e.g., fate and decay of organic compounds, microbial activity, immobilization and transformation of chemicals, provision and recycling of nutrients). Structural integrity is the intrinsic capacity of the soil to improve its structural properties (e.g., soil aggregate stability, porosity) and return to the initial conditions. The term soil resilience has evolved from the theory of ecological resilience, widely used to describe reactions of terrestrial and aquatic ecosystems to anthropogenic and natural perturbations. An accurate definition of resilience is difficult because of the dynamic, variable, multi-faceted, and heterogeneous nature of the soil system. Not all soils respond in a similar manner to applied stresses. Thus, the concept of soil resilience can be as complex as the soil itself. An operational definition and assessment methods of soil resilience are debatable. Resilience is specific to each soil and depends on the interaction of soil physical, # The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 H. Blanco, R. Lal, Soil Conservation and Management, https://doi.org/10.1007/978-3-031-30341-8_21

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Ecosystem resilience

Soil Resilience

Planetary resilience

Resilience of an agricultural land Resilience of a soil (pedon) Resilience of soil properties

Fig. 21.1 Soil resilience at small scales can determine resilience at larger scales

chemical, and biological processes. Thus, a single definition of soil resilience may not fully express the variable and complex behavior of soils. An appropriate definition needs to be based on soil’s ability to recover from perturbation to perform a specific process or ecosystem service (e.g., C sequestration). Discussions of soil resilience in the literature tend to stress “return to its original state” or “initial condition” following perturbation. Soil resilience does not necessarily mean that the system will bounce back to a state identical to that prior to perturbation. What it means is that the perturbed soil system recovers to a state where its performance is not significantly different from the one before. Soil resilience is a reflection of soil health (Döring et al. 2015). It reflects the dynamic nature of a living system: soil. Healthy soils are more resilient to perturbations than unhealthy soils (Lehman et al. 2015). Further, soil resilience determines plant, animal, human, and ecosystem resilience. Specifically, the capacity of soil properties (e.g., organic matter level, size of soil aggregates) to recover after stresses such as intensive tillage determines the resilience of a soil, which, in turn, determines the resilience of agricultural lands and ecosystems (Fig. 21.1).

21.2

Importance

The theory of soil resilience allows the understanding of soil functioning in relation to soil stability and productivity. Surprisingly, soil resilience has neither been addressed nor defined in as much detail as it deserves. Resilience is a key soil attribute in that it stands for the capacity of the soil to recover from continuous and

21.3

Classification of Soil Resilience

527

persistent anthropogenic stresses. If it had not been for this vital soil attribute, all managed soils would have ceased to produce ecosystem services long ago. Ludwig et al. (2018) indicated that soil resilience can be a critical “bioindicator” of soil multifunctionality and overall agricultural sustainability. Most soils have some inherent capacity to resist exogenous and endogenous perturbations, and regain and recover, depending on the severity and duration of the degradative processes, and the intensity of restorative mechanisms. The capacity to recover from perturbations is an important and an inherent attribute of a soil. In other words, a soil possesses an inherent regenerative capacity, which, in interaction with proper management, can reverse soil degradation (Hirsch et al. 2017). An example of the capacity of the soil to restore itself can be the soil recovery after moderate compaction. Soils under croplands are often compacted in fall under the use of heavy equipment for harvest. However, natural processes such as freeze– thaw and wet–dry cycles over winter can cause soil to swell and shrink, and facilitate rebounding from compressive or compactive forces. The natural processes may not completely erase the induced compaction but may be sufficient to offset the potential adverse effects of compaction caused by heavy traffic. The concept of soil resilience is gaining importance in the context of increased risks of soil degradation and fluctuating climates (Smith et al. 2022). How a soil responds to droughts, floods, heat waves, and other extremes determine ecosystem health and resilience. The climate-induced changes in soil temperature and rainfall amount directly affect soil structural resilience. While some studies have suggested that moderate increases in soil temperature can enhance plant growth and biological activity, thereby increasing soil organic matter, extreme events such as intense rainstorms, flooding, and droughts may severely diminish the ability of a soil to recover. Experimental data on soil resilience from long-term studies simulating extreme events are needed to understand the magnitude and direction of effects. It is crucial to understand how soil responds to climatic fluctuations, and the nature of factors and processes that control this response. Recurrent degradative events induced by fluctuations can diminish the resilience of the soil by altering both biotic conditions and soil processes.

21.3

Classification of Soil Resilience

Soils are grouped into three categories (resistance, resilience, and regime shift) based on the ecosystem response (Table 21.1). Ecosystems that show resistance exhibit no change in soil state and are thus highly resilient, whereas those that show resilience exhibit some changes in soil state but such change is not permanent (Ludwig et al. 2018; Smith et al. 2022). Ecosystems that undergo regime shift after perturbation exhibit permanent changes in soil state and thus the soil cannot recover to its original state. The classification is often based on the most dominant degradative factor. In some soils, water erosion can be more damaging than wind erosion. In others, drainage and

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Table 21.1 Classification of soil resilience (Ludwig et al. 2018; Smith et al. 2022) Class 1

Resilience High

Ecosystem Response Resistance

2

Medium

Resilience

3

Low

Regime shift

Consequences No consequences

Structural change, eventual species composition change. No functional change Past the threshold level, structural and functional collapse

Soil State Change No change

Reversible, temporary change

Irreversible, permanent change

Some Soil Characteristics Deep soils, and high organic matter concentration, aggregate stability, and water infiltration. Moderately deep soils, and moderately high organic matter concentration, aggregate stability, and water infiltration.

Shallow soils, and low organic matter concentration and aggregate stability.

salinization can be major degradative factors. Highly resilient soils can recover rapidly after degradation or even resist degradative stress because of favorable extrinsic (e.g., geomorphology, climate) and intrinsic properties (e.g., profile depth, organic matter content). Conversely, non-resilient soils would collapse rapidly under degradative stress and fail to recover even under favorable conditions. The rate and magnitude of soil response or recovery depend on the specific degradative factors. For example, severely eroded soils may not recover even over extended time periods. In comparison, slightly or moderately eroded soils may be relatively resilient and recover rapidly. Differing responses of soils to degradative processes are confounded by the complex nature of each soil. Even under the same management, some soils can regain their pre-disturbance status sooner than others because of differences in profile depth, horizon thickness, soil organic matter pool, and other soil attributes. A major difficulty for classifying soil resilience is the identification of parameters that enable comparisons of resilience within, between, and among soils. Available classifications of resilience are often qualitative and have limited applicability unless made quantitative based on solid parameters of evaluation. An essential component of soil resilience is elasticity (Benitez et al. 2004), which refers to the speed of recovery after the application of stress has ceased. How fast a soil recovers from disturbance is crucial to identify and adopt proper land use and management strategies in relation to the desired productivity. The projected time for the recovery of soil properties after degradation depends mainly on climatic, ecologic, and management conditions.

21.5

21.4

Factors that Affect Soil Resilience

529

Soil Disturbance Factors

Some of the main factors that disturb soils are summarized in Table 21.2. Soil disturbance refers to abrupt or gradual changes that alter soil processes and properties, and the normal functioning of the soil system. There are natural and anthropogenic disturbances. Disturbances are part of the soil ecosystem, occur at all times, and may be necessary to perform essential management operations for producing the needed goods and services. Indiscriminate soil disturbance, referred to as soil degradation, however, leads to major changes in physical, hydrological, chemical, and biological processes, affecting soil function. Agriculture is one of the greatest anthropogenic activities that causes soil degradation. Mismanagement of soils with intensive tillage and monocultures creates stresses in the system, causing rapid and non-reversible changes in the soil. Unlike anthropogenic disturbances, natural disturbances are not preventable. Episodic events such as drought and flooding often trigger soil degradation in managed ecosystems.

21.5

Factors that Affect Soil Resilience

Soil resilience depends on the pre-disturbance conditions of the system. Soils that are well-structured, deep, and have high soil organic matter concentration exhibit high resilience (Table 21.1). The combination of intrinsic textural and structural properties controls soil resilience (Corstanje et al. 2015). Surface cover improves soil resilience against erosion. Dense cover of vegetative canopy and residue on the soil surface is critical to maintain and increase soil resilience. Soil resilience is affected by the same factors that govern soil formation (Fig. 21.2). Factors of soil resilience refer to the biophysical parameters including parent material, soil intrinsic properties, soil geomorphology, vegetation, and climate, which interact and revolve over time (Table 21.3). One factor could be more influential than the other, depending on the soil type. As a result, the dominant factor Table 21.2 Types of degradative factors affecting soil resilience Natural Disturbance • Landslides • Earthquakes • Fires • Wind storms • Rainstorms (e.g., runoff) • Snowstorms • Drought • Floods • Heat waves • Water table fluctuations

Anthropogenic Disturbance • Deforestation • Intensive tillage (e.g., moldboard plowing) • Cropping systems (e.g., low biomass production) • Fertilization (e.g., leaching) • Pesticide application (e.g., pollution) • Irrigation with low-quality water • Salinization and acidification • Traffic (e.g., animal, equipment traffic) • Urban development (e.g., scraping, excavation, creation of impervious surface)

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Climate

Time

Topography

Organisms

Factors

Parent material

Additions

Removals

Processes

Translocations

Soil Resilience

Soil Resilience

Transformations

Fig. 21.2 Factors and processes of soil formation affecting soil resilience Table 21.3 Factors affecting soil resilience (Corstanje et al. 2015; Hirsch et al. 2017; Wang and Li 2019) Soil Characteristics • Parent material (residual, colluvial, alluvial, marine, lacustrine, glacial, eolian, and organic) • Soil physical properties (e.g., texture, aggregate stability) • Soil chemical properties • Soil biological properties (e.g., microbial biomass)

Landscape Characteristics and Biota • Land topography (aspect, gradient, length, and shape) • Soil biota (flora and fauna) • Land use and management • Level of landscape disturbance

Climate and Time • Precipitation (e.g., rainfall, snow) • Temperature (maximum and minimum) • Radiation • Relative humidity • Length of soil degradation and restoration • Rate of soil formation

determines sequences in soil formation and affects the rate and magnitude of soil recovery. Factors and processes that affect soil resilience are continuous, simultaneous, and interdependent (Corstanje et al. 2015). In addition to the natural five soil forming factors (parental material, topographys, organisms, time, and climate), external mechanisms such as the socio-economic characteristics of farmers, landowners, and land policy programs influence soil resilience. Understanding the cause-effect relationship of soil resilience is critical to long-term soil productivity and development of proper land use and management strategies to improve soil functions.

21.5.1 Parent Material The nature of parent material determines the soil texture, which in turn influences soil resilience because it governs the fluxes of water, air, and heat through the soil. For example, soil resilience mechanisms such as leaching of chemicals and translocation of fine soil particles within the profile (e.g., eluviation, illuviation) are

21.5

Factors that Affect Soil Resilience

531

controlled by soil textural differences. Total soil pore space increases with increase in clay content. Thus, clayey soils retain more water than sandy soils. Sandy soils are, however, more permeable than clayey soils as they have large and wellconnected pores. Rates of runoff and soil erosion are also functions of soil texture. Soils with high silt and fine sand content are more susceptible to rill, interrill, and gully erosion than either clayey or sandy soils. This does not, however, imply that sandy and clayey soils are more resilient than silty soils. Management can affect soil resilience. Degraded silty soils of alluvial origin can be more rapidly revegetated or restored if they have thick horizons and deep profile. The clay content and mineralogy are also crucial components that influence soil resilience. Soils containing shrink-swell or high-activity clays (e.g., montmorillonite) are more resilient to compaction than those containing predominantly low-activity clays and low shrink-swell capacity (Seybold et al. 1999). Clays that disperse easily in water are highly erodible and less resilient. Aggregate stability, crusting, surface sealing, and water transmission characteristics related to soil erodibility are directly influenced by water dispersion properties of clays. The physical and chemical composition of primary and secondary particles also influence the macro-scale physical and chemical properties of the system.

21.5.2 Climate Climatic parameters influence the magnitude of soil resilience (Smith et al. 2022). The capacity of a soil to recover from a disturbance is lower under drier than wetter climates. Climatic factors affecting resilience include precipitation, temperature, radiation (albedo), air humidity, and evaporation demand. Fluctuations or seasonal distribution of climatic parameters have a major effect on soil biota and the intensity of weathering of the parent material. Effective precipitation and temperature are drivers of all physical, chemical, and biological processes of soil resilience (Smith et al. 2022). Rain water that infiltrates into the soil carries fine soil particles and dissolved substances and contributes to soil formation and restoration. Thus, in regions with low annual precipitation, most of the processes responsible for the differentiation of horizons are less intense because of the absence of percolating water. Temperature is essential to moderate plant growth and microbial processes, which are sensitive indicators of soil resilience. Rates of soil biochemical reactions double for every 10 °C increase in soil temperature (Brady and Weil 2001). Climate is the most important soil factor that sets the biotic activities (e.g., plant growth, soil animals). Humid and temperate climates promote the rapid growth of plants in degraded soils as compared to semi-arid and arid climates with slow soil recovery.

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21.5.3 Biota Soil biota are critical to the resilience and resistance of soil to external forces because of their role in C and N cycling, C sequestration, and other vital processes. Management practices that alter soil biota also alter ecosystem stability and services. Flora and fauna are two interrelated biotic factors that affect soil resilience. Resilient soils have abundant flora and fauna.

21.5.3.1 Flora Soils are more resilient under vegetative cover than when denuded. Soil erosion and physical degradation set in when protective vegetative cover is removed. Increases in vegetative cover decrease soil erosion by protecting the soil against raindrop impacts and reducing soil splash and detachment (Nouri et al. 2021). Plant roots create a network of channels through the soils, which can exert resiliency to soil properties. Fibrous grass roots are often concentrated near the soil surface and form continuous and fine pores while adding vital soil organic matter. Roots of trees and shrubs penetrate deep into the soil profile influencing water infiltration and nutrient cycling with depth and integrating the surface and subsoil processes. The interactive action of the aboveground surface cover and the belowground biomass adds organic matter and contributes to enhanced soil resilience. Vegetation imparts significant differences in soil properties essential to improving soil resilience. For example, forest soils often have lower bulk and particle densities and higher organic matter concentration compared with agricultural soils. The accumulation of soil organic matter in grasslands generally results from the addition of belowground biomass (root system) whereas that in forest soils results from the aboveground biomass (surface litter or leaves falling on the soil surface). 21.5.3.2 Fauna A healthy soil is teeming with life. It is home to an extraordinary number of organisms, which are the drivers of key processes of soil resilience. Soil animals can be divided into three main groups: microfauna (2 mm diameter) (Bradford et al. 2002). These animals may differ in size and activity but their essentiality to soil resilience is similar. Soil fauna are key determinants of soil resilience because they affect nutrient turnover and cycling, soil organic matter turnover, and soil aggregation. Changes in population and composition of soil animals impact soil ecosystem services. The macrofauna (e.g., earthworms, termites, ants) through pedoturbation, mixing of soil materials, contribute to the structuring of the soil and thus are considered by many as “ecosystem engineers” (Phillips et al. 2019). Earthworms mix inorganic and organic soil particles and improve porosity and aggregation. They also create interconnected, heterogeneous, vertical, and extensive biological macropores (e.g., burrows). These biopores become the pathways for rain and runoff water infiltration, decreasing the runoff rate and volume. The mesofauna and microfauna also affect

21.5

Factors that Affect Soil Resilience

533

chemical reactions (solubilization and transformation) and exchanges between plant roots and soil. Interactions among earthworms, microbes, and plant roots influence soil restoration through soil structuring, nutrient cycling, and the turnover of soil organic matter.

21.5.4 Anthropogenic Influence Anthropogenic activities are the leading cause of altered soil formation and degradation of well-formed soils. Deforestation, land clearing, intensive tillage, irrigation, overgrazing, and mining are among the major degradative interventions and perturbations of humans. Mechanized tillage overturns, mixes, and exposes the soil to climate elements. As a result, the soil is exposed to a range of degradative processes. What is required is adjustment in soil management strategies to counteract soil degradation and enhance soil resilience. Also, the socio-economic and political forces, which include landowner’s predisposition, land policies, incentives, and education, affect soil resilience and deserve consideration.

21.5.5 Topography Differences in elevation, slope length, slope steepness, and landscape position influence soil resilience. Sloping soils are susceptible to the erosivity of concentrated runoff and are prone to accelerated soil erosion as the water infiltration opportunity time is reduced compared with nearly-level soils. Also, growth and diversity of plants interact with soil topography. Sloping soils often have sparse vegetation and low plant diversity due to limited water storage, low organic matter concentration, and shallow profile as compared to deep soils in flat terrains. Deep-rooted plant species are often confined to footslope positions leaving upland landscape positions degraded and with sparse vegetation. Lower landscape positions can be more resilient than upper positions because of higher soil organic matter concentration and greater nutrient-enriched sediment accumulation.

21.5.6 Time Soil recovery generally follows a sigmoidal response and is a function of duration for which the restorative practices have been adopted. When soil degradation ceases, the curve of soil recovery rises as time passes. It often takes a long period of time before the soil returns to a desired level of performance (Smith et al. 2022). Soils need time for self-restoration after improved management practices are imposed (Ludwig et al. 2018). When other factors are favorable, soil organic C accumulates with time following degradation until it reaches a dynamic equilibrium level. Organic inputs darken the upper surface of the soil and contribute to the differentiation of A horizon within

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Soil Resilience

10 or 20 yr. Development of B horizon, however, requires longer periods of time (>100 yr.; Kalinina et al. 2015). Formation of 0.3–1 cm of new soil requires about 100 yr in most soils. The speed of soil recovery depends on climate. In regions with abundant rain, translocations and transformations of organic and inorganic materials occur more rapidly than in dry regions, modifying the soil profile characteristics.

21.6

Soil Processes and Resilience

Processes affecting the magnitude and rate of soil recovery include physical, chemical, and biological mechanisms (Table 21.4). These mechanisms interact and occur simultaneously, influencing various interrelated soil functions. The rate and magnitude of soil processes vary among themselves and affect the speed and time of soil recovery. Processes such as decomposition of soil organic matter and activity of microorganisms are more dynamic and rapid than weathering of minerals. Biological processes are responsible for nutrient cycling, absorption and release of nutrients, and processing of organic and inorganic components. Thus, soil resilience may mainly apply to biological processes, which are reversible, sensitive, and rapidly affected by soil management unlike slow processes such as weathering of rocks or parental material. The major processes of soil resilience are related to those of soil formation (Table 21.4). For example, erosion can remove as much as 1 cm of topsoil in a few hours or days, but it could take hundreds of years to naturally recover or form such a thin layer of soil. Lost topsoil may be regenerated by weathering but this is an extremely slow process (Kalinina et al. 2015). The rate of soil formation ranges between 0.01 and 0.003 cm yr-1 in most soils. Soil resilience is often measured by the rate of topsoil development after severe erosion. A soil can be renewable if only the rate of soil depletion is lower or equal to the rate of soil formation. Recovery of topsoil after disturbance requires a long-term monitoring of physical, chemical, and biological attributes to assess the amplitude and elasticity of soil resilience. Addition of eroded sediments and dust from neighboring environments and translocations of materials by water and soil organisms to deeper horizons are

Table 21.4 Processes affecting soil resilience (Lehman et al. 2015; Nouri et al. 2019) Physical • Physical weathering (e.g., freezing or thawing, exfoliation, crystallization) • Soil water, air, and heat fluxes • Macro- and micro-aggregation • Flocculation • Shrinking and swelling • Clay formation

Chemical • Weathering (e.g., cation, solution, hydration, hydrolysis, oxidation) • Immobilization • Transformation • Nutrient cycling • Buffering capacity • C sequestration (e.g., formation of organomineral complexes)

Biological • Biological weathering (e.g., burrowing) • Root growth • Activity of macro- and microorganisms • Soil organic matter decomposition and accumulation • Biodegradation and biotransformation

Resilience of Soil Properties

535

Deposition Translocations

Erosion

Uptake

• Aggregation • Soil organic matter decomposition • Humification • Weathering

Leaching

Runon

Transformations

Volatilization

21.7

Fig. 21.3 Processes affecting soil formation and resilience (Buol et al. 2011)

essential physical mechanisms of soil formation and restoration (Fig. 21.3). Soil aggregation is a fundamental process to soil erosion control. Immobilization and transformation of nutrients are part of nutrient cycling (Nouri et al. 2019). First, organic materials react with clay particles through adsorption. Second, clay surfaces polymerize humic substances. Third, organic compounds are physically and chemically sequestered by clay crystals and are inaccessible to soil organisms. Interactions among polysaccharides, humic and fulvic acids, and clay particles moderate soil aggregation and soil organic matter dynamics (Tisdall and Oades 1982). The chemical processes operating along with physical and biological processes are crucial drivers of soil recovery. Soil microorganisms, plants, and animals contribute to soil resilience by weathering minerals, creating pathways for the translocation of materials, and recycling nutrients. The biological mechanisms occur simultaneously with physical and chemical mechanisms.

21.7

Resilience of Soil Properties

Resilience of physical, mechanical, chemical, and biological properties affects the resilience of the whole soil and agroecosystem at different spatial and temporal scales. For example, resilience at the micro-scale level (e.g., soil aggregate stability) can determine resilience at the macro-scale level (e.g., precipitation capture, erosion

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rate). Precipitation capture is often high and runoff low when soil macroporosity and water infiltration are high. A resilient soil property can withstand changes and regenerate itself to a stable condition upon changes in degradative processes. Resilience of soil properties is highly dynamic, somewhat uncertain, and varies greatly during the recovery stages. Discussions about soil resilience should address resilience of individual soil properties.

21.7.1 Soil Physical Resilience Soil physical resilience is the soil’s ability to recover its physical properties after disturbance in response to the introduction of restorative land use and management. Soil physical resilience is a fundamental attribute because it controls fluxes of water, heat, and air through the soil system. Highly resilient soils often have lower bulk density and higher wet aggregate stability and plant available water than soils with low resilience. Following disturbance, some properties can regain their original values much quicker than others owing to differences in their intrinsic dynamic attributes. For instance, on a soil severely affected by landslides, soil macroporosity of the topsoil had recovered its original value in 24 yr, bulk density 90% in 50 yr, particle density 71% in 79 yr., aggregate stability 33% in 10 yr and 100% in 45 yr (Sparling et al. 2003). Soil dynamic properties including bulk density, porosity, saturated hydraulic conductivity, water infiltration, water-stable aggregates, and penetration resistance are significantly improved when degraded soils are reverted back to natural fallow (Nouri et al. 2021). Soils that have the ability to recover their physical properties following degradation are suited to agricultural land use and are valuable assets.

21.7.2 Soil Chemical and Biological Resilience Soil chemical and biological resilience is as important as soil physical resilience for the maintenance of overall soil resilience. Resilient soils not only have high physical resilience (e.g., low bulk density, high aggregate stability) but also high chemical (e.g., high C and N concentrations) and biological (e.g., high microbial biomass, high earthworm population) resilience. Changes in total C and N concentrations and microbial biomass are often used as sensitive chemical and biological parameters to monitor soil recovery (Döring et al. 2015). Soil microorganisms, through their dynamic activities, play a major role in moderating soil organic matter decomposition and enrichment, and enhancing soil resilience. Microbial activities act upon the aboveground and belowground plant biomass and contribute to soil fertility concentrations. Organic C and N recover rapidly during initial periods (5 Mg ha-1) of crop residue increase soil organic matter concentration and related soil properties. Systems that

21.12

Summary

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incorporate legumes, high residue-producing crops, and perennial crops can be beneficial to improving soil resilience. Soil resilience is usually higher under pastures than under annual crops. Thus, maintaining a permanent vegetative cover such as by adding cover crops during fallow periods can enhance soil resilience. Intensive traditional cropping has resulted in a rapid soil degradation. Thus, reverting to natural fallow should be considered especially when soils are highly degraded. In the US, the Conservation Reserve Program is an option to restore degraded soils by removing erodible or degraded croplands from cultivation. Examples of rapid improvement in soil properties following the conversion of croplands to permanent vegetation or natural fallow abound in literature (Nouri et al. 2019). Mulching with crop residues and adding green manure, livestock manure, poultry manure, compost, and biochar are effective strategies to improve soil resilience, especially when managed properly. Use of organic amendments not only improves the resilience of the soil to mechanical stresses but makes the soil more malleable or friable. Soils amended with organic materials have higher ability to rebound once the mechanical stresses (e.g., tillage operations) are removed. Fresh organic materials (e.g., green manure, manures) revitalize the soil system, activate biological processes of soil fungi and bacteria, and increase the soil’s ability to recover (Larney et al. 2016). Organic amendments are preferable over inorganic fertilizers because the former improve microbial biomass and activity and nutrient cycling while improving crop yields (Song et al. 2015). Adding biochar is another strategy to improve soil properties and thus soil resilience. Ajayi and Horn (2017) found that the application of wood biochar at high rates (5%) improved resilience of soil aggregates and reduced soil compressibility while increasing soil porosity and plant available water in fine sand and sandy loam soils. These findings suggest that biochar-amended soils might be better equipped to recover from stresses relative to soils receiving no biochar. The high C concentration in biochar can be one of the reasons for the positive impacts of biochar on soil properties. Establishing the optimum rate of biochar application for different soils is needed to expand the use of biochar for managing soil resilience.

21.12 Summary

Soils are prone to rapid degradation under intensive cultivation, accelerated erosion, mismanagement, and fluctuating climates. There are natural (e.g., earthquakes, fires, rainstorms, drought, floods) and anthropogenic (intensive tillage, monocultures, salinization, traffic, grazing) causes of soil degradation. The intrinsic ability of soils to counteract degradation or recover from stresses is termed soil resilience. Soil resilience has paramount implications for the (continued)

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maintenance of soil ecosystem services. A unique definition of soil resilience is complex because of the dynamic and heterogeneous nature of the soil system. Changes in soil properties including topsoil depth, microbial biomass, organic matter and nutrient concentrations, macroporosity, wet aggregate stability, root biomass, compaction level, and salinity and acidity levels are used as indicators of soil resilience. For example, deep soils with high organic matter concentration, aggregate stability, and biological activity have high resilience. Soil type, slope, biota, management, and climate influence the ability of a soil to recover from degradation. The same factors and processes that affect soil health influence the resilience of soils. Some equations based on dynamic soil properties, initial condition of soil, equilibrium state, rate of renewal, rate of soil degradation, and management input exist to simulate soil degradation and resilience, but further development of process-based models is a priority to fully simulate resilience and multifunctionality of soils. Some of the management strategies that can enhance soil resilience include conservation tillage (e.g., no-till), residue management, cover crops, manure, biochar, integrated nutrient management, conservation buffers, and others. A degraded soil may not recover to its original condition but to a level where its performance is not considerably different from that of the pre-degradation level. Developing soil resilience and preventing severe soil degradation are priorities to avoid costly restoration practices. Questions 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Define soil resilience and discuss its importance. Compare and contrast differences between soil resilience and soil health. Discuss the scale (soil properties vs. planetary resilience) of soil resilience. List and discuss the different indicators of soil resilience. Explain the different types of soil disturbance and their impacts on soil resilience. Discuss the relationship between soil resilience and factors of soil formation. Explain the strategies to improve soil resilience. What are the mechanisms by which biochar application can promote soil resilience? Discuss the influence of cropping systems on soil resilience. How can soil resilience be modeled?

References Ajayi AE, Horn R (2017) Biochar-induced changes in soil resilience: effects of soil texture and biochar dosage. Pedosphere 27:236–247

References

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Benitez E, Melgar R, Nogales R (2004) Estimating soil resilience to a toxic organic waste by measuring enzyme activities. Soil Biol Biochem 36:1615–1623 Bradford MA, Jones TH, Bardgett RD et al (2002) Impacts of soil faunal community composition on model grassland ecosystems. Sci 298:615–618 Brady NC, Weil RR (2001) The nature and properties of soils, 13th edn. Prentice Hall, New Jersey Buol SW, Southard RJ, Graham RC, McDaniel PA (2011) Soil genesis and classification. Wiley, Hoboken Corstanje R, Deeks LR, Whitmore AP, Gregory AS, Ritz K (2015) Probing the basis of soil resilience. Soil Use Manag 31:72–81 Döring TF, Vieweger A, Pautasso M, Vaarst M, Finckh MR, Wolfe MS (2015) Resilience as a universal criterion of health. J Sci Food Agric 95:455–465 Herrick JE, Wander M 1997 Relationships between soil organic carbon and soil quality in cropped and rangeland soils: the importance of distribution, composition, and soil biological activity R. Lal, J.M. Kimble, R.F. Follett, B.A. Stewart (Eds.), Soil Processes and the Carbon Cycle, CRC Press, Boca Raton, pp. 405–425 Hirsch PR, Jhurreea D, Williams JK, Murray PJ, Scott T, Misselbrook TH, Goulding KWT, Clark IM (2017) Soil resilience and recovery: rapid community responses to management changes. Plant Soil 412:283–297 Kalinina O, Goryachkin SV, Lyuri DI, Giani L (2015) Post-agrogenic development of vegetation, soils, and carbon stocks under self-restoration in different climatic zones of European Russia. Catena 129:18–29 Kay BD, Rasiah V, Perfect E (1994) Structural aspects of soil resilience. In: Greenland DJ, Szabolcs I (eds) Soil resilience and sustainable land use. CABI Wallingford, Oxon, UK, pp 449–469 Larney FJ, Li LL, Janzen H, Angers DA, Olson BM (2016) Soil quality attributes, soil resilience, and legacy effects following topsoil removal and one-time amendments. Can J Soil Sci 96:177– 190 Lehman RM, Acosta-Martinez V, Buyer JS, Cambardella CA, Collins HP, Ducey TF, Halvorson JJ, Jin VL, Johnson JMF, Kremer RJ (2015) Soil biology for resilient, healthy soil. J Soil Water Conserv 70:12A–18A Ludwig M, Wilmes P, Schrader S (2018) Measuring soil sustainability via soil resilience. Sci Total Environ 626:1484–1493 Nouri N, J. Lee X. Yin DD, Tyler A Saxton 2019 Thirty-four years of no-tillage and cover crops improve soil quality and increase cotton yield in Alfisols, Southeastern USA Geoderma, 337 https://doi.org/10.1016/j.geoderma.2018.10.016 Nouri A, Yoder DC, Raji M, Ceylan S, Jagadamma S, Lee J, Walker FR, Yin X, Fitzpatrick J, Trexler B, Arelli P, Saxton AM (2021) Conservation agriculture increases the soil resilience and cotton yield stability in climate extremes of the southeast US. Commun Earth Environ 2:155 Phillips HR, Guerra CA, Bartz ML, Briones MJ, Brown G, Crowther TW, Orgiazzi A (2019) Global distribution of earthworm diversity. Science 366:480–485 Seybold CA, Herrick JE, Brejda JJ (1999) Soil resilience: a fundamental component of soil quality. Soil Sci 164:224–234 Singh KP, Mandal TN, Tripathi SK 2001 Patterns of restoration of soil physciochemical properties and microbial biomass in different landslide sites in the sal forest ecosystem of Nepal Himalaya. Ecol Eng 17:385–401 Smith C, Jayathunga S, Gregorini P, Pereira FC, McWilliam W (2022) Using soil sustainability and resilience concepts to support future land management practice: a case study of mt Grand Station, Hāwea, New Zealand. Sustainability 2022(14):1808 Song Z, Gao H, Zhu P, Peng C, Deng A, Zheng C et al (2015) Organic amendments increase corn yield by enhancing soil resilience to climate change. Crop J 3:110–117

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Sparling G, Ross D, Trustrum N et al (2003) Recovery of topsoil characteristics after landslip erosion in dry hill country of New Zealand, and a test of the space-for-time hypothesis. Soil Biol Biochem 35:1575–1586 Tisdall JM, Oades JM (1982) Organic matter and water stable aggregates in soils. J Soil Sci 33:141– 163 USEPA (U.S. Environmental Protection Agency) (2022) Contaminated land. https://www.epa.gov/ report-environment/contaminated-land. Accessed 17 Nov 2022 Wang L, Li X (2019) Steering soil microbiome to enhance soil system resilience. Crit Rev Microbiol 45:743–753

Food, Water, and Climate

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Soil as a Centerpiece

Soil is the center of all systems including food, water, and climate (Fig. 22.1). Most recent discussions have focused on food, energy, and water security within the framework of “water-food-energy nexus” (Endo et al. 2017; Simpson and Jewitt 2019). The foundation of ecosystem functioning, which is soil, has been somewhat neglected. A comprehensive nexus should include all systems. Most importantly, it should include soil in the nexus as soil–water–energy–food–climate nexus. Food, fiber, energy, water, and climate revolve around soil. Indeed, wellmanaged soils can help with adaptation to fluctuating climates or extreme weather events. Maintaining and improving the soil resource are essential to ensure that the ecosystem services that soils provide continue. Some have called this soil security (Koch et al. 2015). Soil security, similar to food, energy, and water security, has agricultural, environmental, economic, and societal implications. It is important to remember that soil is the epidermis of planet Earth, fragile, and is 1 m thick on average (Amundson et al. 2015). Human existence depends on how well soil and other natural resources are appreciated and managed. Figure 22.2 shows an example of soil’s interconnectedness with other systems. An improvement in water infiltration into the soil via innovative management practices increases the amount of precipitation water capture and groundwater recharge, reduces risks of runoff, and increases plant productivity (e.g., biomass production), which can lead to an overall adaptation to fluctuating climates (Lal et al. 2017). Another example is the accumulation of soil organic matter via proper management, which not only uses the abundant CO2 in the atmosphere but also improves soil aggregation, porosity, water retention, and other soil structural and hydraulic properties, leading to sustained crop production, improved environmental quality, and enhanced adaptation to fluctuating climates.

# The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 H. Blanco, R. Lal, Soil Conservation and Management, https://doi.org/10.1007/978-3-031-30341-8_22

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Fig. 22.1 Soil as a foundation of all systems and services

Food, Water, and Climate

CLIMATE

FOOD

ENERGY

WATER

SOIL

Increased water infiltration

Reduced runoff and water pollution Increased water retention and groundwater recharge

Increased plant productivity

Increased resilience against climatic fluctuations Fig. 22.2 How a change in a soil property leads to changes in other systems

22.3

22.2

Soils and Food Security

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Soils and Water Security

Water security is directly linked to soil and food security. Water security refers to “an acceptable level of related risks to humans and ecosystems, coupled with the water availability of sufficient quantity and quality to support livelihoods, national security, human health, and ecosystem services” (Bakker 2012). Approximately 80% of the world’s population is facing risks of water insecurity (Bakker 2012). Creating a water and food secure world is a priority. Declines in water quality and quantity can pose a threat to food security, economic growth, and human health and well-being (Lal 2020). Also, recent climatic fluctuations including droughts and floods, are a serious threat to food, water, and energy security, and human health. Freshwater is a valuable natural and often insufficient resource, particularly in subtropics, arid, and semiarid regions. The high vulnerability of water resources to climate fluctuations underscores the need for the development of technologies for water management and conservation. Erratic rainfall is an increasing concern in agricultural systems. Because agriculture uses a high percentage of available water (>70%), developing water-efficient agricultural systems is important for both rainfed and irrigated systems. Management practices to manage soil water were discussed in previous chapters.

22.3

Soils and Food Security

Soil is the basis for crop production because about 98.8% of food is produced in the soil (Kopittke et al. 2019). Food production directly depends on soil productivity. Soil erosion, C and nutrient depletion, acidification, and salinization are among principal causes of reductions in soil productivity and increased risks of global food insecurity (Fig. 22.3). Soil erosion is the leading agent of soil degradation that can adversely affect food security. The magnitude of erosional impacts on ecosystem productivity and food security is, however, complex, variable, and soilspecific. Crop production in regions with highly mechanized agriculture and large-scale farms coupled with the use of improved crop varieties, fertilizers, irrigation practices, and other advanced technological inputs has progressively increased since the 1960s, thereby masking the potential threat of erosion on food security. The increase in food production under intensive farming practices, however, should not be generalized across all ecoregions because food production is still limited in some regions, especially in sub-Saharan Africa, due to increased soil degradation and limited access to technology (Giller 2020). Impoverished regions of the world with fragile soils, poorly developed markets, harsh climate, and limited access to technological input (e.g., fertilizers, modern farm machinery) face increasing concerns of food, water, and energy insecurity (Nkiaka et al. 2021). Millions of resource-poor farmers depend solely on the amount of food produced annually on small pieces of land. The low and meager seasonal crop yields are often insufficient to meet demands for food and other essentials such

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Fig. 22.3 A cropland affected by severe rill and ephemeral gully erosion (Courtesy USDA-NRCS)

as purchase of fertilizers, seeds, and farm equipment. Food insecurity in developing countries is confounded by extreme weather events (e.g., frequent drought, floods) and poor socioeconomic and political stability (Kaur et al. 2020). Increasing demand for food and decreasing crop production in these regions are intrinsically related to the soil’s ability to support crop growth and sustain agronomic production. Soil erosion affects crop production both directly and indirectly (Lal et al. 2017). The direct effects include reduction in topsoil thickness, alteration in soil properties, sedimentation and inundation of lowlands, and depletion of soil organic matter and nutrients (Fig. 22.4). An indirect effect of erosion is an increase in costs of production because of additional need for fertilizers, pesticides, irrigation, and tillage operations. Tilling exposed hardpans and claypans, repairing ephemeral gullies, and removing sediment from depositional sites increase the cost of production. Changing crop rotations and varieties or changing planting and replanting times to offset erosion also requires costly input. Further, accelerated erosion increases the crop’s susceptibility to damages by insects and diseases, thereby increasing the use of pesticides.

22.3.1 Soil Erosion and Crop Yields Because soil erosion is the leading agent of soil degradation and thus a threat to food security, its relationship with crop yields deserves further discussion. The relationship between erosion and crop yield is complex and often masked by practices including fertilization, organic amendments, and lime (Zhang et al. 2021). Crop yields vary randomly among years due to fluctuations in climatic conditions during

22.3

Soils and Food Security

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Crop Yield

Fig. 22.4 Water erosion removes topsoil thickness and reduces crop establishment and yields (Courtesy USDA-NRCS)

A Erosion Rate

B Erosion Rate

C Erosion Rate

D Erosion Rate

Fig. 22.5 Different types (a, b, c, and d) of crop yield response curves to erosion

the growing season (e.g., air temperature, rainfall amount, intensity, distribution, solar radiation, wind velocity). Crop yields can vary from one season to another even under optimal conditions. This temporal yield variability makes it difficult to precisely characterize and predict erosional impacts on agronomic production. Furthermore, the negative effects of soil erosion on crop yields are often gradual and go unnoticed until after the soil is severely eroded and no longer productive. Crop production is often negatively correlated with the rate of soil erosion. Crop yield vs. erosion relationships do not always, however, follow a straight line. Crop yields may decrease in a linear, quadratic (concave), logarithmic, exponential, and power or convex function with incremental increase in erosion (Fig. 22.5a through 22.5d; Bakker et al. 2004; Zhang et al. 2021). A linear function indicates that crop yield decreases incrementally with an increase in erosion (Fig. 22.5a). Convex response curve portrays a situation where increasing topsoil loss leads to increasing crop yield losses, but the effects of removal of the upper few centimeters of soil are

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small (Fig. 22.5b). A quadratic or concave function (Fig. 22.5c), in turn, indicates that the removal of the uppermost soil layers has the greatest effect, sharply decreasing crop yields while removal of the lower soil layers causes only minor or no significant reductions in yield. Knowledge of the shape of the response curve is important to effectively manage eroded soils. Crop yields that decrease in a straight line (Fig. 22.5a) or convex relationship (Fig. 22.5b) with an increase in erosion rates suggest that yields decrease with further increase in erosion. Erosion in these soils needs to be controlled to minimize risks of severe yield reductions. However, even a costly restoration of eroded soils with concave yield vs. erosion curves (Fig. 22.5c) may not be feasible because additional increases in soil erosion may have only minor effects on crop reduction. Generally, deficiency in available water and deterioration in soil structural properties produce convex yield-erosion curves, whereas deficiencies in nutrient supply result in linear or concave functions (Bakker et al. 2004). In some soils, topsoil removal may allow plants roots to reach the groundwater zone and offset some of the yield losses due to erosion. In buried soils, removal of infertile topsoil may also improve crop yields (Fig. 22.5d). Erosion impacts on crop yields depend on soil type, climate, crop type, and erosion-induced changes in soil properties, among other factors.

22.3.2 Soil Type, Climate, and Crop Type Soil erosion impacts can vary with soil intrinsic characteristics. Crop production on deep soils with high soil organic matter concentrations is affected less by erosion than that on shallow soils with low organic matter concentration. Crop yields can also vary with landscape position (Munoz et al. 2014). In some cases, soils on steep or convex slopes (e.g., shoulder slopes) often produce lower yields due to greater losses of soil, thinner topsoil, shallower soil profile, and lower organic matter concentration, water infiltration rates, and water retention capacity compared to those on footslopes or concave slopes (den Biggelaar et al. 2004; Fig. 22.6). Climate can influence erosion impacts on crop yields. A similar magnitude of erosion reduces crop yields more in tropical than in temperate climate because of lower soil resilience, concentration of organic matter, and nutrient reserves in tropical soils. Erosion-prone and agriculturally marginal soils are being brought under cultivation in fragile ecosystems under harsh climates (e.g., mountainous areas or drylands) because of the scarcity of prime agricultural lands (Lal et al. 2017). Unlike temperate regions, data on the erosion and crop yield relationships are scanty for soils of tropical regions. The decrease in crop yields due to erosion can also vary with crop type. For example, a global meta-analysis concluded that soybean can be the most sensitive crop to erosion followed by corn and wheat (Zhang et al. 2021). Crops that produce high amounts of biomass (e.g., corn) or cover the soil surface uniformly with residues (e.g., wheat) can protect the soil better and have lower sensitivity to erosion than low-biomass producing crops (e.g., soybean).

22.3

Soils and Food Security

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Fig. 22.6 Crop yields are lower in summit and backslope positions than in lower landscape positions due to accelerated erosion (Courtesy USDA-NRCS)

22.3.3 Erosion-Induced Changes in Soil Properties Severe erosion can reduce crop production by (Bakker et al. 2004; Zhang et al. 2021): • Reducing topsoil thickness and rooting depth • Causing soil compaction and reducing root development • Inducing surface sealing and crusting which results in reduced seedling emergence • Reducing the concentration of soil organic matter and macro- and micronutrients • Exposing subsoil with high clay content and reduced structural stability • Reducing plant available water capacity • Decreasing soil macroporosity and aggregation • Degrading soil chemical properties (e.g., pH, salinity, CEC) • Reducing water infiltration, hydraulic conductivity, and groundwater recharge

22.3.3.1 Physical Hindrance Eroded soils are truncated and have limited effective rooting depth (Zhang et al. 2021). Soils with root restrictive surface and subsurface layers (e.g., claypans, fragipans, hardpans) and those with bedrock at shallow depths are most susceptible to erosion-induced productivity decline. Erosion reduces topsoil thickness if it exceeds the rate of soil formation. The topsoil, primarily comprising the Ap horizon, is the physical medium where the largest amount of available water and nutrients is stored and plant roots are concentrated. A complete removal of topsoil adversely

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affects plant growth. Reduction in rooting depth also increases the sensitivity of plants to anomalies in water, temperature, and nutrient regimes. On an artificially desurfaced soil in Nigeria, corn yield decreased by 17 to 65% when 15 cm of topsoil was removed and 38 to 95% when 25 cm was removed (Salako et al. 2007). Also, a meta-analysis found that soil erosion does not reduce crop yields when the remaining A horizon depth is greater than 25 cm or when erosion is less than 5 cm depth (Zhang et al. 2021). Thus, if erosion removes less than 5 cm of soil, erosion impacts on crop yields can be small in soils with thick A horizons relative to shallow soils.

22.3.3.2 Compaction and Available Water Eroded soils, with exposed subsoil horizons, are prone to compaction because of high clay or gravel contents, and low organic matter concentration (Sonderegger and Pfister 2021). Thus, the exposed subsoil generally has higher bulk density and cone index, lower water infiltration rates, and higher runoff losses than non-eroded soils. Increase in susceptibility to compaction with soil erosion is common in clayey soils with Bt horizon (e.g., Alfisols). Excessive compaction restricts water and air flux, root growth, nutrient absorption, thereby reducing yields. Plant available water is one of the principal determinants of crop yield. In general, crop yields decrease with a decrease in plant available water content in the root zone. Soil erosion reduces plant available water by reducing the topsoil depth and depleting soil organic matter pool. Truncation and exposure of subsoil decrease available water content because of high cohesiveness and affinity of clay for water. An increase in clay content in eroded soils also decreases nutrient uptake. Shallowrooted crops are more likely to suffer from topsoil loss than deep rooted crops. Erosion also reduces available water content because of high losses of water by surface runoff. 22.3.3.3 Soil Organic Matter and Nutrient Reserves The nutrient-rich fraction of soil organic matter (e.g., particulate soil organic matter) is concentrated in vicinity of the soil surface and is preferentially removed by water and wind erosion because of its low density. The preferential removal reduces the availability of essential nutrients in the topsoil. Higher levels of soil organic matter are associated with higher crop yields because soil organic matter is a storehouse of macro- and micro-nutrients. A global review found that corn and wheat yields generally increase as soil organic C concentration increases up to about 2% (Oldfield et al. 2019). Because most cropland soils have 10 yr) cover crop experiments and their implications on soil ecosystem services. Most research data on cover crops are short-term (