Salt-affected Soils and Marginal Waters: Global Perspectives and Sustainable Management (Springer Water) 3030784347, 9783030784348

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Ranbir Chhabra

Salt-affected Soils and Marginal Waters Global Perspectives and Sustainable Management

Salt-affected Soils and Marginal Waters

Ranbir Chhabra

Salt-affected Soils and Marginal Waters Global Perspectives and Sustainable Management

Ranbir Chhabra Former Head (retired), Division of Soil and Crop Management ICAR-Central Soil Salinity Research Institute Karnal, Haryana, India

ISBN 978-3-030-78434-8 ISBN 978-3-030-78435-5 https://doi.org/10.1007/978-3-030-78435-5

(eBook)

© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 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. Cover Illustration: Biodrainage by eucalyptus trees as interceptor to control waterlogging due to seepage from canal (Photograph by: Ranbir Chhabra). This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Preface

The provision of adequate irrigation has long been recognized as one of the key inputs for increasing and sustaining agricultural production in arid and semi-arid regions. To achieve this, huge amounts are being spent on major and minor irrigation projects to create substantial irrigation potential by most of the countries. However, this development has not been without misgivings. In spite of best efforts, adverse effects of irrigation in the form of salinity development, alkalinity and environmental problems have been seen in almost all the irrigation command areas. Increasing population pressure has forced farmers to reclaim uncultivated salt-affected soils and use marginal waters which were earlier thought unsuitable for modern high-input agriculture. Extensive research has been done to address these problems and how to use the marginal-quality irrigation waters so as to increase production while sustaining productivity of soil. The author has attempted to synthesize the efforts of research workers in different countries under diverse agro-ecological conditions. Nature and origin of salts as well as their geochemical mobility, classification, factors leading to the genesis of salt-affected soils, area in different countries, tools of identification, new criteria for classification, methods of chemical and biological reclamation, and new amendments like flue gas desulphurization gypsum, phosphogypsum, sulphur and biochar have been presented. Management of coastal deltaic and tsunami-affected saline soils as well as inland and waterlogged saline soils has been addressed in detail. Sources of different nutrients in soil and their availability in terms of biotic and abiotic stress; interaction of salinity and sodicity with different nutrients, and methods to increase their efficiency; salt index of fertilizers; deficiency symptoms of different nutrients; and principles of fertilizer application in alkali and saline soils have been disused. Mechanisms of tolerance to salts and waterlogging have been deliberated. Quality criteria, effects of specific toxic ions to judge their suitability, and classification of irrigation waters have been discussed. Methods to control irrigated salinity through leaching as well as amelioration of saline, alkali waters and those with specific toxic ions have been incorporated. Surface, subsurface and vertical drainage to reclaim saline soils as well as methods to reduce drainage effluents and their use in land-locked countries have v

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been presented. Technologies for raising trees and grasses as alternate strategies for management of common salt-affected lands and where agricultural crops cannot be profitably grown have been included. Development of halophytic fodder farms, eco-reserves and wetlands to use non-reclaimable saline and waterlogged soils are discussed. Biodrainage, an eco-friendly technology for reclaiming and preventing the formation of waterlogged soils, control of surface stagnation, and use of wastewaters have been discussed. Environment-friendly methods of using non-conventional sources of irrigation, especially urban and treated industrial wastewaters, to prevent pollution of fresh waters and to increase irrigation potential of the area have been discussed. Another chapter on emerging issues of environmental impacts of reclamation including falling water tables, deterioration in groundwater quality, pollution due to burning of paddy straw and the problems of poisonous gases has been included. Policy guidelines for rationalizing the cost of irrigation and to minimize area under high water requiring crops have been discussed. An attempt has been made to deal with the subject as sustainable management of salt-affected soils, marginal waters, plant, animal, human health and environment continuum. The book combines scientific information with field experiences for understanding the problems of salinity, alkalinity, waterlogging and marginal irrigation waters, and it discusses various technologies and practical solutions for their profitable utilization on sustainable basis and preventive measures to control waterlogging and development of soil salinity. It can serve as a useful tool for research workers, teachers and students of agriculture, soil science, agronomy, plant breeding and irrigation engineering, extension workers, technocrats, environmentalists, foresters, planners, and technologists in developed and developing countries. The author is thankful to Prof. Jan Feyen, former Director, Centre for Irrigation Engineering, KUL, Belgium, for his wholehearted support and encouragement for writing this book. The critical suggestions by Dr. S.K. Kamra, former Head, Division of Agricultural Engineering, CSSRI, Karnal; Prof. Ram Lal Ahuja, Haryana Agricultural University, Hisar; Dr. Hans Raj Ghai, Professor Emeritus of Soil Science, Federal University of Campina Grande, Brazil; Dr. S. Arora, Principal Scientist, CSSRI, Lucknow, India, are highly acknowledged. The author also thanks Prof. I. Scheys, Prof. A. Cremers and Dr. D. Lamberts (KUL, Belgium); Dr. A. Ringoet (ITAL, Wageningen, The Netherlands); Dr. T. Flowers (Sussex University, Brighton, UK); Dr. I.P. Abrol and Dr. N.T. Singh, former Directors CSSRI, Karnal; and Drs. S.B. Singh, K.L. Chawla, Khajanchi Lal, N.P. Thakur, Anoop Singh, H.S. Baddesha and V.S. Arya for their valuable contributions. Technical help received from Shri Mohinder Bhatia, Madan Singh, R.K. Bhatia and K.N. Pahwa is gratefully acknowledged. The author is highly thankful to his wife, late Dr. Aruna Chhabra, Principal Scientist, National Dairy Research Institute, Karnal, and sons Dhiraj and Anuj and their families for constant support during compilation of this manuscript. Karnal, Haryana, India April 24, 2021

Ranbir Chhabra

Contents

1

Nature and Origin of Salts, Classification, Area and Distribution of Salt-affected Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 General Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Nature and Solubility of Salts . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Origin/Source of Salts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.1 Weathering of Rocks and Minerals . . . . . . . . . . . . . 1.3.2 Transportation and Accumulation of Salts on Surface Due to Irrigation . . . . . . . . . . . . . . . . . . 1.3.3 Irrigation with Salt-Laden Groundwaters . . . . . . . . . 1.3.4 Accumulation of Run-Off in Cavities and Un-Drained Basins . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.5 Shallow Water Table . . . . . . . . . . . . . . . . . . . . . . . 1.3.6 Fossil Salts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.7 Seepage from Upslopes Containing Salts . . . . . . . . . 1.3.8 Oceans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.9 Salt Laden Wind Drifts . . . . . . . . . . . . . . . . . . . . . . 1.3.10 Chemical Fertilizers and Waste Materials . . . . . . . . . 1.4 Classification of Salt-affected Soils . . . . . . . . . . . . . . . . . . . . . 1.4.1 The USDA System . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.2 The USSR System . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.3 The European System . . . . . . . . . . . . . . . . . . . . . . . 1.4.4 The Australian System . . . . . . . . . . . . . . . . . . . . . . 1.4.5 The FAO-UNESCO System . . . . . . . . . . . . . . . . . . 1.4.6 The Indian System . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 Type of Salt-affected Soils and Methods of their Reclamation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6 Solution of Saline-Alkali Soils . . . . . . . . . . . . . . . . . . . . . . . . 1.7 Soil Taxonomy and Classification of Salt-affected Soils . . . . . . 1.8 Classification of Salt-affected Soils as per Their Geographical Location and Methods of Formation . . . . . . . . . .

1 1 2 6 6 8 8 9 9 9 10 10 12 12 12 13 13 14 15 15 16 19 19 25 28 vii

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1.9 1.10

Area of Salt-affected Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . Geographical Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.10.1 Africa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.10.2 Asia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.10.3 Australia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.10.4 Europe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.10.5 North America . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.10.6 South America . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.11 Modern Technologies for Estimating Extent of Salt-affected Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.12 Human Role in Development of Salt-affected Soils . . . . . . . . . 1.13 Impact of Salt-affected Soils . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2

Saline Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Definition and Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Type of Soil Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 Primary Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.2 Secondary Salinity . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.3 Subsoil Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Development of Inland Saline Soils . . . . . . . . . . . . . . . . . . . . 2.3.1 Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2 Soil Texture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3 Use of Poor-Quality Groundwaters . . . . . . . . . . . . . 2.4 Causes of Waterlogging and Development of Inland Saline Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.1 Hydrological Conditions . . . . . . . . . . . . . . . . . . . . . 2.4.2 Changes in Land Use and Vegetation . . . . . . . . . . . . 2.4.3 Introduction of Canal Irrigation . . . . . . . . . . . . . . . . 2.4.4 Decrease in Use of Groundwater . . . . . . . . . . . . . . . 2.4.5 Changes in Cropping Pattern from Dry-Land Farming to High-Water Requiring Crops . . . . . . . . . 2.4.6 Blockage of Natural Drainage . . . . . . . . . . . . . . . . . 2.5 Mechanism of Soil Salinization from Shallow Water Table . . . 2.5.1 Concept of Critical Water Table Depth . . . . . . . . . . . 2.6 Diagnosing Salinity Problems in Field . . . . . . . . . . . . . . . . . . 2.7 Diagnosing Salinity Problems in Laboratory . . . . . . . . . . . . . . 2.7.1 Relationship between Salt Content and ECe . . . . . . . 2.7.2 Relationship Between Osmotic Pressure, ECe and Moisture Percentage . . . . . . . . . . . . . . . . . . . . . 2.8 Monitoring Soil Salinity in Field . . . . . . . . . . . . . . . . . . . . . . 2.9 Effect of Salinity on Plant Growth . . . . . . . . . . . . . . . . . . . . . 2.9.1 Water Availability . . . . . . . . . . . . . . . . . . . . . . . . . 2.9.2 Crop Production and Water Use . . . . . . . . . . . . . . . 2.9.3 Effect of Salinity on Evapo-transpiration . . . . . . . . . 2.9.4 Specific Toxic Ions . . . . . . . . . . . . . . . . . . . . . . . . .

29 31 31 34 39 40 40 40 40 43 43 44 49 49 51 51 51 52 53 53 53 54 54 55 56 57 58 59 60 60 61 63 64 65 68 70 70 71 72 73 74

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2.10 2.11 2.12 2.13

Effect of Waterlogging on Soil Properties . . . . . . . . . . . . . . . Waterlogging and Active Ion Uptake . . . . . . . . . . . . . . . . . . Mechanism of Tolerance to Waterlogging . . . . . . . . . . . . . . . Salinity Tolerance of Crops . . . . . . . . . . . . . . . . . . . . . . . . . 2.13.1 Effect of Environmental Factors on Salinity Tolerance of Crops . . . . . . . . . . . . . . . . . . . . . . . . 2.13.2 Level of Soil Salinity and Crop Growth . . . . . . . . . 2.13.3 Quantification of Salinity Effects . . . . . . . . . . . . . . 2.14 Mechanism of Salt Tolerance in Plants . . . . . . . . . . . . . . . . . 2.14.1 Salt Exclusion or Avoidance at Root Level . . . . . . . 2.14.2 Accumulation and Compartmentalization of Absorbed Toxic Ions within Plant . . . . . . . . . . . 2.14.3 Immobilization of Absorbed Salts in Specialized Structures and within Cell . . . . . . . . . . . . . . . . . . . 2.14.4 Salt Excretion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.14.5 Abscission of Leaves . . . . . . . . . . . . . . . . . . . . . . 2.14.6 Synthesis of Osmotica Compounds to Adjust Internal Osmotic Pressure . . . . . . . . . . . . . . . . . . . 2.14.7 Synthesis of Plant Growth Regulators and Organic Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.15 Salt Tolerance vs Drought Tolerance . . . . . . . . . . . . . . . . . . 2.16 Criteria for Selection of Salt Tolerant Crops . . . . . . . . . . . . . 2.16.1 Agronomic and Morphological Criteria . . . . . . . . . 2.16.2 Physiological and Biological Criteria . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Management and Reclamation of Saline Soils . . . . . . . . . . . . . . . . 3.1 Management of Saline Soils . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Management of Coastal and Deltaic Saline Soils . . . . . . . . . . 3.2.1 Major Problems of Coastal Areas . . . . . . . . . . . . . . 3.2.2 Hydrological Cycles and Inundation of Coastal Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3 Farming Systems Practiced in Coastal Areas . . . . . . 3.2.4 Strategies for Management of Coastal Saline Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.5 Management of Seafront . . . . . . . . . . . . . . . . . . . . 3.2.6 Establishment of Subsurface Fresh Water Skimming System (Doruvu Technology) . . . . . . . . 3.3 Management of Acid Sulphate Saline Soils . . . . . . . . . . . . . . 3.4 Suitability of Rice in Saline Soils and Soils Irrigated with Saline or Sodic Waters . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 Management of Inland Saline Soils . . . . . . . . . . . . . . . . . . . 3.5.1 Choice of Cropping Pattern . . . . . . . . . . . . . . . . . . 3.5.2 Choose Relatively Tolerant Crops to Soil Salinity . .

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3.5.3 3.5.4 3.5.5 3.5.6 3.5.7 3.5.8 3.5.9 3.5.10 3.5.11

Proper Seed Placement . . . . . . . . . . . . . . . . . . . . . . Method of Raising Plants . . . . . . . . . . . . . . . . . . . . Methods of Irrigation . . . . . . . . . . . . . . . . . . . . . . . Multiple and Need Based Use of Water . . . . . . . . . . Frequency of Irrigation . . . . . . . . . . . . . . . . . . . . . . Rootstock-Scion Relationship . . . . . . . . . . . . . . . . . Rainwater Harvesting and Conservation . . . . . . . . . . Use of Mulches . . . . . . . . . . . . . . . . . . . . . . . . . . . Proper Use of Plant Nutrients and Organic Manures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6 Reclamation of Inland Saline Soils . . . . . . . . . . . . . . . . . . . . . 3.7 Reclamation of Waterlogged Inland Saline Soils . . . . . . . . . . . 3.7.1 Definition of Water Table . . . . . . . . . . . . . . . . . . . . 3.7.2 Definition and Classification of Waterlogged Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.7.3 Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.7.4 Subsurface Drainage . . . . . . . . . . . . . . . . . . . . . . . . 3.8 Methods to Increase Contribution of Groundwater to Crop Water-Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.9 Bioremediation of Saline Soils . . . . . . . . . . . . . . . . . . . . . . . . 3.9.1 Through Continuous Cropping . . . . . . . . . . . . . . . . 3.9.2 Through Raising Halophytes . . . . . . . . . . . . . . . . . . 3.9.3 Through Use of Halophilic Microorganisms . . . . . . . 3.9.4 Through Nutrient Fixing and Solubilizing Microorganisms . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.10 Utilization of Saline Wet-Lands as Natural Eco-Reserves . . . . . 3.11 Establishment of Halophytic Fodder Farms . . . . . . . . . . . . . . . 3.12 Salinity and Pest Attack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.13 Salinity and Quality of Crop . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Biodrainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Concept of Biodrainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Principles of Biodrainage . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 Role of Water in Plants . . . . . . . . . . . . . . . . . . . . . 4.2.2 Why Plants Transpire? . . . . . . . . . . . . . . . . . . . . . 4.2.3 Factors Affecting Opening of Stomata . . . . . . . . . . 4.2.4 Effect of Transpiration on Dry Matter Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Energy Spent by Plants to Absorb Water . . . . . . . . . . . . . . . 4.3.1 Foliar Uptake of Water . . . . . . . . . . . . . . . . . . . . . 4.3.2 Zone of Water Absorption in Root . . . . . . . . . . . . . 4.3.3 Pathways of Water Movement in Leaves . . . . . . . . 4.3.4 Water Movement from Soil into Roots . . . . . . . . . .

123 124 124 127 127 130 131 132 132 133 134 134 135 136 139 146 147 147 148 149 151 152 153 155 155 156

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Sources of Energy Affecting Transpiration . . . . . . . . . . . . . . . 4.4.1 Albedo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.2 Transpiration and Leaf Energy Balance . . . . . . . . . . 4.4.3 Advection: An Additional Source of Energy for Forest Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Factors Affecting Quantity of Water Transpired Through Biodrainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.1 Matric Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.2 Osmotic Potential . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.3 Rate of Water Movement from Bulk of Soil to Root Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.4 Rate of Water Absorption by Roots from Soil . . . . . . 4.5.5 Internal or Vascular Conductance / Resistance of Water through Stem and Leaves . . . . . . . . . . . . . 4.5.6 Leaf and Canopy Characteristics . . . . . . . . . . . . . . . 4.5.7 Evaporating Capacity of the Atmosphere . . . . . . . . . 4.5.8 Silvicultural Practices . . . . . . . . . . . . . . . . . . . . . . . 4.6 Transpiration as Luxury Consumption of Water . . . . . . . . . . . 4.7 Biodrainage Capacity of Trees . . . . . . . . . . . . . . . . . . . . . . . . 4.7.1 Effect of Season on Biodrainage Capacity of Trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7.2 Effect of Groundwater Depth and Its Salinity on Biodrainage Capacity of Trees . . . . . . . . . . . . . . 4.8 Biodrainage to Control Rise in Water Table Depth . . . . . . . . . 4.9 Biodrainage to Control Secondary Soil Salinity . . . . . . . . . . . . 4.10 Biodrainage to Control Surface Water Stagnation . . . . . . . . . . 4.11 Effect of WTD and GWS on Growth of Tree Species . . . . . . . 4.12 Selection of Tee Species Suitable for Biodrainage . . . . . . . . . . 4.12.1 Tolerant to Waterlogging, Drought and Soil Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.12.2 Evergreen Vs Deciduous Trees . . . . . . . . . . . . . . . . 4.12.3 Canopy Characteristics . . . . . . . . . . . . . . . . . . . . . . 4.12.4 Leaf Characteristics . . . . . . . . . . . . . . . . . . . . . . . . 4.12.5 Root Characteristics . . . . . . . . . . . . . . . . . . . . . . . . 4.12.6 Growth Rate and Economical Use . . . . . . . . . . . . . . 4.13 Misconceptions About Biodrainage . . . . . . . . . . . . . . . . . . . . 4.14 Adverse Effects of High Transpiring Trees on Soil Moisture Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.15 Comparison of SSD with Biodrainage as Applicable to the Land-Locked Areas in Arid and Semi-arid Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

175 175 175 176 176 176 177 178 178 180 180 181 181 184 186 188 193 194 194 195 197 197 198 198 198 198 199

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Alkali Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Definition and Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Sources of Soluble Sodium . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Genesis of Soda (Na2CO3) . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Mode of Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.1 Sodification Due to Weathering of Na-Containing Rocks and Minerals In Situ . . . . . . . . . . . . . . . . . . . 5.4.2 Sodification Due to Shallow Brackish Groundwaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.3 Sodification Due to Use of High RSC-Waters . . . . . . 5.4.4 Sodification Due to Use of Saline Irrigation Waters Low in Cl :SO42 Ratio . . . . . . . . . . . . . . . 5.4.5 Sodification Due to Use of Mg2+-Rich Irrigation Waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 Diagnosing Alkali Soils in Field . . . . . . . . . . . . . . . . . . . . . . . 5.6 Measurement of Sodicity Status in Laboratory . . . . . . . . . . . . 5.6.1 Exchangeable Sodium Percentage . . . . . . . . . . . . . . 5.6.2 Sodium Adsorption Ratio . . . . . . . . . . . . . . . . . . . . 5.6.3 pHs as a Measure of ESP . . . . . . . . . . . . . . . . . . . . 5.6.4 Alkaline Earth Carbonate . . . . . . . . . . . . . . . . . . . . 5.6.5 Alkalinity of Alkali Soils and pH . . . . . . . . . . . . . . . 5.6.6 Problems of Coloured Aqueous Extracts . . . . . . . . . 5.7 Physical Properties of Alkali Soils . . . . . . . . . . . . . . . . . . . . . 5.7.1 Infiltration Rate and Hydraulic Conductivity . . . . . . . 5.7.2 Slaking, Dispersion, Swelling and Crust Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.7.3 Water Permeability and Concept of Threshold Electrolyte Concentration . . . . . . . . . . . . . . . . . . . . 5.8 Shear Stress and Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.9 Duplex Alkali Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.10 Degraded Alkali Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.11 Waterlogging, Redox Potential, pH and Solubility of Micro-Nutrients in Alkali Soils . . . . . . . . . . . . . . . . . . . . . 5.12 Methods to Alleviate Adverse Effects of Waterlogging in Alkali Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reclamation and Management of Alkali Soils for Crop Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 Factors Affecting Plant Growth in Alkali Soils . . . . . . . . . . . . 6.2 Relative Tolerance of Crop to Soil ESP . . . . . . . . . . . . . . . . . 6.3 Reclamation of Alkali Soils . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.1 Reclamation Technologies . . . . . . . . . . . . . . . . . . . . 6.4 Chemical Reclamation Technology . . . . . . . . . . . . . . . . . . . . 6.4.1 Chemical Amendments . . . . . . . . . . . . . . . . . . . . . .

209 209 210 215 216 216 222 222 223 224 226 227 227 228 230 232 233 234 235 235 237 238 243 244 245 246 248 249 255 255 257 261 261 272 272

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6.4.2 Organic Amendments . . . . . . . . . . . . . . . . . . . . . . 6.4.3 Industrial by-Products as Amendments . . . . . . . . . . 6.4.4 Physical Amendments . . . . . . . . . . . . . . . . . . . . . . 6.5 Gypsum Requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.1 Determination of GR . . . . . . . . . . . . . . . . . . . . . . 6.5.2 pH and Gypsum Requirement . . . . . . . . . . . . . . . . 6.5.3 Efficiency of Gypsum and Nature of Soluble Salts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.4 Quantity of Amendment Required . . . . . . . . . . . . . 6.5.5 Fineness of Amendment . . . . . . . . . . . . . . . . . . . . 6.6 Method of Gypsum Application . . . . . . . . . . . . . . . . . . . . . . 6.6.1 Depth of Mixing . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6.2 Split Application of Gypsum . . . . . . . . . . . . . . . . . 6.7 Removal of Salts and Reaction Products: Flushing Vs Leaching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.8 Water Requirement for Dissolution of Gypsum . . . . . . . . . . . 6.9 Role of Rice as a Reclamation Crop . . . . . . . . . . . . . . . . . . . 6.10 Geo-Hydrological Situations and Suitability of Soil for Rice Cultivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.11 Cultural Practices for Reclamation and Cropping in Alluvial Alkali Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.11.1 On-Farm Development . . . . . . . . . . . . . . . . . . . . . 6.11.2 Field Preparation . . . . . . . . . . . . . . . . . . . . . . . . . 6.11.3 Crop Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.11.4 Plant Population and Nursery Preparation . . . . . . . . 6.11.5 Age of Seedlings . . . . . . . . . . . . . . . . . . . . . . . . . 6.11.6 Green Manuring . . . . . . . . . . . . . . . . . . . . . . . . . . 6.11.7 Continuous Cropping . . . . . . . . . . . . . . . . . . . . . . 6.11.8 Nutrient Management . . . . . . . . . . . . . . . . . . . . . . 6.12 Water Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.12.1 Rainwater Management . . . . . . . . . . . . . . . . . . . . . 6.12.2 Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.12.3 Water Availability and Irrigation . . . . . . . . . . . . . . 6.13 Yield Potential of Upland Crops in Reclaimed Alkali Soils . . 6.14 Post-Reclamation Measures for Sustainable Management of Alkali Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.14.1 Resodification of Reclaimed Alkali Soils and Repeat Application of Amendments . . . . . . . . . 6.14.2 Proper and Balance Use of Fertilizers . . . . . . . . . . . 6.14.3 Application of FYM and Green Manure . . . . . . . . . 6.14.4 Timely Sowing of Crops . . . . . . . . . . . . . . . . . . . . 6.14.5 Diversification of Rice Based Crop Rotation . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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283 286 303 304 304 304

. . . . . .

305 306 308 309 309 311

. 311 . 312 . 315 . 318 . . . . . . . . . . . . . .

319 320 321 322 322 323 324 326 327 327 327 328 328 330

. 331 . . . . . .

331 332 334 334 335 336

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Nutrient Management in Salt-affected Soils . . . . . . . . . . . . . . . . . . . 7.1 Concept of Essential Plant Nutrients . . . . . . . . . . . . . . . . . . . . 7.1.1 Location of Nutrient Deficiency Symptoms . . . . . . . 7.2 Factors Affecting Nutrient Availability . . . . . . . . . . . . . . . . . . 7.2.1 Total Nutrient Content or Capacity Factor . . . . . . . . 7.2.2 Intensity Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.3 Chemical Form of the Nutrient . . . . . . . . . . . . . . . . 7.2.4 Mobility of the Nutrient . . . . . . . . . . . . . . . . . . . . . 7.2.5 Antagonistic and Synergetic Effects . . . . . . . . . . . . . 7.2.6 Soil Physical Conditions . . . . . . . . . . . . . . . . . . . . . 7.3 Fertilization of Alkali Soils . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.1 Calcium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.2 Magnesium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.3 Nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.4 Phosphorus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.5 Potassium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.6 Sulphur . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.7 Zinc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.8 Iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.9 Manganese . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.10 Boron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.11 Molybdenum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.12 Fluorine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.13 Silicon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4 Effect of Fertilizers on Physical Properties of Alkali Soils . . . . 7.5 Fertilization of Saline Soils . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5.1 Salt Index of Fertilizers . . . . . . . . . . . . . . . . . . . . . . 7.5.2 Effect of Salinity on Nutrient Availability . . . . . . . . 7.5.3 Calcium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5.4 Magnesium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5.5 Nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5.6 Phosphorus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5.7 Potassium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5.8 Sulphur . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5.9 Micronutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6 Control of Cl Toxicity Through Fertilizer Application . . . . . . 7.7 Fertilizer Applications and Water-Use Efficiency in Saline Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

349 349 352 352 353 354 354 355 355 356 357 357 361 362 369 375 380 381 384 387 390 392 394 396 398 399 400 404 404 405 405 409 414 416 416 417

Irrigation Water: Quality Criteria . . . . . . . . . . . . . . . . . . . . . . . . 8.1 Salinity Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1.1 Concentration of Soluble Salts . . . . . . . . . . . . . . . . 8.1.2 Puri’s Salt Index . . . . . . . . . . . . . . . . . . . . . . . . . .

431 431 431 434

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Sodicity Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.1 Sodium Per Cent (Na%) or Soluble Sodium Percentage (SSP) . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.2 Kelley’s Ratio (KR) or Kelley’s Sodium Ratio . . . . . 8.2.3 Figure of Merit (f) . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.4 Sodium Adsorption Ratio (SAR) . . . . . . . . . . . . . . . 8.2.5 Residual Sodium Carbonate (RSC) . . . . . . . . . . . . . 8.2.6 Residual Sodium Bicarbonate (RSBC) . . . . . . . . . . . 8.2.7 Adjusted SAR (SARadj) . . . . . . . . . . . . . . . . . . . . . 8.2.8 Sodium:Calcium Activity Ratio (SCAR) . . . . . . . . . 8.2.9 Permeability Index . . . . . . . . . . . . . . . . . . . . . . . . . 8.3 Hardness of Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4 pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5 Specific Ion Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.1 Calcium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.2 Sodium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.3 Potassium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.4 Magnesium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.5 Chlorides and Sulphates . . . . . . . . . . . . . . . . . . . . . 8.5.6 Carbonates and Bicarbonates . . . . . . . . . . . . . . . . . . 8.5.7 Boron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.8 Lithium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.9 Nitrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.10 Silicon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.11 Selenium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.12 Recommended Safe Levels of Toxic Elements for Irrigation and Drinking Waters . . . . . . . . . . . . . . 8.6 Quality of Irrigation Water as a Function of its Origin . . . . . . . 8.6.1 Rainwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.6.2 Surface Waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.6.3 Groundwaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.6.4 Seawater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.7 Water Quality Classifications . . . . . . . . . . . . . . . . . . . . . . . . . 8.7.1 Classification of Irrigation Waters Based on Salinity and Sodicity Hazards . . . . . . . . . . . . . . . 8.7.2 Classification of Irrigation Waters Based on Major Toxic Ions . . . . . . . . . . . . . . . . . . . . . . . . 8.8 Factors Affecting Suitability of Water for Irrigation . . . . . . . . . 8.8.1 Chemical Composition of Irrigation Water . . . . . . . . 8.8.2 Salt Tolerance of Crops to Be Irrigated . . . . . . . . . . 8.8.3 Properties of Soils to Be Irrigated . . . . . . . . . . . . . . 8.8.4 Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.8.5 Methods of Irrigation and Drainage . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

435 435 436 436 438 441 441 447 448 448 451 452 452 453 453 453 455 458 459 460 461 464 465 466 467 467 469 469 473 474 474 476 477 477 480 481 481 482 482

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Irrigation and Salinity Control . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1 Leaching and Reclamation of Saline Soils . . . . . . . . . . . . . . . 9.2 Salt Balance and Leaching Fraction . . . . . . . . . . . . . . . . . . . 9.3 Leaching Requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3.1 LR as a Function of Quality of Irrigation Water . . . 9.3.2 LR as a Function of Water Consumptive Use . . . . . 9.3.3 LR and Drainage Capacity . . . . . . . . . . . . . . . . . . 9.4 Factors Affecting Leaching Requirement . . . . . . . . . . . . . . . 9.4.1 Rainfall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.4.2 Salt Precipitation and Dissolution . . . . . . . . . . . . . 9.4.3 Salt Uptake by Plants . . . . . . . . . . . . . . . . . . . . . . 9.4.4 Salinity of Different Soil Layers . . . . . . . . . . . . . . 9.4.5 Method and Frequency of Irrigation for Leaching . . 9.4.6 Application of Amendments . . . . . . . . . . . . . . . . . 9.5 Calculations of Leaching Requirement . . . . . . . . . . . . . . . . . 9.6 Timing of Leaching Salts . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.7 Methods to Reduce Leaching Requirement . . . . . . . . . . . . . . 9.8 Salinity/Sodicity Control During Use of Marginal Waters . . . 9.8.1 Ameliorate Quality of Available Water . . . . . . . . . 9.8.2 Amelioration of Waters with Specific Toxic Ions . . 9.9 Salinity Control Through Change of Irrigation Water . . . . . . . 9.9.1 Salinity Control Through Conjunctive Use and Blending Saline Water Supply . . . . . . . . . . . . . . . . 9.9.2 Salinity Control by Changing the Method of Irrigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.10 Salinity Control During Use of Drainage Effluents . . . . . . . . 9.10.1 Reduction in Volume of Drainage Effluent . . . . . . . 9.10.2 Use of Drainage Effluents for Salt Leaching and Cop Production . . . . . . . . . . . . . . . . . . . . . . . 9.10.3 Harvest Salts Through Farm Evaporation Ponds . . . 9.10.4 Injection into Deep Aquifers . . . . . . . . . . . . . . . . . 9.11 Crop Tolerance to Salinity of Irrigation Water . . . . . . . . . . . . 9.12 Agronomic Practices to Minimize the Use of Saline Water . . . 9.12.1 Select Salt Tolerant Crops and Varieties . . . . . . . . . 9.12.2 Choose Less Water Demanding Crops . . . . . . . . . . 9.12.3 Deficit Irrigation . . . . . . . . . . . . . . . . . . . . . . . . . . 9.12.4 Avoid Irrigation with Saline Water at Critical Stages of Plant Growth . . . . . . . . . . . . . . . . . . . . . 9.12.5 Pre-sowing Irrigation with God Quality Water . . . . 9.12.6 Monocropping . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.12.7 Cultivation and Deep Tillage . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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487 488 489 492 493 494 494 495 495 496 496 497 497 498 499 500 501 502 502 509 513

. 513 . 514 . 520 . 520 . . . . . . . .

521 523 523 524 531 531 533 534

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Wastewaters as Non-conventional Sources of Irrigation . . . . . . . . . 10.1 Quantity of Wastewaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.2 Quality of Wastewaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.3 Irrigation Potential of Wastewaters . . . . . . . . . . . . . . . . . . . . . 10.4 Nutrient Potential of Wastewaters . . . . . . . . . . . . . . . . . . . . . . 10.5 Pollution Hazards of Wastewaters . . . . . . . . . . . . . . . . . . . . . 10.6 Quality Criteria for Use of Wastewaters for Irrigation . . . . . . . 10.6.1 Salinity, Sodicity and Specific Ion Hazards . . . . . . . . 10.6.2 Contamination Due to Pathogens . . . . . . . . . . . . . . . 10.6.3 Odour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.6.4 Concentration of Toxic Elements . . . . . . . . . . . . . . . 10.6.5 Residual Insecticides, Pesticides and Hormones . . . . 10.7 Problems with Utilization of Sewage Water . . . . . . . . . . . . . . 10.8 Systems for Management of Domestic Wastewaters . . . . . . . . . 10.8.1 Sewage Treatment Plants (STP) . . . . . . . . . . . . . . . . 10.8.2 Oxidation Ponds and Fish Culture . . . . . . . . . . . . . . 10.8.3 Soaking Pits and Lagoons . . . . . . . . . . . . . . . . . . . . 10.8.4 Injection into Deep Aquifers . . . . . . . . . . . . . . . . . . 10.8.5 Wastewaters for Irrigated Agriculture . . . . . . . . . . . . 10.8.6 Limitations of Using Domestic Wastewaters in Agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.8.7 Guidelines for Choice of Vegetative Cover to Use Wastewaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.9 Sewage Water Utilization through Plantations . . . . . . . . . . . . . 10.9.1 Principles of Karnal Technology . . . . . . . . . . . . . . . 10.9.2 Management of Effluents during Rainy Season . . . . . 10.9.3 Volume of Water Consumed by Trees Vs Agricultural Crops . . . . . . . . . . . . . . . . . . . . . . . . . 10.9.4 Response of Tree Species to Irrigation with Untreated Sewage . . . . . . . . . . . . . . . . . . . . . . . . . . 10.9.5 Effect of SW Application on Soil Properties . . . . . . . 10.9.6 Effect of Sewage Disposal on Composition of Groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.9.7 Prevention of Soil Contamination through Karnal Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.9.8 Suitable Tree Species for Karnal Technology . . . . . . 10.9.9 Type of Land Suitable for Plantation with Sewage/ Effluent Irrigation . . . . . . . . . . . . . . . . . . . . . . . . . . 10.9.10 Cost of Treating SW through Different Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.9.11 Benefits of Karnal Technology . . . . . . . . . . . . . . . . 10.10 Use of Industrial Wastewaters for Irrigated Agriculture . . . . . .

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545 547 547 550 551 552 553 553 555 557 557 560 560 561 561 562 564 564 565 565 567 567 567 573 574 574 576 578 579 581 583 583 584 585

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Karnal Technology for Utilizing Wastewaters from Agro-Based Industries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.11.1 Precautions for Use of Karnal Technology for Industrial Effluents . . . . . . . . . . . . . . . . . . . . . . . . 10.12 Decontamination of Heavy Metal Polluted Soils . . . . . . . . . . 10.12.1 Physical and Chemical Extraction of Heavy Metals from Wastewaters . . . . . . . . . . . . . . . . . . . 10.12.2 Immobilization of Heavy Metals in Soil . . . . . . . . . 10.12.3 Bioremediation of Heavy Metal Polluted Soils . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

. 586 . 587 . 588 . . . .

Trees and Grasses as Alternate Strategies for Management of Salt-affected Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Aims of Afforestation of Salt-affected Soils . . . . . . . . . . . . . . 11.2 Afforestation of Alkali Soils . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.1 Constraints Faced by Trees in Alkali Soils . . . . . . . . 11.2.2 Site Preparation Techniques . . . . . . . . . . . . . . . . . . 11.2.3 Composition of Filling Mixture . . . . . . . . . . . . . . . . 11.2.4 Method of Filling Pits/Auger Holes . . . . . . . . . . . . . 11.2.5 Relative Tolerance of Forest Species to ESP . . . . . . . 11.2.6 Choice of Forest Species for Afforestation of Alkali Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.7 Water Consumption, Litter Production and Nutrient Recycling by Tree Species . . . . . . . . . . 11.2.8 Methods of Raising Nursery of Tree Species . . . . . . 11.2.9 Time of Planting . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.10 Irrigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.11 Drainage Needs of Forest Area . . . . . . . . . . . . . . . . 11.2.12 Fertilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.13 Spacing and Pruning . . . . . . . . . . . . . . . . . . . . . . . . 11.2.14 Provision of Mixed Plantations . . . . . . . . . . . . . . . . 11.2.15 Effect of Trees on Crop Production and Vice Versa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.16 Sequence of Plantation . . . . . . . . . . . . . . . . . . . . . . 11.3 Suitable Grasses for Alkali Soils . . . . . . . . . . . . . . . . . . . . . . 11.4 Afforestation of Saline Soils . . . . . . . . . . . . . . . . . . . . . . . . . 11.4.1 Planting Methods for Saline Soils . . . . . . . . . . . . . . 11.4.2 Use of Amendments . . . . . . . . . . . . . . . . . . . . . . . . 11.4.3 Irrigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.4.4 Relative Tolerance of Forest Species to the Rootzone Salinity . . . . . . . . . . . . . . . . . . . . . 11.5 Tree Species Suitable for Coastal Areas . . . . . . . . . . . . . . . . . 11.5.1 Tree Species Suitable for Coastal Saline Soils . . . . . . 11.5.2 Tree Species Suitable for Salty Sprays and Wind Breaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.5.3 Tree Species Suitable for Waterlogged/Swampy Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

588 589 589 594 599 599 600 600 601 608 609 610 611 616 619 620 621 622 622 624 625 625 626 627 629 630 632 635 635 637 637 637 638

Contents

xix

11.6 11.7 11.8

Tree Species Suitable for Waterlogged Saline Soils . . . . . . . . . Suitable Grasses and Bushes for Saline Soils . . . . . . . . . . . . . . Raising Fruit Plants in Salt-affected Soils . . . . . . . . . . . . . . . . 11.8.1 Methods of Planting Fruit Plants in Alkali Soils . . . . 11.8.2 Relative Tolerance of Fruit Plants to Soil Sodicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.8.3 Relative Tolerance of Medicinal and Fruit Trees to Soil Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.9 Aromatic Grasses, Medicinal and Flower Plants for Salt-affected Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.10 Reclamative Role of Trees and Grasses . . . . . . . . . . . . . . . . . . 11.11 Economics of Afforestation of Salt-affected Soils . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Environmental Impact of Reclamation of Salt-affected Soils and Intensive Irrigated Agriculture . . . . . . . . . . . . . . . . . . . . 12.1 Falling Water Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.1.1 Factors Contributing to Falling Water Table . . . . . . 12.1.2 Strategies to Minimize Decline in Water Table . . . . 12.2 Deterioration in Groundwater Quality . . . . . . . . . . . . . . . . . . 12.3 Decrease in Soil Fertility Leading to Poor Yields and Low Water-use Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.4 Incidences of Poisonous Gases Causing Loss of Life . . . . . . . 12.4.1 Nature and Properties of the Poisonous Gases . . . . . 12.4.2 Sources of Carbon-di-Oxide in Pit-Wells . . . . . . . . 12.4.3 Methods to Detect Deficiency of Oxygen and Presence of Toxic Levels of CO2 . . . . . . . . . . . . . . 12.4.4 Methods of Degasification . . . . . . . . . . . . . . . . . . . 12.4.5 Other Precautions . . . . . . . . . . . . . . . . . . . . . . . . . 12.5 Pollution Due to Burning of Paddy Straw and Sugarcane Trash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.5.1 Eco-Friendly Techniques for In Situ Straw Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.5.2 Microbial Composting of Rice Straw In Situ . . . . . 12.5.3 Alternate Economic Use of Rice Straw . . . . . . . . . . 12.5.4 Policy Decisions to Bring Changes in the Mindset of Farmers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

638 640 642 642 642 644 646 648 651 652

. . . . .

659 659 661 666 677

. . . .

678 678 679 682

. 684 . 686 . 688 . 689 . 691 . 691 . 692 . 693 . 693

Authors Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 697 Subject Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707

Abbreviations

AEC bgl BH BOD CEC cm COD conc. cumec cv. DCR dS m 1 DSR DW EC ECe ECDW e.g. ECIW E0 Eq. ES ESP Es ESR ET FC FYM g GHG GM

anion exchange capacity, me 100 1 g soil depth of water below ground level breast height, 1.30 m from the base biological oxygen demand, mg L 1 cation exchange capacity, me 100 1 g soil centimetre chemical oxygen demand, mg L-1 concentration cubic meter per second cultivar divalent cation ratio deci Siemens per meter direct sown rice drainage water electrical conductivity EC of the saturated soil paste extract, dS m EC of the drainage water “exempli gratia”; for example EC of the irrigation water potential evaporation equation exchangeable sodium exchangeable sodium percentage evaporation from the bare soil exchangeable sodium ratio evapo-transpiration field capacity farm yard manure gram greenhouse gases Green manure

1

xxi

xxii

GR GWL ha i.e. IW kg L LF lbs lcd LAI LR LSD M ha me L 1 mg OC OM mld mm OP pHs pH2 pm PTE q RSC SAR SMBC SOM PSI SP t TDS Wb WP

Abbreviations

gypsum requirement, t ha 1 groundwater level hectare (100 m  100 m) “Id est”, “in other words” irrigation water kilogram litre leaching fraction ponds litres of water per capita per day leaf area index leaching requirement least significant difference million hectares milliequivalent per litre milligram organic carbon organic matter million litres per day milli meter osmotic pressure, bars pH of the saturated soil paste pH of 1:2 soil water suspension picometer phytotoxic elements quintal (100 kg) residual sodium carbonate, me L 1 sodium adsorption ratio of the saturated soil paste extract soil microbial biomass carbon soil organic mass Puri’s salt index saturation percentage tonnes (1000 kg) total dissolved solids amount of water lost through biodrainage wilting point

Chapter 1

Nature and Origin of Salts, Classification, Area and Distribution of Salt-affected Soils

1.1

General Aspects

All soils contain salts either in soluble or exchangeable forms or as a part of weatherable rocks and minerals which constitute the basic soil fabric. Many of these salts act as a source of essential nutrients for healthy growth of plants. However, when quantity of salts in the rootzone exceeds a particular value, growth, yield and or quality of most crops is adversely affected to a degree, depending upon kind and amount of salts present, stage of growth, type of plant, and the environmental factors. Thus, soil that contains excess salts so as to impair its productivity is called salt-affected soil. The term salinity in general, includes all problems the plant faces directly or indirectly due to salts present in its rhizosphere. These may be due to soluble salts present in soil solution, exchangeable ions, and or salts added through saline irrigation water/groundwater. Salt is flavour of ocean but when it comes to land, it spells trouble for the tiller, miller and the ruler. Soil and water are two basic natural resources, which are finite, but essential for agricultural production. However, due to ever-increasing demand and compulsion to produce more food grains and other agricultural products, these resources have been over exploited and are continuously being degraded. The man-made pressures have put these ecologically vulnerable resources under great stress. Whereas compulsions to expand crop area have brought arable farming to lands otherwise unsuitable for crop cultivation, intensive agriculture supported by irrigation has rendered many productive soils infertile. Flourishing of the Sumerian civilization in south of Mesopotamia in modern Iraq and Kuwait (Russel et al. 1965); civilization of Mesopotamia between rivers Tigris and Euphrates in Egypt; Nile Valley civilization in Egypt; Mohenjo-Daro civilization in the Indus Valley; Harappan civilization at Kalibangan in Rajasthan, India and several other places along the banks of rivers and their subsequent fall due to development of salinity in agriculture is a reminder for future generations of the world to manage these resources in a rational way on

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 R. Chhabra, Salt-affected Soils and Marginal Waters, https://doi.org/10.1007/978-3-030-78435-5_1

1

1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

2

sustainable basis. Had we managed our irrigation water well and on scientific basis, then the present problems of secondary salinization have not risen. Continuous depletion of nutrients from soils, waterlogging and secondary salinization are some of the attendant problems threatening sustainability of crops in irrigated areas. Owing to these degradation processes, large areas of otherwise productive irrigated lands have already gone out of production or are producing sub-optimal yields. In many areas the problem is latent and could assume serious proportions if proper care is not taken to conserve these resources and to control rise of water table upon introduction of irrigation.

1.2

Nature and Solubility of Salts

The chief ionic combinations which give rise to occurrence of salts, originate within the series Ca2+, Mg2+, Na+, K+, Cl
, HCO3
, CO32
and SO42
. These ionic species are formed from 15 most abundant elements found in the earth crust (Table 1.1), top cover of the earth down to 16.5 kms. Their occurrence in solutions circulating the earth, in oceans, and in marine deposits can therefore be ascribed at least in parts to weathering of rocks and minerals. Geochemistry of salts formed on land is based on solubilization and extraction of ions from minerals in the course of weathering, followed by their precipitation and accumulation under specific physical-geographic conditions (Fersman 1934). Sequence of extraction of ions, their speed of migration and capacity to accumulate in depressions in the form of salt masses is proportional to coefficient of energy (CE) of the ions (Table 1.2), ionic radius, valency and stability of the crystal network of the compound. Mobility of compounds formed and amounts in which they accumulate as soluble salts increases with decrease in coefficient of energy, ionic radius and valency of ions. The process of precipitation and accumulation of less soluble salts occurs in the reverse order. The longest to remain in solution of marine, on-ground (in surface waters like lakes etc. and in soil solutions) and groundwaters are the ions with lowest Table 1.1 Concentration of common elements found in the earth crust Element Oxygen (O) Silicon (Si) Aluminium (Al) Iron (Fe) Calcium (Ca) Sodium (Na) Magnesium (Mg) Potassium (K)

% Content 49.13 26.00 7.45 4.20 3.25 2.40 2.36 2.35

Source: Clark and Washington (1924)

Element Hydrogen (H) Titanium (Ti) Carbon (C) Chlorine (Cl) Phosphorus (P) Sulphur (S) Manganese (Mn)

% Content 1.00 0.61 0.35 0.20 0.12 0.10 0.10

1.2 Nature and Solubility of Salts

3

Table 1.2 Sequence of ion-extraction during weathering of rocks and minerals I Ions Cl
, Br
NO3
SO42
CO32


CE 0.23 0.18 0.66 0.78

Sequence of extraction, category II III Ions CE Ions CE Na+ 0.45 SiO3 2.75 K+ 0.36 Ca2+ 1.75 Mg2+ 2.10

IV Ions Fe2+ Al3+

CE 5.15 4.25

Source: Fersman (1934)

Table 1.3 Relative mobility/leachability of different elements in soil

b

Degree of mobility/ leachability Practically non-leachable Slightly leachable

c

Leachable

d

Highly leachable

e

Very highly leachable

Group a

Elements Si in quartz Fe and Al as sesquioxides; Al and Si as aluminium silicates; P as PO43
from rock phosphate [Ca3(PO4)2]; Ca as SO42
from gypsum (CaSO4.2H2O); CO32
from calcium carbonate CaCO3, and F as CaF2 from fluorapatite [2Ca3(PO4)2.CaF2]. Si as sodium silicate; P as sodium pyro-phosphate (Na3PO4); Mn and Fe under reduced conditions as in waterlogged and acidic soils and F
as sodium fluoride (NaF) as in alkali soils. Na+ and Mg2+ as salts of Cl
and SO42
Na+ as salt of CO32
. Na+, Ca2+ and Mg2+ as salts of Cl
.

Source: Adopted from Polynov (1923)

coefficient of energy i.e. monovalent and bivalent cations and monovalent anions of category I and II. That means that chlorides, nitrates, sulphates and carbonates of Na+, K+, Ca2+ and Mg2+ are main salts which form the salinized areas. Subsequent to weathering process (hydrolysis, hydration, oxidation, reduction and carbonation etc.), these elements depending upon their geochemical mobility and leachability, have been divided into five categories, their mobility/leachability sequence in the increasing order (Polynov 1923 and Kovda 1965; Table 1.3). This determines their accumulation in soil in situ, migration/transportation from the site of weathering to other areas and enrichment of groundwaters. Salt formation and their accumulation in soil is therefore expected to result from a combination of group “d” and “e” to a variety of possible combinations such as NaCl, Na2SO4, MgCl2, MgSO4, CaCl2, CaSO4, Na2CO3, NaHCO3, MgCO3, Mg (HCO3)2, Ca (HCO3)2 and CaCO3. Their solubility and differential geochemical mobility within a close area may explain formation of alkali soils adjacent to normal soils and the cause of slick spots development in otherwise normal soils. Salts of monovalent cation (Na+) are more soluble than salts of divalent cations (Ca2+ and Mg2+, Table 1.4 and 1.5) and thus have more mobility than those of divalent cations making those as dominant salts in saline soils. Similarly, Cl
and

1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

4

Table 1.4 Solubility of different inorganic salts in water at different temperatures Salt NaCl Na2SO4 NaHCO3 Na2CO3 Mean CaCl2 CaSO4 Ca(HCO3)2 CaCO3 Mean MgCl2 MgSO4 Mg(HCO3)2 MgCO3 Mean



0 C 35.7 4.9 7.0 7.0 13.7 59.5 0.223 16.1 – 19.0 52.9 25.5 14.0 – 23.1

Solubility, g 100 ml21 water at 10 C 20  C 30  C 35.7 36.0 36.1 9.1 19.5 40.8 8.1 9.6 11.1 12.5 21.7 39.7 16.4 21.7 31.9 64.7 74.5 100.0 0.224 0.255 0.264 – 16.6 – – 0.000617 – 20.4 22.8 29.2 53.6 54.6 55.8 30.4 35.1 39.7 14.2 14.4 14.9 – 0.039 – 24.6 26.0 27.6 

40  C 36.4 48.8 12.7 49.0 36.7 128.0 0.265 17.1 – 36.3 57.5 44.7 15.9 – 29.5

Source: Richard (2013)

Table 1.5 Mean solubility of inorganic salts depending upon the associated cations Mean solubility, g 100 ml21 water at 0 C 10  C 20  C 30  C 40  C 13.7 16.4 21.7 31.9 36.7 

Type of cations Na+-salts (Monovalent cation) (NaCl + Na2SO4 + NaHCO3 + Na2CO3)/4 Ca2+ and Mg2+-salts (Divalent cations) 21.1 22.5 24.4 [CaCl2 + CaSO4 + Ca (HCO3)2 + CaCO3 + MgCl2 + MgSO4 + Mg (HCO3)2 + MgCO3]/8 Per cent increase in solubility with increase in temperature over 0  C Na+-salts (Monovalent cation) – 19.7 58.4 Ca2+ and Mg2+-salts (Divalent cations) – 6.6 15.6

28.8

32.9

132.9 36.5

167.9 55.9

Source: Based on Table 1.4

SO42 salts are more soluble than those of CO32
and HCO3
(Table 1.6). Due to these reasons, in a topographical sequence, saline soils with dominant anions of Cl
and SO42
are formed in low-lying areas while alkali soils with dominant anions of CO32
and HCO3
are formed in relatively upslope areas. This also explains why concentration of Na+, Cl
and SO42
is more as compared to concentration of Ca2+, Mg2+, CO32
and HCO3
as salinity of groundwater increases from 2 to 10 dS m
1 (Table 1.7, Paliwal 1972). This is the reason why residual sodium carbonate is high only in low EC waters. Similarly, Achuta Rao

1.2 Nature and Solubility of Salts

5

Table 1.6 Mean solubility of inorganic salts depending upon the associated anions Type of anions Cl
-salts (NaCl + CaCl2 + MgCl2)/3 SO42
-salts (Na2SO4 + CaSO4 + MgSO4)/3 HCO3
-salts (NaHCO3 + Ca(HCO3)2 + Mg(HCO3)2)/3 CO32 -salts (Na2CO3 + CaCO3 + MgCO3)/3

Mean solubility, g 100 ml21 water at 0 C 10  C 20  C 30  C 40  C 49.4 51.3 55.0 64.0 74.0 

10.2

13.2

18.3

26.9

31.3

12.4

12.8

13.5

14.2

15.2

2.3

4.2

7.2

13.2

16.3

Source: Adopted from Table 1.4

Table 1.7 Distribution of ions in relation to EC of groundwaters of Rajasthan, India 21

Ions, me L Na+ K+ Ca2+ Mg2+ Cl
SO42
HCO3
+ CO32
SARa RSCa No. of samplesb Samples, % a

10 74.1 1.6 9.2 15.1 75.3 15.2 9.5 21.3
14.8 344 9

Calculated from the original data. Source: Paliwal (1972)

(1975) observed that groundwaters in the Cambrian sandstones and limestones and their lower Jurassic Lathi sandstone, containing mostly oxides and carbonates of Ca and Mg, have low EC, < 3 dS m
1. Percent increase in mean solubility of salts containing monovalent cation (Na+), with increase in temperature is more than of those salts containing divalent cations (Table 1.5). Solubility of Cl
and SO42
salts at higher temperatures is more than solubility of HCO3
and CO32
(Table 1.6) Thus, in tropical regions their leachability to groundwater and mobility from the place of formation to other areas is more. This explains why development of saline soils and existence of saline groundwaters is more in tropical as compared to those in temperate regions. However, one should note that soil solution is a complex mixture of many salts, solubility of which also changes due to common ion effects, preferential adsorption, fixation of different ions and geohydrology of the area.

1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

6

1.3

Origin/Source of Salts

Weathering of rocks and minerals in the earth’s crust is the chief (primary) source of soluble salts in soils and sea. Although the salts currently occurring in oceans arise mainly from weathering process of the earth crust, oceans now function as important “source term” for redistribution of salts. The main origin of salts for a particular area can be from one or combination of the following sources:

1.3.1

Weathering of Rocks and Minerals

Salts are formed and released in soil as a result of weathering of rocks and aluminium silicate minerals. To start with, chemical composition of soil and soil solution depends upon the mineral composition of rocks (Table 1.8). Apart from Si, Al and Fe, rocks are rich sources of Ca, Mg, Na and potassium. Basalt and carbonate rocks are rich sources of Ca while ultramafic rocks are rich sources of magnesium. Ultramafic volcanic rocks are generated in upper mental of the earth crust and composed of olivine [(Mg,Fe)2SiO4], orthopyroxene [(Mg,Fe)SiO3], and clinopyroxene [(Ca(Mg,Fe)Si2O6]. Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are i) limestone, which is composed of calcite (CaCO3), and ii) dolostone which is composed of dolomite [CaMg(CO3)2]. Aragonite (crystal form of CaCO3) formed due to biological and biochemical process including precipitation in marine and freshwater deposits is not found on land. Black shale, a sedimentary rock is a rich source of iron and sulphur while syenite, an igneous rock is a rich source of sodium, potassium and aluminium. Water flowing through acid magmatic rocks (Igneous rocks containing large crystals of quartz and feldspar) like granite, porphyry; and gneiss (Metamorphic rock containing mostly feldspar, quarts and mica formed under high temperature and Table 1.8 Elemental composition, g kg
1, of some common rocks Igneous rocks Element Si Al Fe Ca Mg Na K Cl S

Ultramafic 205.000 20.000 94.300 25.000 204.000 4.200 0.040 0.085 0.300

Basalt 230.000 78.000 86.500 76.000 46.000 18.000 8.300 0.060 0.300

Granite 314.000 82.000 29.600 530.000 9.400 28.400 25.200 0.130 0.300

Syenite 291.000 88.000 36.700 18.000 5.800 40.400 48.000 0.520 0.300

Source: Adopted from Turekian and Wedepohl (1961)

Shale 73.000 80.000 47.200 25.000 15.000 9.600 26.600 0.180 2.400

Sedimentary rocks Carbonate Sandstone stone 368.000 24.000 25.000 42.000 9.800 3.800 39.100 302.000 7.000 47.000 3.300 0.400 10.700 2.700 0.001 0.150 0.240 0.120

1.3 Origin/Source of Salts

7

pressure) etc. are least mineralized and practically contain carbonates, chlorides, silicates and sulphates. While water flowing through alkali magmatic rocks like basalt (Igneous rock formed due to rapid cooling of lava) and diabase (also called dolerite is an igneous rock containing augite and feldspar) are more mineralized and contain mainly carbonates, sulphates and silicates of Mg2+, Ca2+ and Fe2+. Rains containing dissolved CO2 can react with insoluble CaCO3 forming soluble Ca (HCO3)2 and carry it away from the site of its origin. That is the reason why soils in areas with high rainfall, do not have free calcium carbonate. It is assumed that most of Cl
in the earth crust comes through rains from seas. In the second phase it comes via irrigation through saline groundwaters. Chlorides may also be contributed from brine trapped in Paleozoic strata’s which are scattered within the earth crust. Paleozoic era refers to the first geological time from 542 to 252 million years ago when about 90 per cent of the marine life forms were wiped out. Weathering of rocks leads to formation of primary and secondary aluminosilicate soil forming minerals like orthoclase [Sanidine (Potassium feldspar, KAlSi3O8); albite (Sodium feldspar, NaAlSi3O8), Anorthite (Calcic feldspar, CaAl2Si2O8)]; augite [(CaNa)(MgFeALZnMn)(AlSi)2O6], biotite also called black mica or iron mica, [K(Mg,Fe)3AlSi3O10(OH)2], muscovite also called white mica [(KAl2(AlSi3O10)(FOH)], pyroxene [(CaNa)(MgFeAl)(AlSi)2O6] and silicate minerals like olivine [(MgFe)2SiO] etc. Hydrolysis of these orthoclase releases salts in the form of oxides of Si, Al and Fe with varying quantities of Ca, Mg, Na and K and free alkalinity (Eqs. 1.1 and 1.2) which in the presence of CO2 (atmospheric and or biological) give rise to bicarbonates of Na+ and calcium ions. 2NaAlSi3 O8 þ H2 O þ 2CO2 ! Al2 O3 þ 6SiO2 þ 2NaHCO3 Albite

CaAl2 Si2 O8 þ H2 O þ 2CO2 ! Al2 O3 þ 2SiO2 þ CaðHCO3 Þ2 Anorthite

ð1:1Þ ð1:2Þ

Even clay minerals like montmorillonite may hydrolyse to form kaolinite with the release of Na+, Ca2+ and Mg2+ (Eq. 1.3). ðNaCaÞ0:33 ðAlMgÞ2 ðSiO4 ÞðOHÞ4 :nH2 0 Montmorillonite

! Al2 Si2 O5 ðOHÞ4 þ nNaþ þ nCa2þ þ nMg2þ þ nðOHÞ


ð1:3Þ

Kaolinite

Weathering of rocks also leads to formation of non-silicate secondary minerals like iron oxide, [Hematite (Fe2O3), magnetite (Fe3O4)], iron bearing hydroxide minerals [Goethite (FeO(OH) and (FeMn)O(OH), ferrihydrite (Fe3+2O3.nH2O)], pyrites (FeS2); aluminium minerals like gibbsite (Al(OH)3); carbonate minerals like calcite (CaCO3), dolomite [CaMg(CO3)2], siderite (FeCO3), apatite

8

1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

[(Ca3(PO4)2.CaCO3]; and gypsum (CaSO4.2H2O) etc. These are sparingly soluble minerals and their mobility is governed by pH of the medium and climatic conditions. Under humid conditions, the released salts get leached from surface layers and do not accumulate in situ to cause salinization. Most of the salts are transported with runoff water to seas by streams and rivers. Therefore, inland salt-affected soils are rarely formed in humid areas. But under arid and semi-arid conditions, these weathering products accumulate in situ and result in development of salinity, referred as dry-land salinity. This process of formation of salt-affected soils as a result of accumulation of salts released during weathering in situ is called primary salinization. One of the reasons for development of salt-affected soils on introduction of canal water irrigation, which itself contains very little salts, is increase in the rate of weathering of already present primary aluminosilicate minerals, releasing more salts in soil solution.

1.3.2

Transportation and Accumulation of Salts on Surface Due to Irrigation

As a result of irrigation, applied water during post-irrigation cycle, transports salts already present in the soil profile to surface layers and leaves them behind after evapo-transpiration. Thus, over a period of time, salts which were earlier evenly distributed in the whole profile or were trapped in lower layers, may selectively accumulate in surface layers (active rootzone) leading to development of salinity. This process is called secondary salinization, and is the major limiting factor affecting productivity of irrigated agriculture.

1.3.3

Irrigation with Salt-Laden Groundwaters

Due to shortage of good quality surface waters, groundwaters are increasingly being exploited for supplementing irrigated agriculture in arid and semi-arid regions. These groundwaters are mostly loaded with varying quantities of minerals and when used for irrigation are the direct source of salts on otherwise good quality non-saline soils. Similarly, when groundwaters with high amounts of sodium, carbonate and bicarbonate ions are used for irrigation, these lead to poor permeability and sodification of good soils (Yaron and Thomas 1968).

1.3 Origin/Source of Salts

1.3.4

9

Accumulation of Run-Off in Cavities and Un-Drained Basins

In low lying areas as is the case between valleys, flat areas between two hillocks or sand dunes and un-drained (closed) basins or terminal basin, accumulation of salt loaded run-off from uplands and its subsequent evaporation is the major cause of salinity development.

1.3.5

Shallow Water Table

It is a common observation that water table in an area rises on introduction of canal irrigation. That is mainly due to inadequate drainage and inappropriate management of water, both during transport from dams, canals and on-farm use. In several irrigation commands, water table rise at the rate of 1 to 2 meter per year have been recorded (Table 1.9). Such groundwaters are often mineralized to some extent and as a result of capillary rise enrich surface soils with salts, following evaporation. In the absence of drainage to check rise in water table, this becomes the major factor leading to development of salty lands in irrigated areas. The salinization risks of high-water table are however, related to combination of its salt load (salt concentration and quantity of water that reaches the surface), depth and soil texture. It is generally only after some “critical depth” that these effects occur and start influencing crop yields. Knowledge of this phenomenon is of course quite important for irrigation and drainage operations in arid and semi-arid areas and is discussed in detail in Chap. 2.

1.3.6

Fossil Salts

Salt accumulation in arid regions often involves “fossil salts” derived from earlier deposits or entrapped solutions in former marine deposits. Fossil salts (e.g. rock salt, Table 1.9 Rise in water table, m, in different irrigation commands of India Irrigation Command a IGNP, Rajasthan Ghaggar Flood Plain, Rajasthan Ghaggar Depressions, Rajasthan Gang canal, Uttar Pradesh Bhakra canal, Punjab Source: Rao and Kamra (1991) Indira Gandhi Nahar Project

a

1982 0.92 0.50 1.08 0.33 0.58

1983 1.02 1.17 0.93 0.60 0.87

Year of measurement 1984 1985 1986 1987 1.14 1.17 1.16 0.70 1.06 1.11 1.02 0.60 0.68 0.80 0.80 0.70 0.83 0.79 0.77 0.62 0.91 0.87 0.79 0.80

1988 0.90 0.85 0.78 0.55 0.82

1989 1.05 0.98 0.90 0.70 0.89

1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

10

rock phosphate and gypsum etc.) are found in sedimentary rocks where due to rapid burial, precipitation or evaporation, these crystallize in compact areas called salt beds. Release of salts from these deposits may occur naturally or as a result of human activities. An example of the former is rise of salt bearing groundwater through an originally impervious cap (which becomes permeable as a result of weathering process) overlaying saline strata. Examples of the latter are building of canals, ponds or water works in saline strata and use of salty groundwater for irrigation. Highly pressurized brines penetrating in fresh groundwater by dissolution of salts or by puncturing of intervening soil layer may be another source of fossil salts. In Rajasthan, India, a canal built on an underlying gypsum layer has resulted in development of salinity in the area within only few years of its construction. This has been due to the perched water table as a result of seepage from canal and contribution of salts from underground gypsum layer.

1.3.7

Seepage from Upslopes Containing Salts

Under certain situations, seepage resulting from water inflow from upslope area can cause severe salinity of downward areas especially when the sub-surface water flow takes place through strata that are rich in salts and or marine deposits. Mineral springs owe their salts to such situations.

1.3.8

Oceans

Oceans are the biggest store-houses of soluble salts on the earth’s surface. Salts contained in present-day oceans have their origin in rocks and minerals found on the earth crust and vice-versa. These salts through dissolution, leaching and runoff are brought from mountains, the place of weathering of rocks, to rivers which deliver these regularly to oceans where they get concentrated through evaporation, and precipitate at the bottom. Though composition of sea water remains almost constant yet it can increase over time as in the Dead Sea which with 34.2% salts is 9.6 times saltier as compared to other oceans. The Dead Sea bordering Jordan, Israel and Palestine is 304 m deep and is a hyper-saline lake in the world. The Black sea between Eastern Europe and Western Asia having borders with Bulgaria, Georgia, Romania, Russia, Turkey and Ukraine is another example having salinity between 17.5 to 18.0%. Average salinity of the Indian Ocean varies between 3.2 to 3.7%. These sea-salts are the major cause of salinity development in coastal areas. Soils generally get loaded with salts from sea through the following processes: (i) Inundation of surface soil by seawater during high tides is a regular phenomenon in coastal areas. In addition to that serious inundation of coastal areas deep into the mainland can also take place through tsunami. These can leave behind

1.3 Origin/Source of Salts

11

huge quantities of salts, which can salinize agricultural lands and contaminate surface waters. (ii) Ingress of seawater through rivers, estuaries during high tides results in increase in salinity of these otherwise fresh waters which when used for irrigation result in salinization of soils. (iii) Due to over-exploitation of groundwater in areas near seacoast, there is decline in water table depth. It prompts subsurface inflow of seawater towards inland coastal areas. This results in increase in salinity of groundwater which when used for irrigation, results in salinization of soils. (iv) Salt-laden aerosols, which can be transported to many kilometres inland from seacoast and deposited as “dry fallout” or “wash-out” by showers can be another regular source of salts from sea to nearby mainland. Bursting bubbles at the ocean surface eject droplets of seawater into marine atmosphere. This is in addition to forceful separation of seawater droplets at the top of waves caused by strong winds. These saline water droplets are carried by strong winds in the form of sea sprays and deposit salts in nearby coastal regions. Sea sprays and waterspout in comparison to dry aerosols, directly impact nearby coastal regions. But dry aerosols may transport salts further inland and cause salinization of soils in agricultural areas far from seacoast. Through this process, inland depositions of NaCl @ 20 to 100 kg ha
1 year
1 are quite common. In many nearby areas, as much as 100–200 kg ha
1 year
1of salt deposits due to aerosols have been recorded. Even rainwater near sea may contain 6–50 mg NaCl per litre (Munns and Tester 2008), the concentration of course decreases with distance from seacoast (van Riehm and Quelimaiz 1959; Yaalon 1963). Although this amount may appear small, regular deposits over a long period of time may lead to salinization of the area. Carrol (1972) found an average amount of Na+ 2.05, K+ 0.35, Ca2+ 1.42, Mg2+ 0.39, Cl
3.47, SO42
2.19, NO3
0.27 and NH4+ 0.41 mg per ml in rainwater in Europe. Not only the amount of salts but also the ratio of ions carried by rainwater may be affected due to distance from the sea (Table 1.10; Hutton and Leslie 1958). Junge and Werby (1958) reported that as one goes away from coast, rainwater contains more calcium than sodium leading to narrow Na+:Ca2+ ratio and more SO42
than chloride ions. Table 1.10 Variations in composition of rainwater with distance from the seacoast Distance from seacoast, kms 1.6 32 104 192 256 320

Rainfall, mm annum21 800 828 617 447 335 264

Source: Hutton and Leslie (1958)

Na+, ppm 13.8 5.5 2.5 0.9 1.1 1.3

Na+:Cl2 0.9 1.0 1.0 1.5 1.5 1.5

Na+:Ca2+ 6.8 7.8 3.9 1.4 0.9 0.6

12

1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

(v) Salt sprays can directly deposit salts on foliage of trees and shrubs along sea-side and damage leaves, growing tips and buds and slow down rate of growth. Many buildings near sea get damaged due to salt sprays and salt laden winds from sea. In mountains where road salts, mostly CaCl2 and NaCl, are applied as de-icing agents to melt frozen ice, may cause salinity for vegetation along roadside.

1.3.9

Salt Laden Wind Drifts

In areas near desserts, dry marshy lands and large tracks of barren saline soils, the wind drafts in hot months may transport significant quantities of surface salts through wind erosion and deposit those on adjoining non-saline areas. As per “Aeolian theory”, wind-blown salts from adjoining salty areas may be one of the reasons for increase in salinity in desert areas. Within a small area, strong winds may also carry salt efflorescence from adjoining non-reclaimed alkali soils and deposit it on nearby reclaimed soils causing resodification (Chhabra 1996).

1.3.10 Chemical Fertilizers and Waste Materials Though use of chemical fertilizers (which are inorganic salts) and manures in agricultural fields is increasing, yet their contribution to overall salt built up is insignificant. In most of the developing countries, their level of use is so low that it cannot be a source of salts to cause salinity of agricultural lands. However, under certain situations such as dumping of cow dung slurry, piggery manure, droppings from poultry farms, sewage sludge, and industrial by-products like press mud, fly ash and pyrites etc. where doses of use are high amounting to many tonnes per ha, these can contribute to excessive accumulation of certain elements that can limit soil productivity. Salt injury due to heavy application of fertilizers can also occur at the time of seeding.

1.4

Classification of Salt-affected Soils

Based on pH of saturated soil paste (pHs), total soluble salts (% or g kg
1 soil) or electrical conductivity of saturated soil paste extract (ECe), and exchangeable sodium percentage (ESP), various attempts have been made to classify salt-affected soils into different categories/classes. Systems adopted by different countries and limits used for various classes are discussed below:

1.4 Classification of Salt-affected Soils

1.4.1

13

The USDA System

The USDA Salinity Laboratory Staff (Richards 1954) classified these soils into three categories (Table 1.11); saline, alkali and saline-alkali soils. Since 50% reduction in yield for most of agricultural crops takes place at ECe of 4 dS m
1, this was proposed as a “critical value” to distinguish saline from non-saline soils. Similarly, as physical properties, especially dispersion and permeability of soil was significantly affected at ESP more than 15, it was taken as a “critical value” for differentiating alkali from normal soils.

1.4.2

The USSR System

In former USSR, salt-affected soils have been classified into two groups: Solonchak and Solonetz. (a) Solonchak soils: Instead of expressing salt concentration on the basis of ECe, soil salinity is expressed in USSR on the basis of salt content as per cent of dry soil weight (Kovda 1965). On that basis, Solonchak soils are defined as those that contain more than 2% of soluble salts in upper 30 cm soil. In Russian language Solonchak means “salt marsh”. In Ukrainian language it means “salty soil”. In Ukraine there is a village by the name Solonchaky. Russian scientists consider CO32
, HCO3
, Cl
, SO42
, Na+, Mg2+ and K+ as toxic ions for growth of plants. Depending upon the total salt content, referred as toxic ions, expressed as percent of the soil mass (Stoxic,%), predominant type of soluble salts, and exchangeable-Na+, Lyubimova et al. (2009) have distinguished five categories of saline soils i.e. non-saline, slightly saline, moderately saline, strongly saline and very strongly saline (Solonchak) (Table 1.12). Relationship between the total salt content and category depends upon the nature and mixture of salts present i.e. predominately chloride, or predominately sulphate or predominately carbonate and bicarbonate ions, respectively. (b) Solonetz soils: Solonetz soils are defined as those characterized by high ESP in B horizon of soil profile. Mainly, based on type of clay minerals and ESP, Solonetz soils have been divided into four categories (Table 1.13).

Table 1.11 USDA Salinity Laboratory Staff system of classification Type of soil Saline Alkali Saline-alkali Source: Richards (1954)

pHs < 8.5 > 8.5 > 8.5

ECe, dS m21 > 4.0 < 4.0 > 4.0

ESP < 15 > 15 > 15

1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

14

Table 1.12 Assessment of soil salinity based on sum of toxic salts and content of separate ions in USSR

Degree of soil salinity Non-saline Slightly saline Moderately saline Strongly saline Very strongly saline

Soil salinity index in relation to composition of salts Predominately SO422 (including Predominately CO322 Predominately Cl2 Cl 2-SO422) and HCO32 Exch. Exch. Exch.Na+, Na+, C Na+, C mole mole S toxic, Cl2, S toxic, HCO32. C mole kg21 soil kg21 soil % %a % S toxic, % kg21 soil % < 0.05 < 0.03 0.05–0.12 0.3– 1.0 0.12–0.35 1.0– 3.0 0.35–0.70 3.0– 7.0 > 0.70 > 7.0

< 0.06 0.6–2.0

< 0.15 8.0

> 1.0

> 12

0.15– 0.30 0.30– 0.60 > 0.60

> 3.0

> 8.0

Sum of toxic salts (CO32
+ HCO3
+ Cl
+ SO42
+ Na+ + Mg2 + K+) expressed as percentage of the soil mass Source Lyubimova et al. (2009)

a

Table 1.13 The USSR classification of Solonetz soils Category Weakly solonetzic Moderately solonetzic Strongly solonetzic Solonetz

Exchangeable Sodium Percentage Chernozem soils Chestnut and Brown soils < 10 30 > 16

Source: Kovda (1965)

1.4.3

The European System

In addition to limits provided for ECe, ESP and pHs by the USDA Salinity Laboratory Staff, the Europeans (Szabolcs 1974) introduced in 1968 a genetic parameter i.e. structure of B horizon, and further classified these soils into two major groups: (a) Saline soils with or without structural B horizon. (b) Sodic soils with or without structural B horizon.

1.4 Classification of Salt-affected Soils

1.4.4

15

The Australian System

The Australian scientists have classified salt-affected soils into saline soils mainly on the basis of per cent salt content; sodic soils based on ESP, and alkaline soils based on pHs (Table 1.14), each with three categories. Considering that hydraulic conductivity problems in Vertisols start at very low ESP (McIntyre 1979), they used much lower threshold values of ESP to distinguish problems of sodicity in black soils.

1.4.5

The FAO-UNESCO System

In the FAO-UNESCO system (FAO 1974), salt-affected soils have been grouped in two categories: (a) Solonchaks: This group is characterized by high salinity within 125 cm of surface soil. High salinity is defined as an ECe of more than 15 dS m
1 at some time of the year within 125, 90 or 75 cm of surface with coarse, medium and fine textured soils, respectively; or an ECe of more than 4 dS m
1 within 25 cm of surface soil. The main sub-units are ascribed as orthic (too thin and too dry surface horizon with too high a colour value or chroma but very low content of organic carbon), mollic (thick dark coloured humus rich surface horizon), takyric and gleyic. (b) Solonetz: These soils are defined as having (i) natric B horizon in upper 40 cm layer of which ESP is more than 15 or (ii) having more exchangeable Na+ + Mg2+ than Ca2+ + exchangeable acidity (at pHs 8.2) within upper 40 cm of horizon and an ESP above 15 in sub-horizon within 2 m of surface. Soils without a natric horizon but having an ESP above 6 in some horizon within 1 m of surface are categorized as “alkaline phase”. The relationship between widely used classification systems is given in Table 1.15.

Table 1.14 The Australian system of classification Soil Type Saline soils, based on per cent salt content Sodic soils, based on ESP Alkaline soils, based on pHs Source: McIntyre (1979)

0 Non-saline 0.1% NaClClay >0.2% NaCl Moderately sodic6–14

2 Highly saline> 0.3% NaCl in B horizon Highly sodic> 14

Alkaline9.0–9.5

Strongly alkaline> 9.5

1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

16

Table 1.15 Correlation between widely used classification systems for salt-affected soils Basic grouping Saline

FAO-UNESCO Classification Solonchak Orthic solonchak

USDA Taxonomy Classification Salorthid

Salorthidic

Alkali

Mollic solonchak

Calciustoll Haplustoll

Takyric solonchak Gleyic solonchak Solonetz

Halaquept (in parts)

Orthic solonetz

Mollic solonetz

Gleyic solonetz

Salinealkali soils

Solodic planosol –

Natragrid Nadurardig Natriboralf Natrustalf Natrixeralf Natralboll Natriborol Natrustoll Natrixeroll Natraquoll Natraqualf Argialboll (in parts) Salidic Natraustalfs Saline/sodic phases of Calciorthids, Camborthids Pellusterts, Chromusterts, Vertic Ustochrepts

USSR Classification Fluffy solonchak (Non-steppic) Crust solonchak Fluffy solonchak (Steppic) Takyrs Meadow solonchak

Desert-steppe and desert solonetz Steppe solonetz

Meadow solonetz Solod Soda solonchak (Non steppic)

Source: Chhabra (1996)

1.4.6

The Indian System

In India’s Vedas and ancient scriptures there is frequent mention of urvara or fertile and anurvara meaning infertile or “barren” soils. Based on cause of their infertility, salt-affected soils were called usar or kallar soils, equivalent to modern alkali soils; and lunak equivalent to present-day saline soils. The cause of formation of lunak soils was assigned to the use of saline water known as khara pani (brackish water). Alkali salts, mostly Na2CO3 and NaHCO3 were harvested from surface scrapings of “usar” soils and used for washing of cloths.

1.4 Classification of Salt-affected Soils

17

In modern agriculture, Indian scientists adopted the USA system of classification and categorized salt-affected soils as saline, alkali and saline-alkali based on pHs, ESP and ECe limits prescribed by the USDA, Salinity Laboratory Staff (Richards 1954). National Bureau of Soil Survey and Land Use Planning, Nagpur, India prepared maps of salt-affected soils of different states using only ECe as criteria for saline soils (Table 1.16a), ESP for sodic soils (Table 1.16b) and pH for describing soil reaction (Table 1.16c). But it was realized that such a classification, based on only one property of soil, creates confusion especially with respect to choice of crops to be raised and the method of reclamation of such soils. It was also realized that since plant faces soluble salts, ESP and pH simultaneously so all the three parameters must be used together to classify salt-affected soils. But uncultivated alkali soils, under arid and sub-arid conditions, have high soluble salts associated with high pH and high ESP and thus were classified as saline-alkali soils. After reclamation, these soils have no problem of excess soluble salts and behave like alkali soils. Further, these soils have high ESP i.e. more than 15 even at pH less than 8.5. To solve these problems, the Indian scientists considered the nature of soluble salts in addition to the parameters proposed by the USDA Salinity Laboratory Staff, as an important index for classifying these soils (Bhargava

Table 1.16 Criteria adopted for classification and mapping of salt-affected soils by National Bureau of Soil Survey and Land Use Planning, Nagpur, India (a) Saline soils (S) based on ECe of saturated soil paste extract Symbol Degree of salinity effect S1 Slight S2 Moderate S3 Moderately strong S4 Strong S5 Severe S6 Very severe (b) Sodic soils (N) based on ESP Symbol Degree of sodicity effect N1 Slight N2 Moderate N3 Strong (c) Soil reaction based on pH Symbol Degree of soil reaction 1 Strongly acidic 2 Moderately acidic 3 Slightly acidic 4 Neutral 5 Slightly alkaline 6 Moderately alkaline 7 Strongly alkaline The values of ECe, ESP and pHs refer to those of 0–15 cm soil

ECe, dS m21 2–4 4–8 8–15 15–25 25–50 > 50 ESP 15 pHs < 4.5 4.5–5.5 5.5–6.5 6.5–7.5 7.5–8.5 8.5–9.5 > 9.5

1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

18

et al. 1976; Bhumbla 1977 and Chhabra 2005). It was further argued that pHs of 8.5 is too high, as the iso-electrical pH of precipitation of CaCO3, at which the sodification process starts is 8.2 and mostly this pHs is associated with ESP of 15 or more (Abrol et al. 1980). Abrol and Bhumbla (1978), Bhumbla and Abrol (1978) and Abrol et al. (1980, 1981) pointed out that the level of ECe should not be a criteria for classifying an alkali soil. They observed that instead of total salt concentration as measured through ECe, nature of soluble salts should be a stronger and reliable index for distinguishing alkali soils from saline soils. They observed that alkali soils contain soluble salts capable of alkaline hydrolysis and are predominately CO32
and HCO3
of Na+. While saline soils contain neutral soluble salts of Cl
and SO42
of Na+, Ca2+ and Mg2+. Carbonates (CO32
) are absent from saline soils. Chhabra (2005) further reported that instead of ECe, relative concentration of soluble ions is more appropriate in differentiating alkali from saline soils. Quantitatively when these soils have either (CO32
+ HCO3
)/(Cl
+ SO42
) > 1 and/or Na+/(Cl
+ SO42
) > 1 then these soils are to be treated as alkali soils. But when such soils have both Na+/ (Cl
+ SO42
) and (CO32 + HCO3
)/(Cl
+ SO42
) < 1, then irrespective of their pHs and SAR, these are to be treated as saline soils (Table 1.17). Considering these points, they have grouped these soils in two categories i.e. saline and alkali soils. Based on nature of major problem the plant faces for its optimum growth and the strategy to be adopted for reclamation, the soils previously classified as saline-alkali because of their high pHs, ESP and ECe are to be treated as either saline or alkali. In alkali Vertisols, there is no relationship between pHs and ESP. In these soils, pHs generally do not exceeds more than 9.0, while ESP at that pHs may go even up to 90.

Table 1.17 The Indian system of classifying salt-affected soils Soil properties pHs ESP

Saline soils < 8.2 < 15

ECe Nature & relative conc. of soluble ions, me L
1

> 4 dS m
1 Neutral, mostly Cl
and SO42
of Na+, Ca2+& Mg2+. HCO3
may be present but CO32
are absent. (CO32
+ HCO3
)/(Cl
+ SO42
) < 1 and Na+/ (Cl
+ SO42
) < 1

Nature of sparingly soluble salts

May contain gypsum.

Source: Chhabra (2005)

Alkali soils > 8.2 > 15, > 6 for Vertisols. In case of soils being irrigated with Mg-rich waters, ESP + EMgP >15 Variable, mostly 1 and or Na+/ (Cl
+ SO42
) > 1 Always contain free calcium carbonate.

1.6 Solution of Saline-Alkali Soils

1.5

19

Type of Salt-affected Soils and Methods of their Reclamation

Reclamation of saline soils involves removing excess soluble salts from the rootzone through leaching and lowering water table by providing drainage. While reclamation of alkali soils involves application of chemical amendments to lower ESP and pHs and leaching to push the reaction products below the rootzone; in case of salinealkali soils both leaching of excess soluble salts and lowering of high ESP are required for successful crop production. Since in nature, most of salt-affected soils of the Indo-Gangetic plains of India and elsewhere in the world, are high in pHs, have high ESP and contain high amounts of soluble salts (Chhabra 2005; Table 1.18), these have been classified as saline-alkali as per the criteria proposed by USDA (Bhargava 1972; Bhumbla et al. 1973; Bhargava and Abrol 1978; Sharma et al. 1982). However, large-scale reclamation of such soils has been achieved through application of chemical amendments like gypsum to lower ESP and pHs of soil (Chhabra 1996). Excess soluble salts present originally in those soils got leached down slowly and slowly along with the reaction products and moved below the effective rootzone. In these soils, conventional sub-surface drainage was neither necessary nor feasible because of their low hydraulic conductivity (Pandey et al. 1975; Dhruva Narayana et al. 1977; Dhruva Narayana 1980). Such soils were reclaimed by treating those as alkali soils only (Table 1.19).

1.6

Solution of Saline-Alkali Soils

Theoretically, soils with pHs > 8.2, ESP > 15 or ESR > 13 and ECe > 4 dS m
1 are referred as saline-alkali soils or soda-saline Solonetz or Soda Solonchak. When cropped directly i.e. without adopting any soil amelioration measures, plant growth in these soils suffers due to adverse effects of high pHs, high ESP/SAR and high Table 1.18 Composition of saturated soil paste extract of alluvial salt-affected soils of the IndoGangetic plains of India Concentration of ions in saturated soil paste extract, me L21 Na+ Ca2+ Mg2+ K+ CO322 HCO3 2 Cl2 SO4 22 248.3 0.70 0.20 0.40 141.6 136.2 6.6 3.9

Location of profile CSSRI Farm, Karnal, Haryana CSSRI Farm, Karnal, 1084.3 0.80 Haryana Guda, Karnal, Haryana 39.6 Tr. Khiranwali, Kapurthala, 41.5 7.5 Punjab Kurwal, Etah, U.P. 14.0 0.50 Dhadha, Partapgarh, U.P. 70.0 Tr. Nauner, Mainpuri, U.P. 70.2 0.40 Hirapur, Aligarh, U.P. 174.0 1.70 Source: Chhabra (2005)

0.40

3.60 560.0

236.0

273.6 19.6

0.25

2.30 138.0 0.50 19.4

47.6

38.0 21.5 28.5 0.7

1.70 0.50 1.20 2.20

0.20 0.10 0.10 0.40

27.5 63.5 182.0 21.0

13.7 22.4 12.0 25.0 74.5 29.5 19.0 3.0

149.0 392.0 105.0 132.0

Source: Chhabra (2005)

Location of profile CSSRI Farm, Karnal, Haryana CSSRI Farm, Karnal. Haryana Guda, Karnal, Haryana Khiranwali Kapurthala Punjab Kurwal, Etah, U.P. Dhadha, Partapgarh, U.P. Nauner, Mainpuri, U.P. Hirapur, Aligarh, U.P.

pHs 10.6 9.0 10.3 9.5 10.5 9.8 10.4 10.7

ECe, dSm21 22.3 102.3 22.6 4.8 14.4 30.4 29.3 12.4 ESP 96.0 95.5 92.4 69.3 89.4 92.5 95.4 93.0

SAR 370.2 1399.8 677.6 21.4 204.0 940.0 413.9 124.6

Old soil classification Saline-sodic Saline- sodic Saline-alkali Saline-alkali Saline- sodic Saline-sodic Saline-sodic Saline-sodic

CO322 + HCO32/Cl2 + SO422 26.46 2.72 3.12 0.66 5.68 12.31 2.76 3.83

Present soil classification Alkali soil Alkali soil Alkali soil Alkali soil Alkali soil Alkali soil Alkali soil Alkali soil

Table 1.19 Classification of salt-affected soils of the Indo-Gangetic plains of India based on pHs, ECe, ESP, nature and relative concentration of soluble salts

20 1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

1.6 Solution of Saline-Alkali Soils

21

concentration of soluble salts. Such soils are formed under a situation when irrigation is given with high RSC-water leading to precipitation of soluble and exchangeable-Ca2+ of soil as CaCO3. This enables Na+ to enter soil exchange complex leading to increase in ESP and rise in pHs, especially of surface layers. Mostly such soils occur in geographically transitional zone of alkali and saline soils. Further, soils with high pHs and high ECe as in alkali soils formed in situ; soils with high pHs and high ECe formed due to use high RSC-waters and soils with moderate pHs but high SAR and high ECe formed due to shallow saline water table high in SAR are all called saline-alkali soils. While all the three categories need different reclamation technologies. This creates a lot of confusion in mind of soil survey officials, development authorities and extension workers. An examination of composition of saturated soil paste extract of these soils shows that in contrast to saline soils, these contain sufficient amount of CO32
ions and in contrast to alkali soils these contain high amounts of Cl
and SO42
. Chhabra (2005), reported that when these soils have either (CO32
+ HCO3
)/ (Cl
+ SO42
) > 1 and/or Na+/(Cl
+ SO42
) > 1 then these soils are to be treated as alkali soils. But when such soils have both Na+/(Cl
+ SO42
) and (CO32
+ HCO3
)/(Cl
+ SO42
) < 1, then irrespective of their pHs and SAR, these soils are to be treated as saline soils. Considering this, soils of Khiranwali, Kapurthala Punjab, India, which were earlier classified as saline-alkali (Sharma et al. 1982) are to be classified as alkali soils and reclaimed through application of chemical amendments. Further, in Mg2+-rich soils, in addition to ESP, exchangeable magnesium percentage (EMgP) should also be considered as an index of soil physical problems. Because it has been observed that Mg2+ behaves like Na+ when it is in excess over Ca2+ in soil exchange complex. Based on these criteria, soils of various irrigation commands of Bihar, India which were earlier classified as saline-alkali soils (Pandey 1986) due to their high pHs (9.2–10.3), high ESP (61.9–91.4) and high SAR (70.0–716.6) of epipedon, are to be classified as alkali soils since the ratio of Na+/(Cl
+ SO42
) in their saturated paste extracts is >1 (Table 1.20). In Pakistan, most of soils labelled as saline-sodic (Thur bara, Qureshi and Barrett-Lennard 1998) are in fact alkali (bara) soils as these need Ca-based amendments for reclamation and maintaining their permeability. In Brazil, most of the present-day saline-sodic soils (Furquim et al. 2017) may behave either as saline or alkali soils. Similarly, because of their high pHs and high SAR, Sharma and Jha (1989) classified salt-affected soils of Madhubani district (now Darbhanga district) of Bihar, India (Table 1.21) as saline-alkali soils. But these soils which have been formed due to irrigation with high RSC waters, behaved like alkali soils. This is confirmed from the fact that these soils have (CO32
+ HCO3
)/(Cl
+ SO42
) > 1 and Na+/(Cl
+ SO42
) > 1. When an attempt is made to leach excess soluble salts from these soils, their pHs and ESP increases and there is decrease in infiltration rate. Such soils cannot be reclaimed without application of chemical amendments, which is required to lower their ESP and pHs. Alternatively, when gypsum is added to treat

Source: Chhabra (2005)

(a) Composition of saturated soil paste extract Location of profile Na+ Ca2+ Bijaipur, Gandak Com1480.0 4.01 mand, Bihar Bangaon, Kosi Command, 78.5 0.25 Bihar Garhani, Sone Command, 70.0 0.21 Bihar (b) Chemical properties and classification Location of profile pHs ECe, dSm21 Bijaipur, Gandak Com10.3 36.8 mand, Bihar Bangaon, Kosi Command, 10.2 4.6 Bihar Garhani, Sone Command, 10.1 3.0 Bihar SAR 716.6 111.0 70.0

91.4 61.9 50.5

0.03

1.80

ESP

0.20

Saline- sodic

Saline- sodic

Old soil classification Saline-sodic

7.5

19.0

0.31

0.70

CO322 + HCO3 2/ Cl2 + SO422 0.48

8.5

12.5

1.33

1.75

Na+/ Cl2 + SO422 3.44

22.2

22.0

Concentration of ions in saturated soil paste extract, me L21 K+ CO322 HCO3 2 Cl2 5.50 125.0 80.0 70.0

0.75

Mg 4.52

2+

Table 1.20 Chemical properties of salt-affected soils of Bihar, India and their classification as per the criteria of Chhabra (2005)

Alkali soil

Alkali soil

Present soil classification Alkali soil

30.3

22.8

SO4 22 360.6

22 1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

1.6 Solution of Saline-Alkali Soils

23

Table 1.21 Characteristics of salt-affected soils of village Subhankarpur, district Madhubani, Bihar, India Profile 1 Soil pH2a depth, cm

a

ECe, dSm21

SAR

0–9 9.6 9–40 9.0 40–76 8.6 76–140 9.1 + 140 8.8 Profile 2 Soil pH2a depth, cm

3.8 0.9 0.5 0.9 0.8

28.2 5.7 1.7 4.1 2.1

ECe, dSm21

SAR

0–12 12–30 30–85 85–124 +124

1.1 1.6 0.7 8.0 6.2

8.1 14.3 6.1 74.4 87.3

8.5 9.0 8.5 10.1 8.9

Concentration of ions in saturated soil paste extract, me L21 Na+ [Ca2++ K+ CO322 HCO32 Cl2 SO4 22 Mg2+] 31.3 3.5 0.1 7.0 9.0 3.0 2.0 5.9 3.0 0.2 nil 6.0 3.0 2.0 2.2 3.5 0.1 nil 3.0 2.0 1.5 5.0 3.0 0.1 nil 6.8 2.0 1.0 3.5 6.0 0.1 nil 4.0 4.0 5.0 Concentration of ions in saturated soil paste extract, me L21 + 2+ + Na [Ca + K CO322 HCO32 Cl2 SO4 22 Mg2+] 8.1 2.0 1.6 nil 4.0 7.0 5.0 14.3 2.0 2.6 5.0 10.5 2.0 3.3 4.3 1.0 1.1 nil 5.0 7.0 2.5 74.4 2.0 3.2 8.0 41.0 6.0 3.0 61.7 1.0 1.4 7.0 40.0 4.0 7.0

pH of 1:2 soil water suspension. Source: Sharma and Jha (1989)

high RSC of irrigation waters, which is the cause of formation of such soils, these get reclaimed without provision of extra leaching and drainage. However, when so called “saline-alkali soils” have both Na+/(Cl
+ SO42
) and (CO32
+ HCO3
)/(Cl
+ SO42
) < 1, then irrespective of their pHs and ESP/SAR, these soils are to be treated as saline soils. This is due to the fact that excess of Cl
and SO42
ions over Na+ ions keep sufficient Ca2+ and Mg2+ ions soluble in soil solution. Such a situation does not allow SAR to increase and thus prevents dispersion of soil particles which is required to maintain permeability/infiltration rate during leaching. While working on salt-affected soils in Iraq, Dieleman (1963) observed that some of the soils classified as saline-sodic behaved as saline soils. It is commonly apprehended that when such soils are leached there is disproportionate reduction in ECe and SAR. That may lead to rise in pH and subsequent dispersion of clay particles making these soils difficult to leach. These apprehensions are based on the fact that on leaching, ECe decreases linearly while SAR which depends upon the activity ratio of ions in soil decreases as a square root function (SAR ¼ Na+/√Ca2+ + Mg2+/2). Such phenomenon may lead to physico-chemical process of alkalinity production during leaching due to hydrolysis of exchangeable sodium causing increase in pH and reduction in soil permeability. But various studies done with soils where Na+/(Cl
+ SO42
) ratio is 8.5), which do not favour reduction. Their chroma values remain 2. These soils were classified under the taxonomical order Aridisols, an order characteristic of arid regions with light coloured surface soils and one or more alluvial horizons. The Salorthids group has saline horizon and corresponds approximately to Solonchaks of the FAO-UNESCO classification. The arid suborder with clay horizon may have a sodium-rich layer (Natragids) or both i.e. compact clay horizon and sodium rich layers, and corresponds to Solonetz soils. Other orders, particularly Mollisols and Alfisols, may be subject to salinity or sodicity phases where conditions favour their developments. Murthy et al. (1980) compiled information on benchmark profiles of salt-affected soils from all over India and classified those into association of great groups (Table 1.22). The mapping legend consisted of 12 associations. Natrustalf, Natraqualf, Haplaquept and saline phases of Calciorthids, Haplargids, Camborthids, Ustochrept, Fluvaquent and Haplaquept occur in Northern Indian plains; Salorthids, Natragids, Haplaquept and saline phases of Ustochrept form major units in the Western regions; Haplaquept and saline phases of Halaquept occur in the Eastern region; and largely saline and sodic phases of Pellustert, Chromustert, Ustifluvent and Haplaquept are found in Peninsular India. Soil Taxonomy is based on the observable properties and measurable thresholds, which in case of salt-affected soils do not correspond to the management thresholds. The current limit of ECe > 30 dS m
1 as a measure of salt concentration for salic horizon considered in these classifications for Alfisols, Aridisols, Inceptisols and Mollisols; and that of >15 dS m
1 for halic horizon under Vertisols, is too high for survival of plants and economic production of most agricultural crops. Thus, it fails to diagnose the soil’s limitation in cultivated lands, which are highly significant beyond an ECe of 4 dS m
1. World Reference Base for Soil Resources (FAO 1998) classifies these soils based on ECe for salic horizon as Solonchaks and ESP for natric horizon as Solonetz. This, as well as the U.S. Soil Taxonomy does not consider pHs, ECe, ESP, nature and relative concentration of soluble salts simultaneously to characterize salic or natric diagnostic horizon and thus falls short of giving solutions to difficulties encountered in field. Soil Taxonomy, in some cases does consider ECe along with ESP to classify salt-affected soils as in Salidic Natraustalfs and Halaquepts. This however, creates confusion similar to the term “saline-alkali” as given by the U.S. Salinity Laboratory

1.7 Soil Taxonomy and Classification of Salt-affected Soils

27

Table 1.22 Classification of salt-affected soils of India into association of great groups Great group Association level Saline Natragids, Salorthids, Halaquepts, Cypsiorthids.

Climate Arid to semi-arid

States Gujarat Rajasthan

Semi-arid

Southern part of Gujarat, Maharashtra, Karnataka, Andhra Pradesh, Tamil Nadu.

Saline/sodic phases of Pellusterts, Chromusterts, Vertic Ustochrepts.

Semi-arid in the West to sub-humid in the East

North India plains Punjab, Haryana, Delhi and West Uttar Pradesh.

Coastal and inundated (Sea water) humid areas

Kuttanad regions of Kerala, 24-Parganas of West Bengal.

Sodic Natraustalfs, Natraqualfs, Halaquepts, Saline/sodic phases of Calciorthids and Camborthids. Acid sulphate soils Tropaquept, Fluvaquent, Haplaquept.

Management problems Drainage and permeability problems make the reclamation uneconomical and difficult. Slow permeability, occurrence in depressions, dominance of montmorillonite causes high dispersion even at ESP 10–15; reclamation is difficult. Reclamation can be effective by application of gypsum; leaching and suitable cropping pattern. Engineering aspects include control of flooding by sea water and its ingress in to subsoil, drainage, leaching and liming to remove acidity and salt toxicity.

Source: Murthy et al. (1980)

System. These difficulties can be overcome by considering the criteria given by Chhabra (2005, Table 1.17). World Reference Base for Soil Resources (FAO 1998) also considers a high value of ECe i.e. 15 dS m
1 for defining a salic horizon. Because of such high limits, soils of Lath, Gohana, Haryana, India which have an ECe of 9.0 dS m
1 and those of Lunkaransar, Rajasthan which have an ECe of 14.4 dS m
1 in B horizon, do not qualify for salic horizon. These and many other similar soils, where crops completely fail or give very low yields due to harmful effects of high salt concentration, can only be classified as saline when limit of ECe for salic horizon is lowered to bring it within the threshold value for crop production i.e. 4 dS m
1. Soil Taxonomy takes into account characteristics of subsurface horizons i.e. salic and natric as diagnostic horizon for classification of salt-affected soils. Since, most of the cultivated soils in the tropics have also problems of salinity and sodicity in surface layer i.e. epipedon, directly affecting growth of most crops, this system in many cases fails to point out surface soil’s limitations as constraints for agricultural production. Manchanda and Khanna (1981) suggested the terms epihalic, epinatric and epihalonatric to represent surface salinity, sodicity or salinity-sodicity, respectively. It is similar to the term “external” as used in the World Reference Base for Soil Resources (FAO 1998). It is suggested that considering the criteria of Chhabra

1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

28

Table 1.23 Chemical properties of soils of Bijapur Gandak Irrigation Command of Bihar and their classification Properties pHs ESP ECe, dS m
1 (CO32
+ HCO3
)/(Cl
+ SO42
) Na+/(Cl
+ SO42
) Classification as per USDA Salinity Staff (!954) Classification as per Soil Taxonomy (1999) Classification as per Chhabra (2005)

Epipedon 10.3 91.4 36.8 0.19 1.40 Saline-alkali Typic Natrustalfs Epinatric Natrustalfs

B horizon 9.3 43.8 3.8 0.18 1.39

Source: Chhabra (2005)

(2005), the term “epihalonatric”, which refers to the confusing term “saline-alkali” should be dropped. Based on these considerations and taking into account chemical properties of epipedon and structural B horizon, soils of Bijapur Gandak Irrigation Command of Bihar, India, which were earlier classified as saline-alkali soils are classified as Epinatric Natrustalfs indicating that these soils have problem of sodicity in surface as well as in subsurface layers and will need chemical amendments for reclamation (Table 1.23).

1.8

Classification of Salt-affected Soils as per Their Geographical Location and Methods of Formation

From practical point of view, salt-affected soils are classified as per their geographical location into inland and coastal salt-affected soils (Fig. 1.3). Mainly based on pH and ECe, coastal saline soils are further classified as saline soils and acid-saline soils. Based on pHs, ECe, ESP, nature and relative concentration of soluble salts, inland salt-affected soils are further classified as saline and alkali soils. Based on method of formation, inland saline soils are classified into those affected by primary salinity as under non-irrigated dry-land conditions and the one formed due to secondary salinization as in irrigation commands. Saline soils, developed in irrigation commands, are further classified into those formed due to use of saline groundwaters and those formed due to shallow groundwaters (waterlogged saline soils). Alkali soils are classified as those with good quality groundwaters, with brackish shallow groundwaters, and those formed due to use of high RSC-waters. Such a classification helps in knowing their properties, problems the plants face, influence of climate and method of reclamation to be adopted. Such a general view of salt-affected soils also helps in understanding the causes of their formation and location-specific remedial measures for successful cropping.

1.9 Area of Salt-affected Soils

29

Salt-affected soils Inland salt-affected soils

Coastal salt-affected soils

Saline soils

Saline soils

Acid saline soils

Alkali soils

Primary salinity (Dry land salinity) Secondary salinity

Saline soils with shallow brackish groundwater (Waterlogged saline soils)

Alkali soils with good quality underground water Alkali soils with shallow brackish underground water Alkali soils formed due to use of high RSC waters

Saline soils formed due to use of underground saline water

Fig. 1.3 Classification of salt-affected soils as per their geographical location and method of formation

1.9

Area of Salt-affected Soils

Salt-affected soils have always existed on the landscape of earth in every country. Natural soil salinity in the form of saline springs, saline seeps, basin lands, salty alluvial deposits, saline fossil salts and saline marshes have always been there and predate the modern agriculture. It was only when the pressure on good agricultural land increased; these barren salt-affected lands were noticed for additional land area to increase production. But more importance was given to these soils when on introduction of irrigation, productivity of existing good soils decreased due to secondary salinization. Comprehensive information on distribution and extent of salt-affected soils in a country is important to know the amount of degeneration of these vital natural resources and to plan and execute strategies for their amelioration and utilization. At present, exact information on area and degree of deterioration is not available for all the countries, but a number of estimates have been made on global basis. Dregne (1977) estimated that 2 to 2.1 billion ha were affected by salinization and waterlogging, respectively. Massoud (1974) using the FAO-Unesco

30

1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

Table 1.24 Estimate of salt-affected soils in the world (area in 1000 ha) Regions Australia North and Central Asia South America South and West Asia Africa Europe Southeast Asia North America Mexico and Central America Total

Saline soils 17,597 91,383 69,410 82,676 53,492 7839 20,617 6191 1965 351,170

Alkali soils 339,971 120,065 59,753 1798 26,946 22,918 NA 9564 NA 581,015

Total 357,568 211,448 129,163 84,474 80,438 30,757 20,617 15,755 1965 932,185

Source: Massoud (1974)

Soil Map of the World, made an estimate of 932 million ha (Table 1.24), of which 316 million ha are in developing countries. By harmonizing world soil data base, FAO (2009) estimated 1327 million ha of salt-affected soils on global scale which shows an increase of 41.93% in salinity problems as compared to those in 1974. The largest areas of salt-affected soils are in Australia followed by North and Central Asia, South America and South and West Asia. Balba (1980) from desertification maps of the world (FAO 1977) estimated that total area subjected to salinization and sodification was about 600 million ha. Of these, 45 and eight million ha of land can be brought under cultivation by improving irrigation systems and drainage, respectively. According to Dudal and Purnell (1986), salt-affected soils occupy nearly 7% of the world’s land area. Updating the World Soil Resources using Soil and Terrain (SOTER) digital database methodology, FAO/Unesco Soil Map of the World (1970–80), FAO estimated that globally the total area of saline soils was 397 M ha and that of alkali soils 434 M ha (Table 1.25). Further, out of then 230 M ha of irrigated land, 45 M ha (19.5%) were salt-affected soils: and out of 1500 M ha of dry-land agriculture, 32 M ha (2.1%) were salt-affected soils, showing that the problem of salinity was more in irrigated areas (Olsen 1981) Umali (1993) in a World Bank Report estimated that by that time 1 to 1.5 M ha were lost every year to salinization in developing countries. Data from FAO’s data base Aquastat showed that in some countries, area affected by salinity can be as high as 50% of the area fully provided with irrigation. Nelson and Mareida (2001) estimated that about 12 M ha of irrigated land in the world may have gone out of production as a result of salinization. Munns and Tester (2008) reported that 20% of irrigated lands in the world are salt-affected. Some of these estimates are based on expert’s judgment or aggregation of statics which have been collected by different methods and different sources, and therefore are difficult to compare. Nevertheless, these point out gravity of situation and clearly bring out that the problem is increasing on introduction of irrigation. This also draws our attention to the point that huge investments being made in developing irrigation

1.10

Geographical Distribution

31

Table 1.25 Estimate of area under salt-affected soils as per Soil Maps of the World Total geo-graphical Regions area Asia and 3107.2 the Pacific and Australia Latin 2038.6 America Europe 2010.8 North 1923.7 America Africa 1899.1 Near 1801.9 East Total 12781.3

Per cent of the geo-graphical Alkali area soils 6.3 248.6

Per cent of the geo-graphical area 8.0

Total area of salt-affected soils 443.7

60.5

3.0

50.9

2.5

111.4

6.7 4.6

0.3 0.2

72.7 14.5

3.6 0.8

79.4 19.1

38.7 91.5

2.0 5.1

33.5 14.1

1.8 0.8

72.2 105.6

397.1

3.1

434.3

3.4

831.4

Saline soils 195.1

Source: FAO-Unesco (1981)

projects to increase agricultural production by the world communities will be at risk if we do not control the degradation processes of waterlogging and salinization.

1.10

Geographical Distribution

Salt-affected soils are found under varied soil, climate and physiographic conditions. Their developments are serious constraints in agricultural production in many countries and in every continent. Their distribution and estimated area are given in Table 1.26 and discussed below:

1.10.1 Africa It has been estimated (Fournier 1965) that about 2% of land area of Africa is saltaffected. Margat (1961) stated that in the North African region of Morocco, salt accumulation is the main cause of low agricultural production. Aubert (1962) cited by Fournier (1965) stated that many of Sierozems of Morocco, Algeria and Tunisia have high salt contents and contain layers of gypsum. In Egypt, primary salinity is widely distributed in northern lakes region and the Wadi-EL-Natrun area. Secondary salinization due to insufficient drainage, affects very large areas in and around Nile Valley. According to El-Gabaly (1959), soil salinity and alkalinity are major problems in Egyptian agriculture, affecting about 800,000 ha of cultivated soils. In Sudan, soil salinity is a major problem in Gezira and in the Northern Province (Ayoub 1960).

32

1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

Table 1.26 World distribution of salt-affected soil

Continent North America

Mexico andCentral America South America

Africa

Country Canada United States of America Cuba Mexico Argentina Bolivia Brazil Chile Colombia Ecuador Paraguay Peru Venezuela Afars and Issas Algeria Angola Botswana Chad Egypt Ethiopia Gambia Ghana Guinea Guinea Bissau Kenya Liberia Jamahiriya Madagascar Mali Mauritania Morocco Namibia Niger Nigeria Rhodesia Senegal Sierra Leone Somalia Sudan Tunisia

Saline (Solonchak) 264 5927 316 1649 32,473 5233 4141 5000 907 387 20,008 21 1240 1741 3021 440 5009 2417 7360 10,608 150 200 525 194 4410 362 2457 37 2770 640 1148 562 NA 665 NA 765 307 1569 2138 990

Area, 1000 ha Alkali (Solonetz) 6974 2590

Total 7238 8517

NA NA 53,139 716 362 3642 NA NA 1894 NA NA NA 129 86 670 5850 NA 425 NA 118 NA NA 448 44 NA 1287 NA NA NA 1751 1389 5837 26 NA NA 4033 2736 NA

316 1649 85,612 5949 4503 8642 907 387 21,902 21 1240 1741 3150 526 5679 8267 7360 11,033 150 318 525 194 4858 406 2457 1324 2770 640 1148 2313 1389 6502 26 765 307 5602 4874 990 (continued)

1.10

Geographical Distribution

33

Table 1.26 (continued)

Continent

South and West Asia

North and Central Asia

Southeast Asia

Australia

Europe

Country United Rep. of Cameroon United Rep. of Tanzania Zaire Zambia Afghanistan Bangladesh India Iran Iraq Israel Jordan Kuwait Muscat and Oman Pakistan Qatar Sarawak Saudi Arabia Sri Lanka Syrian Arab Republic United Arab Emirates China Magnolia Former USSR Democratic Kampuchea Indonesia Malaysia Myanmar (Former Burma) Socialist Republic of Vietnam Thailand Australia Fiji Solomon Islands Czechoslovakia France Hungary Italy Rumania

Saline (Solonchak) NA

Area, 1000 ha Alkali (Solonetz) 671

Total 671

2954 53 NA 3103 2479 23,222 26,399 6726 28 180 209 290 10,456 225 1538 6002 200 532 1089 36,221 4070 51,092 1291 13,213 3040 634

583 NA 863 NA 538 574 686 NA NA NA NA NA NA NA NA NA NA NA NA 437 NA 119,628 NA NA NA NA

3537 53 863 3103 3017 23,796 27,085 6726 28 180 209 290 10,456 225 1538 6002 200 532 1089 36,658 4070 170,720 1291 13,213 3040 634

983 1456 17,269 90 238 6 175 2 50 40

NA NA 339,971 NA NA 15 75 385 NA 210

983 1456 357,240 90 238 21 250 387 50 250 (continued)

34

1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

Table 1.26 (continued)

Continent

Country Former USSR Yugoslavia

Saline (Solonchak) 7546 20

Area, 1000 ha Alkali (Solonetz) 21,998 235

Total 29,544 255

Source: Szabolcs (1974) for data on Europe; Massoud (1974) for all other data

Out of 120 million ha of land, 64 million ha of soils are degraded to varying degrees (Ayoub 1998).

1.10.2 Asia Among the countries of South and South-East Asia, problem is greater in India, Indonesia, Malaysia, Bangladesh, Kampuchea, Thailand and Vietnam. These are otherwise thickly populated countries and need to increase their production to feed the ever-increasing population. In India, first reports of salt-affected soils in modern agriculture, were given by a traveller, Mr. Sleeman (quoted by Moreland 1901) who noticed reh, kallar or usar (local names for salt-affected soils) in the united province of Agra and Oudh and later on at Unao, Partapgarh and Rae. Bareli. Later Dr. J.W. Leather, an Imperial Agricultural Chemist appointed by the British Government, toured extensively the princely states of Uttar Pradesh and gave account in the form of tour reports (Leather 1887, 1893 and 1895), annual report (Leather 1906) and published his observations as review of salt-affected soils in Agricultural Journal of India (Leather 1911). In Haryana, India, the first report of salt-affected soils came in the year 1855 from a farmer in village Moonak, district Karnal, near headquarter of the present Central Soil Salinity Research Institute, after remodelling of Western Yamuna Canal indicating that the soils were deteriorating after introduction of canal irrigation. In Punjab, a part of old Indus Valley, incidences of soil salinity were noticed even before introduction of modern irrigation. Jameson (1852) reported large chunks of barren soils in villages Jag and Gaura of Kapurthala district, situated on the west of “Jamuna” (present day Yamuna river), were without crop because of want of water and partly due to soil salinity. Salt lands, called Kallar or present-day alkali soils were also wide spread in Sind part of the Indus plains now in Pakistan. Mann and Tamhane (1910) reported that salt lands in Nira canal area, 80 kms from Pune, Maharashtra, India, were due to salty subsoil water which existed within 1.5 m and was coming to surface due to waterlogging in almost all the canal irrigated areas. They suggested construction of open drains and deepening of existing drains to remove subsoil salty water. Waterlogging and salt built up had also been reported in tank irrigated areas of Southern India. Using stone and tile drains, experiments

1.10

Geographical Distribution

35

were conducted at Saidapet in Madras Presidency to reclaim waterlogged saline soils. At Central Rice Farm, Coimbatore, India, drains made from loose stone tiles and bamboo pieces were successfully tried to reduce salinity in rice lands under tank irrigation (Wood 1914). Singh (2005) has given detailed review of present and past salinity problems in the Indian sub-continent. The first estimate of area under salt-affected soils as 3,129,053 acres (1,271,997 ha) was prepared by the Director of Land Records and Agriculture in the year 1888. This was almost the same as given by Tiwari et al. in the year 1989. In post-independent India, estimates of total area affected, ranged from 6.1 M ha (Raychaudhuri 1965) and 7 M ha (Abrol and Bhumbla 1971) to 23.8 M ha (Massoud 1974). Forty per cent of this lies in the Indo-Gangetic plain, which is the most productive area of the country. Salt-affected soils exist in all the agro-climatic regions and agro-climatic zones of India. Bhumbla (1975) produced a map of saltaffected soils in India, depicting six categories of salt-affected soils i.e. alkali soils, saline soils, potentially saline soils, coastal saline soils, deltaic saline soils and acidsaline soils. Bhumbla (1977) further classified salt-affected soils of India into four broad groups (Table 1.27) based on nature of soil problem and their geographical distribution (Fig. 1.4). Singh (1992) estimated an area ranging from 7.162 to 7.877 M ha spread over the Indo-Gangetic alluvial region (Alkaline zone), the Indo-Gangetic alluvial region (Saline zone), red and grey desert soil region (Saline zone), medium and deep black soil region (Alkaline/saline zone), coastal saline soil region, and acid sulphate soils of humid region. Same author (Singh 1994) revised this figure to 8.5 M ha, out of which 3.03 M ha are located outside canal commands and thus represent dry-land salinity or saline soils developed under rain-fed conditions (Table 1.28). Another estimate pointed out that there are 8.38 M ha of saltaffected soils in India, which is 2.6% of the total cultivated area (329 M ha). These

Table 1.27 Type of salt-affected soils, their geographical distribution and approximate area in India Sr. No. 1.

2. 3. 4.

Type of soils Coastal salt-affected soils a) Coastal salt-affected soils of arid regions b) Deltaic coastal salt-affected soils of the humid region c) Acid salt-affected soils Salt-affected soils of the medium and deep black soil regions Salt-affected soils of the arid and semi-arid regions Sodic soils of the Indo-Gangetic plains

Source: Bhumbla (1977)

States in which they occur

Approx. area, M ha

Gujarat

0.714

West Bengal, Orissa, Andhra Pradesh and Tamil Nadu Kerala Karnataka, Madhya Pradesh, Andhra Pradesh and Maharashtra Gujarat, Rajasthan, Punjab, Haryana and Uttar Pradesh Haryana, Punjab, Uttar Pradesh, Bihar, Rajasthan and Madhya Pradesh Total

1.394 0.016 1.420 1.000 2.500 7.044

36

1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

Fig. 1.4 Problem soils in India (Extracted from India Salt-affected Soils, CSSRI, Karnal)

comprise of 2.36 M ha alkali soils, 3.83 M ha of inland saline soils and 2.19 M ha of coastal saline soils. Bhargava (2004, personal communication) based on information given in soil maps of different states prepared by the Institute of Soil Survey and Land Use Planning, Nagpur, estimated that in India, 15.6 M ha are affected by soil salinity and alkalinity including 2.1 M ha of Run and Kutch. Since different agencies used different limits for salinity and sodicity, and classes for mapping salt-affected soils, there are lots of discrepancies regarding the total area as well as area under saline and alkali soils. After a series of meetings with all stake holders, Sharma (1996) reported 7.42 million ha of salt-affected soils in different states of India. An attempt was made to harmonize the data available with different agencies by grouping all the 15 categories of salt-affected soils (Table 1.29a, b) into

1.10

Geographical Distribution

37

Table 1.28 Extent and distribution of waterlogged and salt-affected soils in India (1000 ha) Waterlogged area

State Andhra Pradesh Bihar Gujarat Haryana Karnataka Kerala Madhya Pradesh Maharashtra Orissa Punjab Rajasthan Tamil Nadu Uttar Pradesh West Bengal Total

Canal Uncommands classified Total 266.4 72.6 339.0

Canal commands 139.4

Salt-affected area Outside canal commands Coastal 390.6 283.3

362.6 172.6 229.8 36.0 11.6 57.0

NA 311.4 45.4 NA NA NA

362.6 484.0 275.2 36.0 11.6 57.0

224.0 540.0 455.0 51.4 NA 220.0

176.0 372.1 NA 266.6 NA 22.0

Nil 302.3 Nil 86.0 26.0 Nil

400.0 1214.4 455.0 404.0 26.0 242.0

6.0

105.0

111.0

446.0

NA

88.0

534.0

196.3 198.6 179.5 18.0 455.0

NA NA 168.8 109.9 1525.6

196.3 198.3 348.3 127.9 1980.6

NA 392.6 138.2 256.5 606.0

NA 126.9 983.8 NA 689.0

400.0 NA NA 83.5 Nil

400.0 519.5 1122.0 340.0 1295.0

NA

NA

NA

Nil

NA

800.0

800.0

2189.4

2338.7

4528.1

3469.1

3027.0

2069.1

8565.2

Total 813.3

Source: Singh (1994) Table 1.29 Limits for salinization/alkalization in Vertisols/Non-Vertisols used for mapping saltaffected soils in India (a) Limits for salinity and sodicity in Vertisols and non-Vertisols Sr. No. Severity class Salinity, ECe dS m21 Sodicity, ESP Vertisols Non-Vertisols Vertisols Non-Vertisols 1. Slight 2–4 4–8 5–10 15–40 2. Moderate 4–8 8–16 10–20 40–60 3. Severe >8 >16 > 20 > 60 (b) Classes used for mapping salt-affected soils (NRSA 2014) Sr. No. Soil type Type of effect Slight Moderate Severe S1 S2 S3 2. Sodic N1 N2 N3 3. Saline-sodic S1N1 S2N2 S1N3, S2N3, S3N1, S3N2, S3N3

two classes i.e. saline soils (ECe > 4 dS m
1) and alkali soils (ESP >15) in the GIS format. In doing so they grouped soils containing soluble CO32
as alkali whiles others as saline soils. Based on that harmonized data (Sharma et al. 2004 and Mondal

38

1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

Table 1.30 Estimates of area under salt-affected soils by remote-sensing (based on 1986 and 1987 satellite data with adequate field checks) State Gujarat Uttar Pradesh Maharashtra West Bengal Rajasthan Tamil Nadu Andhra Pradesh Haryana Bihar Punjab Karnataka Orissa Madhya Pradesh Andaman & Nicobar Islands Kerala Total

Saline soils 1680, 570 21,989 184,089 441,272 195,571 13,231 77,598 49,157 47,301 NA 1893 147,138 NA 77,000 20,000 2,956,809

Alkali soils 541, 430 1,346,971 422,670 0 179,371 354,784 196,609 183,399 105,852 151,717 148,136 0 139,720 0 0 3,770,659

Total 2,222,000 1,368,960 606,759 441,272 374,942 368,015 274,207 232,556 153,153 151,717 150,029 147,138 139,720 77,000 20,000 6,727,468

Source: Sharma et al. (2004), Mondal et al. (2011)

et al. 2011), the total area under salt-affected soils is estimated to be 6.727 M ha of which 2.956 and 3.771 M ha is under saline and alkali soils, respectively (Table 1.30). Out of these, 2.5 M ha are in the Indo-Gangetic plains. These estimates given by various workers and development agencies of India varied significantly because of the following reasons: (i) Many of the estimates are based on conjectures, presumptions and personal experiences of the administrators and experts. (ii) Different limits are used for classifying soils in different states of the country. Thus, it is possible that in few states only barren salt-affected soils are counted while in other states, soils with mild salinity/alkalinity are also accounted as salt-affected soils. (iii) Most of the estimates are based on secondary data collected by Department of Wastelands Development, Soil Conservation Departments, Agricultural Departments, Irrigation Command Authorities, Groundwater Cells and State Universities. Revenue Department mostly records fields where crops have failed, as area affected by salts. While the reason for failure can be lack of irrigation, failure of rains (Barani soils), poor seed quality, inadequate fertilizer use, attack by insects and pests or simply left as fallow. (iv) Thar Desert of Run and Kutch, in Gujarat, the great Indian Dessert, which is about 2.1 M ha and is severely affected by waterlogging and seawater salinity, was not included in the earlier estimates. During summer this area dries up and white coat of salts appear on surface; while during monsoons the marshland is flooded and transformed into inland sea.

1.10

Geographical Distribution

39

(v) Most of the irrigated Vertisols virtually have ESP > 6 and thus are to be included in alkali soils category. But many estimates do not include such areas as salt-affected as these are producing good cotton crop. Nazir (1965) stated that in Pakistan there are about 2 M ha of salt-affected soils in the Indus Valley and about 1.5 M ha in the Punjab. Khan (1988) reported that there are 6.67 M ha of salt-affected soils in Pakistan. In China, according to Syun, quoted by Bernstein and Hayward (1962), there are 20 M ha of salt-affected soils. Massoud (1974) has put that figure at 36.7 M ha. Kovda (1965) stated that salinity is wide spread in the Sungari Valley in Manchuria and the Hwang-Ho Delta, particularly near the Yellow Sea. These also occur in many arid and semi-arid regions of the country. Salinity near the Yellow sea is mainly due to marine chloride salts. Saline and alkali soils occur widely in the Asiatic USSR. Large areas occur in the river valleys of Eastern and Western Siberia in the Urals region and in the Araxes Valley in Armenia (Kovda 1965). Middle Eastern countries are much affected by salinity. In Syria, it is found in the Palmyra region, in the Euphrates, El-Khabour and Dan Valleys (Muir 1951). Salinity has been a problem in Iraq since ancient times, affecting most of the Euphrates and Tigri Valleys, whether irrigated or not (Buringh and Edelman 1955; Dieleman 1963; Russel et al. 1965; Sehgal and Sys 1980). In Iraq rising groundwater tables are damaging 5% of the cultivated lands annually. Salinity has decreased 70% potential of irrigated lands and up to 30% have completely gone out of production (Qureshi and Al-Falahi 2015). Qadir et al. (2008) estimated that 34 M ha including 4.1 M ha of irrigated lands are salt-affected in Iran. Salt-affected soils in Afghanistan are saline rather than alkali in character. The largest areas of salt-affected soils in this region, however, are in Iran and Saudi Arabia.

1.10.3 Australia Salt-affected soils are wide spread in many parts of Australia; both as naturally occurring alkali and saline soils and those formed as a result of man’s activities in sensitive dry-land situations. These soils are not widely cultivated and left as natural reserves. Because of the undulating topography, salinity develops in low-lying non-irrigated areas due to seepage from uplands. This phenomenon of dry-land salinity is quite common in Australia. Inland salinity is increasing and becoming a serious problem in irrigated areas. Almost 90% of the cultivated areas are alkaline in reaction. In these areas, subsoil sodicity is quit a serious problem leading to waterlogging in the rootzone. These soils, commonly known as “Duplex alkali soils” occur in wheat growing region of Western Australia, Queensland and Victoria states. Northcote and Skene (1972) estimated that sodic soils covered approximately 28% of the Australian continent. Massoud (1974) estimated that 17.269 and 339.971 M ha of saline and alkali soils, respectively occur in Australia. Later, Stoneman (1978) has put the area under saline soils to 16.700 M ha. Ford et al.

1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

40

(1993) estimated that at least 59% of the Victoria soils (i.e.13.4 M ha) were sodic which represent 73.4% of the total agricultural lands.

1.10.4 Europe Salt-affected soils are found in the alluvial regions of the Danube, Dnieper and Don in former USSR. These also occur in Eastern Europe in Hungary, Czechoslovakia, Rumania and Yugoslavia, where these account for about 10% of land area (Szabolcs 1989). In Western Europe, Spain have about 600,000 ha in Andalusia, Aragon and Catalonia (Ayers et al. 1960). The Netherlands (Holland) 1 s a special case as in that country though about 40% of land was originally under sea and thus saline, it has subsequently been drained and leached free of salts through a system of polders and intensive drainage (Brinkman 1980).

1.10.5 North America Salt-affected soils are found in 17 Western states of America, notably in Arizona, California, New Mexico, Texas and Utah and in parts of Canada. There are 77.6 M ha of saline and 69.3 M ha of alkali soils which together represent 15.8% of the total geographical area of America (Abrol et al. 1988). Significant areas of saline soils of varying origin also exist in Cuba (Blazhnil, 1957, cited by Bernstein 1962) and in Mexico.

1.10.6 South America Salt-affected soils are found in most countries of South America, particularly in Argentina, Brazil and Chile. Salinity and waterlogging have developed in coastal belt of Peru in an area 2000 km long and 10 km wide because of introduction of irrigation without providing drainage. Zavaleta (1965) estimated that crop production was reduced by salt accumulation in 25–30% area of that belt.

1.11

Modern Technologies for Estimating Extent of Salt-affected Soils

High cost of measuring salinity and sodicity (collection of samples and analysis in laboratory), inconsistency in data collection, variations in methods of analysis and limits for various classes and groups, and reporting methods have resulted in

1.11

Modern Technologies for Estimating Extent of Salt-affected Soils

41

incomplete and often contradictory information on nature, extent and distribution of salt-affected soils at state, country and on global levels. Considering vast areas to be surveyed, it is important that modern technologies involving remote sensing and geographical information system (GIS) coupled with ground truth should be adopted to map salt-affected soils. This involves development of nation-wide mapping legends, decision on extent of area in mapping unit, interpretation of satellite data, ground truth collection, uniform and standard procedures for analysis of soil samples in laboratory, post-field interpretation, reconciliation and area estimation. Except for subsoil sodicity and salinity, salt-affected soils are manifested by surface salt appearance. A variety of soil parameters and conditions, either individually or in association, contribute to several reflectance patterns of soils. Parameters like pHs, ESP, ECe, organic matter, soil texture, moisture status, concentration of iron oxide, nature of clay minerals and terrain conditions affect the ultimate reflectance pattern. Salt-affected soils invariably exhibit higher spectral reflectance than normal soils. These soils are seen as dull-white with bluish ting in false colour composites (FCC) print. False colour composite refers to a group of colours rendering methods used to display images in colour which were recorded in visible or non-visible parts of electromagnetic spectrum. These FCC show vegetation in red tone, as vegetation reflects most light in near infrared. The true-colour image shows area in actual colours, e.g. vegetation appears in green. It covers full visible spectrum using red, green and blue (primary colours) spectral bands of satellite. Combinations of red and infrared bands help in separating saline from alkali soils. Sharma (1989) has established the following legends for mapping of salt-affected soils (Table 1.31). However, the remote sensing technique should be used with caution as in some cases like sand dunes it can lead to wrong conclusions. Sand dunes like saline soils reflect higher energy in band 2, 3 & 4 of the satellite data, making their differentiation difficult. One way to differentiate between the two is to compare the data taken during different times especially that of summer and winter. Tabet et al. (1997) found that data taken in March (Summer period for their area) due to higher groundwater capillary and thus higher salinity built up on surface, showed higher Table 1.31 Legends for mapping of salt-affected soils of the Indo-Gangetic plain, India Soil class Highly alkali

pH > 9.5

Tone Clear white

Texture Smooth

Highly alkali Moderately alkali Saline soils

> 9.5 8.5–9.5

Streaked white Greenish blue, red or white intrusions White or red proximity of dark grey rims

Smooth Rough

< 8.5

Source: Sharma (1989)

Rough

Landscape Barren, 3–4 cm salt crust Barren Covered with coarse grasses Intermittently cropped

42

1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

Table 1.32 Distinguishing sandy from saline soils using Landsat Thematic Mapper (TM) bands

Soil Class Sandy soils Saline soils

2 0.52–0.60 Very easily separable Very easily separable

Landsat TM bands wavelength, μm 3 4 0.63–0.69 0.76–0.90 Very easily Inseparable separable Very easily Easily separable separable

6 10.40–1 2.40 Very easily separable Inseparable

Source: Sharma et al. (2004)

reflectance for saline soils than for sand dunes. Thus, by comparing the data taken in winter with that of summer, they could exclude area under sand dunes. Other way is to compare thermal reflectance and optical reflectance together to separate sand dunes from saline soils. Sand dunes by virtue of their coarse texture and extremely dry conditions record high emission in thermal band number 2 and 3 in comparison to that of saline soils (Sharma et al. 2004). Now- a-days, Thematic Mapper (TM) which is an advance multi spectral sensor, is used to scan earth’s resources. It primarily detects reflected radiation from the earth’s surface in visible and nearinfrared (IR) wavelengths and gives higher image resolution, sharp spectral separation, and more radiometric information than the Multispectral Scanner System (MSS) sensor. By using ETM + (Enhanced Thematic Mapper plus) which carries four detectors for thermal-IR band, provides four scan lines on each active scan, one can separate saline soils from sand dunes. Choosing the right time and integrating thermal band interpretation with FCC, helps in resolving the problem of spectral similarity between saline soils and sand dunes (Table 1.32). This technology also has difficulties in identification and mapping of soils with low degree of salinity, soils with subsoil salinity and sodicity, and saline Vertisols which lack any perceptible evidence of salt efflorescence on surface. In most of the irrigated agricultural lands, salt-affected soils appear in patches or irregular strips and not as a big chunk of land. This makes them difficult to identify and characterize through remote sensing. Suitable soil sensors and reflectance libraries for various soils are needed to resolve these issues. With these modifications, GIS can provide tools and standardize methodologies which can be used and extrapolated to other locations for estimating area under salt-affected soils and monitor their changes over the period. Benchmark sites should be established in each irrigation command for periodic monitoring of salinity, sodicity, and water quality; to develop and use early warning mechanisms to undertake preventive measures; and to develop farmerfriendly salinity assessment and monitoring systems. Assessment and monitoring of salinity should include associated toxic salts/ions such as boron, iron, aluminium, manganese, arsenic, selenium, nitrates etc. Legends for detecting presence of salts in sub-surface layers and depth of water table should also be developed.

1.13

1.12

Impact of Salt-affected Soils

43

Human Role in Development of Salt-affected Soils

Good agricultural lands have become salt-affected because of several faulty human activities such as: (i) Construction of roads, railway lines, dams, canals and bunds, there by blocking natural surface drainage, which leads to surface stagnation, rise in water table, waterlogging and ultimately to salinization of the area. (ii) Use of saline groundwaters for irrigation without providing adequate drainage for leaching of salts. This is converting good soils into saline soils. (iii) Use of high RSC groundwaters without treating is creating sodicity and permeability problems in normal soils and affecting their productivity. (iv) Faulty transport of water through unlined canals, field channels and mismanagement in on-farm use of irrigation water is leading to higher seepage, over irrigation and ultimately rise in water table and development of secondary salinity. It may be mentioned that “if construction of storage and conveyance system is the end in development of irrigated agriculture, the appearance of soil salinity is the beginning of the end”. Most farmers tend to over-irrigate because of unsure canal water supply and ignorance about proper depth and frequency of irrigation, leading to rise in water table. Similarly, though some soils may be well drained and non-saline under natural rain-fed conditions, but their permeability may not be adequate for irrigated agriculture. (v) Change of land-use from forest to agricultural crops (there are reports that flow of springs water increases after clearing of forest lands); change of cropping pattern from water sparing crops like millets to high water requiring crops like rice and sugarcane; rain-fed agriculture to irrigated agriculture and increase in intensity of cropping leading to more percolation losses of applied irrigation water, causing rise in water table and thus secondary salinization of many areas. Practice of leaving land fallow normally encourages more accumulation of salts on surface affecting production of the following crop.

1.13

Impact of Salt-affected Soils

Salts not only decrease agricultural production of most crops, but also, as a result of their effect on soil physico-chemical proprieties, adversely affect the associated ecological balance of the area. Some of the harmful impacts of salts are: (i) Low agricultural production due to decrease in yield and quality. (ii) Increase in soil erosion, by both water and wind, due to high dispersibility of soil and decrease in shear stress. (iii) Increase in floods due to higher runoff as a result of decreased permeability of soil. (iv) Low groundwater recharge leading to falling water tables. (v) Change in type of marine life from fresh to brackish water.

44

1 Nature and Origin of Salts, Classification, Area and Distribution of. . .

(vi) Ecological imbalances due to changes in plant cover from mesophytes to halophytes; from trees to bushes etc. (vii) Poor human and animal health due to a) toxic effect of elements such as F, B, Li, As and Se, and b) frequent outbreak of malaria and other diseases. (viii) Low economic returns due to high cost of cultivation. (ix) High maintenance cost and short life of buildings, roads, dams, tube wells and farm machinery.

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Russel JC, Kadry L, Hanna AB (1965) Sodic soils in Iraq. Agrokem. es Talajt 14(Suppl):91–98 Sehgal JL, Sys C (1980) Criteria for mapping salt-affected soils of the Mesopotamian and IndoGangetic plains. In: Proc. Symp. Salt-affected soils. Central Soil salinity Research Institute, Karnal, pp 56–66 Sharma BM, Jha SN (1989) Comparative studies on some salt-affected soils. J Indian Soc Soil Sci 37:524–531 Sharma PK, Singh C, Sehgal JL, Kanwal HS (1982) The soils of Kapurthala district for land-use planning, Soil Bull. 3. Punjab Agri. Univ, Ludhiana, 83p Sharma RC (1989) Mapping and characterization of salt-affected soils in Haryana using remote sensing techniques. Ph.D. thesis. Kurukshetra University, Kurukshetra Sharma RC (1996) Comments on the report on the status of land degradation in India. Department Soil and Water Conservation. Govt. of India, New Delhi, 6p Sharma RC, Rao BR, Saxsena RK (2004) Salt-affected soils in India- current assessment. In: Advances in Sodic Land Reclamation. Proc. Intern. Conf. Sustainable Management of Sodic Lands, Lucknow, India, pp 1–26 Singh NT (1992) Salt-affected soils in India. In: Khoshoo TN, Deekshatulu BL (eds) Land and soil. Har-Anand Publ, New Delhi, pp 65–100 Singh NT (1994) Land degradation and remedial measures with reference to salinity, alkalinity, waterlogging and acidity. In: Deb DL (ed) Natural resources management for sustainable agriculture and environment. Angkor Publication, New Delhi, pp 442–443 Singh NT (2005) Irrigation and soil salinity in the Indian sub-continent: Past and present. Lehigh University Press, Cranbury, 404p Soil Survey Staff (1975) Soil Taxonomy: a basic system of soil classification for making and interpreting soil surveys, Agriculture Handbook. 436. U.S. Department Agriculture, Natural Resources Conservation Services, Washington, DC, 869p Soil Survey Staff (1999) Soil Taxonomy- a basic system of soil classification for making and interpreting soil surveys, Agriculture Handbook. 436, 2nd edn. U.S. Department Agriculture, Natural Resources Conservation Service, Washington, DC, 863p Stoneman TC (1978) The nature and extent of salinity problems in Western Australia. In: Dryland saline seep control. 11th Cog. Intern. Soil Sci. Soc. Edmonton, Canada. Proc. Sub-Commission on salt-affected soils, pp 30–35 Szabolcs I (1974) Salt-affected soils of Europe. Martinus Nijhoff, The Hague, 63p Szabolcs I (1989) Salt-affected soils. CRC Press, Florida, 274p Tabet D, Vidal A, Zimmer D, Asif S, Aslam M, Kuper M, Strosser P (1997) Soil salinity characterization in SPOT images - a case study in one irrigation system of Punjab, Pakistan. In: 7th Intern. Symp. Physical measurements and signatures in remote sensing. Courchevel, France Tiwari KN, Sharma DN, Tripathi SK (1989) Salt affected soils of Uttar Pradesh, their reclamation and management. C.S. Azad Univ. Agric. & Tech, Kanpur, 34p Turekian KK, Wedepohl KH (1961) Distribution of the elements in some major units of the Earth’s crust. Geol Soc Am Bull 72:175–192 Umali DL (1993) Irrigation induced salinity: a growing problem for development and the environment, World Bank Technical Report. 215, Washington, DC, 78p Wood CR (1914) Sub-soil drainage in paddy lands. Agric J India 9:295–298 Yaalon DH (1963) The origin and accumulation of salts in groundwater and in soils of Israel. Research Council of Israel Bull Section 11G:105–131 Yaron B, Thomas GW (1968) Soil hydraulic conductivity as affected by sodic water. Water Resour Res 4:545–552 Zavaleta AG (1965) The nature of saline and alkali soils of the Peruvian Coastal Zone. Proc. Symp. Sodic Soils. Budapest. Agrokem. es Talajt. 14:415–424

Chapter 2

Saline Soils

2.1

Definition and Characteristics

Saline soils, also known as Solonchaks or “white alkali soils”, are those that contain appreciable amounts of soluble salts so as to interfere with plant growth. Electrical conductivity of saturated soil pastes extract (ECe) of these soils is >4 dS m
1, pH of saturated soil paste (pHs) is K > Na. The exchange of Zn with different ions is non-spontaneous and significantly influenced by pH of the suspension. Large

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7 Nutrient Management in Salt-affected Soils

Fig. 7.17 Zinc-deficiency symptoms in the form of rusty-brown spots on the leaves of paddy grown in a gypsum amended alkali soil (Chhabra 1996)

application of P-fertilizers to soils, low in available-Zn, can also cause “P-induced Zn- deficiency” in plants. This is due to reduced mobility and solubility of Zn in soil because of formation of zinc phosphate [Zn3(PO4)2], which being insoluble in water also reduces Zn absorption by roots. This can also be due to precipitation of Zn within the plant tissues making it unavailable for metabolic activities, commonly referred as biological inactivation of the absorbed zinc. This is one of the reasons of Zn-deficiency in P-rich alkali soils. Rice crop, though tolerant to soil sodicity, is sensitive to Zn-deficiency, which may appear 15–21 days after transplanting in the form of rusty-brown spots in strips along the length of fully matured leaves (Fig. 7.17) causing stunted growth, poor tillering, and low yields. In extreme cases the whole leaf becomes dark brown and the field gives a burned appearance. Commonly known as “Khaira” disease in most of the rice-growing areas, it is a physiological disorder due to Zn-deficiency. In marginal cases, plants recover after 30–45 days and put-up new leaves and tillers, but maturity is delayed by 7–10 days. Moderate to severe yield reduction due to Zndeficiency have been reported by several workers (Kanwar and Randhawa 1974; Chhabra 1976a; Takkar and Randhawa 1978; Singh et al. 1979a, b, c, d). Besides addition of amendments and nitrogen, application of Zn is important for getting optimum crop yields in alkali soils. From results of field studies, Singh et al. (1987) reported that in an alkali soil amended with 10 t ha
1 of gypsum (which was equal to 100% gypsum requirement of the soil), 10–20 kg ZnSO4.7H2O ha
1 was enough to meet Zn-requirement of rice and wheat crops (Table 7.11). At optimum dose of gypsum, increase in amount of ZnSO4 application beyond 10 kg ha
1 did not increase grain yield significantly. At low levels of gypsum application (0, 2.5 and 5 t

7.3 Fertilization of Alkali Soils

383

Table 7.11 Effect of gypsum and zinc sulphate on yield, t ha
1, of rice in an alkali soil Gypsum level, t ha21 0 2.5 5.0 10.0 ZnSO4.7H2O, kg ha 0 0.12 0.98 2.14 2.65 10 0.49 1.87 3.06 3.77 20 0.58 2.00 3.14 3.85 30 0.68 1.75 2.99 3.92 40 1.05 2.02 3.29 3.89 Mean 0.59 1.72 2.93 3.62 LSD at P ¼ 0.05 for Gypsum levels ¼ 0.36; Zinc levels ¼ 0.28; Interaction ¼ NS 21

Mean 1.48 2.30 2.39 2.34 2.56 –

Source: Singh et al. (1987)

ha
1) and moderate dose of applied-Zn, the plants suffer more from Na-toxicity and Ca-deficiency rather than from Zn-availability. It was further observed that at all levels of gypsum application, increase in dose of zinc sulphate increased Zn content of plants. The mean Zn content of rice plant at tillering stage increased from 13 (control) to 23, 26, 28 and 36 mg kg
1 by application of 10, 20, 30 and 40 kg ZnSO4.7H2O ha
1. However, that did not increase the grain yield showing that in alkali soils, not only Zn content but also optimum concentration of other nutrients plays major role in increasing the grain yield. This was also due to the fact that when Zn concentration in the plant reached beyond a threshold concentration of 20 mg kg
1, there was no response to additional application of zinc sulphate. Since recovery of added Zn by plants is