Methods of Soil Analysis, Part 5: Mineralogical Methods 0891188460, 9780891188469

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Published 2008

Methods of Soil Analysis Part 5—Mineralogical Methods

Methods of Soil Analysis Part 5—Mineralogical Methods APRIL L. ULERY & L. RICHARD DREES, Co-editors

Book and Multimedia Publishing Committee David Baltensperger, Chair Kenneth Barbarick, ASA Editor-in-Chief Craig Roberts, CSSA Editor-in-Chief Sally Logsdon, SSSA Editor-in-Chief Mary Savin, ASA Representative Hari Krishnan, CSSA Representative April Ulery, SSSA Representative Managing Editor: Lisa Al-Amoodi

Number 5 in the Soil Science Society of America Book Series Published by Soil Science Society of America, Inc., Madison, Wisconsin, USA

Copyright © 2008 by the Soil Science Society of America, Inc.

ALL RIGHTS RESERVED. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. The views expressed in this publication represent those of the individual Editors and Authors. These views do not necessarily reflect endorsement by the Publisher(s). In addition, trade names are sometimes mentioned in this publication. No endorsement of these products by the Publisher is intended, nor is any criticism implied of similar products not mentioned.

Soil Science Society of America, Inc. 677 South Segoe Road, Madison, WI 53711-1086 USA ISBN: 978-0-89118-846-9 Library of Congress Control Number: 2008922682

Cover: Selenite crystals exposed in a deflational zone. Inset: A secondary electron image of kaolinite vermiforms. Back: Thin section of exfoliating selenite. Photos courtesy of Curtis Monger, New Mexico State University and G. Norman White, Texas A&M and Texas Commission on Environmental Quality.

Printed in the United States of America.

Dedication This monograph is dedicated to L. Richard Drees, the first editor of this project. Unfortunately, he fell ill and had to relinquish his editorial duties before this book was complete. Richard was instrumental in getting this project approved, lining up chapter authors, and establishing the aim and scope of the book. Although it was generally agreed upon that the 1986 Methods of Soil Analysis. Part 1. Physical and Mineralogical Methods was in need of updating, no one else stepped forward to lead the effort. Richard was born and raised in Ohio and earned B.S. and M.S. degrees from The Ohio State University. In 1977, he joined the Soil and Crop Sciences Department at Texas A&M University as a research technician working with Dr. Larry Wilding. In the 1980s he began work, part-time, toward a Ph.D. degree in soil science, which he received in 1986. He remained at Texas A&M as a research scientist working in soil mineralogy and soil genesis. He was the author or co-author of more than 50 scientific publications and became internationally recognized in the area of soil micromorphology. Richard served as an associate editor for the Soil Science Society of America Journal, chaired the SSSA Soil Mineralogy Division, and was active in many professional organizations. Dr. Richard Drees was widely recognized for the number and quality of his research publications published in prestigious outlets. The results of his research were timely, generated through meticulous investigations, creative, and widely cited in the literature. Richard’s assistance was sought by graduate students and faculty that needed his expertise in X-ray analysis, X-ray spectroscopy, thin section microfabrics, spatial soil variability, sampling theory, and image analysis procedures. He was a very unassuming individual and commonly gave credit to his peers and students rather than claiming his rightful recognition for seminal contributions. He received numerous awards for excellence in research, teaching, and service. Richard’s family was the single most important thing in his life, although he spent many hours helping students complete their degrees and assisting colleagues with their research. He died in October 2005 surrounded by his family. April Ulery Mike Vepraskas Larry Wilding

v

Contents Foreword Preface Contributors Conversion Factors for SI and Non-SI Units

ix xi xiii xv

Chapter 1

Sampling Soils for Mineralogical Analyses D.A. Soukup L.R. Drees W.C. Lynn

1

Chapter 2

Preparing Soils for Mineralogical Analyses D.A. Soukup B.J. Buck W. Harris

13

Chapter 3

Selective Dissolution Techniques for Mineral Analysis of Soils and Sediments Chao Shang Lucian W. Zelazny

33

Chapter 4

X-ray Diffraction Techniques for Soil Mineral Identification Willie Harris G. Norman White

81

Chapter 5

Thermal Analysis of Soil Minerals A.D. Karathanasis

117

Chapter 6

Petrographic Microscope Techniques for Identifying Soil Minerals in Grain Mounts Warren Lynn J.E. Thomas L.E. Moody

161

Chapter 7

Soil Micromorphology: Concepts, Techniques, and Applications M.J. Vepraskas M.A. Wilson

vii

191

viii Chapter 8

Digital Image Analysis of Soil Micromorphology A. J. VandenBygaart R. Protz C. Duke

227

Chapter 9

Transmission Electron Microscopy for Soil Samples: Preparation Methods and Use 235 Françoise Elsass Claire Chenu Daniel Tessier Chapter 10

Scanning Electron Microscopy G. Norman White

269

Chapter 11

Use of Atomic Force Microscopy to Study Soil Particle Properties and Interactions Patricia A. Maurice Steven K. Lower

299

Chapter 12

Electron Microprobe Techniques Renald N. Guillemette

335

Chapter 13

Diffuse Reflectance Spectroscopy José Torrent Vidal Barrón

367

Chapter 14

Analysis of Soils and Minerals Using X-ray Absorption Spectroscopy S.D. Kelly D. Hesterberg B. Ravel

387

Chapter 15

Structural Allocation of Clay Mineral Elemental Components A.D. Karathanasis

465

Chapter 16

Analysis of Layer Charge, Cation and Anion Exchange Capacities, and Synthesis of Reduced Charge Clays David Laird Pierce Fleming Subject Index

485

509

Foreword The Soil Science Society of America is extremely pleased to publish this comprehensive compilation of modern mineralogical methods. Co-editors April L. Ulery and L. Richard Drees have done an outstanding job of assembling this volume. This valuable work began with the vision of Dr. L. Richard Drees, who unfortunately fell ill during the early stages of the monograph and was unable to complete the task. Co-editor Dr. April Ulery has done a great job of bringing it to completion. The authors contributing to this new installment in Methods of Soil Analysis are scientists at the forefront of research in mineralogy, and their expertise brings great credibility to this work. Research scientists and students from a broad range of disciplines will benefit greatly from this assemblage of proven and practical methodology. The Soil Science Society of America certainly appreciates the efforts of the editors, Drs. Ulery and Drees, who skillfully guided the development of the book. Thank you also to the Members of the Editorial Committee, which included Will Gates, David Laird, William “Billy” Kingery, Mark Elless, and Michael Vepraskas. The editors, along with the highly qualified authors, provide a truly excellent book, one of which our Society can be justly proud. We hope you will find this book to be a highly valued resource for your laboratories. Gary A. Peterson, President of the Soil Science Society of America

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Preface Soil mineralogy has a profound influence on the chemical characteristics and dynamic behavior of soils and the environment. An understanding of the mineralogical composition provides insight into the fundamental behavior of soils and their response to environmental conditions and management. This book is intended to give students and scientists proven methods for measurement of soil mineralogical properties. In this volume we have updated Methods of Soil Analysis. Part 1. Physical and Mineralogical Methods (1986) to reflect improvements in techniques, new techniques, newer instruments, and more quantitative analysis. There has been a proliferation of instrumentation and the interface of computer manipulation, data acquisition, and data analysis with new and old methodologies. Several methodologies and instruments were not even on the minds of soil scientists just a few years ago, e.g., atomic force microscopy and X-ray absorption spectroscopy. While this volume does not represent a comprehensive treatise of all mineralogical methods, we present a range of valuable techniques and subjects that will enable researchers to analyze mineralogy for a wide variety of applications—from soil classification to environmental remediation. Highlights include extensive coverage of new techniques, such as X-ray absorption and diffuse reflectance spectroscopy, and updated chapters on thermal analysis and selective dissolution methodologies. Our target audience is researchers and advanced students in soils, geology, mineralogy, environmental engineering, and environmental sciences. The text was written with soil minerals in mind, not geological specimens or ideal endmembers that have perfect crystallinity or morphology. Soils are dynamic and diverse, and so are soil minerals. The emphasis of this volume is on the analysis and interpretation of data to aid in identifying soil minerals and understanding their impact on soils and the environment. The goal of each chapter is to equip the reader with an understanding of the basic principles and theory of the analytical method, guide the reader through the method itself, and finally assist in the interpretation and analysis of results collected. This title in the Methods of Soil Analysis series began with the vision of my co-editor, Richard Drees, to whom I am personally grateful and this book is dedicated. The authors are acknowledged for their cooperation in updating all of their chapters when I came on as co-editor. All of the chapters were reviewed by at least two scientists familiar with the method and I sincerely appreciate all of their efforts and professionalism. Special recognition and thanks go to Drs. Will Gates and David Laird for their constructive reviews and revisions of several chapters each. Members of the Editorial Committee also included William “Billy” Kingery, Mark Elless, and Michael Vepraskas. I also want to acknowledge the Managing Editor, Lisa Al-Amoodi. She and the SSSA Headquarters Staff were always professional, extremely competent, and a pleasure to work with. April Ulery, Co-editor, New Mexico State University, Las Cruces xi

Contributors Barrón, V.

Dep. de Ciencias y Recursos Agrícolas y Forestales, Universidad de Córdoba, Edificio C4, Campus de Rabanales, 14071 Córdoba, Spain ([email protected])

Buck, B.J.

Dep. of Geosciences, University of Nevada, 4505 Maryland Pkwy., Las Vegas, NV 89154 ([email protected])

Chenu, C.

AgroParisTech, BIOEMCO, Bâtiment EGER, F-78850 Thiverval Grignon, France ([email protected])

Drees, L.R.

deceased, formerly Soil and Crop Sciences Dep., Texas A&M University, College Station

Duke, C.

Ontario Ministry of Agriculture, Food and Rural Affairs, Guelph, Ontario, Canada

Elsass, F.

Institut National de la Recherche Agronomique, Centre de Géochimie de Surface, 1 rue Blessig, F-67084 Strasbourg, France ([email protected])

Fleming, P.

USDA-ARS, National Soil Tilth Laboratory, 2150 Pammel Drive, Ames, IA 50011

Guillemette, R.N.

Dep. of Geology and Geophysics 3115, Texas A&M University, College Station, TX 77843-3115 (guillemette@ geo.tamu.edu)

Harris, W.G.

Soil and Water Science Dep. 2169 McCarty Hall, University of Florida, Gainesville, FL 32611 ([email protected])

Hesterberg, D.

North Carolina State University, College of Agriculture and Life Sciences, Dep. of Soil Science, Box 7619, Raleigh, NC 27695 ([email protected])

Karathanasis, A.D.

Dep. of Plant & Soil Sciences, N-122K Ag. Science-North, University of Kentucky, Lexington, KY 40546 (akaratha@ uky.edu)

Kelly, S.D.

Argonne National Laboratory, Bioscience Division, 9700 South Cass Avenue, Argonne, IL 60439 ([email protected])

Laird, D.A.

USDA-ARS, National Soil Tilth Laboratory, 2150 Pammel Drive, Ames, IA 50011 ([email protected])

Lower, S.K.

Dep. of Geological Sciences and The School of Natural Resources, The Ohio State University, Columbus, OH 43210

Lynn, W.

retired, formerly USDA-NRCS, National Soil Survey Center, Lincoln, NE

xiii

xiv

Maurice, P.A.

Dep. of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, IN 46556 ([email protected])

Moody, L.E.

Earth & Soil Sciences Dep., California Polytechnic State University, San Luis Obispo, CA

Protz, R.

deceased, formerly University of Guelph, Ontario, Canada

B. Ravel

Argonne National Laboratory, Bioscience Division, 9700 South Cass Ave., Argonne, IL 60439; currently at National Institute of Standards and Technology, Ceramics Division, 100 Bureau Drive, Gaithersburg, MD 20899-8520 ([email protected])

Shang, C.

Dep. of Crop and Soil Environmental Sciences Virginia Polytechnic and State University, Blacksburg, VA

Soukup, D.A.

Geoscience Dep., University of Nevada, 4505 Maryland Pkwy., Las Vegas, NV 89154 ([email protected])

Tessier, D.

Institut National de la Recherche Agronomique, PESSAC Unit RD 10, Route de Saint-Cyr, F-78026 Versailles, France ([email protected])

Thomas, J.E.

USDA-NRCS, National Soil Survey Center, Lincoln, NE

Torrent, J.

Dep. de Ciencias y Recursos Agrícolas y Forestales, Universidad de Córdoba, Edificio C4, Campus de Rabanales, 14071 Córdoba, Spain ([email protected])

Ulery, A.L.

New Mexico State University, Plant and Environmental Sciences, P.O. Box 30003, MSC 3Q, Las Cruces, NM 88003-8003 ([email protected])

VandenBygaart, A.J.

Agriculture & Agri-food Canada, 960 Carling Avenue/960 Carling Avenue, Ottawa, Ontario, K1A 0C6 ([email protected])

Vepraskas, M.J.

Soil Science Dep., Box 7619, North Carolina State University, Raleigh, 27695-7619 ([email protected])

White, G.N.

formerly Dep. of Soil and Crop Science, Texas A&M University, College Station, TX; currently Texas Commission on Environmental Quality, MC-150, P.O. Box 13087, Austin, TX 78711-3087 ([email protected])

Wilson, M.A.

USDA-Natural Resources Conservation Service, 100 Centennial Mall N., Rm. 152, MS 41, Lincoln, NE 685083866 ([email protected])

Zelazny, L.W.

Dep. of Crop and Soil Environmental Sciences Virginia Polytechnic and State University, Blacksburg, VA ([email protected])

Conversion Factors for SI and Non-SI Units

To convert Column 1 into Column 2 multiply by

Column 1 SI unit

Column 2 non-SI unit

Length mile, mi yard, yd foot, ft micron, μ inch, in Angstrom, Å

0.621 1.094 3.28 1.0 3.94 × 10−2 10

kilometer, km (103 m) meter, m meter, m micrometer, μm (10−6 m) millimeter, mm (10−3 m) nanometer, nm (10−9 m)

2.47 247 0.386 2.47 × 10−4 10.76 1.55 × 10−3

hectare, ha square kilometer, km2 (103 m)2 square kilometer, km2 (103 m)2 square meter, m2 square meter, m2 square millimeter, mm2 (10−3 m)2

9.73 × 10−3 35.3 6.10 × 104 2.84 × 10−2 1.057 3.53 × 10−2 0.265 33.78 2.11

cubic meter, m3 cubic meter, m3 cubic meter, m3 liter, L (10−3 m3) liter, L (10−3 m3) liter, L (10−3 m3) liter, L (10−3 m3) liter, L (10−3 m3) liter, L (10−3 m3)

2.20 × 10−3 3.52 × 10−2 2.205 0.01

gram, g (10−3 kg) gram, g (10−3 kg) kilogram, kg kilogram, kg

To convert Column 2 into Column 1 multiply by

1.609 0.914 0.304 1.0 25.4 0.1

Area acre acre square mile, mi2 acre square foot, ft2 square inch, in2

0.405 4.05 × 10−3 2.590 4.05 × 103 9.29 × 10−2 645

Volume acre-inch cubic foot, ft3 cubic inch, in3 bushel, bu quart (liquid), qt cubic foot, ft3 gallon ounce (fluid), oz pint (fluid), pt

102.8 2.83 × 10−2 1.64 × 10−5 35.24 0.946 28.3 3.78 2.96 × 10−2 0.473

Mass pound, lb ounce (avdp), oz pound, lb quintal (metric), q

454 28.4 0.454 100 continued

xv

xvi To convert Column 1 into Column 2 multiply by

Column 1 SI unit

Column 2 non-SI unit

1.10 × 10−3 1.102 1.102

kilogram, kg megagram, Mg (tonne) tonne, t

ton (2000 lb), ton ton (U.S.), ton ton (U.S.), ton

0.893 7.77 × 10−2

kilogram per hectare, kg ha−1 kilogram per cubic meter, kg m−3 kilogram per hectare, kg ha−1 kilogram per hectare, kg ha−1 kilogram per hectare, kg ha−1 liter per hectare, L ha−1 tonne per hectare, t ha−1 megagram per hectare, Mg ha−1 megagram per hectare, Mg ha−1 meter per second, m s−1

To convert Column 2 into Column 1 multiply by

907 0.907 0.907

Yield and Rate

1.49 × 10−2 1.59 × 10−2 1.86 × 10−2 0.107 893 893 0.446 2.24 10 1000

pound per acre, lb acre−1 pound per bushel, lb bu−1

1.12 12.87

bushel per acre, 60 lb bushel per acre, 56 lb bushel per acre, 48 lb gallon per acre pound per acre, lb acre−1 pound per acre, lb acre−1 ton (2000 lb) per acre, ton acre−1 mile per hour

67.19 62.71 53.75 9.35 1.12 × 10−3 1.12 × 10−3 2.24 0.447

Specific Surface square centimeter per gram, square meter per kilogram, cm2 g−1 m2 kg−1 square millimeter per gram, square meter per kilogram, mm2 g−1 m2 kg−1

1.00

megagram per cubic meter, Mg m−3

Density gram per cubic centimeter, g cm−3

9.90 10 2.09 × 10−2 1.45 × 10−4

megapascal, MPa (106 Pa) megapascal, MPa (106 Pa) pascal, Pa pascal, Pa

Pressure atmosphere bar pound per square foot, lb ft−2 pound per square inch, lb in−2

1.00 (K − 273) (9/5 °C) + 32

kelvin, K Celsius, °C

9.52 × 10−4 0.239 107 0.735 2.387 × 10−5 105 1.43 × 10−3

Temperature Celsius, °C Fahrenheit, °F

Energy, Work, Quantity of Heat joule, J British thermal unit, Btu joule, J calorie, cal joule, J erg joule, J foot-pound calorie per square centimeter joule per square meter, J m−2 (langley) newton, N dyne calorie per square centimeter watt per square meter, W m−2 minute (irradiance), cal cm−2 min−1

0.1 0.001

1.00

0.101 0.1 47.9 6.90 × 103 1.00 (°C + 273) 5/9 (°F − 32) 1.05 × 103 4.19 10−7 1.36 4.19 × 104 10−5 698

continued

xvii To convert Column 1 into Column 2 multiply by

3.60 × 10−2 5.56 × 10−3 10−4 35.97

57.3 10 104 9.73 × 10−3 9.81 × 10−3 4.40 8.11 97.28 8.1 × 10−2

Column 1 SI unit

Column 2 non-SI unit

Transpiration and Photosynthesis milligram per square meter gram per square decimeter hour, second, mg m−2 s−1 g dm−2 h−1 milligram (H2O) per square micromole (H2O) per square meter second, mg m−2 s−1 centimeter second, μmol cm−2 s−1 milligram per square meter milligram per square centimeter second, mg m−2 s−1 second, mg cm−2 s−1 milligram per square meter milligram per square decimeter second, mg m−2 s−1 hour, mg dm−2 h−1 radian, rad

Plane Angle degrees (angle), °

Electrical Conductivity, Electricity, and Magnetism millimho per centimeter, siemen per meter, S m−1 mmho cm−1 tesla, T gauss, G Water Measurement cubic meter, m3 acre-inch, acre-in cubic meter per hour, m3 h−1 cubic foot per second, ft3 s−1 3 − U.S. gallon per minute, cubic meter per hour, m h 1 gal min−1 hectare meter, ha m acre-foot, acre-ft hectare meter, ha m acre-inch, acre-in hectare centimeter, ha cm acre-foot, acre-ft

0.1 1

Concentration centimole per kilogram, cmol milliequivalent per 100 grams, kg−1 meq 100 g−1 percent, % gram per kilogram, g kg−1 milligram per kilogram, mg kg−1 parts per million, ppm

2.7 × 10−11 2.7 × 10−2 100 100

Radioactivity becquerel, Bq curie, Ci becquerel per kilogram, Bq kg−1 picocurie per gram, pCi g−1 gray, Gy (absorbed dose) rad, rd sievert, Sv (equivalent dose) rem (roentgen equivalent man)

2.29 1.20 1.39 1.66

Elemental P K Ca Mg

1

To convert Column 2 into Column 1 multiply by

Plant Nutrient Conversion Oxide P2O5 K2O CaO MgO

27.8 180 104 2.78 × 10−2

1.75 × 10−2 0.1 10−4 102.8 101.9 0.227 0.123 1.03 × 10−2 12.33 1 10 1 3.7 × 1010 37 0.01 0.01

0.437 0.830 0.715 0.602

Published 2008 Chapter 1

Sampling Soils for Mineralogical Analyses D. A. SOUKUP, University of Nevada, Las Vegas L. R. DREES, deceased, formerly Texas A&M University, College Station W. C. LYNN, USDA-NRCS, National Soil Survey Center, Lincoln, Nebraska Soil mineralogy has a profound influence on the chemical characteristics and dynamic behavior of soils. The chemical composition of the soil solution is often maintained by weathering and/or precipitation of minerals. The reactive nature of the surface of many minerals and the ability to form chemical bonds with soluble constituents also serves to maintain the chemical composition of the soil solution. If soils were not capable of binding with chemical elements and compounds, the fertilizers, pesticides, herbicides, and other constituents applied to soils may be leached and eventually transported to groundwater or discharged to surface water bodies. Increasing recognition of the significance of soil mineralogy and its relationship to environmental quality has resulted in the performance of numerous soil mineralogical studies during recent years. Although soil mineralogical studies are primarily performed in the laboratory, it should be emphasized that mineralogical analysis typically begins in the field. Therefore, it is critical that the soil samples collected in the field are representative of the soils being studied. This chapter summarizes general procedures that will ensure the collected samples are appropriate for the specific objectives of the soil mineralogical study. PURPOSE OF SAMPLING Soil samples may be collected for a variety of different objectives. The number and types of samples ultimately collected from a site will be determined by the objectives of the study. The following sections discuss some potential study objectives, the role of soil variability in achieving those objectives, and some considerations when selecting a site. Objectives There are three general types of projects for which sampling objectives are developed. These include reference, characterization, and geomorphic and/or stratigraphic projects (Natural Resources Conservation Service [NRCS], 1996). Reference projects are those projects that are designed to answer specific questions or for collection of calibration standards. A reference project, for example, may focus on establishing the variation in clay mineralogy in soils in a given mapping unit. In this situation, samples may be collected from specific horizons in three to five locations that are representative of the map unit. A Copyright © 2008 Soil Science Society of America, 677 S. Segoe Road, Madison, WI 53711, USA. Methods of Soil Analysis. Part 5. Mineralogical Methods. SSSA Book Series, no. 5.

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Soukup, Drees, & Lynn

limited number of analyses that address the variation in clay mineralogy between these samples would be performed. Characterization projects are designed to obtain comprehensive characterization data for a representative pedon of a map unit or a pedon included in a research study. A characterization project would typically include detailed analysis of the physical, chemical, and mineralogical characteristics of the sampled pedon. Geomorphic and/or stratigraphic projects are designed to study relationships between soils, landforms, and/or the stratigraphy of parent materials. For example, a project may be undertaken to study how redoximorphic features and hydrologic regime vary in soils along a catena. Representative pedons occupying different landscape positions would be sampled and their redoximorphic features, often expressed as specific soil minerals, and their hydrologic regimes compared. Soil Variability Pedologists have long been aware of the spatial variability of soils in a landscape (Wilding and Drees, 1983). Soils as landscape bodies often exhibit wide ranges of physical, chemical, morphological, and mineralogical characteristics, both laterally and vertically. Many characteristics, such as hydraulic conductivity and water retention, also vary with transient soil features, do not vary randomly in space, and therefore are not normally distributed (Wilding and Drees, 1983). Spatial variability in soils can be grouped into two general categories, systematic and random. Systematic variability is a gradual or marked change in soil properties occurring as a function of: • • • •

Landforms—mountains, plateaus, basins, plains, terraces, fans, valleys, etc. Geomorphic position—summit, shoulder, backslope, or toeslope Soil-forming factors—climate, parent material, time, biota, topography Interactions of the above factors.

Random variability refers to those changes in soil properties that cannot be related to a known cause (Wilding and Drees, 1983). Systematic and random variability in soil properties may occur concurrently and in association with one another. Causes of random variability include: • • • • • •

Differential lithology Differential intensity of weathering Differential erosion and deposition Differences in biological factors, including anthropogenic activities Differences in hydrology Sampling and analytical errors

These causes of random variability, with the exception of sampling and analytical errors, may also result in systematic variability. Site Selection Selecting the proper site or study area is critical to the successful completion of any investigation, and the specific objectives of the study should be considered during site selection. If possible, uncultivated and undisturbed sites should be utilized for sampling, unless one of the study objectives is to characterize cultivated or disturbed soils (Buol et al., 2003). Similarly, sites selected for sampling should be located away from roads, fence

sampling

3

lines, utility locations, and any other anthropogenic features that may have altered soil characteristics, unless the study objective is to characterize or quantify the degree of alteration. Historical aerial photographs, topographic maps, and other relevant information may also be obtained from government agencies, libraries, private companies, and potentially other sources to document the history of a site, which may be useful in selecting and characterizing a study site. Information about geomorphology, geologic and hydrogeologic conditions, and dominant soil types at the site or its vicinity may be available from the USGS, the Bureau of Land Management (BLM), the USDA-NRCS, other government agencies, and published literature. Many USDA-NRCS soil surveys have been digitized and are available electronically. These and other reports can be combined with geographical information systems (GIS) tools to identify potential study sites. Review of readily available site information from a variety of sources is recommended to facilitate selection of specific sites and/or pedons for detailed study. The selection of a specific site or pedon(s) is determined by the objectives of a study but may often be selected to represent typical landform segments. If a transect is to be sampled, it is important that the variable to be studied can be adequately evaluated after considering the other variables in the transect. The distances between pedons included in the study may vary from a few meters to kilometers, depending on the objectives of the study. Reid et al. (1996) studied smectite mineralogy and charge characteristics along an arid geomorphic transect to evaluate the relationship between smectite properties and geologic and pedologic factors. Wilcke and Amelung (1996) investigated heterogeneity of Al and other heavy metals in soil aggregates along a climatic transect from Saskatchewan in Canada to Texas. DEVELOPING A SAMPLING STRATEGY Detailed planning is critical for successful execution of field activities and project completion. Mobilizing equipment and personnel to the project site is expensive and timeconsuming. Therefore, it is important to ensure that the field activities performed provide the information, documentation, and samples needed to achieve the project objectives. The following sections describe some of the site-specific and other factors to be considered when developing a sampling plan. Specific-Site Characteristics and Considerations There are several site characteristics that should be considered when developing a sampling plan or strategy. These include both pre-field and field activities. Pre-field activities to consider, and questions to ask, include: Site Accessibility Do you need to secure permission from the owner (including the state or federal government), operator, or some other entity to enter a site and perform sampling activities? Can personnel and equipment be transported easily to the site? Obtaining Required Permits and Insurance Are any permits or other paperwork required from any governmental agency or other entity to perform the planned sampling activities? Does a Certificate of Insurance naming the owner or some other entity as Additional Insured need to be obtained before the field activities?

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Soukup, Drees, & Lynn

Clearance of Underground Utility Locations Have the proposed sampling locations been marked and utility-marking companies contacted to “clear” locations? In California, for example, Underground Service Alert (USA) must be notified a minimum of 48 h before the start of work to mark utility locations within the proposed work area. If USA clearance is not obtained, the company and/or the individual(s) performing excavation activities are liable for any damage to subsurface utilities. Whenever possible, it is also recommended that the owner or operator or their representative be contacted to clear locations where other underground utilities and/or irrigation system components are located. Many land owners with drip-line and/or other subsurface irrigation systems may be unwilling to allow sampling because of the potential for irrigation system damage. Resources Required for Field Activities What resources (i.e., personnel and equipment) are required to complete the field sampling activities? Is any specialized equipment required for the sampling and transport to the laboratory? Does any equipment need to be rented or purchased? Types of Samples There are several different methods available for sample collection. The method(s) selected depend on the research objectives, time, and resources available for the sampling effort. The following sections describe some of the different methods of sampling. Soil Pits or Trenches A large backhoe pit, approximately 2 m long, 1 to 2 m wide, and 2 m or more in depth, is recommended for describing and sampling a soil pedon. One of the major advantages to excavating a large pit or trench is that it allows for observation and sampling of horizontal as well as vertical variability in the landscape. Such variability may not be apparent in smaller exposures. One disadvantage is that excavation of large pits or trenches requires access for heavy equipment, including backhoes or excavators. The rental costs for equipment and operator may also be substantial. Soil pits may also be dug by hand, but this is more labor intensive, and the pits are not usually as large or as deep as those excavated by heavy equipment. Regardless of the digging and sampling methodologies employed, personal safety should be the primary consideration during field work. Special precautions should be taken whenever work is performed in close proximity to machinery such as backhoes, drilling rigs, and hydraulic probes. Soil pits that are deeper than 1.25 m (5 feet) are required to be shored in accordance with U.S. Department of Labor Occupational Safety and Health Administration (OSHA) requirements. In many states, shoring is also required for Vertisols and soils with vertic properties. Road Cuts or Other Exposures Road cuts or other exposures, such as stream banks, may also expose a large horizontal and vertical area of soil. However, road cuts and other exposures are not satisfactory for sampling unless they have been freshly exposed and there has been no disturbance of topsoil (Buol et al., 2003). Wetting–drying cycles, oxidizing conditions, plant root and animal activity, and cross contamination from dust or other atmospheric pollutants at these sites may result in modification of the soil structure and other physical and chemical characteristics. As a result, samples obtained from such sites may not be representative of undisturbed

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soils in the area. Extreme caution must be taken when parking and working on roadsides, which also may be illegal on many highways. Auger Borings, Probes, or Tube Samples A wide variety of equipment is available to advance soil boreholes and obtain soil samples. Borings may be advanced with a hand auger, power tools, or a truck-mounted drill or direct-push rig. Depending on the type of equipment used, the sample diameter may range from approximately 2 to 12 cm. Larger diameter cores up to 1.5 m in length may also be collected using a truck-mounted drill or coring rig. These cores may be split apart for description and sampling. One advantage of this type of sampling is that numerous intact cores and/or samples from boreholes may be collected across the landscape in a relatively short period of time. However, samples collected in this manner do not allow for delineation and sampling of the various horizons as they occur in the pedon because of the small surface area available for observation (Buol et al., 2003). There is also a risk of cross contamination due to sloughing of the borehole walls as samples are lifted from the hole. Additionally, it is not always possible to retrieve intact cores or samples because of incomplete recovery (i.e., the sample tubes or core barrel are not full of soil). In this situation, it is not known at which depth the material in the tubes or core barrel was obtained. Incomplete recovery is fairly common in gravelly soils or soils with abundant coarse fragments. Compaction of soil when using a push probe also occurs and may further complicate identifying the sample depth. Composite Samples In some soil investigations, laboratory analyses may be performed on a composite of the samples rather than on each individual sample collected in the field. The composite sample consists of a number of samples that have been mixed together in equal proportions. All of the samples that constitute the composite sample must be from the population being studied, and each sample must contribute the same amount to the composite. The assumption when samples are composited is that a valid estimate of the mean of some characteristic of the population may be obtained from the analysis of the composite sample (Petersen and Calvin, 1986). This assumption may or may not be true. It should be noted that the composite samples only provide an estimate of the mean of the population from which the samples making up the composite were collected. No estimate of the variance of the mean and the precision with which the mean is estimated can be obtained from a single composite sample. The accuracy with which a population mean is estimated from a composite sample is dependent on the variability among sampling units within the population and the number of sampling units included in the composite (Petersen and Calvin, 1986). Composite samples are commonly used in agricultural nutrient testing and in certain environmental characterization studies. For example, composite samples may be collected from soil stockpiles generated during excavation of contaminants to evaluate potential offsite disposal options for the stockpiled material. Composite sampling may also be used to evaluate the effectiveness of bioremediation of soils impacted by petroleum hydrocarbons that are being mitigated by aboveground land treatment. One of the advantages of compositing is that the analytical costs and time required for analyses to be performed are reduced. However, Petersen and Calvin (1986) advised, “If no estimate of variability is available, compositing should be avoided if possible.” If environmental sampling is being performed, the regulatory agency with site oversight should

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be contacted before sample collection to ensure that the results of composite sampling are acceptable to their agency. Number of Samples The number of samples collected depends on the specific objective(s) and the desired accuracy for measuring a particular characteristic of the soil population being studied. The true value of each characteristic in the population is called a parameter (Petersen and Calvin, 1986). The purpose of sampling is to estimate the parameter of interest with the desired accuracy at the lowest possible cost. If the population of interest is relatively homogeneous, collection of a few samples may be adequate to characterize the population. However, heterogeneity is common in soils, and additional sample collection will be necessary for parameter estimation and population characterization. Additional information concerning sampling and statistical analysis of data is provided in Petersen and Calvin (1986). If possible, consultation with a statistician may facilitate development of an appropriate sampling plan. SAMPLE COLLECTION The importance of selecting pedons that are representative of the study area for sampling purposes cannot be overemphasized. Buol et al. (2003) cautioned, “The time, effort, and expense invested in lab analyses of the profile samples will be wasted if the samples are not representative of the soil.” These authors also noted that data generated from a given study may be used by numerous investigators and other individuals for different purposes. Additionally, any interpretations and extrapolations made by individuals using the data will likely be erroneous if the samples are not representative. Buol et al. (2003) concluded with this recommendation: “Soil profile samples should be taken from a pedon determined by field studies and observations to be truly representative of the area under study.” The following sections summarize some of the important site and pedon observations that should be documented during field activities. Field Observations There are several field observations that are important to document for any study or investigation. These include: •

Location. The geographical location of the area of interest needs to be recorded as precisely as possible. Latitude and longitude recorded in degrees, minutes, seconds, direction, and associated datum is the preferred method for documenting location (Schoeneberger et al., 2002). Avoid using constructed landmarks such as roads and buildings to locate a sampling area, as these will invariably change with time.

•

Topographic quadrangles/geologic maps. The topographic quadrangle, typically a USGS topographic map, for the study area should be documented. Similarly, existing geologic maps of the study area that may be available from the USGS and possibly other sources should be recorded.

•

Soil survey area. If the study area is covered by an existing soil survey, the survey information should be used to document the soil series and map units within the study area. This information may also be useful for interpreting the results of the research.

•

Geomorphic information. If available, the physiographic location including division, province, section, and state physiographic area for the study area should be

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noted. The researchers should record the landscape position, landform, microfeatures, and surface morphometry, including slope gradient, complexity, and shape. •

Water status. The water status, including drainage, flooding, ponding, observed soil water status, and depth to water table should be recorded or estimated based on field observations.

•

Vegetation and land cover. The dominant land cover at the site should be recorded.

•

Parent material. The parent material and kinds of unconsolidated material within the study area should be documented.

•

Erosion and runoff. Evidence of erosion and surface runoff should be described.

•

Site-specific information. The slope, aspect, soil surface conditions (i.e., native or under cultivation) and an estimate of exposed materials >2 mm within the surface horizon should be recorded. If Vertisols are present, the size, depth, and distribution of gilgai features should be recorded. Any other surface feature(s) that may affect horizonation within the soil profile should also be measured, described, and recorded.

Additional information and details concerning field observations that should be documented were provided by Schoeneberger et al. (2002). Pedon Descriptions The methodology for describing soils has been developed and refined by soil scientists since the Soil Survey Program began in the United States more than a century ago. The USDA first published booklets entitled Instructions to Field Parties in 1902–1904, 1906, and 1914 (Schoeneberger et al., 2002). These booklets included soil descriptions. The first USDA guide for identification and description of soil horizons was published in 1937 and has since been revised several times (Schoeneberger et al., 2002). Soil science is a dynamic and evolving field, and changes to the existing methodologies for describing and sampling soils will occur in the future. The information provided in the following sections is intended to emphasize some important points about pedon description and sampling. It should not be considered as a comprehensive guide to pedon description and sampling. The reader is referred to Schoeneberger et al. (2002) for additional details and recommendations regarding description and sampling of soils in the field, which may be helpful before performing field study and soil sampling. Soil macromorphology refers to field observations that are made with the unaided eye and is best evaluated from the in situ examination of a freshly exposed soil profile (Buol et al., 2003). Old exposures should only be used for preliminary observations, because soil characteristics and mineralogy are often altered after exposure to the elements. Once a profile has been exposed, it can be prepared for examination, description, photographing, and sampling using the following procedures: 1.

One side of the soil pit should be selected for description, sampling, and photographing. The soil surface on this side of the pit should not be walked on or stood on to minimize any topsoil disturbance. Access into, and exit from the pit should be on one of the other three sides of the pit that will not be described or sampled. A ramp is often constructed on one side of the pit to facilitate access.

2.

Probe the exposed profile by hand using a small knife to remove alterations resulting from the digging equipment. The objective of this step is to expose the natural condition of the soil. The probing may also assist in the designation of soil horizon boundaries, because textural and structural changes may be readily apparent during probing.

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3.

A measuring tape should be placed on the exposed profile to allow references to depth during description. The tape also provides depth references for photographs of the soil, which we recommend taking at this time. Photographs may also be taken after description and sampling have been completed, but the profile will need to be probed again to expose the natural condition of the soil. Excess soil that may have sloughed off the walls during sampling may also need to be removed from the bottom of the profile before photographing.

4.

Mark the depths in the profile where differences in color, structure, or texture are observed as an initial approximation of soil horizon boundaries. Nails or golf tees work well for marking horizon boundaries. For soils that have noncontiguous horizons, string may be used for marking the horizons. This allows for a complete description and ensures sampling of all genetic horizons. Some pedologists prefer to prepare detailed drawings of the pedon or polypedons while in the field.

5.

Begin the detailed examination of the profile, describing horizons according to their color, texture, structure, consistence, root quantity and size, boundary characteristics, horizon continuity, nodules or concretions, mottles, redoximorphic features, voids, pores, pH (field method) and effervescence on treatment with a ~1 M hydrochloric acid (HCl) solution. The approximate soil horizon boundaries may be adjusted, as needed, as the detailed examination progresses. Sampling Procedures and Equipment

The sampling methodology and the location of the soil material collected for analysis will ultimately be determined by the objective(s) of the study (Schoeneberger et al., 2002). General information and some recommendations concerning soil sampling procedures are provided below. Additional details regarding soil sampling are provided in Soil Survey Investigations Rep. 42 (Soil Survey Staff, 1996) and Schoeneberger et al. (2002). 1.

As described above, all sampling locations should be documented as precisely as possible. Buol et al. (2003) summarized the consequence of not doing so: “A soil sample without complete documentation of the location is merely a handful of dirt.”

2.

The sampling procedure is the same for both hand-dug and backhoe pits. Once the horizons or zones from which samples will be collected are marked, the profile may be sampled from top to bottom or from bottom to top. Bottom-to-top sampling is generally recommended to reduce the potential for cross-contamination during sampling. If top to bottom sampling is performed, care should be taken to ensure that material sloughing off the upper horizons is removed before deeper horizons are sampled. Top-to-bottom sampling is recommended if a large number of undisturbed cores will be collected and the soil is dry and hard (Buol et al., 2003).

3.

Each horizon should be sampled vertically from boundary to boundary and laterally to include observable short-range variability. The sample should be collected in a sampling tray, mixed thoroughly, placed into a sampling bag or other collection vessel and labeled. The amount of sample collected will vary depending on the purposes of the study. Collecting additional sample is recommended to ensure that sufficient sample is available for future, unanticipated analyses. If a horizon is especially thick, it may be split for sampling if desired by the sampling personnel. For horizons with two distinct materials, such as tongues of an E horizon into a Bt horizon, separate samples of each material should be collected, noting the relative volume percentage of each. Care should be taken not to sample krotovina material. This may be difficult if a large portion of the pedon or horizons being sampled have been mixed by burrowing

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animals. This is especially difficult for soils that are used for crawfish production. Under these circumstances, a different location may have to be used for sampling. Special sampling techniques are also required for organic soils, permafrost-affected soils and Vertisols (Soil Survey Staff, 1996). Collecting samples from organic soils may be difficult because of the high water contents characteristic of these soils. Permafrost-affected soils may be resistant to excavation and commonly exhibit cryoturbation that disrupts horizon morphology. In this case, hand drawing and photographing the pit face before sample collection is recommended. The shear failure that forms slickensides in Vertisols disrupts the soil so that conventional horizon designations do not adequately describe the morphology. The gilgai surface topography characteristic of many Vertisols is reflected in the subsurface by bowl-shaped lows and highs across a distance of several meters. Both the high and low areas are commonly sampled since these areas represent the extremes in the cyclic morphology of Vertisols. Additional details regarding sampling procedures for organic soils, permafrost-affected soils, and Vertisols are provided in Soil Survey Investigations Rep. 42 (Soil Survey Staff, 1996) and Schoeneberger et al. (2002). 4.

We recommend using indelible ink or paint pens for marking so that the sample identification labels do not smear, smudge, or fade with time. It is also recommended that both the outside and inside of the sample container be marked with the sample identification information.

5.

Soil clods or blocks of undisturbed soil approximately 100 to 500 cm3 may also be collected from each horizon for micromorphology studies, determination of bulk density and coefficient of linear extensibility (COLE), and possibly other physical and chemical characteristics. The orientation of the clods or blocks should be marked to show which was the upper side within the profile or sediments sampled. We have found that brightly colored nail polish works well for marking the upper side of the clods or blocks. Once the upper side of the clods or blocks has been marked, they should be wrapped in paper towels or packing material and placed into a paper can or some other protective container. The containers should be labeled both inside and out with the sample identification and other relevant information. Soil Survey Staff (1996) recommended collecting three clods for bulk density analysis and two additional clods for preparation of thin sections and micromorphological study. The actual number of clods collected will depend on the specific objectives of the study. SAMPLE PRESERVATION

Equilibrium conditions change as soon as a sample is collected and removed from its native environment. Some of these changes may result in alteration of the mineralogy and other physical and chemical characteristics of the sample. As a result, procedures should be followed during collecting and transporting and/or shipping samples to the laboratory to ensure that cross contamination does not occur and the condition of the samples is not compromised. Some general procedures to be followed to preserve sample integrity and some special handling procedures that may be required are described in the following sections. Transporting Samples from the Field to the Laboratory Bulk soil samples may be placed into prelabeled plastic bags or other collection vessels for transport to the laboratory. Using plastic bags with a minimum thickness of 8-mil and/or double bagging is recommended to prevent breakage of the bags and cross contamination of samples during transport.

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Once the upper side of clods or blocks have been marked, they should be wrapped in paper towels and placed into a paper can or some other container that protects them from physical damage during transport and before preparation for analysis. The containers should be labeled both inside and out with the sample identification and other relevant information. Special handling procedures may also be required for samples collected for microbial, redox, and evaporite mineralogy studies. Samples for microbial studies, for example, may need to be placed on ice and/or protected from sunlight and air. Several soil minerals also have specific hydration and oxidation states (e.g., halloysite and iron oxides) that may change irrevocably if not stored or handled properly. Initial Preparation of Samples for Analyses Once the samples have been transported to the laboratory, the samples are prepared for further analyses or archived (discussed below). Preparation of samples for subsequent mineralogical and other chemical analyses typically involves the following: 1.

In most cases, the field-moist samples should initially be air dried. This is typically accomplished by placing the samples on brown paper on a bench in the greenhouse or in the laboratory. The paper that the samples are dried on should be labeled with the sample identification and any other relevant information. It should be noted that volcanic ash soils high in amorphous clay-sized materials are very resistant to dispersion, particularly after air or oven-drying (Gee and Bauder, 1986). Kubota (1972) reported that clay contents for one volcanic ash soil ranged from 1 to 56% (w/w) depending on pretreatment. The maximum clay content was determined when the soil was retained at field moisture before dispersion. Warkentin and Maeda (1980) recommended that volcanic ash soils be maintained at field moisture and dispersed at either pH 3 or above pH 9. Organic and continually saturated soils, especially clayey saturated soils, also dry irreversibly like many volcanic ash soils. These soils should not be air dried or allowed to change temperature, particularly if Fe, Mn, and other redox sensitive elements are present. Gypsum-containing and gypsiferous soils may also be altered by air drying when exposed directly to sunlight or temperatures exceeding 30°C.

2.

Once the samples have been air dried, the entire sample should be passed through a 2-mm sieve. Larger soil aggregates may be gently crushed using a wooden rolling pin or mortar and pestle. Care should be taken when crushing the aggregates to prevent disintegration of coarse-fragments larger than 2 mm or sand-sized particles, including quartz, feldspar, mica, and nodules. Samples should not be ground using any mechanical grinding equipment if particle-size analyses are to be performed. After the entire sample has been crushed, it should be thoroughly mixed. A sample splitter, if available, may be used if the sample is to be divided.

3.

The sieved samples should be segregated from the coarse fragments (i.e., particles >2 mm) and placed into labeled plastic bags, paper cans, or some other container for storage. Sample Archiving

If sufficient quantities of samples remain, archiving bulk and ground soil material, soil clods, coarse fragments, and other materials is recommended. Careful records must

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be kept and sample identities preserved. The results of current investigations may suggest the need for additional studies. It is also possible that temporal changes in soil characteristics may be of scientific interest. Graham and Wood (1991) were able to measure the time and conditions required to form an argillic horizon in uniformly packed lysimeter soils in southern California by comparing archived soil samples from the 1930s to the soil profiles that developed in the lysimeters over the next 41 yr. Perhaps the most famous use of archived samples is from the plots of Rothamsted, England where soil samples collected and carefully preserved since the 1800s have allowed quantitative assessment of changes in a variety of soil properties, including nutrients, heavy metals, and organic chemicals, with time and management (e.g., Green et al., 2001). Other examples of important comparative studies that were made possible because of archived samples are provided in Ulery et al. (1995) and De Clerck et al. (2003). REFERENCES Buol, S.W., R.J. Southard, R.C. Graham, and P.A. McDaniel. 2003. Soil genesis and classification. 5th ed. Iowa State Press, Ames. De Clerck, F., M.J. Singer, and P. Lindert. 2003. A 60-year history of California soil quality using paired samples. Geoderma 114:215–230. Gee, G.W., and J.W. Bauder. 1986. Particle-size analysis. p. 383–411. In A. Klute (ed.) Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. Graham, R.C., and H.B. Wood. 1991. Morphologic development and clay redistribution in lysimeter soils under chaparral and pine. Soil Sci. Soc. Am. J. 55:1638–1646. Green, N.J.L., J.L. Jones, A.E. Johnston, and K.C. Jones. 2001. Further evidence for the existence of PCDD/Fs in the environment prior to 1900. Environ. Sci. Technol. 35:1974–1981. Kubota, T. 1972. Aggregate formation of allophonic soils: Effects of drying on the dispersion of the soils. Soil Sci. Plant Nutr. 18:79–87. Petersen, R.G., and L.D. Calvin. 1986. Sampling. p. 33–51. In A. Klute (ed.) Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. Reid, D.A., R.C. Graham, L.A. Douglas, and C. Amrhein. 1996. Smectite mineralogy and charge characteristics along an arid geomorphic transect. Soil Sci. Soc. Am. J. 60:1602–1611. Schoeneberger, P.J., D.A. Wysocki, E.C. Benham, and W.D. Broderson (ed.). 2002. Field book for describing and sampling soils. Version 2.0. USDA-NRCS, National Soil Survey Center, Lincoln, NE. Soil Survey Staff. 1996. Soil survey laboratory methods manual. Soil Survey Investigations Rep. 42. U.S. Gov. Print. Office, Washington, DC. Ulery, A.L., R.C. Graham, O.A. Chadwick, and H.B. Wood. 1995. Decade-scale changes in soil carbon, nitrogen, and exchangeable cations under chaparral and pine. Geoderma 65:121–134. Warkentin, B.P., and T. Maeda. 1980. Physical and mechanical characteristics of Andisols. p. 281–301. In B.K.G. Theng (ed.) Soils with variable charge. New Zealand Society of Soil Science, Lower Hutt, New Zealand. Wilcke, W., and W. Amelung. 1996. Small-scale heterogeneity of aluminum and heavy metals in aggregates along a climatic transect. Soil Sci. Soc. Am. J. 60:1490–1495. Wilding, L.P., and L.R. Drees. 1983. Spatial variability and pedology. p. 83–116. In L.P. Wilding et al. (ed.) Pedogenesis and soil taxonomy. I. Concepts and interactions. Elsevier Science Publishers, B.V., Amsterdam, The Netherlands.

Published 2008 Chapter 2

Preparing Soils for Mineralogical Analyses D. A. SOUKUP, University of Nevada, Las Vegas B. J. BUCK, University of Nevada, Las Vegas W. HARRIS, University of Florida, Gainesville Sample preparation is an important aspect of soil mineralogical analysis. The use of pretreatments is often necessary to facilitate sample dispersion and/or to concentrate a particular size fraction for subsequent analyses. However, pretreatments may alter, or even destroy, certain fractions of the soil (Kunze and Dixon, 1986). The pretreatments described in the following sections of this chapter are designed to have a minimum effect on constituents other than those being eliminated. In spite of this, the analyst must still be careful to perform only those pretreatments that are essential to accomplish the study objectives. Additionally, the analyst should have a clear understanding of the possible consequences for data interpretation. The reagents used for the various pretreatments do not need to be prepared with a high degree of precision. For example, the reagents may be mixed in beakers rather than in a volumetric flask. SOIL PREPARATION As discussed in Chapter 1 (Soukup et al., 2008, this volume), special field sampling and preservation techniques are required for organic soils, permafrost-affected soils, and Vertisols (Soil Survey Staff, 1996; Schoeneberger et al., 2002). To preserve organic soils, Blevins et al. (1968) recommended freezing blocks of soil in the field with liquid N2 and transporting them to the laboratory in a frozen state. Other soils, including those affected by salts, reducing conditions, or high water contents, may also require special sampling, transportation, and preparation techniques before mineralogical analysis. Once collected, it is critical that such samples be transported and stored under conditions similar to those existing at the field site because many of the minerals in such soils may hydrate, dehydrate, oxidize, or dissolve during transport and storage. We strongly recommend that when working with potentially “problematic” soils researchers consult the literature, local NRCS personnel and other investigators regarding sampling, transport, and preparation techniques that have been employed previously on similar soils. The relative merits of each technique must be evaluated on a soil by soil basis to determine the most appropriate method(s). We also recommend that when there is the potential for mineralogical and other changes, samples should be analyzed as quickly as possible after sampling. The amount of soil required for mineralogical analyses will vary depending on the study objectives and the sample characteristics. Generally, a sufficient amount of sample Copyright © 2008 Soil Science Society of America, 677 S. Segoe Road, Madison, WI 53711, USA. Methods of Soil Analysis. Part 5. Mineralogical Methods. SSSA Book Series, no. 5.

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should be utilized to yield approximately 5 to 10 g of clay (80% (Buck et al., 2006a, 2006b). After this has been achieved, removing the soluble salts and gypsum is recommended because it simplifies other mineralogical analyses (such as XRD and differential thermal analyses [DTA]) (Kunze and Dixon, 1986). If done in this order, then identification and quantification of all soil constituents is possible. Carbonates may also make it difficult or impossible to fractionate the sample and effectively separate the silt and clay fractions. Moreover, the presence of carbonates may result in poor X-ray diffractograms, because the degree of orientation of clay-sized particles (i.e.,