Soil Geography of the USA

Soil Geography of the USA

James G. Bockheim Soil Geography of the USA A Diagnostic-Horizon Approach

James G. Bockheim Soil Science Department University of Wisconsin Madison, WI, USA ISBN 978-3-319-06667-7 ISBN 978-3-319-06668-4 (ebook) DOI 10.1007/978-3-319-06668-4 Springer Cham Heidelberg New York Dordrecht London Library of Congress Control Number: 2014943766 Springer International Publishing Switzerland 2014 This work is subject to copyright. All rights are reserved 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. Exempted from this legal reservation are brief excerpts in connection with reviews or scholarly analysis or material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Duplication of this publication or parts thereof is permitted only under the provisions of the Copyright Law of the Publisher s location, in its current version, and permission for use must always be obtained from Springer. Permissions for use may be obtained through RightsLink at the Copyright Clearance Center. Violations are liable to prosecution under the respective Copyright Law. 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. While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein. Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com)

Preface A soil geography textbook or reference book has been lacking for the United States since Soil Geography and Land Use was published 34 years ago by Foth and Schafer (1980). Since that time, our understanding of the factors and processes governing the distribution of soils on the Earth s surface has increased dramatically, as have the techniques for studying soil patterns. Although Soil Taxonomy (ST; Soil Survey Staff, 1999) is the official US soil classification system, it is used in more than 45 countries and, along with the World Reference Base for Soil Resources (IUSS Working Group, WRB, 2007), is the most commonly used scheme in the professional literature. Soil Taxonomy is a hierarchical system that is based primarily on diagnostic surface horizons (epipedons) and subsurface horizons that appear in the system at different taxonomic levels. Although there are maps of the soil orders at the national and global scales and maps of soil suborders for the USA, maps of diagnostic horizons generally have not been available, primarily because these horizons cross taxonomic borders. These horizons form the primary basis of ST, and a geography based on the diagnostic horizons seems reasonable or, perhaps, more reasonable than one devoted to soil orders, suborders, or great groups. The approach used herein relies on the National Resources Conservation Service (NRCS) databases to delineate the distribution of each of the eight diagnostic epipedons and 19 subsurface horizons, to identify the taxonomic level at which each of these horizons is used, to develop an understanding of the role of the factors and processes in their formation, and to summarize our latest understanding of their genesis. The last comprehensive book on soil orders was Pedogenesis and Soil Classification (Wilding et al. 1983). In the present book, a chapter is devoted to each diagnostic horizon (or in some cases combined horizons), with the general outline of an introduction specifying the importance of the horizon and previous work, properties of the horizon from the NRCS Laboratory database and in some cases from the published literature, classification of soils containing the horizon, distribution and total area of soils containing the horizon within the USA, factors influencing formation of the horizon, a discussion of the genesis of the horizon, and a summary. Three additional chapters have been added that discuss ultramafic soils and soils with pedogenic lamellae and plinthite. To appreciate this book, the reader v

vi Preface should have a general understanding of the principles of soil classification and Soil Taxonomy: A Basic System of Soil Classification for Making and Interpreting Soil Surveys. Six of the chapters of this book have been published by the author in a different format in technical journals; acknowledgement is made to these journals for permission to include these articles as chapters in this book. It is the author s desire that this book serve as a textbook in soil geography; a reference book for geographers, ecologists, geologists, and others; and a tool for soil instructors, landlookers, mappers, classifiers, and information technologists. Madison, WI, USA, June 10, 2014 James G. Bockheim

Acknowledgments The idea for this book was inspired by my colleague and friend, Alfred Hartemink, who also collaborated on some of the published papers from which some of this information has been drawn. Graphics were prepared by Paul Reich, Adolfo Diaz, and Nick Haus, to whom I am grateful. I am especially appreciative of the professional soil surveyors and scientists of USDA NRCS, the laboratory technicians, and information technologists that have made the data used in this study generously available to the public. My wife, Julie, offered me encouragement in this endeavor, and it is to her that this book is dedicated. Madison, WI, USA June 10, 2014 James G. Bockheim vii

Contents 1 Introduction... 1 1.1 Diagnostic Horizons and the Soil-Forming Factors... 5 1.2 Diagnostic Horizons and the Soil-Forming Processes... 8 References... 9 2 Approach... 11 References... 12 3 Anthropic and Plaggen Epipedons: Products of Human Disturbance... 13 3.1 Introduction..... 13 3.2 Properties of Soils with Anthropic and Plaggen Epipedons... 16 3.3 Classification of Soils with Anthropic and Plaggen Epipedons in ST................................... 16 3.4 Soil-Forming Factors and Development of Anthropic and Plaggen Epipedons... 16 3.5 Genesis of Anthropic and Plaggen Epipedons..... 18 3.6 Summary... 18 References... 19 4 Melanic Epipedon... 21 4.1 Introduction..... 21 4.2 Properties of Soils with a Melanic Epipedon.............. 21 4.3 Classification of Soils with a Melanic Epipedon...... 22 4.4 Distribution of Soils with a Melanic Epipedon..... 22 4.5 Factors Influencing the Development of the Melanic Epipedon... 25 4.6 Genesis of the Melanic Epipedon... 26 4.7 Summary... 27 References... 27 ix

x Contents 5 Mollic Epipedon... 29 5.1 Introduction..... 29 5.2 Properties of the Mollic Epipedon... 30 5.3 Classification of Soils with a Mollic Epipedon or Intergrade... 32 5.4 Distribution of Soils with a Mollic Epipedon...... 39 5.5 Factors Influencing the Formation of Mollic Epipedons...... 40 5.6 Genesis of Mollic Epipedons.......................... 43 5.7 Summary... 44 References... 45 6 Umbric Epipedon... 47 6.1 Introduction..... 47 6.2 Properties of Soils with Umbric Epipedons........ 47 6.3 Classification of Soils with an Umbric Epipedon...... 48 6.4 Distribution of Soils with Umbric Epipedons... 48 6.5 Factors Influencing the Distribution of Soils with Umbric Epipedons... 53 6.6 Genesis of Soils with an Umbric Epipedon.... 53 6.7 Summary... 53 References... 54 7 Ochric Epipedon... 55 7.1 Introduction..... 55 7.2 Properties of Soils with an Ochric Epipedon... 55 7.3 Classification of Soils with an Ochric Epipedon... 56 7.4 Distribution of Soils with an Ochric Epipedon............. 56 7.5 Factors Influencing the Development of the Ochric Epipedon... 60 7.6 Genesis of Soils with an Ochric Epipedon... 61 7.7 Summary... 61 References... 62 8 Histic and Folistic Epipedons... 63 8.1 Introduction..... 63 8.2 Properties of Folistic and Histic Epipedons... 63 8.3 Classification of Soils with Folistic and Histic Epipedons..... 68 8.4 Distribution of Soils with Folistic and Histic Epipedons...... 68 8.5 Factors Influencing the Formation of Folistic and Histic Epipedons....................... 71 8.6 Genesis of Folistic and Histic Epipedons... 73 8.7 Summary... 73 References... 74 9 Agric Horizon... 75 9.1 Introduction..... 75 9.2 Properties of Soils with an Agric Horizon...... 75 9.3 Classification and Distribution of Soils with an Agric Horizon...... 75

Contents xi 9.4 Processes Leading to the Formation of the Agric Horizon..... 78 9.5 Summary... 78 References... 78 10 Albic Horizon... 79 10.1 Introduction.... 79 10.2 Properties of the Albic Horizon...... 80 10.3 Classification of Soil Series with an Albic Horizon.......... 83 10.4 Distribution of Soils with an Albic Horizon............... 84 10.5 Factors Influencing the Development of the Albic Horizon.... 84 10.6 Genesis of the Albic Horizon......................... 84 10.7 Summary... 86 References... 86 11 Argillic, Kandic, and Natric Horizons... 89 11.1 Introduction.... 89 11.2 Historical Overview of Clay-Enriched Horizons.... 90 11.3 Soil Taxa Containing Taxonomic Clay Enrichment...... 94 11.4 Distribution of Soils with Clay Enrichment............... 96 11.5 Soil-Forming Factors and Clay-Enriched Horizons.... 97 11.6 Genesis of Clay-Enriched Horizons.... 101 11.7 Summary... 104 References... 105 12 Calcic and Petrocalcic Horizons... 109 12.1 Introduction.... 109 12.2 Properties of Calcic and Petrocalcic Horizons............. 110 12.3 Classification of Soils with Calcic and Petrocalcic Horizons... 110 12.4 Distribution of Soils with Calcic and Petrocalcic Horizons.... 114 12.5 Factors Influencing the Formation of Calcic and Petrocalcic Horizons... 115 12.6 Genesis of Calcic and Petrocalcic Horizons... 119 12.7 Summary... 119 References... 120 13 Cambic Horizon... 123 13.1 Introduction.... 123 13.2 Properties of Cambic Horizons... 123 13.3 Classification of Soils with Cambic Horizons... 128 13.4 Distribution of Soils with Cambic Horizons.... 129 13.5 Soil-Forming Factors Influencing the Formation of Cambic Horizons... 130 13.6 Genesis of Cambic Horizons..... 131 13.7 Summary... 131 References... 132

xii Contents 14 Duripan Horizon and Durinodes... 133 14.1 Introduction.... 133 14.2 Characteristics of Soils with Duripans and Durinodes........ 134 14.3 Classification of Soils with Duripans and Durinodes.... 140 14.4 Distribution of Soils with Duripans and Durinodes... 144 14.5 Soil-Forming Factors Influencing the Formation of Duripans and Durinodes... 144 14.6 Genesis of Duripans and Durinodes..................... 147 14.7 Summary... 149 References... 149 15 Fragipan Horizon... 153 15.1 Introduction.... 153 15.2 Characteristics of Soils with Fragipans... 154 15.3 Classification of Soils with Fragipans..... 158 15.4 Distribution of Soils with Fragipans..................... 160 15.5 Factors Influencing the Formation of Fragipans.... 161 15.6 Genesis of Fragipan.... 163 15.7 Summary... 165 References... 166 16 Glossic Horizon... 169 16.1 Introduction.... 169 16.2 Properties of Soils with a Glossic Horizon...... 170 16.3 Classification of Soils with Glossic Horizon............... 173 16.4 Distribution of Soils with a Glossic Horizon... 173 16.5 Soil-Forming Factors and the Development of Glossic Soils................................... 175 16.6 Genesis of the Glossic Horizon... 175 16.7 Summary... 176 References... 177 17 Gypsic and Petrogypsic Horizons... 179 17.1 Introduction.... 179 17.2 Characteristics of Gypsic and Petrogypsic Horizons......... 180 17.3 Classification of Soils with Gypsic and Petrogypsic Horizons... 181 17.4 Distribution of Soils with Gypsic and Petrogypsic Horizons... 184 17.5 Factors Influencing the Formation of Gypsic Horizons..... 184 17.6 Genesis of Gypsic Horizons............ 186 17.7 Summary... 187 References... 187 18 Ortstein and Placic Horizons... 189 18.1 Introduction.... 189 18.2 Properties of Soils with Ortstein or Placic Horizons... 191

Contents xiii 18.2.1 Ortstein................................... 191 18.2.2 Placic....... 195 18.3 Classification of Soils with Ortstein or Placic Horizons....... 196 18.3.1 Ortstein................................... 196 18.3.2 Placic....... 196 18.4 Distribution of Soils with Ortstein and Placic Horizons....... 198 18.5 Factors Influencing the Distribution of Ortstein and Placic Horizons...... 200 18.5.1 Ortstein................................... 200 18.5.2 Placic....... 203 18.6 Genesis of Ortstein and Placic Horizons... 204 18.6.1 Ortstein................................... 204 18.6.2 Placic....... 205 18.7 Summary... 208 References... 208 19 Oxic Horizon... 211 19.1 Introduction.... 211 19.2 Properties of Oxic Horizons... 212 19.3 Classification of Soils with Oxic Horizons....... 212 19.4 Distribution of Soils with Oxic Horizons in the USA........ 212 19.5 Factors Influencing the Development of Oxic Horizons... 212 19.6 Genesis of Oxic Horizons............................ 217 19.7 Summary... 218 References... 218 20 Salic Horizon... 221 20.1 Introduction.... 221 20.2 Properties of Salic Horizons.... 222 20.3 Classification of Soils with a Salic Horizon..... 223 20.4 Distribution of Soils with a Salic Horizon... 229 20.5 Comparison of Salic Horizon Properties in USA with Other Areas...... 230 20.6 Factors Influencing the Formation of Salic Horizons......... 230 20.7 Genesis of Salic Horizons...... 232 20.8 Summary... 234 References... 234 21 Sombric Horizon... 237 21.1 Introduction.... 237 21.2 Properties of Sombric Horizons.... 238 21.3 Classification of Soils with a Sombric Horizon............. 249 21.4 Factors Leading to the Development of Sombric and Sombric-Like Horizons... 250 21.5 Genesis of Sombric Horizons......................... 250 21.6 Proposal for Improving the Definition of the Sombric Horizon... 252

xiv Contents 21.7 Summary... 253 References... 253 22 Spodic Horizon... 257 22.1 Introduction.... 257 22.2 Properties of Soils with a Spodic Horizon............ 257 22.3 Classification of Soils with a Spodic Horizon... 258 22.4 Distribution of Soils with a Spodic Horizon... 262 22.5 Factors Influencing the Development of the Spodic Horizon............................... 262 22.6 Genesis of the Spodic Horizon... 264 22.7 Summary... 264 References... 265 23 Ultramafic Soils... 267 23.1 Introduction.... 267 23.2 Properties of Ultramafic Soils......................... 268 23.3 Classification of Ultramafic Soils...... 268 23.4 Distribution of Ultramafic Soils... 275 23.5 Factors Influencing the Development of Ultramafic Soils... 276 23.6 Genesis of Ultramafic Soils... 279 23.7 Endemic Soils...... 279 23.8 Summary... 280 References... 280 24 Soils with Lamellae... 283 24.1 Introduction.... 283 24.2 Properties of Soils with Lamellae... 284 24.3 Classification of Soils with Lamellae.................... 285 24.4 Distribution of Soils with Lamellae... 286 24.5 Factors Influencing the Development of Lamellae.......... 295 24.6 Genesis of Lamellae.... 298 24.7 Summary... 299 References... 299 25 Soils with Plinthite... 301 25.1 Introduction.... 301 25.2 Properties of Soils with Plinthite... 302 25.3 Classification of Soils with Plinthite.... 302 25.4 Distribution of Soils with Plinthite.... 303 25.5 Factors Influencing the Formation of Plinthite...... 307 25.6 Genesis of Plinthitic Soils... 307 25.7 Summary... 308 References... 309

Contents xv 26 Conclusions... 311 26.1 Relative Abundance of Diagnostic Horizons... 311 26.2 Soil-Forming Factors and Diagnostic Horizons.... 313 26.3 Geographic Distribution of Diagnostic Horizons............ 315 26.3.1 Epipedons.... 315 26.3.2 Subsurface Horizons......................... 315 Reference..... 316 27 The Future of Soil Taxonomy... 317 Reference..... 320

Abbreviations CEC COLE C:N Db EC ECEC MAAT MAP NMR NRCS NSSL ODOE OSD PSC ph SAR SMR SOC ST STR STATSGO SSURGO USDA WRB XRD Cation-exchange capacity Coefficient of linear extensibility Carbon-to-nitrogen ratio Bulk density Electrical conductivity Effective cation-exchange capacity Mean annual air temperature Mean annual precipitation Nuclear magnetic resonance spectroscopy Natural Resources Conservation Service National Soil Survey Laboratory Optical density of the oxalate extract Official Soil Series Description Particle size class Hydrogen ion potential Sodium adsorption ratio Soil moisture regime/class Soil organic carbon Soil Taxonomy Soil temperature regime/class State soil geographic database Soil survey geographic database United States Department of Agriculture World Reference Base for Soil Resources X-ray diffraction detection [Note: state and chemical-element abbreviations are given in the text.] xvii

List of Figures Fig. 3.1 Plaggen epipedon from the Bulkhead Archaeological site in lower Manhattan, New York (top; photo compliments of Luis Hernandez), and an anthropic epipedon from the Turtle Mound site in Florida (bottom; photo compliments of John Galbraith)... 17 Fig. 4.1 A soil containing a melanic epipedon from the southern Oregon coast (Photo by J. Bockheim)... 22 Fig. 4.2 Counties in western USA containing soils with a melanic epipedon... 25 Fig. 5.1 Pachic Argiudolls (left), Typic Endoaquolls (middle), and Typic Argiudolls (right) all from Wisconsin, USA (Photos by A.E. Hartemink)... 30 Fig. 5.2 Distribution of Mollisols in the USA. Soils in other orders with a mollic epipedon are not shown (Figure courtesy of USDA, NRCS)... 39 Fig. 5.3 Genesis of the mollic epipedon... 43 Fig. 6.1 A soil containing an umbric epipedon from a Humicryepts in the subalpine zone of west-central Rocky Mountains, Colorado (Photo by J. Bockheim)... 48 Fig. 6.2 Counties with a taxonomic umbric epipedon in the USA... 52 Fig. 7.1 A Typic Haplocryepts (Fairbanks silt loam) containing an ochric epipedon (Photo by J. Bockheim)... 56 Fig. 7.2 Distribution of soils with an ochric epipedon in the USA (Map prepared by Paul Reich)... 60 Fig. 8.1 A landform on Blackhawk Island, Wisconsin (left), and its associated unsaturated organic soil with a folistic epipedon (Photos by A.E. Hartemink)... 64 Fig. 8.2 A Typic Sapristels showing sapric materials down to the groundwater table (Photo by J. Bockheim)... 64 xix

xx List of Figures Fig. 8.3 Distribution of soils with a folistic epipedon in four regions of the USA. (a) Northern USA. (b) Alaska. (c) Hawaiian Islands. (d) Southern Florida (Graphics by P. Reich)... 70 Fig. 8.4 Distribution of soils with a histic epipedon in the USA (Source: NRCS)... 71 Fig. 9.1 A soil with an agric horizon, including a trench through the plow layer and agric horizon (top); a cross-sectional view of the plow layer and underlying agric horizon (middle); and the effects of compaction on corn roots (bottom; Photos by R. Wolkowski)... 76 Fig. 10.1 A soil with an albic horizon in Michigan s Upper Peninsula (Photo by J. Bockheim)... 80 Fig. 10.2 Distribution of soils with an albic horizon in the USA (areas with light gray are dominantly Spodosols and areas in black are Alfisols and Mollisols)... 85 Fig. 11.1 Examples of soils with an argillic (upper left; Photo by A.E. Hartemink), kandic (upper right), and natric (lower left)... 93 Fig. 11.2 Distribution of orders containing clay-enriched subsurface horizons (From Bockheim and Hartemink 2013)... 97 Fig. 12.1 A calcic horizon reacting to 10 % HCl (top) and a petrocalcic horizon in a Petrocalcic Paleargids in southern Nevada (bottom; photos by J. Bockheim).......... 111 Fig. 12.2 Family classes of soils with calcic and petrocalcic horizon...... 114 Fig. 12.3 Counties containing soils with calcic and petrocalcic horizons... 115 Fig. 13.1 Distribution of soils in the USA with cambic horizons (Prepared by Paul Reich)... 130 Fig. 14.1 (a) Argidurid in the Mojave Desert, California. The calcareous duripan begins at 30 cm with several overlapping discontinuous layers and krotovina within the duripan. (b) Durixeralf in the Sacramento Valley, CA. Duripan at 50 cm has clay films and MnO 2 coatings. (c) Thin section of a duripan from a Durixeralf in CA. Crossed polarizers. Durinode, with incorporated sand grains, occupies most of the right half of the image. Stringers of opal, probably mixed with clay coat the durinode. Frame width represents about 1.7 mm (Images provided by Dr. Randy Southard)........ 135 Fig. 14.2 Families of abundant (>30,000 ha) soil series containing a duripan or durinodes... 143 Fig. 14.3 Distribution of Durids suborder and major Dur- great groups in conterminous USA (Prepared by Dr. Paul Reich)... 144 Fig. 14.4 Genesis of duripans under three contrasting conditions... 148

List of Figures xxi Fig. 15.1 A fragipan (30 50 cm depth) in an Alfic Fragiorthods, Upper Peninsula, Michigan (Photo by J. Bockheim)... 155 Fig. 15.2 Frequency distribution of fragic soil series by family (Bockheim and Hartemink 2013)... 160 Fig. 15.3 Distribution of soils with fragipans by order with the conterminous USA (From Bockheim and Hartemink 2013).... 161 Fig. 16.1 Dromedary soil series, classified as a loamy-skeletal, mixed Mollic Haplocryalfs, from the Uinta Mountains in Utah (Photo by J. Bockheim). The glossic horizon occurs at a depth of 33 42 cm and includes zones of E and Bt materials... 170 Fig. 16.2 Family classes of soils with a glossic horizon... 174 Fig. 16.3 Broad occurrence of soils with a glossic horizon in environmental tension zones... 175 Fig. 17.1 A Leptic Haplogypsids with a gypsic horizon (top) and a Typic Petrogypsids with a petrogypsic horizon (bottom), White Sands, New Mexico (Photos compliments of Dr. C. Monger)... 180 Fig. 17.2 Frequency distribution of soil series with a gypsic horizon in various families... 181 Fig. 17.3 Counties with soils containing a high frequency of gypsic or petrogypsic horizons... 185 Fig. 18.1 Ortstein: (a) Finch soil series (Typic Duraquods) from the Upper Peninsula of Michigan; (b) Blacklock series (Typic Duraquods) from coastal Oregon; and (c) fragments of ortstein from the Blacklock series (Bockheim 2011)... 190 Fig. 18.2 A placic horizon in Blacklock soil (Typic Duraquods), coastal Oregon (Photo by J. Bockheim)... 191 Fig. 18.3 Areas containing soils with ortstein horizons in the conterminous USA and AK (From Bockheim 2011)... 200 Fig. 19.1 A Kandiustox from Santa Catarina state, Brazil; the oxic horizon occurs within the zone of the shovel and below (Photo by J. Bockheim)... 215 Fig. 19.2 Distribution of soils with an oxic horizon in the USA and its territories (Map by NRCS)... 215 Fig. 20.1 Landform and soil with a salic horizon, White Sands Missile area, New Mexico (Photo by Dr. C. Monger)... 222 Fig. 20.2 Distribution of soils with a salic horizon in the USA (From Bockheim and Hartemink 2013)... 229 Fig. 21.1 A road cut in Rwanda showing a continuously traceable sombric horizon in a Sombriudox (Photo by P. Reich).... 247 Fig. 21.2 Sombric horizon from a Sombriudox in Rwanda (Photo by W. Sombroek)... 247

xxii List of Figures Fig. 22.1 A Typic Haplorthod with a spodic horizon (Photograph by J. Bockheim)... 258 Fig. 22.2 Distribution of soils with a spodic horizon (Map from NRCS)... 262 Fig. 23.1 A landform and soil derived from the New Idria Formation (ultramafic materials, Coast Range, central California) (Photos by Dr. R. Graham)... 269 Fig. 23.2 Families of soil series derived from ultramafic materials... 275 Fig. 23.3 Counties containing soils derived from ultrabasic materials... 276 Fig. 24.1 Lamellae in the Spinks soil series at 40 cm (L) and 100 cm (R) depth. The soil is a sandy, mixed, mesic Lamellic Hapludalfs under coniferous forest in NE Dane County in Wisconsin, USA. The lamellae at 40 50 cm were less than 2 mm thick and slightly finer than the interlamellae soil textures. Below 100 cm the lamellae were thicker (1 2 cm) and had sandy loam textures, whereas the interlamellae matrix was a loamy sand (Bockheim and Hartemink 2013)... 285 Fig. 24.2 Lamellae in the Oshtemo soil series below 185 cm depth. The soil is a coarse-loamy, mixed, active, mesic Typic Hapludalfs under forest in Adams County in Wisconsin, USA. The lamellae at that depth were seveal cm thick and slightly finer than the interlamellae soil textures. The lamellae are not described in the Official Series Description of USDA-NRCS but commonly associated soils (Coloma series) have lamellae below 99 cm (Bockheim and Hartemink 2013)... 285 Fig. 24.3 Frequency distribution of soil series with lamellae by family (Bockheim and Hartemink 2013)... 294 Fig. 24.4 Distribution of soils with lamellae in the USA (Published in Bockheim and Hartemink 2013)... 294 Fig. 25.1 Plinthite in the Dothan series (near blade of shovel; photo compliments of Dr. Joey Shaw)... 303 Fig. 25.2 Family classes of soils with plinthite in the USA... 306 Fig. 25.3 Counties containing soils with plinthite... 307 Fig. 26.1 Relation between the number of soil series in a soil order and the area of the soil order (Gelisols not included)... 312

List of Tables Table 1.1 Abbreviated descriptions of diagnostic horizons at various levels in Soil Taxonomy... 2 Table 1.2 Diagnostics of epipedons at different taxonomic levels in ST... 3 Table 1.3 Diagnostics of subsurface horizons at different taxonomic levels in ST... 3 Table 1.4 Diagnostic epipedons used per suborder, great group, and subgroup for each soil order... 6 Table 1.5 Diagnostic subsurface horizons used per suborder, great group, and subgroup for each soil order... 7 Table 1.6 Role of soil-forming factors in diagnostic horizons... 8 Table 1.7 Soil-forming processes in relation to diagnostic horizons, properties, and materials by order in Soil Taxonomy... 9 Table 3.1 Properties of selected soils from the literature with an anthropic or plaggen epipedon... 14 Table 3.2 Classification of soils with anthropic and plaggen epipedons in soil taxonomy... 18 Table 4.1 Properties of selected soils with a melanic epipedon (source: NSSC SSL)... 23 Table 4.2 Classification of soil series containing a melanic epipedon... 25 Table 4.3 Factors influencing the development of the melanic horizon.... 26 Table 5.1 Properties of mollic epipedons by soil order... 31 Table 5.2 Soil taxa with mollic epipedons... 33 Table 5.3 Family distribution of soil orders containing a mollic or mollic-color epipedon... 37 Table 5.4 Relation of soil-forming factors to the development of mollic epipedons and intergrades... 41 Table 6.1 Properties of selected soils with an umbric (Source: NSSC SSL)... 49 Table 6.2 Soil taxa with taxonomically defined umbric epipedons... 51 xxiii

xxiv List of Tables Table 6.3 Factors influencing the development of the umbric epipedon... 53 Table 7.1 Properties of selected soils with an ochric epipedon (Source: NSSC SSL)... 57 Table 7.2 Approximate classification of soil series with an ochric epipedon... 60 Table 7.3 Influence of soil-forming factors on development of the ochric epipedon... 61 Table 8.1 Analytical properties of Folists... 65 Table 8.2 Properties of selected soils with a histic epipedon (Source: NSSC SSL)... 66 Table 8.3 Classification of soil series with a folistic epipedon... 68 Table 8.4 Classification of soil series with a histic epipedon... 69 Table 8.5 Factors influencing the development of the folistic epipedon... 72 Table 8.6 Factors influencing the development of the histic epipedon... 72 Table 9.1 Impacts of soil compaction on physical and hydraulic properties of soils... 77 Table 10.1 Properties of selected soils with an albic horizon (Source: NSSC SSL)... 81 Table 10.2 Classification of soil series with an albic horizon... 83 Table 10.3 Factors influencing the development of the albic horizon...... 85 Table 11.1 Soil textural horizons and their approximate history and current definition in Soil Taxonomy (Bockheim and Hartemink 2013)... 91 Table 11.2 Soil taxa with argillic, kandic, natric, and agric horizons (Bockheim and Hartemink 2013)... 95 Table 11.3 Proportion of soil series with argillic and related horizons within each order in the USA (Bockheim and Hartemink 2013)... 97 Table 11.4 Relation of soil-forming factors and argillic horizons (Bockheim and Hartemink 2013)... 98 Table 11.5 Genesis of argillic, natric, and kandic horizons (Bockheim and Hartemink 2013)... 102 Table 12.1 Properties of calcic and petrocalcic horizons as derived from the NCRS SSURGO database (mean values followed by standard error)... 112 Table 12.2 Classification of soil series with calcic and petrocalcic horizons in the USA... 112 Table 12.3 Relation of soil-forming factors to the development of calcic and petrocalcic horizons... 116

List of Tables xxv Table 13.1 Properties of selected soils with a cambic horizon (Source: NSSC SSL)... 124 Table 13.2 Distribution of soils containing a cambic... 128 Table 13.3 Factors influencing the development of the cambic horizon... 131 Table 14.1 Silica stage in relation to taxonomic level for duric soils... 135 Table 14.2 Analytical properties of selected duric soils (Source: NSSC SSL)... 136 Table 14.3 List and areas of duric soils by taxa... 140 Table 14.4 Relation of soil-forming factors to the development of duripans... 145 Table 15.1 Analytical properties of fragic soils (Bockheim and Hartemink 2013)... 156 Table 15.2 Classification of soils with fragipans in the USA (Bockheim and Hartemink 2013)... 158 Table 15.3 Relation of soil-forming factors to the development of fragipans (Bockheim and Hartemink 2013)... 162 Table 15.4 Hypotheses for the genesis of fragipans (Bockheim and Hartemink 2013)... 164 Table 16.1 Properties of Cryalfs with glossic horizons... 171 Table 16.2 Classification of soil series with a glossic horizon... 173 Table 16.3 Factors influencing the development of the glossic horizon... 176 Table 17.1 Chemical and physical properties of soils with a gypsic horizon, SSL database... 182 Table 17.2 Classification of soils with gypsic and petrogypsic horizons in Soil Taxonomy... 184 Table 17.3 Relation of soil-forming factors to the development of gypsic and petrogypsic horizons... 186 Table 18.1 Statistical comparison of analytical properties of soils with >50 % ortstein, <50 % ortstein, and geographically associated Spodosols without ortstein. Data for seven soils with placic horizons are included (Bockheim 2011)... 192 Table 18.2 Frequency distribution of morphological features of soils with >50 % ortstein, <50 % ortstein, and geographically associated Spodosols without ortstein. Percent of total is given in parentheses. Data for seven soils with placic horizons are included (Bockheim 2011)... 193 Table 18.3 Distribution of taxa for soils with >50 % ortstein, <50 % ortstein and geographically associated soils without ortstein. Data are included for seven pedons with placic horizons (Bockheim 2011)... 197 Table 18.4 Areas of soil series by region (Bockheim 2011)... 199 Table 18.5 Site conditions favoring ortstein development from the literature and from this review (Bockheim 2011).... 201

xxvi List of Tables Table 18.6 Statistical comparison of site factors for soils with >50 % ortstein, <50 % ortstein, and geographically associated Spodosols without ortstein. Data for seven soils with placic horizons are included (Bockheim 2011)... 201 Table 18.7 Nature of cementing agents and origin of ortstein and placic horizons from a review of the literature (Bockheim 2011)..... 206 Table 19.1 Properties of soils with an oxic horizon (Source: NRCS Soil Lab Data)... 213 Table 19.2 Soil series with an oxic horizon in the USA and its territories... 216 Table 19.3 Factors influencing the development of the oxic horizon... 217 Table 20.1 Chemical and physical properties of soils with a salic horizon, SSL database... 224 Table 20.2 Mineralogy of soils with salic horizons (Bockheim and Hartemink 2013)... 228 Table 20.3 Classification of soils with a salic horizon in Soil Taxonomy (Bockheim and Hartemink 2013)... 228 Table 20.4 A global comparison of properties of soils with salic horizons (Bockheim and Hartemink 2013c)... 231 Table 20.5 Relation of soil-forming factors to the development of salic horizons (Bockheim and Hartemink 2013c)... 233 Table 21.1 Analytical properties of soils with sombric horizons (Bockheim 2012)... 239 Table 21.2 Classification of soils with sombric-like or sombric horizons in Soil Taxonomy (see Table 21.3 for additional information) (Bockheim 2012)... 248 Table 21.3 Site factors for soils with sombric and sombric-like horizons (Bockheim 2012)... 251 Table 22.1 Properties of soils with spodic horizons (Source: NRCS soil lab data)... 259 Table 22.2 Classification of soil series with spodic horizons or in spodic subgroups... 261 Table 22.3 Factors influencing the development of the spodic horizon.... 263 Table 23.1 Analytical properties of selected serpentinitic soils (Source: NSSC SSL)... 270 Table 23.2 Classification of serpentinitic soils... 274 Table 23.3 Factors influencing the development of ultramafic soils... 277 Table 24.1 Characteristics of lamellae from Official Soil Descriptions (Bockheim and Hartemink 2013a)... 284 Table 24.2 Frequency distribution of textural classes of E part and Bt part of lamellic (E & Bt) horizons (Adapted from Official Soil Series Descriptions of 118 pedons in lamellic subgroups) (Bockheim and Hartemink 2013)... 286

List of Tables xxvii Table 24.3 Analytical properties of soils with lamellae (Source: USDA, NRCS; published in Bockheim and Hartemink 2013)... 287 Table 24.4 Classification of soils with lamellae in Soil Taxonomy (Bockheim and Hartemink 2013)... 292 Table 24.5 Relation of soil-forming factors and lamellae development (Bockheim and Hartemink 2013)... 295 Table 24.6 Relation between soil taxa criteria and characteristics of lamellae and the E & Bt horizon (Bockheim and Hartemink 2013)... 297 Table 25.1 Properties of soils with plinthite (Source: NRCS Soil Lab Data)... 304 Table 25.2 Classification of soils with plinthite in the USA... 305 Table 25.3 Factors influencing the development of plinthite... 308 Table 26.1 Number of soil series and dominant orders of diagnostic horizons... 312 Table 26.2 Influence of soil-forming factors on development of diagnostic horizons... 314 Table 27.1 A comparison of diagnostic horizons between ST and the WRB (boldface indicates epipedon)... 318 Table 27.2 A comparison of orders in ST with reference soil groups in the WRB... 319