Contents
Authors
Preface to the First Edition
Preface to the Second Edition
Preface to the Third Edition
Preface to the Fourth Edition
Preface to the Fifth Edition
Preface to the Sixth Edition
SOIL GENESIS AND CLASSIFICATION
1 Introduction
Subdivisions of Pedology
Perspective on the Role of Soil Genesis and Classification
Developmental Stages of a Discipline
Historical Developments in Soil Genesis
Concepts of Soil Genesis
A Soil as an Anatomical Specimen
A Soil as an Energy Transformer
A Soil as an Open System
Methods of Soil Genesis Study
Some Definitions of Soil Classification
General Perspective of Soil Classification
Principles of Soil Classification
Succession of Classifications
Avoiding Rigor Mortis in Classification
Historic Perspective of Soil Classification
Soil Morphology
Soil Individuals on the Landscape
Other Soil Genesis and Classification Activities
Soil Survey
Perspective
2 Morphology and Composition of Soils
Soil Macromorphology: Examination and Description
Soil Composition and Characterization
Mineralogical Composition
Soil Micromorphology
Dynamic Soil Properties
Perspective
3 Soil-forming Factors: Soil as a Component of Ecosystems
The Place of Soils in Ecosystems
Parent Material
Climate
Relief (Topography)
Organisms
Time as a Factor in Soil Formation
Perspective
4 Soil Materials and Weathering
Weathering
Products of Weathering
Equilibria and Stability Ranges for Clay Minerals
5 Soil-forming Processes
Conceptualizing the Environment of Soil Formation
Intrasolum Translocations and Transformations
Simplified Model of Solum Development
Perspective
6 Modern Soil Classification Systems
Logic and Cognitive Science in Soil Classification
Indigenous Soil Classifications
Regional and National Soil Classification Systems
World Reference Base (WRB)
Numerical Classification of Soils
Perspective
7 U.S. Soil Taxonomy
Desired Attributes
Definition of the Classes
Nomenclature
Structure of the System
Perspective
8 Alfisols: High Base Status Soils with Finer-textured Subsoil Horizons
Setting
Pedogenic Processes
Uses of Alfisols
Classification of Alfisols
Perspective
9 Andisols: Soils with Andic Soil Properties
Setting
Pedogenic Processes
Uses of Andisols
Classification of Andisols
Perspective
10 Aridisols: Soils of Dry Regions
Setting
Pedogenic Processes
Uses of Aridisols
Classification of Aridisols
Perspective
11 Entisols: Recently Formed Soils
Setting
Pedogenic Processes
Uses of Entisols
Classification of Entisols
Perspective
12 Gelisols: Very Cold Soils
Setting
Pedogenic Processes
Uses of Gelisols
Classification of Gelisols
Perspective
13 Histosols: Organic Soils
Setting
Geological Processes of Organic Matter Accumulation
Pedogenic Biogeochemical Processes
Uses of Histosols
Describing Histosols
Classification of Histosols
Perspective
14 Inceptisols: Embryonic Soils with Few Diagnostic Features
Setting
Pedogenic Processes
Uses of Inceptisols
Classification of Inceptisols
Perspective
15 Mollisols: Grassland Soils of Steppes and Prairies
Setting
Pedogenic Processes
Uses of Mollisols
Classification of Mollisols
Perspective
16 Oxisols: Low Activity Soils
Setting
Pedogenic Processes
Uses of Oxisols
Classification of Oxisols
Perspective
17 Spodosols: Soils with Subsoil Accumulations of Humus and Sesquioxides
Setting
Pedogenic Processes
Uses of Spodosols
Classification of Spodosols
Perspective
18 Ultisols: Low Base Status Soils with Finer-textured Subsoil Horizons
Setting
Pedogenic Processes
Uses of Ultisols
Classification of Ultisols
Perspective
19 Vertisols: Shrinking and Swelling Dark Clay Soils
Setting
Pedogenic Processes
Uses of Vertisols
Classification of Vertisols
Perspective
20 Spatial Arrangement of Soils: Soilscapes and Map Units
Definitions
Distinction between Soil Taxa and Soil Map Units
Kinds of Soil Map Units
Orders and Standards of Soil Surveys
Assessing Map Unit Composition
Relation Between Soilscape and Soil Classification
Perspective
21 Interpretations of Soil Surveys and Technical Soil Classification
Soil Survey Interpretations
Interpretive Uses of Taxonomic Information and Soil Maps
Perspective
Bibliography
Plates
Index
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This edition first published 2011
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Library of Congress Cataloging-in-Publication Data
Soil genesis and classification / S.W. Buol ... [et al.]. – 6th ed.
p. cm.
Includes bibliographical references and index.
ISBN-13: 978-0-8138-0769-0 (hardcover : alk. paper)
ISBN-10: 0-8138-0769-7
1. Soil science. 2. Soil formation. 3. Soils–Classification. I. Buol, S. W.
S591.B887 2011
631.4–dc22
2011012321
A catalogue record for this book is available from the British Library.
This book is published in the following electronic formats: ePDF 9780470960592; Wiley Online Library 9780470960622; ePub 9780470960608; Mobi 9780470960615
Authors
STANLEY W. BUOL is a Distinguished Professor Emeritus of Soil Science at North Carolina State University, Raleigh, where he held William Neal Reynolds Distinguished and Alumni Distinguished Graduate Professorships before retirement. He earned B.S., M.S., and Ph.D. degrees from the University of Wisconsin-Madison. Prior to moving to North Carolina State University, he was a faculty member of the Agricultural Chemistry and Soils Department at the University of Arizona. He is a Fellow in both the Soil Science Society of America and American Society of Agronomy. He has received the International Soil Science Award and Distinguished Service Award from the Soil Science Society of America and the Achievement Award from the North Carolina Soil Science Society. In addition to several papers in scientific journals and book chapters, he has authored the book Soils, Land, and Life.
RANDAL J. SOUTHARD is Professor of Soil Genesis and Morphology and Soil Scientist in the California Agricultural Experiment Station at the University of California, Davis. He holds a B.S degree in biology and a M.S. degree in soil science from Utah State University and a Ph.D. in soil science from North Carolina State University. He is a member of the Soil Science Society of America, Sigma Xi, Gamma Sigma Delta, and the International Union of Soil Sciences and is a Fellow of the Soil Science Society of America. He served as Associate Dean of Environmental Sciences in the College of Agricultural and Environmental Sciences at UC Davis from 1999 to 2009. He teaches courses in introductory soil, pedology, and environmental sciences. He served as president of the Western Society of Soil Science from 1995 to 1996 and was an associate editor for the Soil Science Society of America Journal from 1999 to 2002. He has published articles in various journals including Soil Science Society of America Journal, Geoderma, Soil Science, Clays and Clay Minerals, Soil Survey Horizons, California Agriculture, Journal of Environmental Quality, Global Change Biology, and Atmospheric Environment.
ROBERT C. GRAHAM is professor of Soil Mineralogy and Pedology at the University of California, Riverside. He has degrees in soil science from the University of California at Davis, Utah State University, and North Carolina State University. He is a member of the Soil Science Society of America, International Union of Soil Sciences, Professional Soil Scientists Association of California, California Forest Soils Council, and the Geological Society of America. He has served as Associate Editor for the Soil Science Society of America Journal and is a Fellow in the Soil Science Society of America. At UC Riverside he advises graduate students and conducts research and teaches courses in soil mineralogy, soil geomorphology, and soils of natural ecosystems and landforms. He has published articles on these topics in a variety of journals including Soil Science Society of America Journal, Geoderma, Soil Science, Biogeochemisty, Clays and Clay Minerals Forest Ecology and Management, Canadian Journal of Forestry, Oecologia, Geology, Vadose Zone Journal, Catena, International Journal of Wildland Fire, and Journal of Arid Environments.
PAUL A. McDANIEL is Professor of Pedology at the University of Idaho in Moscow. He is also an Affiliate Faculty member at the Centro Agronómico Tropical de Investigación y Enseñanza (CATIE) in Turrialba, Costa Rica, and the Idaho Agricultural Experiment Station representative to the National Cooperative Soil Survey program. He holds a B.S. degree in Biology from University of Kentucky, an M.S. in Soil Science from Montana State University, and a Ph.D. in Soil Science from North Carolina State University. He served as Associate Editor for the Soil Science Society of America Journal from 2000–2006 and as Technical Editor for the Pedology, Soil Mineralogy, and Wetland Soils sections from 2007 to present. He is a member of Western Society of Soil Science, Gamma Sigma Delta, and the International Union of Soil Sciences, and is a Fellow of the Soil Science Society of America. He teaches courses in introductory soil science, pedology, and soil mineralogy, and has published research articles in various journals, including Soil Science Society of America Journal, Geoderma, Soil Science, Clays and Clay Minerals, Catena, Journal of Environmental Quality, Forest Science, Water Resources Research, Hydrological Processes, and Vadose Zone Journal.
Preface to the First Edition
We have intended in this work to summarize the body of knowledge called pedology, to direct readers to sources of additional information in the literature, and to encourage students to learn directly from the soil in its natural setting. This book is one in a succession of periodic reviews of soil morphology, genesis, and classification that may serve as stepping stones across the seeming morass of terminology and information.
These are exciting times in pedology. The “information explosion” in the several fields of soil science has enabled us to better understand soils and define them more quantitatively. The adoption and use of the Comprehensive Soil Classification System has provided new concepts and nomenclature. And the uses of soil survey, the end product of our classification, have greatly increased through their interpretation for application to land use and productivity studies, especially for nonfarm land use problems.
Yet the student, formally enrolled in college or a self-taught learner, has not had access to any summary in the form of an up-to-date reference or text. We have designed this book with the hope and desire that it will be equally useful to graduates and advanced undergraduates, professional pedologists and geographers, ecologists, and all others interested in or involved with the land. Portions of this book we hope and expect will be of use to planners, to highway engineers, and to sanitarians involved with disposal problems. An understanding of soil genesis and classification is a prerequisite to sound land use planning and land management. Soil science can help people learn to live adequately and significantly in a varied ecosystem and derive necessities from it without damaging it.
Limited use has been made of sketches to illustrate soil profiles. It is our intent that these be supplemented by color slides to illustrate classroom lectures. The Marbut memorial collection of 2-by-2-inch color slides assembled by the Soil Science Society of America is excellent for this purpose.
Our effort is in appreciation of the direction and motivation of which we have been the fortunate recipients in the past and an attempt to share what we have learned. We are grateful to the many persons who helped us in preparing this manuscript. The responsibility for any oversights is ours.
Madison, Wis., 1973
S. W. Buol
F. D. Hole
R. J. McCracken
Preface to the Second Edition
The second edition has entailed considerable revision that includes updating those portions that deal with Soil Taxonomy, which had not been formally published at the time of preparation of the first edition. We have also updated the soil classification systems of other countries and of FAO according to revisions and additions that have been made since the early 1970s. Chapters 25 and 26 have been completely rewritten, consistent with what we believe to be desirable trends in considering soils in three dimensions (as soilscapes) and in increasing interpretation of soil maps and scientific comprehensive soil classification systems for many specific technical applications. The recent publication of Minerals in Soil Environments by the Soil Science Society of America (J. B. Dixon and S. B. Weed, eds.) has greatly added accessibility to soil mineralogical literature. The experiences of the authors since 1973, as well as comments from students and other readers, have led to the removal of some ambiguous and erroneous statements and to the addition of some new material in most of the chapters.
Madison, Wis., 1978
S. W. Buol
F. D. Hole
R. J. McCracken
Preface to the Third Edition
The third edition reflects an update of literature and experience during the past seven years. More than that, it attempts to reflect the “coming of age” of Soil Taxonomy as a major unifying force in promoting worldwide communication and understanding of soil morphology, genesis, and classification. Since our preparation of the second edition, considerable effort and progress have occurred in bringing global experience to Soil Taxonomy through the formation of international soil classification committees and through the publication of many papers and symposia. The efforts of these committees resulted in major changes with minimum violence to the system. Because of the official recommendations of the international committees, we feel that Soil Taxonomy has now accomplished the most difficult of its objectives, namely, that “the taxonomy should be capable of modification to fit new knowledge with a minimum of disturbance” (Soil Survey Staff 1975, p. 8). Great progress has also been made toward another of its goals that “the taxonomy should provide for all soils that are known, wherever they may be” (Soil Survey Staff 1975, p. 8). Therefore, in this edition we have attempted to adhere more closely to terminology and provisions of Soil Taxonomy, updating the terminology of older literature where necessary and stressing more recent research results. We have included discussions of approved amendments to Soil Taxonomy, such as the Kandi great groups, as well as pending proposals for major changes in the classification of Oxisols and the proposed Andisol order.
We are mindful, and stress to our readers, that classification should neither bias nor limit investigations concerning soils. Students should be encouraged to challenge the “wisdom of the past” that is the basis of any classification. In soil genesis, it is often said that the experiments have been conducted. Thus, the soil scientist is left to observe the result and interpret the processes by which the pedologic transformations have taken place. As such, the systematic and orderly observation of soil in the field, with the assistance of analytical techniques on samples brought back to the laboratory and greenhouse, remains the basis for future advances in soil science.
In this third edition, we have updated our review of soil classification systems used in other countries so readers may fully appreciate how soils are viewed and classified around the world.
We also have added new material reflecting the advances in soil genesis (that we have brought into chapters on flux factors and site factors) and in soil cover (including soils and landscapes and spatial variability). And the new developments and approaches in soil survey interpretation are reflected in a revised and expanded chapter on that subject.
1988
S. W. Buol
F. D. Hole
R. J. McCracken
Preface to the Fourth Edition
This fourth edition reflects advances in concepts and new information based on research and field experience. It also describes the many changes in soil classification reflected in Soil Taxonomy in the six years since the third edition was prepared and distributed. This edition reflects several changes in terminology, advances in technology, and our increased understanding of soil formation processes.
We draw attention to the reorientation and expansion of the range and scope of coverage in soil genesis and classification. This includes additional emphasis on the biogeochemistry of soil systems and the roles of soils in ecosystems.
This edition includes for the first time a definition and description of soils in the coldest regions of the planet that are actively being considered as a new order, Gelisols, in Soil Taxonomy. Also, in this edition you will find more information about the genesis, properties, and classification of soils frequently present in tropical and subtropical regions and soils with andic soil properties, the Andisols.
Also included are discussions and explanations of the use and applications of new technology via soil databases, soil geographic information systems, ground penetrating radar, increased use of aerial photography for soil studies, and new approaches to modeling soil systems. We also discuss the growing problem of trying to characterize and adjust for spatial variability within soil mapping units. Also included in this edition are discussions of concerns about soil quality, measures for remediation of soil problems such as waste disposal, and soil loss by erosion. Certain chapters of the previous editions have been combined and blended to produce a more comprehensive and cohesive picture and description of soil systems.
Another plus is the addition of a fourth author who is actively teaching and conducting research in arid and semiarid areas as well as internationally.
1997
S. W. Buol
F. D. Hole
R. J. McCracken
R. J. Southard
Preface to the Fifth Edition
This fifth edition presents the current understanding of soil as a thin layer of the earth’s surface that forms an interface between the inorganic minerals of the earth’s crust and the organic components of biologic entities living on the land and in the surrounding atmosphere.
Soil genesis, or the more encompassing concept of pedology, is an evolving discipline devoted to understanding how soils differ in form and function. The widely held view that a soil is a formed and therefore a nearly stable entity has evolved into the view that soil is a dynamic natural entity that interfaces with ecosystems and human endeavors. Chemical, biological, and physical reactions are constantly taking place within soil. Some of these reactions produce changes so slowly that human time scales are inadequate for measuring and comprehending soil dynamics. Other changes are rapid, episodic events that are viewed by humans as catastrophic and that challenge soil scientists to devise techniques to quantify the magnitude and probability of their occurrence.
Human efforts to understand and communicate knowledge about soils are reflected in attempts to classify soils. This edition reviews a spectrum of soil classification systems and presents the culmination of more than two decades of testing and revisions in the most detailed and comprehensive system for soil classification as reflected in the 1999 publication of the second edition of Soil Taxonomy. To better reflect the state of knowledge, new nomenclature has been added and improvements have been made in the systematic structure of soil classification categories. New analytical techniques have been utilized to more quantitatively identify soil properties and define class limits.
While we accept that soil changes, as external energy from the sun and rain is dissipated on its mineral components and as new organic components are added from the biological organisms that invade, we have to accept that humans also change. Just as in soil, where new components are formed to replace weathered components, new authors have replaced some of the stalwart authors of earlier editions.
2003
S. W. Buol
R. J. Southard
R. C. Graham
P. A. McDaniel
Preface to the Sixth Edition
This sixth edition presents current concepts of how soils are formed and sustained as an entity on the surface of the land masses on planet earth. Soil is an entity composed of mineral material inherited from geologic rock as altered by the actions of water and additions of organic materials injected by the plants and animals that find root within and tread on its surface. In response to the multitude of geologic materials, climatic conditions, and biologic ecosystems that presently exist and existed in the past, soils have acquired a multitude of properties that defy attempts to characterize soil as a singular entity. Thus, we speak of soils of the earth.
Human efforts to better understand soil properties and behavior and to more efficiently utilize soils for human endeavors have resulted in numerous attempts to classify the various kinds of soil. This is a never-ending endeavor that proceeds as new chemical, physical and biological methods are developed to analyze soil material. There is also the realization that soils have daily and seasonal dynamic features of temperature and moisture that affect human usage. All of these have to be considered and addressed in the search for more comprehensive understanding of the role soils play in ecosystem function, and how humans can best utilize and conserve the various kinds of soil.
This edition builds on the material contained in earlier editions and incorporates more detailed data regarding specific examples of how soils acquire various characteristics. We include a section of color plates that help readers better visualize the various kinds of soil. Also included is the recent recognition that soils periodically covered by shallow water are an important component of the spatial association between land and sea. We have expanded on methods of communicating and analyzing spatial information that have been greatly enhanced by modern electronic technologies. These technologies enable the rapid dissemination of information among soil scientists and users of soil information, and drive the development of new methods for modeling processes of soil formation and resulting patterns of soils on the landscape.
Our knowledge of the soils in the world is ever increasing as we utilize new analytical methods to investigate soil chemical, physical, and biological properties from the nano to the landscape scale and modern methods of transportation to gain access to previously little-studied areas of the world. This has greatly expanded not only our understanding of how soils are formed but also the techniques different human cultures utilize to manage the various kinds of soil from which they obtain human nourishment.
It is through the amalgamation of a multitude of individual observations as reported in scientific publications that this edition has been assembled.
S. W. Buol
R. J. Southard
R. C. Graham
P. A. McDaniel
SOIL GENESIS AND CLASSIFICATION
SIXTH EDITION