The Nature and Properties of Soils. 15th edition

Abstract

This edition updates a narrative that has been at the forefront of soil science for more than a century. The first edition, published in 1909, was largely a guide to good soil management for farmers in the glaciated regions of New York State in the northeastern U.S. Since then, it has evolved to provide a globally relevant framework for an integrated understanding of the diversity of soils, the soil system and its role in the ecology of planet Earth.

The 15th edition is the first to feature full-color illustrations and photographs throughout. These new and refined full color figures and illustrations help make the study of soils more efficient, engaging, and intellectually satisfying. Every chapter has been thoroughly updated with the latest advances, concepts, and applications. Hundreds of new key references have been added. The 15th edition, like preceding editions, has greatly benefited from innumerable suggestions, ideas, and corrections contributed by soil scientists, instructors, and students from around the world. Dr. Nyle Brady, although long in retirement and recently deceased, remains as co-author in recognition of the fact that his vision, wisdom and inspiration continue to permeate the entire book.

This edition,1082 pages in length, includes in-depth discussions on such topics of cutting edge soil science as the pedosphere concept, new insights into humus and soil carbon accumulation, subaqueous soils, soil effects on human health, principles and practice of organic farming, urban and human engineered soils, cycling and plant use of silicon, inner- and outer-sphere complexes, radioactive soil contamination, new understandings of the nitrogen cycle, cation saturation and ratios, acid sulfate soils, water-saving irrigation techniques, hydraulic redistribution, cover crop effects on soil health, soil food-web ecology, disease suppressive soils, soil microbial genomics, indicators of soil quality, soil ecosystem services, biochar, soil interactions with global climate change, digital soil maps, and many others. In response to their popularity in recent editions, I have also added many new boxes that present either fascinating examples and applications or technical details and calculations. These boxes both highlight material of special interest and allow the logical thread of the regular text to flow smoothly without digression or interruption.
For students: This book provides both an exciting, accessible introduction to the world of soils as well as a reliable, comprehensive reference that you will want to keep for your professional bookshelf. What you learn from its pages will be of enormous practical value in equipping you to meet the many natural-resource challenges of the 21st century. The book demonstrates how the soil system provides many opportunities to see practical applications for principles from such sciences as biology, chemistry, physics, and geology. Throughout, the text highlights the countless interactions between soils and other components of forest, range, agricultural, wetland, and constructed ecosystems.

As the global economy expands exponentially societies face new challenges with managing their natural resources. Soil as a fundamental natural resource is critical to sustained economic growth and the prosperity of people in all parts of the world. To achieve balanced growth with a sustainable economy while improving environmental quality, it will be necessary to have a deep understanding of soils, including their properties, functions, ecological roles and management. I have tried to write this textbook in a way designed to engage inquisitive minds and challenge them to understand soils and actively do their part as environmental and agricultural scientists, in the interest of ensuring a prosperous and healthy future for humanity on planet Earth. It is my sincere hope that this book, previous editions of which have served so many generations of soil students and scientists, will continue to help future generations of soil scientists to benefit from a global ecological view of soils.

Full text

ISBN-13: 978-0-13-325448-8
ISBN-10: 0-13-325448-8
9 7 80 1 33 2 54 48 8
90000
RAY R. WEIL NYLE C. BRADY
THE NATURE AND PROPERTIES OF SOILS
FIFTHTEENTH EDITION
Enter the fascinating world of soils! Thoroughly updated and now in full color, the
15th edition of this market leading text brings the exciting field of soils to life.
Explore this new edition to find:
A comprehensive approach to soils with a focus on six major ecological roles of
soil including growth of plants, climate change, recycling function, biodiversity,
water, and soil properties and behavior.
New full-color illustrations and the use of color throughout the text highlights the
new and refined figures and illustrations to help make the study of soils more effi-
cient, engaging, and relevant.
Updated with the latest advances, concepts, and applications including hundreds of
key references.
New coverage of cutting edge soil science. Examples include coverage of the pedo-
sphere concept, new insights into humus and soil carbon accumulation, subaqueous
soils, soil effects on human health, principles and practice of organic farming, urban
and human engineered soils, new understandings of the nitrogen cycle, water-saving
irrigation techniques, hydraulic redistribution, soil food-web ecology, disease sup-
pressive soils, soil microbial genomics, soil interactions with global climate change,
digital soil maps, and many others.
New applications boxes and case study vignettes. A total of 10 new application and
case study boxes bring important soils topics to life. Examples include “Subaqueous
Soils—Underwater Pedogenesis,” “Practical Applications of Unsaturated Water Flow
in Contrasting Layers,” and “Char: Is Black the New Gold?”
New calculations and practical numerical problems boxes. Eight new boxes help
students explore and understand detailed calculations and practical numerical prob-
lems. Examples include “Calculating Lime Needs Based on pH Buffering,” “Leaching
Requirement for Saline Soils,” and “Calculation of Percent Pore Space in Soils.”
WEIL
BRADY
RAY R. WEIL
NYLE C. BRADY
THE NATURE AND PROPERTIES OF SOILS
FIFTHTEENTH EDITION
FIFTHTEENTH
EDITION
www.pearsonhighered.com
THE NATURE AND
PROPERTIES OF SOILS

THE NATURE AND
PROPERTIES OF SOILS
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THE NATURE AND
PROPERTIES OF SOILS
FIFTEENTH EDITION
Ray R. Weil
Professor of Soil Science
University of Maryland
Nyle C. Brady (late)
Professor of Soil Science, Emeritus
Cornell University
Boston Columbus Indianapolis New York San Francisco Hoboken
Amsterdam Cape Town Dubai London Madrid Milan Munich Paris Montreal Toronto
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Executive Editor: Daryl Fox
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www.pearsoned.com/permissions/.
Earlier editions by T. Lyttleton Lyon and Harry O. Buckman copyright © 1922, 1929, 1937, and 1943 by Macmillan
Publishing Co., Inc. Earlier edition by T. Lyttleton, Harry O. Buckman, and Nyle C. Brady copyright © 1952 by
Macmillan Publishing Co., Inc. Earlier editions by Harry O. Buckman and Nyle C. Brady copyright © 1960 and 1969
by Macmillan Publishing Co., Inc. Copyright renewed 1950 by Bertha C. Lyon and Harry O. Buckman, 1957 and
1965 by Harry O. Buckman, 1961 by Rita S. Buckman. Earlier editions by Nyle C. Brady copyright © 1974, 1984,
and 1990 by Macmillan Publishing Company.
Library of Congress Cataloging-in-Publication Data
Names: Brady, Nyle C., author. | Weil, Ray R., author.
Title: The nature and properties of soils / Nyle C. Brady, Ray R. Weil.
Description: Fifteenth edition. | Columbus : Pearson, 2016.
Identifiers: LCCN 2016008568 | ISBN 9780133254488
Subjects: LCSH: Soil science. | Soils.
Classification: LCC S591 .B79 2016 | DDC 631.4--dc23
LC record available at http://lccn.loc.gov/2016008568
ISBN-13: 978-0-13-325448-8
ISBN-10: 0-13-325448-8
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To all the students and colleagues in soil science who have
shared their inspirations, camaraderie, and deep love of the Earth.
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Preface xv
1
The Soils Around Us 1
1.1 What Ecosystem Services Do Soils Perform? 2
1.2 How Do Soils Support Plant Growth? 3
1.3 How Do Soils Regulate Water Supplies? 7
1.4 How Do Soils Recycle Raw Materials? 8
1.5 How Do Soils Modify the Atmosphere? 8
1.6 What Lives in the Soil Habitat? 8
1.7 Soil as an Engineering Medium 11
1.8 The Pedosphere and the Critical Zone? 12
1.9 Soils as Natural Bodies 12
1.10 The Soil Profile and Its Layers (Horizons) 15
1.11 Topsoil and Subsoil 18
1.12 Soil—Interface of Air, Minerals, Water,
andLife 20
1.13 What are the Mineral (Inorganic) Constituents
of Soils? 20
1.14 The Nature of Soil Organic Matter 23
1.15 Soil Water—Dynamic and Complex 25
1.16 Soil Air: A Changing Mixture of Gases 26
1.17 How Do Soil Components Interact to Supply
Nutrients to Plants? 26
1.18 How Do Plant Roots Obtain Nutrients? 28
1.19 Soil Health, Degradation, and Resilience 30
1.20 Conclusions 31
Study Questions 32
References 32
2
Formation of Soils from Parent
Materials 33
2.1 Weathering of Rocks and Minerals 33
2.2 What Environmental Factors Influence Soil
Formation? 41
2.3 Parent Materials 42
2.4 How Does Climate Affect Soil Formation? 55
2.5 How Do Living Organisms (Including People)
Affect Soil Formation? 57
2.6 How Does Topography Affect Soil Formation? 62
2.7 How Does Time Affect Soil Formation 65
2.8 Four Basic Processes of Soil Formation 67
2.9 The Soil Profile 70
2.10 Urban Soils 77
2.11 Conclusion 81
Study Questions 81
References 82
3
Soil Classification 83
3.1 Concept of Individual Soils 83
3.2 Soil Taxonomy: A Comprehensive Classification
System 85
3.3 Categories and Nomenclature of Soil
Taxonomy 92
3.4 Soil Orders 94
3.5 Entisols (Recent: Little If Any Profile
Development) 96
3.6 Inceptisols (Few Diagnostic Features: Inception
of B Horizon) 99
3.7 Andisols (Volcanic Ash Soils) 100
3.8 Gelisols (Permafrost and Frost Churning) 102
3.9 Histosols (Organic Soils Without Permafrost) 103
3.10 Aridisols (Dry Soils) 107
3.11 Vertisols (Dark, Swelling, and Cracking
Clays) 109
3.12 Mollisols (Dark, Soft Soils of Grasslands) 112
3.13 Alfisols (Argillic or Natric Horizon, Moderately
Leached) 114
3.14 Ultisols (Argillic Horizon, Highly Leached) 115
3.15 Spodosols (Acid, Sandy, Forest Soils, Highly
Leached) 117
3.16 Oxisols (Oxic Horizon, Highly Weathered) 118
vii
Contents
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viii 
3.17 Lower-Level Categories in Soil Taxonomy 121
3.18 Conclusion 128
Study Questions 129
References 129
4
Soil Architecture and Physical
Properties 130
4.1 Soil Color 130
4.2 Soil Texture (Size Distribution of Soil
Particles) 134
4.3 Soil Textural Classes 139
4.4 Structure of Mineral Soils 144
4.5 Formation and Stabilization of Soil
Aggregates 148
4.6 Tillage and Structural Management of Soils 156
4.7 Soil Density 161
4.8 Pore Space of Mineral Soils 171
4.9 Soil Properties Relevant to Engineering Uses 175
4.10 Conclusion 185
Study Questions 185
References 186
5
Soil Water: Characteristics and
Behavior 188
5.1 Structure and Related Properties of Water 189
5.2 Capillary Fundamentals and Soil Water 191
5.3 Soil Water Energy Concepts 193
5.4 Soil Water Content and Soil Water Potential 199
5.5 The Flow of Liquid Water in Soil 207
5.6 Infiltration and Percolation 213
5.7 Water Vapor Movement in Soils 217
5.8 Qualitative Description of Soil Wetness 218
5.9 Factors Affecting Amount of Plant-Available
Soil Water 222
5.10 Mechanisms by Which Plants are Supplied
withWater 228
5.11 Conclusion 230
Study Questions 230
References 232
6
Soil and the Hydrologic Cycle 233
6.1 The Global Hydrologic Cycle 234
6.2 Fate of Incoming Water 236
6.3 The Soil–Plant–Atmosphere Continuum
(SPAC) 244
6.4 Control of ET 250
6.5 Liquid Losses of Water from the Soil 255
6.6 Percolation and Groundwater 257
6.7 Enhancing Soil Drainage 262
6.8 Septic Tank Drain Fields 269
6.9 Irrigation Principles and Practices 273
6.10 Conclusion 280
Study Questions 282
References 282
7
Soil Aeration and Temperature 284
7.1 Soil Aeration—The Process 284
7.2 Means of Characterizing Soil Aeration 286
7.3 Oxidation–Reduction (Redox) Potential 288
7.4 Factors Affecting Soil Aeration and Eh 292
7.5 Ecological Effects of Soil Aeration 294
7.6 Soil Aeration in Urban Landscapes 298
7.7 Wetlands and Their Poorly Aerated Soils 301
7.8 Processes Affected by Soil Temperature 308
7.9 Absorption and Loss of Solar Energy 314
7.10 Thermal Properties of Soils 316
7.11 Soil Temperature Control 321
7.12 Conclusion 324
Study Questions 325
References 325
8
The Colloidal Fraction: Seat of Soil
Chemical and Physical Activity 327
8.1 General Properties and Types of Soil Colloids 328
8.2 Fundamentals of Layer Silicate Clay
Structure 332
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 ix
8.3 Mineralogical Organization of Silicate Clays 334
8.4 Structural Characteristics of Nonsilicate
Colloids 342
8.5 Genesis and Geographic Distribution of Soil
Colloids 344
8.6 Sources of Charges on Soil Colloids 346
8.7 Adsorption of Cations and Anions 348
8.8 Cation Exchange Reactions 350
8.9 Cation Exchange Capacity (CEC) 356
8.10 Exchangeable Cations in Field Soils 362
8.11 Anion Exchange 364
8.12 Sorption of Pesticides and Groundwater
Contamination 366
8.13 Binding of Biomolecules to Clay and Humus 369
8.14 Conclusion 371
Study Questions 372
References 372
9
Soil Acidity 374
9.1 What Processes Cause Soil Acidification? 375
9.2 Role of Aluminum in Soil Acidity 379
9.3 Pools of Soil Acidity 380
9.4 Buffering of pH in Soils 385
9.5 How Can We Measure Soil PH? 386
9.6 Human-Influenced Soil Acidification 390
9.7 Biological Effects of Soil pH 397
9.8 Raising Soil pH by Liming 404
9.9 Alternative Ways to Ameliorate the Ill Effects
of Soil Acidity 410
9.10 Lowering Soil pH 414
9.11 Conclusion 415
Study Questions 417
References 417
10
Soils of Dry Regions: Alkalinity, Salinity,
and Sodicity 420
10.1 Characteristics and Problems of Dry Region
Soils 421
10.2 Causes of High Soil pH (Alkalinity) 429
10.3 Development of Salt-Affected Soils 431
10.4 Measuring Salinity and Sodicity 435
10.5 Classes of Salt-Affected Soils 438
10.6 Physical Degradation of Soil by Sodic Chemical
Conditions 441
10.7 Biological Impacts of Salt-Affected Soils 444
10.8 Water-Quality Considerations for Irrigation 449
10.9 Reclamation of Saline Soils 452
10.10 Reclamation of Saline–Sodic and Sodic Soils 456
10.11 Management of Reclaimed Soils 461
10.12 Conclusion 461
Study Questions 462
References 463
11
Organisms and Ecology of the Soil 464
11.1 The Diversity of Organisms in the Soil 465
11.2 Organisms in Action 470
11.3 Abundance, Biomass, and Metabolic Activity 475
11.4 Earthworms 477
11.5 Ants and Termites 482
11.6 Soil Microanimals 486
11.7 Plant Roots 490
11.8 Soil Algae 494
11.9 Soil Fungi 494
11.10 Soil Prokaryotes: Bacteria and Archaea 502
11.11 Conditions Affecting the Growth and Activity
of Soil Microorganisms 509
11.12 Beneficial Effects of Soil Organisms on Plant
Communities 510
11.13 Soil Organisms and Plant Damage 512
11.14 Ecological Relationships among Soil
Organisms 517
11.15 Conclusion 521
Study Questions 522
References 523
12
Soil Organic Matter 526
12.1 The Global Carbon Cycle 526
12.2 Organic Decomposition in Soils 530
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x 
13.20 Sulfur Oxidation and Reduction 634
13.21 Sulfur Retention and Exchange 637
13.22 Sulfur and Soil Fertility Maintenance 638
13.23 Conclusion 639
Study Questions 639
References 640
14
Soil Phosphorus and Potassium 643
14.1 Phosphorus in Plant Nutrition and Soil
Fertility 644
14.2 Effects of Phosphorus on Environmental
Quality 646
14.3 The Phosphorus Cycle 652
14.4 Organic Phosphorus in Soils 657
14.5 Inorganic Phosphorus in Soils 661
14.6 Solubility of Inorganic Soil Phosphorus 664
14.7 Phosphorus-Fixation Capacity of Soils 667
14.8 Plant Strategies for Adequate Phosphorus
Acquisition from Soils 672
14.9 Practical Phosphorus Management 674
14.10 Potassium: Nature and Ecological Roles 677
14.11 Potassium in Plant and Animal Nutrition 678
14.12 The Potassium Cycle 681
14.13 The Potassium Problem in Soil Fertility 683
14.14 Forms and Availability of Potassium
in Soils 685
14.15 Factors Affecting Potassium Fixation
in Soils 688
14.16 Practical Aspects of Potassium
Management 689
14.17 Conclusion 691
Study Questions 692
References 693
15
Calcium, Magnesium, Silicon, and Trace
Elements 696
15.1 Calcium as an Essential Nutrient 697
15.2 Magnesium as a Plant Nutrient 699
15.3 Silicon in Soil–Plant Ecology 703
15.4 Deficiency Versus Toxicity 708
12.3 Factors Controlling Rates of Residue
Decomposition and Mineralization 535
12.4 Genesis and Nature of Soil Organic Matter
andHumus 543
12.5 Influences of Organic Matter on Plant Growth
andSoil Function 550
12.6 Amounts and Quality of Organic Matter in
Soils 555
12.7 Carbon Balance in the Soil–Plant–Atmosphere
System 556
12.8 Environmental Factors Influencing Soil Organic
Carbon Levels 560
12.9 Soil Organic Matter Management 564
12.10 Soils and Climate Change 568
12.11 Composts and Composting 575
12.12 Conclusion 579
Study Questions 580
References 581
13
Nitrogen and Sulfur Economy of Soils 583
13.1 Influence of Nitrogen on Plant Growth and
Development 584
13.2 Distribution of Nitrogen and the Nitrogen
Cycle 585
13.3 Immobilization and Mineralization 587
13.4 Dissolved Organic Nitrogen 590
13.5 Ammonium Fixation by Clay Minerals 591
13.6 Ammonia Volatilization 591
13.7 Nitrification 593
13.8 Gaseous Losses by Denitrification
andAnammox 596
13.9 Biological Nitrogen Fixation 601
13.10 Symbiotic Fixation with Legumes 603
13.11 Symbiotic Fixation with Nonlegumes 608
13.12 Nonsymbiotic Nitrogen Fixation 610
13.13 Nitrogen Deposition from the
Atmosphere 611
13.14 The Nitrate Leaching Problem 613
13.15 Practical Management of Soil Nitrogen 617
13.16 Importance of Sulfur 625
13.17 Natural Sources of Sulfur 626
13.18 The Sulfur Cycle 631
13.19 Behavior of Sulfur Compounds in Soils 631
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 xi
15.5 Micronutrient Roles in Plants 710
15.6 Sources of Micronutrients 715
15.7 Factors Influencing the Availability of the Trace
Element Cations 719
15.8 Organic Compounds as Chelates 724
15.9 Factors Influencing the Availability of the Trace
Element Anions 728
15.10 Soil Management and Trace Element
Needs 734
15.11 Conclusion 741
Study Questions 742
References 743
16
Practical Nutrient Management 745
16.1 Goals of Nutrient Management 745
16.2 Nutrients as Pollutants 749
16.3 Natural Ecosystem Nutrient Cycles 762
16.4 Recycling Nutrients Through Animal
Manures 766
16.5 Industrial and Municipal By-Products 775
16.6 Practical Utilization of Organic Nutrient
Sources 778
16.7 Inorganic Commercial Fertilizers 782
16.8 Fertilizer Application Methods 788
16.9 Timing of Fertilizer Application 792
16.10 Diagnostic Tools and Methods 793
16.11 Soil Analysis 798
16.12 Site-Index Approach to Phosphorus
Management 804
16.13 Some Advances and Challenges in Fertilizer
Management 807
16.14 Conclusion 812
Study Questions 814
References 815
17
Soil Erosion and Its Control 818
17.1 Significance of Soil Erosion and Land
Degradation 819
17.2 On-Site and Off-Site impacts of Accelerated
Soil Erosion 825
17.3 Mechanics of Water Erosion 828
17.4 Models to Predict the Extent of Water-Induced
Erosion 831
17.5 Factors Affecting Interrill and Rill Erosion 834
17.6 Conservation Tillage 842
17.7 Vegetative Barriers 849
17.8 Control of Gully Erosion and Mass Wasting 850
17.9 Control of Accelerated Erosion on Range- and
Forestland 853
17.10 Erosion and Sediment Control on Construction
Sites 856
17.11 Wind Erosion: Importance and Factors
Affecting It 860
17.12 Predicting and Controlling Wind Erosion 864
17.13 Tillage Erosion 867
17.14 Land Capability Classification as a Guide
toConservation 871
17.15 Progress in Soil Conservation 873
17.16 Conclusion 875
Study Questions 876
References 877
18
Soils and Chemical Pollution 879
18.1 Toxic Organic Chemicals 880
18.2 Kinds of Organic Contaminants 885
18.3 Behavior of Organic Chemicals in Soil 887
18.4 Effects of Pesticides on Soil Organisms 894
18.5 Remediation of Soils Contaminated with
Organic Chemicals 896
18.6 Soil Contamination with Toxic Inorganic
Substances 906
18.7 Potential Hazards of Chemicals in Sewage
Sludge 912
18.8 Prevention and Remediation of Inorganic Soil
Contamination 916
18.9 Landfills 919
18.10 Radionuclides in Soil 925
18.11 Radon Gas from Soils 929
18.12 Conclusion 932
Study Questions 932
References 933
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xii 
20.3 Soils and Global Ecosystem Services 993
20.4 Using Plants to Improve Soil Health 996
20.5 Feeding the Human Population 999
20.6 Intensified Agriculture—the Green
Revolution 1000
20.7 Impacts of Vastly Increased Ratios of People
to Land 1005
20.8 Sustainable Agriculture in Developed
Countries 1010
20.9 Biochar: Hype or Hope for Soil Quality? 1017
20.10 Organic Farming Systems 1019
20.11 Sustainable Agriculture Systems for Resource-
Poor Farmers 1026
20.12 Conclusion 1037
Study Questions 1037
References 1038
Appendix A World Reference Base, Canadian, and
Australian Soil Classification Systems 1041
Appendix B SI Units, Conversion Factors, Periodic
Table of the Elements, and Plant Names 1046
Glossary of Soil Science Terms 1052
Index 1071
19
Geographic Soils Information 936
19.1 Soil Spatial Variability in the Field 936
19.2 Techniques and Tools for Mapping Soils 941
19.3 Modern Technology for Soil Investigations 946
19.4 Remote Sensing in Soil Survey 951
19.5 Making a Soil Survey 959
19.6 Using Soil Surveys 962
19.7 Geographic Information Systems (GIS) 968
19.8 Digital Soil Maps: Properties or Polygons? 971
19.9 GIS, GPS, and Precision Agriculture 976
19.10 Conclusion 979
Study Questions 980
References 980
20
Prospects for Soil Health in the
Anthropocene 982
20.1 The Concepts of Soil Health and Soil
Quality 983
20.2 Soil Resistance and Resilience 991
NOTE: Every effort has been made to provide accurate and current Internet information in this book. However, the
Internet and information posted on it are constantly changing, and it is inevitable that some of the Internet addresses
listed in this textbook will change.
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xiii
On 24 November 2015 soil science lost one of its giants. Nyle C. Brady passed away
at the age of 95. Dr. Brady was a global leader in soil science, in agriculture, and in
humanity. He was born in 1920 in the tiny rural town of Manassa, Colorado, USA.
He earned a BS degree in chemistry from Brigham Young University in 1941 and
went on to complete his PhD in soil science at North Carolina State University in
1947. Dr. Brady then served as a member of the faculty at Cornell University in New
York, USA for 26 years, rising from assistant professor to professor and chair of the
agronomy department and finally to Assistant Dean of the College of Agriculture.
During this period, he was elected President of both the American Society of Agron-
omy and of the Soil Science Society of America.
Soon after arriving at Cornell University he was recruited by Professor Harry O.
Buckman to assist in co-authoring the then already classic soil science textbook, The
Nature and Properties of Soils. The first edition of this textbook to bear Nyle Brady’s
name as co-author was published in 1952. Under
Nyle’s hand this book rose to prominence through-
out the world and several generations of soil scientists
got their introduction to the field through its pages.
He was the sole author of editions published between
1974 in 1990. He continued to work on revised
editions of this book with co-author Ray Weil
until 2004. In recognition of his influence on the 15th
edition, Dr. Brady continues to be listed as co-author
of this textbook and his name is widely known and
respected throughout the world in this capacity.
Dr. Brady was of that generation of American soil scientists that contributed so
much to the original green revolution. He conducted research into the chemistry of
phosphorus and the management of fertilizers and he was an early researcher on min-
imum tillage. Known for his active interest in international development and for his
administrative skills, he was recruited in 1973 to be the third Director General of the
International Rice Research Institute (IRRI) in the Philippines. Dr. Brady pioneered
new cooperative relationships between IRRI and the national agricultural research
institutions in many Asian countries, including a breakthrough visit to China at a
time when that country was still quite closed to the outside world. He oversaw the
transition to a second-generation of green revolution soil management and plant
breeding designed to overcome some of the shortcomings of the first generation.
After leaving IRRI, he served as Senior Assistant Administrator for Science and
Technology at the U.S. Agency for International Development from 1981 to 1989.
He was a fierce champion of international scientific cooperation to promote sustain-
able resource use and agricultural development.
During the 1990s Dr. Brady, then in his 70s, served as senior international de-
velopment consultant for the United Nations Development Programme (UNDP) and
for the World Bank, in which capacity he continued to promote scientific collabora-
tion in advances in environmental stewardship and agricultural development.
Dr. Brady was always open-minded and ready to accept new truths supported
by scientific evidence, as can be seen by the evolution of the discussion of such top-
ics as pesticide use, fertilizer management, manure utilization, tillage, soil organic
matter, and soil acidity management in The Nature and Properties of Soils under his
guidance. Nyle Brady had a larger-than-life personality, a deep sense of empathy,
Nyle C. Brady 1920–2015
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xiv N C. B –
and an incredible understanding of how to work with people to get positive results.
He was the kind of person that friends, associates, and even strangers would go to
for advice when they found themselves in a perplexing position as a scientist, ad-
ministrator, or even in their personal life. Dr. Brady is survived by his beloved wife,
Martha, two daughters, a son (a second son preceded him in death), 22 grandchil-
dren, and 90 great grandchildren.He will be very much missed for a long time to
come by his family and by all who knew him or were touched by his work.
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xv
Preface
By opening this 15th edition of The Nature and Properties of Soils, you are tapping into a
narrative that has been at the forefront of soil science for more than a century. The first
version, published in 1909, was largely a guide to good soil management for farmers in
the glaciated regions of New York State in the northeastern United States. Since then,
it has evolved to provide a globally relevant framework for an integrated understand-
ing of the diversity of soils, the soil system, and its role in the ecology of planet Earth.
This latest edition is the first to feature full color illustrations throughout.
If you are a student reading this, you have chosen a truly auspicious time to take up
the study of soil science. This new edition was completed as the United Nations and
countries around the world celebrated the International Year of Soils (2015). Soils are
now widely recognized as the underpinning of terrestrial ecosystems and the source
of a wide range of essential ecosystem services. An understanding of the soil system is
therefore critical for the success and environmental harmony of almost any human en-
deavor on the land. This importance of soils and soil science is increasingly recognized
by business and political leaders, by the scientific community, and by those who work
with the land.
Scientists and managers well versed in soil science are in short supply and becom-
ing increasingly sought after. Much of what you learn from these pages will be of enor-
mous practical value in equipping you to meet the many natural-resource challenges of
the 21st century. You will soon find that the soil system provides many opportunities to
see practical applications for principles from such sciences as biology, chemistry, phys-
ics, and geology.
This newest edition of The Nature and Properties of Soils strives to explain the fun-
damental principles of Soil Science in a manner that you will find relevant to your
interests. Throughout, the text emphasizes the soil as a natural resource and soils as
ecosystems. It highlights the many interactions between soils and other components of
forest, range, agricultural, wetland, and constructed ecosystems. This book will serve
you well, whether you expect this to be your only formal exposure to soil science or
you are embarking on a comprehensive soil science education. It will provide both an
exciting, accessible introduction to the world of soils and a reliable, comprehensive ref-
erence that you will want to keep for your expanding professional bookshelf.
If you are an instructor or a soil scientist, you will benefit from changes in this latest
edition. Most noticeable is the use of full-color throughout which improves the new and
refined figures and illustrations to help make the study of soils more efficient, engaging,
and intellectually satisfying. Every chapter has been thoroughly updated with the latest
advances, concepts, and applications. Hundreds of new key references have been added.
This edition includes in-depth discussions on such topics of cutting edge soil science as
the pedosphere concept, new insights into humus and soil carbon accumulation, sub-
aqueous soils, soil effects on human health, principles and practice of organic farming, ur-
ban and human engineered soils, cycling and plant use of silicon, inner- and outer-sphere
complexes, radioactive soil contamination, new understandings of the nitrogen cycle, cat-
ion saturation and ratios, acid sulfate soils, water-saving irrigation techniques, hydraulic
redistribution, cover crop effects on soil health, soil food-web ecology, disease suppressive
soils, soil microbial genomics, indicators of soil quality, soil ecosystem services, biochar,
soil interactions with global climate change, digital soil maps, and many others.
In response to their popularity in recent editions, I have also added many new
boxes that present either fascinating examples and applications or technical details
and calculations. These boxes both highlight material of special interest and allow the
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xvi 
logical thread of the regular text to flow smoothly without digression or interruption.
Examples of applications boxes or case study vignettes include:
• “DirtforDinner”
• “SubaqueousSoils—UnderwaterPedogenesis”
• “PracticalApplicationsofUnsaturatedWaterFlowinContrastingLayers”
• “Char:IsBlacktheNewGold?”
• “WherehaveAlltheHumicsGone?”
• “TragedyintheBigEasy—ALeveeDoomedtoFail”
• “CostlyAndEmbarrassingSoilpHMystery”
• “Gardeners’FriendnotAlwayssoFriendly
• “SoilMicrobiologyintheMolecularAge”
• “TheLawofReturnMadeEasy:UsingHumanUrine”
Boxes also are provided to explain detailed calculations and practical numerical
problems. Examples include:
• “EstimatingCECandClayMineralogy”
• “CalculatingLimeNeedsBasedonpHBuffering”
• “LeachingRequirementforSalineSoils”
• “CalculationofPercentPoreSpaceinSoils”
• “CalculatingSoilCECFromLabData”
• “TowardaGlobalSoilInformationSystem”
• “CalculationofNitrogenMineralization”
• “CalculatingaSoil-QualityIndexforPlantProductivity”
As the global economy expands exponentially societies face new challenges with
managing their natural resources. Soil as a fundamental natural resource is critical to
sustained economic growth and the prosperity of people in all parts of the world. To
achieve balanced growth with a sustainable economy while improving environmen-
tal quality, it will be necessary to have a deep understanding of soils, including their
properties, functions, ecological roles, and management. I have written this textbook
in a way designed to engage inquisitive minds and challenge them to understand soils
and actively do their part as environmental and agricultural scientists, in the interest of
ensuring a prosperous and healthy future for humanity on planet Earth.
This understanding must include the role of healthy soils in agricultural appli-
cations and the pressing need for increasing food production. However, it must also
include knowledge of the many other ecosystem services provided by soils. In this
textbook I have tried to take a broad view of soils in the environment and in relation
to human society. In so doing, the book focuses on six major ecological roles of soil.
Soils provide for the growth of plants, which, in turn, provide wildlife habitat, food for
people and animals, bio-energy, clothing, pharmaceuticals, and building materials. In
addition to plant production, soils also dramatically influence the Earth’s atmosphere
and therefore the direction of future climate change. Soils serve a recycling function
that, if taken advantage of, can help societies to conserve and reuse valuable and finite
resources. Soils harbor a large proportion of the Earth’s biodiversity—a resource which
modern technology has allowed us to harness for any number of purposes. Water, like
soil, will be a critical resource for the future generations. Soils functions largely deter-
mine both the amount of water that is supplied for various uses and also the quality and
purification of that water. Finally, knowledge of soil physical properties and behavior,
as well as an understanding of how different soils relate to each other in the landscape,
will be critical for successful and sustainable engineering projects aimed at effective and
safe land development.
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 xvii
For all these reasons it will be essential for the next generation of scientists, busi-
ness people, teachers, and other professionals to learn enough about soils to appreciate
their importance and to take them into full consideration for development projects and
all activities on the land. It is my sincere hope that this book, early editions of which
have served so many generations of soil students and scientists, will allow new genera-
tions of future soil scientists to benefit from the global ecological view of soils that this
textbook expounds.
Dr. Nyle Brady, although long in retirement and recently deceased, remains as
co-author in recognition of the fact that his vision, wisdom, and inspiration continue
to permeate the entire book. Although the responsibility for writing the 15th edition
was solely mine, I certainly could not have made all of the many improvements without
innumerable suggestions, ideas, and corrections contributed by soil scientists, instruc-
tors, and students from around the world. The 15th edition, like preceding editions,
has greatly benefited from the high level of professional devotion and camaraderie that
characterizes the global soil science community.
Special thanks go to Dr. Rachel Gilker for her invaluable editorial and research
assistance. I also thank the following colleagues (listed alphabetically by institution)
for their especially valuable suggestions, contributions, reviews, and inspiration: Pichu
Rengasamy (The University of Adelaide); Michéli Erika (Univ. Agricultural Science,
Hungary); Duane Wolf (University of Arkansas); Tom Pigford (University of Califor-
nia, Berkeley); Thomas Ruehr (Cal Poly State University); J. Kenneth Torrence (Car-
leton University); Pedro Sanchez and Cheryl Palm (Columbia University); Harold van
Es and Johannes Lehmann (Cornell University); Eric Brevik (Dickinson State Univer-
sity); Dan Richter (Duke University); Owen Plank (University of Georgia); Robert
Darmody, Laura Flint Gentry, Colin Thorn, and Michelle Wander (University of Illi-
nois); Roland Buresh (International Rice Research Institute); Lee Burras (Iowa State
University); Aurore Kaisermann (Laboratoire Bioemco); Daniel Hillel (University of
Massachusetts, Emeritus); Lyle Nelson (Mississippi State University, Emeritus); Jim-
mie Richardson (North Dakota State University); Rafiq Islam and Rattan Lal (The
Ohio State University); David Munn (Ohio State ATI); Darrell Schultze (Purdue
University); Joel Gruver (Western Illinois University); Ivan Fernandez (University of
Maine); David Lobb (University of Manitoba); Mark Carroll, Glade Dlott, Delvin Fan-
ning, Nicole Fiorellino, Robert Hill, Bruce James, Natalie Lounsbury, Brian Need-
elman, Martin Rabenhorst, Patricia Steinhilber, and Stephane Yarwood (University
of Maryland); Martha Mamo (University of Nebraska); Jose Amador (University of
Rhode Island); Russell Briggs (State University of New York); Allen Franzluebbers,
Jeff Herrick, Scott Lesch, and Jim Rhoades (USDA/Agricultural Research Service);
Bob Ahrens, Bob Engel, Maxine Levine, Paul Reich, Randy Riddle, Kenneth Scheffe,
and Sharon Waltman (USDA/Natural Resources Conservation Service); Markus Kle-
ber (Oregon State University); Henry Lin (The Pennsylvania State University); Joseph
Heckman (Rutgers, The State University of New Jersey); Fred Magdoff and Wendy
Sue Harper (University of Vermont); W. Lee Daniels, John Galbraith (Virginia Tech);
Peter Abrahams (University of Wales); Luther Carter (Washington, DC); Clay Robin-
son (West Texas A & M University); Tor-G. Vagen (World Agroforestry Center); Larry
Munn (University of Wyoming); and Tom Siccama (Yale University).
Last, but not least, I deeply appreciate the good humor, forbearance, and patience
of my wife, Trish, and those students and colleagues who may have felt some degree
of neglect as I focused so much of my energy, time, and attention on this labor of love.
RRW
College Park, Maryland, USA
February 2016
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