Developed for Introduction to Soils or Soil Science courses, The Nature and Properties of Soils, Fifteenth Edition, can be used in courses such as Soil Fertility, Land Resources, Earth Science and Soil Geography.

"The Nature and Properties of Soils has been my labor of love for the past 5 years and updates a narrative that has both reflected and helped to shape soil science thinking for more than a century. 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." - Ray R. Weil

This hallmark text introduces the exciting world of soils through clear writing, strong pedagogy, and an ecological approach that effectively explains the fundamentals of soil science. Worked calculations, vignettes, and current real-world applications prepare readers to understand concepts, solve problems, and think critically. Written for both majors and non-majors, this text highlights the many interactions between the soil and other components of forest, range, agricultural, wetland and constructed ecosystems.

Now in full-color, the Fifteenth Edition includes hundreds of compelling photos, figures, and diagrams to bring the exciting world of soils to life. Extensively revised, new and updated content appears in every chapter. Examples include: coverage of 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; new understandings of the nitrogen cycle; water-saving irrigation techniques; hydraulic redistribution, soil food-web ecology; disease suppressive soils; soil microbial genomics; soil interactions with global climate change; digital soil maps; and many others.

Dr. Raymond Weil, Professor, University of Maryland College Park

B.S. in Crop Science from Michigan State University, East Lansing, MI, 1970.

M.S. in Soil Science from Purdue University, West Lafayette, IN, 1973.

Ph.D. in Soil Ecology from Virginia Tech, Blacksburg, VA, 1977.

Elected Fellow in 2003 of both the Soil Science Society of America and the American Society of Agronomy.

Weil has been active in soil science research since 1972 and has made many contributions in the areas of nutrient cycling and management, environmental impact of soil management, and assessment of soil quality. His current research is focused on the assessment and improvement of soil quality and organic matter. He has conducted research in several countries outside the United States, including Ethiopia, Chad, Brazil, Honduras, Sri Lanka, Zimbabwe, Malawi and Tanzania. In addition to his teaching at the University of Maryland, he has conducted many training workshops for such agencies as the USDA, The World Bank, The Rodale Research Institute, and the International Food Policy Center.

Dr. Weil has authored or coauthored more than 100 scientific publications in soil science and related areas.

Dr. Nyle Brady

Dr. Brady has, since 1947, worked in education, research and research administration, focusing on both international and U.S. issues. He is past president of the SSSA and served six years as Editor-in-Chief of the SSSA Proceedings and is Emeritus Professor at Cornell University. He has served in leadership positions with Cornell University, the International Rice Research Institute, USAID, the United Nations Development Programme and the World Bank. He is recognized around the world as author and co-author of eleven editions of the world's most widely used soil science textbook, The Nature and Properties of Soils.

Contents

Preface xv

1The 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

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

1.10 The Soil Profile and Its Layers (Horizons) 15 3

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 Information 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

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

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

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

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

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

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

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

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 1

9.8 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

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

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