CONTENTS Preface ix I MAPPING, CLASSIFICATION AND FORMATION OF SOILS 1 Soil in the Field: the 'Soil Type' 3 2 Soil Profiles and their Classification 17 3 Soil Formation 35 II THE PHYSICS OF SOIL 4 Introduction to Physical Properties 57 5 Colloids of the Soil 65 6 The Soil as a Reservoir of Water 90 7 Excessive Water: Aeration and Drainage 110 8 Mechanical Composition 123 9 Soil Temperature 129 III THE CHEMISTRY OF THE SOIL 10 General Chemical Considerations 137 11 Soil Organisms and Organic Matter 148 12 The Nitrogen Cycle 166 13 Primary Minerals in Soils 184 14 Acidity and Alkalinity 191 15 Calcium, Magnesium, Potassium, Sodium 202 16 Phosphorus and Sulphur 215 17 Iron, Aluminium, Silicon 227 18 Various Trace Elements 231 IVSOIL EROSION 19 Soil Erosion 243 Appendix:Suggestions for Practice 253 Glossary 266 Abbreviations, Symbols, Units 285 Index 288