It has long been recognized that soil organic matter is the key to soil fertility. As a nutrient store it gradually provides essential elements which the soil cannot retain for long in inorganic form. It buffers growing plants against sudden changes in their chemical environment and preserves moisture in times of drought. It keeps the soil in a friable, easily penetrated physical condition, well-aerated and free draining, providing young seedlings with an excellent medium for growth. But it has another property, the nature and extent of which have been the subject of argu ment and controversy ever since scientists began to study the soil, and that is its ability to affect growth directly, other than by providing nutrient elements. Any one wishing to learn about these effects has been faced with a daunting mass of literature, some confusing, often contradictory, and spread through a multitude of journals. Individual aspects have been covered from time to time in reviews but there has obviously been a need for a modern authoritative text book dealing with the many facets of this subject, so the publication of this volume is timely. The editors and authors are all specialists in their fields, fully familiar with the com plex nature of soil organic matter and with the particular difficulties arising in any study of its properties. Where controversies exist they have presented all sides of the argument and have highlighted areas where further work is badly needed.

Inhalt
List of Contents.- Soil Organic Matter A Perspective on its Nature, Extraction, Turnover and Role in Soil Fertility.- 1. Soil organic matter.- 2. Biological changes in soil organic matter.- 3. Role of soil organic matter in fertility.- 4. Conclusions.- 5. References.- 1 Influence of Humic Substances on Growth and Physiological Processes.- 1. Introduction.- 2. Influence on growth.- 3. Uptake of humic substances.- 4. Nutrient content of plants.- 5. Humic substances and membranes.- 6. Conclusions.- 7. References.- 2 Influence of Humic Substances on Biochemical Processes in Plants.- 1. Introduction.- 2. Energy metabolism.- 3. Nucleic acids.- 4. Protein metabolism.- 5. Biological activity and structure of humic substances.- 6. Conclusions.- 7. References.- 3 Phenolic Acids in Soils and their Influence on Plant Growth and Soil Microbial Processes.- 1. Introduction.- 2. Detection and determination.- 3. Phenolic acids in plant tissues.- 4. Phenolic acids in soils.- 5. Influence of phenolic acids on plant growth.- 6. Influence of phenolic acids on soil micro organisms.- 7. Conclusion.- 8. Acknowledgements.- 9. References.- 4 Origin, Nature and Biological Activity of Aliphatic Substances and Growth Hormones Found in Soil.- 1. Introduction.- 2. Ethylene.- 3. Gibberellins, auxins, cytokinins and abscisic acid.- 4. Aliphatic organic acids.- 5. Hydrogen sulphide.- 6. Alcohols.- 7. Antibiotics.- 8. Conclusion.- 9. Summary.- 10. References.- 5 Soil Enzymes.- 1. Introduction.- 2. Range and assay of soil enzymes.- 3. Activity of soil enzymes.- 4. Activity and properties of extracted soil enzymes.- 5. Conclusions.- 6. References.- 6 The Soil Biomass.- 1. Introduction.- 2. Methods.- 3. Soil organic matter and the biomass.- 4. Growth and activity of the biomass.- 5. The soil biomass andplant nutrition.- 6. The soil biomass as a source of plant nutrients.- 7. Summary and Conclusions.- 8. References.- 7 Carbohydrates in Relation to Soil Fertility.- 1. Introduction.- 2. Biological nutrition.- 3. The formation of stable soil structure.- 4. Influence on the behaviour of water in soil.- 5. Influence on ion exchange and complexing properties.- 6. Influence on plant root growth.- 7. Protection of soil enzymes.- 8. Influence on the growth of soil organisms.- 9. Conclusion.- 10. References.- 8 Soil Nitrogen: Its Extraction, Distribution and Dynamics.- 1. Introduction.- 2. The extraction of soil nitrogen.- 3. Distribution of soil nitrogen.- 4. Soil nitrogen dynamics.- 5. Agriculture and nitrogen.- 6. Modelling.- 7. Conclusions.- 8. References.- 9 Soil Phosphorus.- 1. Introduction.- 2. Global cycle.- 3. P and pedogenesis.- 4. Forms of soil P and their characterisation.- 5. Soil P cycle.- 6. Mineralization and immobilisation.- 7. Factors influencing P transformation.- 8. Availability of Po to plants.- 9. Current perspective.- 10. Acknowledgements.- 11. References.- 10 Sulphur in Soils and Plants.- 1. Introduction.- 2. Soil sulphur.- 3. Sulphur transformations.- 4. Sulphur deficiency in plants and soils.- 5. Anthropogenic sulphur inputs.- 6. References.- 11 Organic Matter and Trace Elements in Soils.- 1. Introduction.- 2. Solution chemistry of trace elements.- 3. Humic substances.- 4. Biochemical substances in the rhizosphere.- 5. Adsorption of trace elements on solid surfaces.- 6. Distribution of soil organic matter in different soils.- 7. Trace element uptake by plants.- 8. A perspective.- 9. References.- 12 Organic Farming.- 1. Introduction.- 2. Historical perspective.- 3. The present situation.- 4. Soil structure.- 5. Comparison of levels of production.- 6. The future.- 7. References.- List of Abbreviations.