Organic substances returned to the soil by plants, animals and microorganisms go through biochemical cycles and subcycles that provide essential media for the growth of plants in the soil. These cycles involve numerous, complicated and interdependent chemical reactions. Many books have been written to describe the genesis, the nature and the reactions of soil organic matter and have contributed much to organizing parts of the knowledge about soil organic matter. Each book is an important contribution but none has duplicated any of the others to any great extent; each has developed essential but loose fitting segments of the knowledge about soil organic matter. Each of these books complements the other. The authors of chapters in this volume have done considerable, scholarly research in their areas and have reported a very comprehensive coverage of their topics. Their contributions will be important supplements to already published works on soil organic matter. The editor wishes to express his appreciation for the vast library resources of the University of Illinois that were used during the production of this volume. He also wishes to express his appreciation for the help of his wife, Flossie Y. Gieseking, who assisted or promoted every operation until it was completed. Urbana, Illinois JOHN E. GIESEKING August 30, 1974 v Contributors Anderson, G., The Macaulay Institute for Soil Research, Craigiebuckler, Aberdeen, Scotland. Babel, U., Biopedologie, Universitlit Hohenheim, Stuttgart, Germany. Beute[spacher, H., Institut fUr Biochemie des Bodens der Forschungsanstalt fUr Landwirt schaft, Braunschweig, Germany.

1 Chemical Composition and Physical Properties of Humic Substances

2 Saccharides
3 Nitrogenous Substances
4 Other Organic Phosphorus Compounds
5 Sulfur in Soil Organic Substances
6 Fats, Waxes, and Resins in Soil
7 Micromorphology of Soil Organic Matter
8 Humus of Virgin and Cultivated Soils.