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Since the beginning of this century production of chemical fertilizers has increased many fold, and the production of pesticides for addition to the soil has become a new major industry. These are not the only chemicals added to the soil, because by accident or design many other chemicals which enter the environment end up in the soil. The soil has to produce the bulk of the food and fiber to sustain this growing population. In this volume a short historical outline of the development of soil science is given, touching briefly on soil formation, soil physics, and soil biology, as it can be misleading to regard soils simply as chemical entities. It is also important to have some appreciation of the several processes which have produced the particular soil found at any one place. The major soil types of the world differ according to their origin. Several systems exist for classifying them, and different names are in use for the same major soil types. The most common names of these are therefore introduced. The following two chapters deal with the inorganic and organic components of soils respectively. The chemical structures of the major inorganic components are now reasonably well known, but this is not true of the organic (or humic) materials in soils. The relevant chapter presents an account of what has been experimentally established regarding the constitution of the peculiarly intractable complex of organic compounds found in soils. Chemical processes in soils are largely determined by reactions at the surfaces of the soil colloids. The final three chapters are therefore concerned with the nature and extent of the surfaces of soil colloids, their electrical characteristics, and the ways in which ions and water are held and arranged at the surfaces.
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