CLASSIFICATION OF SOILS

From the first emergence of civilizations based on agriculture, variations in the nature and productive capacity of the soil were recognized by farmers, and names, usually based on colour or texture, were given to distinctive varieties. In modern times the connection between soils and the rocks which provide their parent materials was generally recognized, and the earliest attempts to classify soils systematically had a geological or petrological basis. Most of these schemes, such as those proposed by Thaer and Fallou in Germany, suffered from their limited geographical scope, and little attention was paid to the effects on soil formation of climate, vegetation, and topography. Soil was conceived primarily as an inert material composed of variously constituted mineral particles mixed with varying quantities of plant residues, and the accent on soil as a material received further emphasis following the publication in 1840 of Liebig's ‘Chemistry in its Application to Agriculture and Physiology’, which suggested that differences in soil fertility were largely determined by differences in chemical constitution.