The Soils That We Classify

Abstract

Soil is the natural medium for the growth of land plants, whether or not it has discernible soil horizons. People consider soil important because it supports plants that supply food, fibers, drugs, and other human needs and because it filters water and recycles wastes. Soil is a natural body comprised of solids (minerals and organic matter), liquid, and gases that occur on the land surface, occupies space, and is characterized by horizons, or layers, that are distinguishable from initial geologic material as a result of additions, losses, transfers, and transformations of energy and matter or the ability to support rooted plants in a natural environment. The upper limit of soil is the boundary between soil and air, shallow water, live plants, or plant materials that have not begun to decompose. For purposes of classification, the lower boundary of soil is arbitrarily set at 200 cm. In areas where soil has thin cemented horizons that are impermeable to roots, the soil extends as deep as the deepest cemented horizon, but not below 200 cm.

The United Arab Emirates Keys to Soil Taxonomy is designed in such a way that the reader makes the correct classification by going through the key systematically, starting at the beginning and eliminating one by one all classes that include criteria that do not fit the soil or layer in question.