What is Soil?
Soil is a reservoir of water and nutrients that supports plant life—and, therefore, all of life. From a human perspective, we are often interested in soil’s ability to support our agricultural systems. Depending on a given soil’s unique properties, it can be better or worse at supporting life.
Soil is formed via the concurrent action of five main phenomena: climate, organisms, relief (topography), parent material, time, or CLORPT for short. These all act on parent material in order to form soil. Their action also differentiates soils from one another, depending on the specific combinations of the CLORPT variables in a given location.
These weathering forces are a combination of physical, chemical, and biological processes. Physical processes include freezing and thawing, and the wearing down of minerals to form sand, silt, and clay particles. Chemical weathering processes include the transformation of primary minerals into secondary minerals via chemical exchanges. Biological processes include soil microorganisms’ digestion of soil organic matter and its transformation into new compounds. In each section of this unit, we’ll look more deeply into these various processes.
Soils are classified similar to the way organisms have been classified by scientists. The levels of classification, from general to specific are: Order, Suborder, Great Group, Subgroup, Family, and Series. In this section, we’ll see examples of some of these soil categories. Another way of understanding soil is via its horizons—that is, the differentiated layers of a soil profile, moving from the surface down to the bedrock.