The soil is at the interface between the atmosphere
(the mantle of rocks making up the Earth's crust). It also has an
interface with the hydrosphere, i.e. the sphere describing surface
water, ground water, and oceans. The soil sustains the growth of many plants
and animals, and so forms part of the biosphere. A combination of
physical, chemical and biotic forces acts on organic and weathered rock
fragments to produce soils with a porous fabric that contain water and
air (pedosphere). Soil is as a natural body of
mineral and organic material that is formed in response to many environmental
factors and processes acting on and changing soil permanently.
Because soil is important for cultivation and agricultural production, soil fertility and productivity are important issues to address. Detailed pedological knowledge is useful for land evaluation purposes, i.e., the classification in fertile productive soils and less valuable soils. Soils are an integral part of landscapes and the knowledge of the distribution of different soils helps to preserve a high standard in environmental quality.
U.S. Govt. Printing Office, Washington D.C. Soil Survey Staff. 1994. Keys to Soil Taxonomy USDA - Soil Conservation Service. 6th ed., Washington D.C.
The vertical dimension, exposed by excavation from the surface to the
parent material, constitutes the soil profile. Layers in the soil,
distinguished on the basis of color, soil texture, soil structure, and other
visible properties, are called horizons. Several horizons make up
the soil profile.
Next, a description of a soil profile developed in a temperate humid environment
is given showing all of the principle soil horizons (Figure 2.): The upper
layer, from which materials are generally washed downwards, is described
as eluvial. Lower layers in which these materials accumulate are
called illuvial. The eluvial horizon is denoted by the notation
E and an illuvial horizon by the notation B. The B and E horizon plus the
top horizon denoted by an A comprise the solum. The unconsolidated
parent material in which the soil is formed is denoted by a C. If unweathered rock (consolidated material) exists below the parent
material it is labelled with a R. Organic litter on the surface,
which is not incorporated in the soil is designed the O layer.
Components of the Soil Soils are made of four main components, i.e.