The Soil Profile
A characteristic common to all soils is the development of distinct layers, or horizons, from the surface downward. The horizons are formed by natural processes described previously. A vertical section of the soil which exposes the layering is called a soil profile (Fig. 1.4). The surface layer is usually high in organic matter and is called the A horizon, or topsoil. Directly below the A horizon is a layer which often contains more clay and may be different in color. This layer is called the B horizon, or subsoil. Beneath the B horizon is the parent material, which is called the C horizon. Together, the A, B, and C horizons constitute the master horizons of the soil profile. Several other horizons can also be present, depending upon the soil forming factors and soil age. Horizons are always designated with a capital letter.