Soil Soil is a mixture of weathered rock, organic matter, water, and air that is capable of supporting plant life.

Soil Soil originates from weathering of the bedrock beneath it or from materials transported from another location.

Soil Soil Horizons The figure shows a complete set of horizons, designated as O, A, E, B, C, and R from the surface to bedrock. The O horizon, for organic, and the A horizon often are referred to as topsoil.

Soil Horizons The E horizon is a zone in which finer sediments and soluble materials are transported downward. The B horizon collects the materials from above and is usually darker than the E horizon.

Soil Horizons The C horizon is partially crumbled and weathered bedrock. The R horizon is unweathered bedrock.

Soil Types Climate often is used as a basis to characterize many different types of soil.

Soil Types They are separated according to composition and physical properties.

1 Soil Types The amount of precipitation and the temperature range of a region, together with the type of parent material, affect the type of soil that is formed.

Weathering and Soil 1 Soil Conservation Soil depletion is a serious agricultural problem in many regions.

1 Soil Conservation Soil depletion is most often corrected by the addition of fertilizers containing nitrogen, phosphorous, or potassium.

1 Soil Conservation Most soil lost to erosion occurs because the vegetative cover has been removed or because the land is overly steep.