Soil Soil is a mixture of minerals and partially decomposed organic matter. Soil begins as rock, but is gradually broken down through erosion. Mechanical erosion is the physically breaking down of rock by wind and water. Chemical erosion changes the molecular structure

O horizon, which is mostly non-decomposed plant litter. A horizon, contains a lot of organic matter mixed with some minerals. Also called topsoil. B horizon is a layer of clay, mostly made of minerals with little organic matter. The C horizon is parent material, which is the bedrock from which the soil was formed.

Erosion from Water Mechanical erosion from rainfall takes four forms, ranked by severity. Splash erosion is a tiny crater caused by the impact of a single drop of water. Sheet erosion is the transportation of loose soil particles along a flow of runoff water. Rill erosion occurs when the flowing water coalesces into small channels.

Gully erosion is the most severe, caused by rapidly flowing water creating deep channels in the ground.

Wind Erosion In arid regions, wind is the major cause of erosion. Topsoil protected from wind erosion by native bluestem grass, New Mexico, 1957.

Soil Conservation Multiple soil conservation techniques were part of the New Deal programs implemented by President Franklin Delano Roosevelt. Contour plowing reduces water erosion by planting crops along the slope of the land rather that straight up and down.

Many important commercial plants are row crops, meaning they must be grown in spaced rows. Strip cropping alternates row crops like corn and cotton with cover crops like oats that completely cover the soil. The cover crops trap any soil that erodes from the row crops.

Terracing converts steeply sloped land into a series of flattened terraces. The stair-like terracing slows the downward runoff of water, reducing erosion.

Rows of trees can serve as windbreaks, reducing erosion by wind. In response to the Dust Bowl, the Great Plains Shelterbelt was built from 1935-1942. 220 million trees.