Topsoil

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Surface runoff, also called nonpoint source pollution, from a farm field in Iowa during a rain storm. Topsoil as well as farm fertilizers and other potential pollutants run off unprotected farm fields when heavy rains occur.

Topsoil is the upper, outermost layer of soil, usually the top 2 inches (5.1 cm) to 8 inches (20 cm). It has the highest concentration of organic matter and microorganisms and is where most of the Earth's biological soil activity occurs. Plants generally concentrate their roots in and obtain most of their nutrients from this layer. The actual depth of the topsoil layer can be measured as the depth from the surface to the first densely packed soil layer known as subsoil.

In soil classification systems, topsoil is known as the "A Horizon," therefore, it is the very top layer.^[1] Topsoil is used in gardens and fields all around the world. A variety of soil mixtures are sold commercially as topsoil, usually for use in improving gardens and lawns, or for ideal growing conditions in container gardens, by using potting soil, for example.

[edit] Erosion

A major environmental concern known as topsoil erosion occurs when the topsoil layer is blown or washed away. Without topsoil, little plant life is possible. It takes approximately 100 years for 1 inch (2.5 cm) of topsoil to be deposited, if there is the correct ratio of organic material, inorganic material, and moisture. This can be improved by using the terra preta system. However, there are 25 billion tons of topsoil lost each year.

[edit] See also

• Erosion control
• Nonpoint source pollution
• Water pollution

[edit] References

[edit] External links

• USDA Electronic Field Office Technical Guide - Detailed soil conservation guides tailored to individual states/counties