Topsoil

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.

Importance

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.

Classification

In soil classification systems, topsoil is known as the "A Horizon," therefore, it is the very top layer.^[1]

Commercial application

A variety of soil mixtures are sold commercially as topsoil, usually for use in improving gardens and lawns, e.g. container gardens, potting soil and peat.

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. The estimated annual costs of public and environmental health losses related to soil erosion exceed $45 billion.^[2] Conventional agriculture encourages the depletion of topsoil because the soil must be plowed and replanted each year. Sustainable techniques attempt to slow erosion through the use of cover crops in order to build organic matter in the soil. The United States alone loses 2 billion tons of topsoil per year^{[citation needed]}. This is of great ecological concern as one inch of topsoil can take 500 years to form naturally.^[3] However, farmer and engineer P. A. Yeomans developed a technique known as Keyline design, which has been proven to convert subsoil into topsoil much faster; Yeomans published a book, called Water For Every Farm, in 1954 about the technique^{[citation needed]}.

See also

Ecology portal

• Agricultural wastewater
• Desertfication
• Dust bowl
• Erosion control
• No-till farming
• Nonpoint source pollution
• Sustainable agriculture
• Waterway degradation

References

1. ^ U.S. Department of Agriculture (USDA), Soil Survey Division Staff (1993). "Soil Survey Manual." USDA Handbook 18. Chapter 3.
2. ^ http://www.ce.cmu.edu/~gdrg/readings/2007/02/20/Pimental_EnvironmentalEnergeticAndEconomicComparisonsOfOrganicAndConventionalFarmingSystems.pdf
3. ^ http://discovermagazine.com/2001/may/feateatlocal

• The lowdown on topsoil: It's disappearing
• Mann, C (2008). "Our Good Earth". National Geographic Magazine 214 (3): 80–107. http://ngm.nationalgeographic.com/2008/09/soil/mann-text. 

External links

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

• UK British Topsoil Suppliers Association - Detailed soil information guides