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Unformatted text preview: Soil Organic Matter Decomposition of Residues Rate of decomposition Very briefly, what is meant by the carbon cycle (or any other nutrient cycle) is simply the cycling between organic and inorganic forms. sugars, starches, proteins > hemicelluloses > cellulose > fats, waxes > lignins Soils and the Greenhouse Effect Increasing concentration of certain gases in the atmosphere may cause a net gain in solar radiation, leading to increased average temperatures, alteration in weather patterns and rise in sea level. Although the burning of fossil fuels is the leading con- tribution in increasing concentration of CO 2 in the atmosphere, deforestation, drainage and tillage has caused and still is causing an increase the rate of soil organic matter decomposition and resultant atmospheric input of CO 2 . In addition to CO 2 , other greenhouse gases are released from soil. These include CO 2 , CH 4 and N 2 O produced by soil microorganisms. Decomposition proceeds with the liberation of CO 2 + H 2 O; release of N, P and S in inorganic forms ( mineralization ) or synthesis into organic combinations ( immobilization ); and the formation of new compounds that are resistant to decomposition. Another aspect of residue composition that affects the rate of decomposition is the C / N ratio. Since the organisms that decompose residues need N (and other essential elements) as well as C, if there is little N in the residue, decomposition is slow. The origin of soil organic matter is plant material. The rate of decomposition of plant residues depends on their composition and soil environmental conditions....
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- Fall '08