Monday, September 22, 2008

Free N, P and S when you grow C

Rather than having to pay for nitrogen, farmers growing their soil organic matter and their carbon could get it for free! Professor Charlie Rice of Kentucky State University explains it this way: Soil Organic Matter is 59% Carbon. It also contains N, P and S. Up to 95% of soil N, 40% of soil P, and 90% of soil S is directly affected by SOM. "Plant productivity is directly associated with SOM content and nutrient turnover by microbial activity. For example, in agricultural soils approximately 2%-4% of the organic N is made available for plant uptake on an annual basis.... In cropping systems, as much as 50%-80% of the N can be supplied from SOM and nearly 100% of the N in native ecosystems." This percentage represents up to 300kg/ha, between $200 and per hectare at recent superphosphate prices ($600 - $2000/tonne). Kimble, J. et. al., Soil Carbon Management, CRC Press

The following appears in P.E.V. Charman's chapter "Soil Nutrient Decline" which appears in SOILS: THEIR PROPERTIES & MANAGEMENT edited by Brian Murphey and Charman: 2nd ed, 2000: "Most nitrogen in soils, and that used by plants, is derived ultimately from nitrogen in the air which has been assimilated by certain soil micro-organisms, many associated with leguminous plants...." "Following fixation, the nitrogen is stored temporarily in the soil in organic forms. These may then be broken down by other soil micro-organisms into ammonium and nitrate forms... for direct uptake by plants in solution."

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