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Fluid Journal : Fluid Journal 1999-2001
1 Fluid Journal Summer 2000 Webster's dictionary says the word organic pertains to a branch of chemistry that deals with compounds containing carbon. Organic phosphorus, then, pertains to compounds containing both phosphorus and carbon. Unlike simple compounds such as calcium phosphate, sodium phosphate, or ammonium phosphate, organic phosphorus compounds are extremely complex compounds that originate from the decomposition of corn stalks or straw by microorganisms in the soil. How it works Why should we be interested in organic phosphorus? Because the plant we fertilize has everything to do with ultimately enriching the soil for future crops. The process works something like this. We know the plant absorbs phosphorus by taking in anions --- (H2PO4)-1, (HPO4)-2 --- in the soil by FFF Review Where Does Organic Phosphorus Fit In Your Fertility Program? Phosphorus is a key ingredient in the DNA molecule. Strange as it may seem, up to 50 percent of the soil's organic phosphorus could be in the form of DNA. solution. These inorganic phosphates are easily supplied by adding commercial fertilizers to the fields. During the growing process, however, plants convert this inorganic phosphorus into organic phosphorus. In what quantities? Substantial. For example, a 200-bu/A corn crop contains about 30 lbs of organic phosphorus in the grain and the same amount---and this is important---in the residue and roots that will he left. This organic phosphorus in the residue will eventually find its way into the phosphorus reserve in the soil and be available for future crops. Also in the soil are what we call "fixed" inorganic phosphates, a group of phosphates that are unavailable to the plant. They include iron, calcium, and aluminum phosphates. Soils have different fixing properties, depending on pH and various metallic ions that can tie up phosphorus. Figure 1 shows the relationship of fixed inorganic phosphates, available phosphates, and organic phosphates. When incorporating inorganic phosphates, the equilibrium can shift toward fixation. On the other hand, as organic matter decomposes (or mineralizes) the equilibrium can shift to the phosphates more available to the plants. It is important to note that the grower can promote decomposition of organic matter and release of phosphates (and nitrogen) during July and August, the two months of maximum uptake by the corn plant. Three key steps How does the grower promote decomposition of organic matter? First, he must manage residue to form the organic matter. Second, pH of the soil should be FIXED INORGANIC PHOSPHATE AVAILABLE PHOSPHATE ORGANIC PHOSPHATE MINERALIZATION IMMOBILIZATION Figure 1 Figure 1. Relationship of fixed inorganic phohphates, available phosphates, and organic phosphates.
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