In the Dairy Production Areas of Texas, nutrient loading of soils amended with dairy waste has resulted in nutrient loading and eutrophication in surface waters. Phosphorus has been determined to be the limiting nutrient for algal growth in these waterways. This has lead to increasing regulation of agricultural non-point source pollution. While it is known that non-point phosphorus loading of surface waters is the problem, little is known about the types and solubility of P from dairy manure. This project focuses on the determination of P fractionation and the solubility of selected P fractions in the attempts to determine a relationship that may connect a known and accepted P test to the amount of P found in runoff from dairy-amend soils. This relationship could be used as a predictor of the potential P loss from a soil and used for BMP recommendations. Ten soils (5 calcareous, 5 non-calcareous) were collected from the dairy producing area's of Texas. Triplicate samples were analyzed for the 0-5cm and 5-15cm. Acid base extractions were used to determine total P, inorganic P, and organic P. Sequential extractions were used to determine the loosely-bound P, iron phosphates, aluminum phosphates, reductant soluble P, occluded apatite, and calcium phosphates for both calcareous and non-calcareous samples. Ammonium oxalate was used to determine extractable iron, aluminum, and silicon. Potassium chloride extract was used to determine soluble Ca, Al, Fe, Mg, and P. Weak NaOH was used to analyze the amount of bioavailable P. Total and Dissolved P in runoff events and pH were collected in a previous study. Preliminary results suggest a relationship between the various extracts, STP, and runoff P concentrations. Correlation is greatly improved when calcareous and non-calcareous soils are separated.
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