Chemical fractionation and solubility of phosphorus in dairy manure-amended soils as a predictor of phosphorus concentration in runoff
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Nutrient over-loading in many dairy manure-amended soils in the dairy producing areas of Texas has led to environmental problems as such eutrophication of local surface water bodies. One of the nutrients contributing to eutrophication problems is phosphorus (P). This project focused on fractionation and solubility of selected P forms in an effort to determine a relationship with P found in runoff from dairy manureamend soils. Ten soils (5 calcareous, 5 noncalcareous) were collected from the dairy producing areas of Texas. Triplicate soil samples were analyzed for 0-5 cm and 5-15 cm depths. An acid-base extraction method was used to determine total P (TP), inorganic P, and organic P. Sequential extractions were used to determine the loosely-bound P, iron (Fe) phosphates, aluminum (Al) phosphates, reductant soluble P, occluded apatite P, and calcium (Ca) phosphates for calcareous and noncalcareous samples. The ammonium oxalate method was used to determine extractable Fe, Al, and silicon (Si). Potassium chloride extraction was used to determine soluble Ca, Al, Fe, Mg, and P. A weak NaOH extract was used to determined the amount of bioavalible P. Dissolved P in runoff events and soil pH were collected in a previous study. Calcareous and noncalcareous soils displayed varying concentrations of P indifferent fractions and with separate comparisons, stronger relationships could be achieved. It was also determined that KCl soluble Mg could be used as a predictor for dissolved and total P in runoff for calcareous soils (r2Ã¢ÂÂs ranging from 0.865 to 0.928 and 0.801 to 0.886, respectively). Ammonium oxalate extractable Al also yielded high correlations in calcareous soils for dissolved and total P in runoff (r2 ranging from 0.798 to 0.991 and 0.766 to 0.973, respectively). In noncalareous soils, pH resulted in a less correlated relationship with dissolved P (r2 = 0.600). This study shows that there are simple and effective ways of predicting dissolved and total P in runoff to improve best management practice recommendations for manure-amended soils.
Harstad, Laura Elizabeth (2005). Chemical fractionation and solubility of phosphorus in dairy manure-amended soils as a predictor of phosphorus concentration in runoff. Master's thesis, Texas A&M University. Texas A&M University. Available electronically from