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Predicting phosphorus desorption from Mid-Atlantic Coastal Plain soils

Vadas, P.A., Sims, J.T.
Soil Science Society of America journal 2002 v.66 no.2 pp. 623
coastal plain soils, sandy soils, phosphorus, desorption, losses from soil, equations, iron oxides, aluminum oxide, soil organic matter, Delaware
Pollution of surface waters by P from agricultural areas is a water quality issue in Delaware. The FHANTM 2.0 computer model can help identify areas with a high potential for P loss, but the model's representation of P desorption from soils to runoff waters needs reevaluation. The equation, P(d) = K P(o) t(alpha) W(beta), has been proposed to predict such P desorption, but equations originally proposed to predict values for the constants K, alpha, and beta from the ratio of soil clay content/soil organic C content may not be accurate for Delaware soils. Therefore, we measured P desorption for 23 sandy Delaware soils for times of 5 to 180 min, water/soil ratios of 10 to 1000 L kg(-1), and three initial levels of soil desorbable P. Values for the constants K, alpha, and beta were calculated and related to soil properties. We found that K, alpha, and beta values were not well related to clay/OC, but were better related to the ratio of oxalate-extractable Fe/OC content (alpha) or the sum of oxalate extractable Fe and Al (beta and K). These results can be used to help refine the FHANTM 2.0 model in predicting P loss from agricultural areas in Delaware and similar landscapes in the Mid-Atlantic Coastal Plain.