Predicting Phosphorus Desorption from Mid‐Atlantic Coastal Plain Soils

Abstract

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 re‐evaluation. The equation, , has been proposed to predict such P desorption, but equations originally proposed to predict values for the constants K, α, and β 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, α, and β were calculated and related to soil properties. We found that K, α, and β values were not well related to clay/OC, but were better related to the ratio of oxalate‐extractable Fe/OC content (α) or the sum of oxalate extractable Fe and Al (β 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.