Transport and Prediction of Sulfate in Agricultural Runoff

Abstract

AbstractThe measurement and simulation of sulfate‐S (SO4‐S) mobility in agricultural watersheds is necessary to evaluate the effect of management practices on associated crop S deficiencies, enhanced leaching loss of nutrient cations, and acidification of percolation waters. The concentrations and amounts of SO4‐S in runoff from six grassed and 13 cropped watersheds in the Southern Plains were, thus, measared over a 4‐yr period. Sulfate‐S transport in runoff was predicted using an equation describing the kinetics of SO4‐S desorption from soil and compared with measured values. No SO4‐S was added to any of the watersheds directly as S fertilizer or indirectly in N or P fertilizer material. No difference (at 5% level) in SO4‐S concentration in runoff from grassed (mean annual value of 12.6 mg L−1) and cropped (mean annual value of 11.0 mg L−1) watersheds was observed. Differences in amounts (0.2–18.9 kg ha−1 yr−1) were a function of runoff volume as influenced by land management. A general trend of increasing SO4‐S concentration in runoff with decreasing pH was observed, which may be a function of S dry deposition and soil and crop conditions. Measured and predicted SO4‐S concentrations in runoff for individual events were not significantly different (at 5% level), with an average predictive standard error of 1.6 mg L−1 for all watersheds, representing 17% of the measured concentration. The equation may, thus, provide a predictive tool in agronomic and environmental studies of SO4‐S movement in agricultural watersheds.