Transport and Prediction of Sulfate in Agricultural Runoff
- Andrew N. Sharpley *,
- S. J. Smith,
- O. R. Jones,
- W. A. Berg and
- G. A. Coleman
USDA-ARS, Water Quality and Watershed Res. Lab., P. O. Box 1430, Durant, OK 74702-1430; USDA-ARS, Conserv. and Production Res. Lab., Drawer 10, Bushland, TX 79012; USDA-ARS, Southern Plains Range Exp. Stn., 2000 18th Street, Woodward, OK 73801; Southern Plains Watershed and Water Quality Lab., P. O. Box 400, Chickasha, OK 73018. Abstract
The 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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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