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This article in JEQ

  1. Vol. 18 No. 3, p. 313-316
    Received: Nov 9, 1988

    * Corresponding author(s):
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Prediction of Soluble Phosphorus Transport in Agricultural Runoff

  1. A. N. Sharpley * and
  2. S. J. Smith
  1. USDA-ARS, Water Quality and Watershed Res. Lab., P.O. Box 1430, Durant, OK 74702-1430.



The soluble phosphorus (SP) concentrations of runoff for individual events from agricultural land were predicted using relationships describing soil P desorption kinetics and effective depth of surface soil-runoff interaction (E). These values were compared with concentrations measured for runoff from 9 grassed and 11 cropped watersheds in the Southern Plains, USA, over a 10-yr period. Using a constant value of E for a given watershed, measured SP concentrations were over-estimated by up to 4415% for runoff events of > 0.75 mm in volume. Using a value of E calculated for each runoff event from soil loss, correlation coefficients between measured and predicted values and prediction errors were improved (R2 = 0.95–0.99 and error = 11–18%) compared to use of a constant E value (R2 = 0.21–0.83 error = 38–380%) averaged for each watershed location. Although these improvements did not significantly (5% level) affect estimates of the amounts of SP transported, the improvements will be important from environmental aspects, in terms of assessing the impact of agricultural management practices on P-related eutrophication for all runoff events.

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