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a USDA-ARS, Pasture Systems and Watershed Management Research Unit, Building 3702, Curtin Road, University Park, PA 16802-3702
b USDA-ARS, Poultry Production and Product Safety Research Unit, 203 Engineering Hall, Fayetteville, AR 72701
* Corresponding author (Peter.Vadas{at}ars.usda.gov)
Received for publication November 10, 2004. Dissolved inorganic P transport in runoff from agricultural soils is an environmental concern. Models are used to predict P transport but rarely simulate P in runoff from surface-applied manures. Using field-plot data, we tested a previously proposed model to predict manure P in runoff. We updated the model to include more data relating water to manure ratio to manure P released during water extractions. We verified that this update can predict P release from manure to rain using published data. We tested the updated model using field-plot and soil-box data from three manure runoff studies. The model accurately predicted runoff P for boxes, but underpredicted runoff P for plots. Underpredictions were caused by runoff to rain ratios used to distribute P into runoff or infiltration. We developed P distribution fractions from manure water extraction data to replace runoff to rain ratios. Calculating P distribution fractions requires knowing rainfall rate and times that runoff begins and rain stops. Using P distribution fractions gave accurate predictions of runoff P for soil boxes and field plots. We observed relationships between measured runoff to rain ratios and both P distribution fractions and a degree of error in original predictions, calculated as (measured runoff P/predicted runoff P). Using independent field-plot data, we verified that original underpredictions of manure runoff P can be improved by calculating P distribution fractions from measured runoff to rain ratios or adjusting runoff to rain ratios based on their degree of error. Future work should test the model at field or watershed scales and at longer time scales.
Abbreviations: W, water to manure ratio • WEP, water-extractable phosphorus
This article has been cited by other articles:
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  M. S. Srinivasan, P. J. A. Kleinman, A. N. Sharpley, T. Buob, and W. J. Gburek Hydrology of Small Field Plots Used to Study Phosphorus Runoff under Simulated Rainfall J. Environ. Qual., October 24, 2007; 36(6): 1833 - 1842. [Abstract] [Full Text] [PDF]
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P. A. Vadas, W. J. Gburek, A. N. Sharpley, P. J. A. Kleinman, P. A. Moore Jr., M. L. Cabrera, and R. D. Harmel A Model for Phosphorus Transformation and Runoff Loss for Surface-Applied Manures J. Environ. Qual., January 9, 2007; 36(1): 324 - 332. [Abstract] [Full Text] [PDF]
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P. A. Vadas and P. J. A. Kleinman Effect of Methodology in Estimating and Interpreting Water-Extractable Phosphorus in Animal Manures J. Environ. Qual., May 31, 2006; 35(4): 1151 - 1159. [Abstract] [Full Text] [PDF]
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 P. A. Vadas, T. Krogstad, and A. N. Sharpley Modeling Phosphorus Transfer between Labile and Nonlabile Soil Pools: Updating the EPIC Model Soil Sci. Soc. Am. J., March 29, 2006; 70(3): 736 - 743. [Abstract] [Full Text] [PDF]
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P. A. Vadas Distribution of Phosphorus in Manure Slurry and Its Infiltration after Application to Soils J. Environ. Qual., February 2, 2006; 35(2): 542 - 547. [Abstract] [Full Text] [PDF]
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