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United States Department of Agriculture

Agricultural Research Service

Title: Predicting Dissolved Phosphorus in Runoff from Manured Field-Plots

Authors
item Vadas, Peter
item Haggard, Brian
item Gburek, William

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 10, 2004
Publication Date: July 5, 2005
Citation: Vadas, P.A., Haggard, B.E., Gburek, W.J. 2005. Predicting dissolved phosphorus in runoff from manured field-plots. Journal of Environmental Quality. 34:1347-1353.

Interpretive Summary: Dissolved phosphorus (P) in runoff from soils is an environmental concern. Computer models are used to assess the risk of P in runoff, but widely-used models do not simulate P in runoff from surface-applied manures. We tested our previously developed runoff P model using field-plot and soil-box runoff data with poultry, dairy, and swine manure. The model accurately predicted runoff P for soil-boxes, but under-predicted runoff P for field-plots by 80%. Under-predictions were caused by a runoff to rain ratio factor in the model. We developed a new P Distribution Fraction from published manure P leaching data to replace the runoff to rain ratio and accurately predicted runoff P from field-plots. We observed a strong empirical relationship between measured runoff to rain ratios and calculated P Distribution Fractions for soil-box and field-plot data. Estimating P Distribution Factors in our runoff model based on this relationship also resulted in accurate predictions of runoff P. With this relationship, our model is thus easily incorporated into existing computer models.

Technical Abstract: Dissolved P transport in surface runoff from agricultural soils to surface waters is an environmental concern. Computer models are used to assess the risk of P transport, but widely-used models do not simulate P in runoff from surface-applied manures. We therefore tested the quantitative runoff P model of Vadas et al. (2004) using field-plot and soil-box data from five rain-runoff studies with surface-applied poultry, dairy, and swine manure. The model accurately predicted runoff P concentrations for soil boxes, but under-predicted runoff P for field plots by 80%. Under-predictions were caused by a runoff to rain ratio factor in the model. We developed a new P Distribution Fraction from the manure P leaching data of Sharpley and Moyer (2000) to replace the runoff to rain ratio. Distribution Fractions, which are based on decreasing incremental P release from manures to rain water and knowledge of when runoff starts and rain stops during a storm, resulted in accurate predictions of runoff P. We also found that single, batch water extractions of manures using various water to manure (W) ratios give linear relationships between W and manure water extractable P (WEP), which were originally used in the P runoff model of Vadas et al. (2004). Sequential batch or flow extractions of manure to achieve various W's give non-linear relationships between W and WEP. We replaced linear relationships with non-linear relationships in the P runoff model and more accurately predicted dissolved P in runoff for soil-box and field-plot data. Finally, we observed a strong empirical relationship between measured runoff to rain ratios and calculated P Distribution Fractions for soil-box and field-plot data. Estimating P Distribution Factors in our runoff model based on this empirical relationship also resulted in accurate predictions of runoff P. Such a method would be easy to incorporate into existing computer models.

Last Modified: 9/22/2014
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