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United States Department of Agriculture

Agricultural Research Service

Title: An Empirical Model for Dissolved Phosphorus in Runoff from Surface-Applied Fertilizers

Authors
item Vadas, Peter
item Owens, Lloyd
item Sharpley, Andrew - UNIV OF ARKANSAS

Submitted to: Agriculture Ecosystems and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 1, 2008
Publication Date: May 8, 2008
Repository URL: http://www.ars.usda.gov/sp2UserFiles/Place/36553000/publications/2008-Vadas-AEE-XXX-XXX.pdf
Citation: Vadas, P.A., Owens, L.B., Sharpley, A.N. 2008. An empirical model for dissolved phosphorus in runoff from surface-applied fertilizers. Agriculture Ecosystems and the Environment. 127:59-65.

Interpretive Summary: Surface-applied fertilizers can release a lot of dissolved phosphorus (P) to runoff, but commonly used computer models do not usually simulate loss of fertilizer P in runoff. Using data from our own rainfall experiments and published runoff studies, we developed a simple model to predict fertilizer P release during rain and the concentration of dissolved P in runoff. The model operates on a day-to-day basis and needs input data on the amount of fertilizer P applied, type of soil cover (bare, residue-covered, grassed) at application, and amount of rain and runoff for each storm during the simulated time period. The model applies fertilizer to the soil surface, adsorbs fertilizer P to soil before the first rain, releases P from fertilizer for each rain event, and divides released fertilizer P into either runoff or infiltration based on the runoff to rain ratio. Using data from seven runoff studies, we found that our model can accurately predict dissolved P in runoff from surface-applied fertilizers. Validation data were for several runoff events for a variety of fertilizer types, soil conditions, storm conditions (i.e., runoff to rain ratio), and plot or field sizes. An analysis showed model predictions are most sensitive to rainfall and runoff data. However, because our model is simple, it should be straightforward to incorporate it into more complex P transport models. Those models should then be able to better predict P loss to the environment for a variety of agricultural land uses.

Technical Abstract: Dissolved phosphorus (P) in runoff from surface-applied fertilizers can be relatively great, but commonly used field or watershed-scale computer models often do not simulate direct transfer of fertilizer P to runoff. Using data from our own simulated rainfall experiments and published runoff studies, we developed a simple model to predict fertilizer P release during rain and the concentration of dissolved P in runoff. The model operates on a daily time step and requires input data on the amount of fertilizer P applied, type of soil cover (bare, residue-covered, grassed) at application, and amount of rain and runoff for each storm during the simulated time period. The model applies fertilizer to the soil surface, adsorbs fertilizer P to soil before the first rain, releases P from fertilizer for each rain event, and distributes released fertilizer P between runoff and infiltration based on the runoff-to-rain ratio. Using data from seven runoff studies, we validated that our model accurately predicts dissolved P in runoff from surface-applied fertilizers. Validation data represented a series of runoff events for a variety of fertilizer types, soil conditions and subsequent fertilizer P adsorption amounts, storm hydrology conditions (i.e., runoff-to-rain ratio), and plot or field sizes (3 m2 to 9.6 ha). An analysis showed model predictions can be quite sensitive to rainfall and runoff data. However, the simplicity of our model should make it straightforward to incorporate into more complex P transport models, thus improving their ability to reliably predict P loss to the environment for a variety of agricultural land uses.

Last Modified: 7/30/2014
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