A SIMPLE METHOD TO PREDICT DISSOLVED PHOSPHORUS IN RUNOFF FROM SURFACE APPLIED MANURES

Authors: Vadas, Peter; Kleinman, Peter; Sharpley, Andrew

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2003
Publication Date: 3/15/2004
Citation: Vadas, P.A., Kleinman, P.J.A., Sharpley, A.N. 2004. A simple method to predict dissolved phosphorus in runoff from surface applied manures. Journal of Environmental Quality. 33:749-756.

Interpretive Summary: Phosphorus (P) loss from agricultural soils contributes to freshwater eutrophication. Simulation models can identify areas in a watershed with a high potential for P loss, but such models poorly simulate release of P from surface applied manures to runoff. We developed an approach to predict dissolved P release from manures based on trends of P release from manures to water with increasing water:manure ratio. The approach provided a good prediction (R2 = 0.83) of dissolved P release from manures and composts for data from leaching experiments, but gave a poor prediction (R2 = 0.14) of dissolved P in runoff from boxes packed with soil where manures had been surface applied. Based on the observed positive correlation between measured P in runoff and runoff volume, multiplying predicted runoff P by the ratio of runoff:rainfall improved the relationship between measured and predicted runoff P (R2 = 0.43). Adjusting the runoff:rainfall factor by 60% for poultry, 70% for dairy, and 130% for swine manure improved the relationship even more (R2 = 0.83). The simplicity of our approach and its reliable prediction of P release from manures to runoff show its potential to make water quality models more reflective of agricultural management practices.

Technical Abstract: Phosphorus (P) loss from agricultural soils contributes to freshwater eutrophication worldwide. Computer simulation models are a rapid, inexpensive way to identify areas in an agricultural watershed with a high potential for P loss. One weakness of such models is their poor simulation of the release of P from surface applied manures to runoff. We developed a simple approach to predict dissolved reactive P release from manures based on observed trends of dissolved reactive P release from dairy, poultry, and swine manures to water with increasing water:manure ratio. The approach provided a good prediction (R2 = 0.83) of dissolved reactive P release from dairy manure and compost, poultry manure, compost, and litter, and swine slurry for data from simulated rainfall leaching experiments. However, it gave a poor prediction (R2 = 0.14) of dissolved reactive P concentrations in runoff from boxes packed with soil and subjected to simulated rainfall, where dairy, poultry, and swine manures had been surface applied. For these soil box runoff experiments, we observed a positive correlation between measured dissolved reactive P concentrations in runoff and runoff volume. Multiplying predicted runoff P concentrations by the ratio of runoff:rainfall improved the relationship between measured and predicted runoff P concentrations (R2 = 0.43). Adjusting the runoff:rainfall factor by 60% for poultry manures, 70% for dairy manures, and 130% for swine slurries improved the measured and predicted relationship even more (R2 = 0.83). Overall, the relative simplicity of our approach and its reliable prediction of P release from several manure types to runoff show its potential to make water quality models more reflective of agricultural management practices.