An empirical model for dissolved phosphorus in runoff from surface-applied fertilizers

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 simplemodel 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), and amount of rain and runoff for each storm during the simulation 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 11 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 cover types and subsequent fertilizer P adsorption amounts, storm hydrology conditions (i.e., runoff to rain ratio), and plot or field sizes (0.2 m 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. ! 2008 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +1 608 890 0069; fax: +1 608 890 0076. E-mail address: [email protected] (P.A. Vadas). G Model AGEE-3192; No of Pages 7