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

Vadas, P.A., Owens, L.B., Sharpley, A.N.
Agriculture, ecosystems & environment 2008 v.127 no.1-2 pp. 59
agricultural land, phosphorus fertilizers, phosphorus, agricultural runoff, prediction, simulation models, model validation, rain, vegetation cover, crop residues, soil, adsorption
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), 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 (0.2m² to 9.6ha). 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.