A New Model for Phosphorus Loss in Runoff from Outdoor Cattle Lots

Abstract

Phosphorus (P) loss from agriculture can compromise the quality of receiving water bodies. For cattle farms, P can be lost from cropland, pastures, and outdoor animal lots. We developed a new model that predicts annual runoff, total solids loss, and total and dissolved P loss from cattle lots. The model requires input for annual precipitation, lot surface type, soil test P for earthen lots, cattle number and type, frequency of cleaning, and percent vegetative cover. The model estimates annual runoff using a precipitation dataset and curve number, annual solids loss based on annual runoff, annual particulate P loss based on solid loss and manure and soil P content, and annual dissolved P loss for each runoff event. Testing showed that the model reliably estimated runoff, solids loss, and P loss from a wide variety of lots and was more accurate than other, currently used models. The new model provides a valuable tool for developing whole-farm estimates of P loss and more effectively targeting P loss mitigation practices.