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A new model for phosphorus loss in runoff from outdoor cattle lots

Vadas, Peter A., Good, Laura Ward, Panuska, John C., Busch, Dennis L., Larson, Rebecca A.
Transactions of the ASABE 2015 v.58 no.4 pp. 1035-1045
animal manures, atmospheric precipitation, cattle, cleaning, climate, cropland, data collection, farms, feedlots, hydrologic models, livestock and meat industry, nutrients, pastures, phosphorus, prediction, runoff, sediments, water quality
Phosphorus (P) loss from agriculture persists as a water quality issue. For cattle farms, nutrients can be lost from cropland, pastures, and barnyards and feedlots. Barnyards and feedlots can be significant sources of P loss, but there are few modeling tools to estimate that loss. We developed a user-friendly, spreadsheet model that predicts annual runoff, sediment loss, and total and dissolved P loss from barnyards and feedlots. The model requires input for only annual precipitation and lot characteristics, including surface type (paved or earthen), cattle number and type, and frequency of lot cleaning. The model estimates annual runoff using a dynamic dataset of precipitation events and a lot Curve Number, which is estimated empirically based on annual precipitation and lot surface type. The model estimates annual sediment loss based on annual runoff, and annual particulate P loss based on sediment loss and P content of manure in the lot, which is a function of animal type. The model estimates dissolved P loss for each runoff event in the precipitation dataset. Testing with data from 12 studies showed the model was able to reliably estimate annual runoff, sediment loss, and P loss from barnyards and feedlots representing a variety of climates and managements. The new model also gave more reliable predictions than the MinnFarm and BARNY models, which are currently used barnyard and feedlot models. The new P runoff model provides a valuable tool to develop whole-farm estimates of P loss and more effectively target P loss mitigation practices.