Description and Application of an Animal Waste Phosphorus Loading Model

Abstract An animal waste loading model was developed to estimate total phosphorus (P) loadings from winter‐spread manure, barnyards and feedlots, and aboveground manure storage facilities. Literature studies were used to establish the percentage of manure P which could potentially be carried in runoff from a specific manure source. Likewise, a critical distance over which manure polluted runoff must travel as overland flow in order for P to be reduced to background levels was established. The model was tested on a 328‐ha watershed in Shawano County, WI, which is devoted to dairy agriculture and where surface water was monitored and intensive land use inventories were completed. For the years 1974 to 1976, the model predicted total P loadings from animal wastes of 96.0 kg yr−1, of which 24.6 kg yr−1 or 26% was attributed to winter spreading, and the balance of 71.4 kg yr−1 or 74% to runoff from barnyards and above‐ground storage facilities. The animal waste model was linked to a model estimating cropland losses of total P to develop a prediction of total P losses from the watershed. Comparison between predicted and monitored values suggested that the animal waste model was a useful tool for estimating total P losses from various waste handling practices on a long‐term basis. As such, it will serve as a valuable planning tool for nonpoint source abatement programs.