SIMULATION OF RUNOFF TRANSPORT OF ANIMAL MANURE CONSTITUENTS

Runoff losses of land-applied animal manure constituents can adversely affect the quality of downstream waters. Reliable mathematical simula tion models can help estimate runoff losses of animal manure constitue nts and identify management measures to reduce these losses. The objec tive of this study was to develop and calibrate an event-based simulat ion model to describe the runoff transport of solids (soil and manure particles) and nutrients (nitrogen and phosphorus) from areas treated with animal manure. The resulting model, consisting of linked hydrolog y, soil/manure transport, and nutrient transport components, is proces s-oriented and uses measurable parameters to the greatest degree possi ble. The three components of the model were calibrated sequentially (h ydrology, soil/manure transport, and nutrient transport, in order) usi ng data from plot-scale field experiments involving grassed plots trea ted with poultry litter. The calibrated parameter values were generall y consistent with previously published values. Transport of total susp ended solids, ammonia-nitrogen, dissolved phosphorus, and total phosph orus was well-predicted by the model. Transport of nitrate-nitrogen, h owever, was overpredicted by approximately an order of magnitude, whil e total Kjeldahl nitrogen transport was underpredicted by approximatel y an order of magnitude. Improvements in model structure (e.g., using different equations to describe the release of nitrate from the litter to the soil and assuming a significant proportion of organic nitrogen to be soluble) and parameter selection appear warranted to improve pr ediction of nitrate and total Kjeldahl nitrogen losses.