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 simulation models can help estimate runoff losses of animal manure constituents and identify management measures to reduce these losses. The objective of this study was to develop and calibrate an event-based simulation 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 hydrology, soil/manure transport, and nutrient transport components, is process-oriented and uses measurable parameters to the greatest degree possible. The three components of the model were calibrated sequentially (hydrology, soil/manure transport, and nutrient transport, in order) using data from plot-scale field experiments involving grassed plots treated with poultry litter. The calibrated parameter values were generally consistent with previously published values. Transport of total suspended solids, ammonia-nitrogen, dissolved phosphorus, and total phosphorus was well-predicted by the model. Transport of nitrate-nitrogen, however, was overpredicted by approximately an order of magnitude, while total Kjeldahl nitrogen transport was underpredicted by approximately 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 prediction of nitrate and total Kjeldahl nitrogen losses.