Environmental and economic comparisons of manure application methods on dairy farms

A dairy farm simulation model was used to compare the environmental and economic impacts of using alternative manure application methods on a dairy farm in Pennsylvania. Model predictions of ammonia emissions, nitrate leaching, and phosphorus runoff were compared to field measurements following no manure application and five application methods. Application methods included broadcast spreading without incorporation, broadcast spreading with immediate incorporation by tillage, band application with aeration, shallow disk injection, and high pressure injection. Following model evaluation, manure application methods were simulated over 25 years of weather on a representative Pennsylvania dairy farm. Immediate incorporation by tillage and the use of the two manure injection techniques reduced ammonia emissions, but nitrate leaching losses were increased. Reductions in ammonia N loss and runoff loss of P were obtained with the use of shallow disk injection without adversely affecting farm profitability.