Nutrient transport in runoff as affected by diet, tillage, and manure application rate

Feedlot operators may increase profitability by including distillers grains in finishing diets. However, the nutrients remaining in the by-product are concentrated by about a factor of three during the distillation process. Manure can be applied to meet single- or multiple-year crop nutrient requirements. The water quality effects of the use of distillers grains in feedlot diets and multiple-year manure application have not been well quantified. The objectives of this study were to (1) compare the runoff water quality effects resulting from the application of manure derived from corn and distillers grain diets, (2) examine the effects of till and no-till conditions on runoff nutrient transport, and (3) compare the water quality impacts of 1-, 2-, and 4-year phosphorus (P) based manure application rates. Simulated rainfall events were applied to 0.75 m wide × 2 m long plots soon after manure application. No significant difference in dissolved phosphorus (DP) or total P (TP) load was found between the corn and distillers grain treatments. The runoff load of TP was significantly larger on the no-till plots than on the till plots. The amount of particulate phosphorus (PP), DP, and TP transported in runoff was significantly affected by multi-year application of manure. The TN content of runoff was similar for till and no-till conditions on the plots containing manure obtained from the distillers grain diet. The environmental effects of the use of manure from a distillers grain diet and multiple-year manure application should be considered when developing nutrient management plans.