Setback Distance Requirements for Removal of Swine Slurry Constituents in Runoff

Abstract

Abstract. The use of setback distances for manure application on cropland areas adjacent to surface water bodies could serve a function similar to vegetative filter strips. However, little information currently exists to identify the setback distances necessary to effectively reduce the transport of contaminants in runoff. The objective of this study was to determine the effects of setback distance and runoff rate on concentrations of selected constituents in runoff following land application of swine slurry to a no-till cropland area in southeast Nebraska. The study site had a residue cover of 7.73 Mg ha-1 and a slope gradient of 4.9%. The twenty plots examined during the investigation were 3.7 m across the slope by 4.9, 7.9, 11.0, 17.1, or 23.2 m long. An initial set of rainfall simulation tests were completed to identify background concentrations of selected constituents. Swine slurry was then applied to the upper 4.9 m of each plot, and additional rainfall simulation tests were conducted on the same plots examined previously. A first-order exponential decay function was used to estimate the effects of setback distance on concentrations of selected constituents. A setback distance of 12.2 m reduced runoff concentrations of dissolved phosphorus (DP), NH4-N, total nitrogen (TN), boron, chloride, manganese, potassium, sulfate, zinc, electrical conductivity (EC), and pH to background values similar to those measured for the no-slurry condition. Runoff rate significantly influenced transport of several of the constituents, with concentrations generally decreasing as runoff rate increased. The transport of selected pollutants in runoff was significantly reduced when setback areas were employed. Keywords: Filter strips, Land application, Manure management, Manure runoff, Nitrogen, Nutrients, Phosphorus, Runoff, Swine slurry, Water quality.