Removal of cattle manure constituents in runoff from no-till cropland as affected by setback distance

Vegetative filter strips located at the bottom of a hillslope have been shown to substantially reduce nutrients and sediment in runoff. Cropland areas could serve a similar function. However, little scientifically derived information is available to help identify the setback distances required 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 the concentrations and mass transport rates of selected constituents following land application of beef cattle manure to a no-till cropland area. The study site had a residue cover of 8.84 Mg ha-1 and a slope gradient of 6.2%. The 20 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 determine background concentrations and mass transport rates of selected constituents. Cattle manure was then applied to the upper 4.9 m of each plot, and additional rainfall simulation tests were conducted. A first-order exponential decay function was used to estimate the effects of setback distance on the concentrations and mass transport rates in runoff. A setback distance of 12.2 m effectively reduced the concentrations of DP, TP, NH4-N, boron, calcium, magnesium, potassium, and sulfate and the mass transport rates of DP, TP, NH4-N, boron, and potassium to background values similar to those measured on the no-manure treatment. Runoff rate was an important variable influencing each the measured constituents, with mass transport rates increasing as runoff rate increased