Retention of Swine Slurry Constituents in Soil and Crop Residue as Affected by Setback Distance

Setbacks are prescribed distances from surface waters within which manure application is not allowed. Little information is available concerning the retention of swine slurry constituents in soil and crop residue materials within setback areas. This study was conducted to measure the retention of selected constituents within a setback area following the upslope application of swine slurry and the introduction of simulated rainfall. The no-till cropland site had a slope gradient of 4.9% and a mean winter wheat residue cover of 7.73 Mg ha⁻¹. Soil and vegetative samples were collected on 3.7 m wide by 23.2 m long plots with and without the addition of slurry. Slurry was added at the 0–4.9 m distance on selected plots, and simulated rainfall was then applied to the entire plot area during two separate events. Soil cores and vegetative samples were collected from each plot at distances of 2.44, 5.18, 7.92, 11.0, 14.0, 17.1, and 20.1 m from the upper plot border. The soil cores were separated into 0–10, 10–20, and 20–30 cm depth increments. Significant increases in soil concentrations of chloride, nitrate, phosphorus, and zinc were found both within and downslope from the slurry application area. Residue materials located both within and downslope from the slurry application area contained significantly increased concentrations of boron, calcium, copper, magnesium, sulfur, and zinc. When estimating the downslope transport of constituents contained in swine slurry, contributions from runoff, soil, and residue should all be considered.