Nutrient Runoff Losses from Liquid Dairy Manure Applied with Low-Disturbance Methods.

Manure applied to cropland is a source of P and N in surface runoff and can contribute to impairment of surface waters. Immediate tillage incorporates manure into the soil, which may reduce nutrient loss in runoff, as well as N loss via NH₃ volatilization. But tillage also incorporates crop residue, which may increase erosion potential. We applied liquid dairy manure in a silage corn-rye cover crop system in late October using methods designed to incorporate manure with minimal soil and residue disturbance. These include strip-till injection (low-disturbance sweep injection ridged with paired disks) and tine aerator-band manure application, which applies bands of manure over aerator slots to encourage manure infiltration. These were compared to standard broadcast application, either incorporated with a disk or left on the surface. Runoff was generated with a portable rainfall simulator (40 mm/h for 30 min) 3 separate times: a) 2 to 5 days after manure application, b) early spring, and c) after tillage and planting. Runoff was collected from 2 x 2 m subplots bordered by a steel frame with a PVC gutter at the lower end to collect runoff. In the post-manure application runoff, the highest losses of total and dissolved P were from surface-applied manure, as would be expected. Dissolved P loss was reduced by 98% by strip-till injection, which was not statistically different from the no-manure control, while reductions from the aerator band method and disk incorporation were 51 and 73%, respectively. Total P losses followed a similar pattern, with 90% reduction from injected manure. In the two spring runoff events P losses were much lower and there were fewer significant differences. Overall, results show that low-disturbance manure application methods can significantly reduce nutrient runoff losses compared to surface application, while maintaining residue cover better than incorporation by tillage.