Effects of Low-Disturbance Manure Application Methods on N2O and NH3 Emissions in a Silage Corn -Rye Cover Crop System.

Incorporation of manure by tillage can conserve manure N by reducing ammonia volatilization losses, but tillage also incorporates crop residue, which may increase erosion potential. This study compared several low-disturbance manure application methods, designed to incorporate manure while maintaining crop residue for erosion control, to conventional broadcast application in a silage corn/winter rye cover crop system. Treatments included low-disturbance sweep injection, strip-till injection (sweep injection ridged with paired disks), coulter injection, aerator-band, and broadcast with and without disk harrow incorporation, plus 0 and 135 kg/ha pre-plant fertilizer N rates in separate non-manured plots. All manure treatments were applied in late Oct/early Nov; all treatments except strip-till injection were field cultivated in the spring. Nitrous oxide flux was greatest in the period following manure application and in spring/early summer, with most (but not all) peaks in flux explained by manure or N fertilizer application, wet soil conditions and/or recent rain events. Total estimated N₂O emission varied by year, with annual totals from manure and N fertilizer treatments ranging from 2 to 6 times that from the non-manured/no N fertilizer control. Relative manure treatment effects also varied by year, but tended to be greatest from one or more of the injected manure treatments. Limited measurements of ammonia emission showed greatest amounts from surface-applied manure, with reductions of 85% or more from injected manure and more modest reductions from aerator/band and disk incorporation. These results indicate that low-disturbance manure application methods can reduce ammonia-N loss compared to surface application but there may be tradeoffs with N₂O emission.