Subsurface manure application to reduce ammonia emissions

Incorporation into soil is generally recommended to reduce ammonia (NH ₃) volatilization and nutrient runoff following land application of manures. A range of subsurface applicators are available for manure incorporation with minimal soil disturbance in reduced tillage systems, but none have been widely adopted in the northeastern US. Research in Pennsylvania has compared NH₃ losses following incorporation of dairy and swine manures using shallow disk injection and rolling-tine aerators with losses following surface broadcast. Additionally, impacts of multiple aerator configurations (toolbar angle and manure placement) on NH₃ losses were investigated. Shallow disk injection reduced NH₃ emissions by 70 to greater than 90%, compared to surface broadcast, throughout the study. Incorporation with the aerator had an inconsistent impact on NH₃ emissions (0 to about 70% reduction relative to surface broadcast). Ammonia emissions were not significantly affected by placement of manure (broadcast ahead of aerator or banded over aeration holes), but emissions were reduced when the aerator toolbar was offset by 10 degrees. We recommend the shallow disk injector for manure application in the northeast. Manure incorporation with the aerator is highly dependent on soil and manure conditions and does not appear to provide a consistent reduction in NH₃ emissions. While offsetting the aerator toolbar can result in much lower NH₃ emissions, the additional soil disturbance when the toolbar is offset may not be compatible with soil conservation plans.