Nitrous Oxide and Ammonia Emissions from Injected and Broadcast-Applied Dairy Slurry

Trade-offs associated with surface application or injection of manure pose important environmental and agronomic concerns. Manure injection can conserve nitrogen (N) by decreasing ammonia (NH3) volatilization. However, the injection band also creates conditions that potentially favor nitrous oxide (N2O) production: an abundant organic substrate-promoting microbial activity, anaerobic conditions favoring denitrification, and large local concentrations of N. We assessed differences in NH3 volatilization and N2O emissions with broadcast application versus shallow disk injection of dairy slurry during the 2011 to 2013 growing seasons on a well-drained silt loam that received average manure-N application rates of 180 kg N ha(-1) via injection or 200 kg N ha(-1) via broadcast. Ammonia emissions were measured using a photoacoustic gas analyzer and chambers, and N2O emissions were measured using syringes to draw timed samples from vented chambers with analysis by gas chromatograph. Results point to a 92 to 98% (3.02-11.05 kg NH3-N ha(-1)) reduction in NH3 volatilization (for the initial sampling) with injection compared with broadcasting manure but also reveal 84 to 152% (725.9-3187.8 g N2O-N ha(-1)) greater cumulative N2O emissions. Although losses of N via N2O emission were at least three orders of magnitude less than NH3 volatilization, their potential role as a greenhouse gas is of concern. Despite the potential greenhouse gas trade-offs associated with shallow disk injection of manure, decreasing NH3 volatilization provides a substantial benefit, especially to farmers who are trying to conserve N and improve the N/P ratio of soil-applied manure.