Nitrous oxide emissions in Midwest US maize production vary widely with band-injected N fertilizer rates, timing and nitrapyrin presence

Nitrification inhibitors have the potential to reduce N2O emissions from maize fields, but optimal results may depend on deployment of integrated N fertilizer management systems that increase yields achieved per unit of N2O lost. A new micro-encapsulated formulation of nitrapyrin for liquid N fertilizers became available to US farmers in 2010. Our research objectives were to (i) assess the impacts of urea-ammonium nitrate (UAN) management practices (timing, rate and nitrification inhibitor) and environmental variables on growing-season N2O fluxes and (ii) identify UAN treatment combinations that both reduce N2O emissions and optimize maize productivity. Field experiments near West Lafayette, Indiana in 2010 and 2011 examined three N rates (0, 90 and 180 kg N ha(-1)), two timings (pre-emergence and side-dress) and presence or absence of nitrapyrin. Mean cumulative N2O-N emissions (Q(10) corrected) were 0.81, 1.83 and 3.52 kg N2O-N ha(-1) for the rates of 0, 90 and 180 kg N ha(-1), respectively; 1.80 and 2.31 kg N2O-N ha(-1) for pre-emergence and side-dress timings, respectively; and 1.77 versus 2.34 kg N2O-N ha(-1) for with and without nitrapyrin, respectively. Yield-scaled N2O-N emissions increased with N rates as anticipated (averaging 167, 204 and 328 g N2O-N Mg grain(-1) for the 0, 90 and 180 kg N ha(-1) rates), but were 22% greater with the side-dress timing than the pre-emergence timing (when averaged across N rates and inhibitor treatments) because of environmental conditions following later applications. Overall yield-scaled N2O-N emissions were 22% lower with nitrapyrin than without the inhibitor, but these did not interact with N rate or timing.