Integrated Nitrogen Rate and Nitrification Inhibitor Application Effects on Nitrogen Use Efficiency and Nitrous Oxide Emission in Rainfed Corn.

Nitrogen (N) management practices that simultaneously improve nitrogen use efficiency (NUE) and reduce nitrous oxide (N₂O) emissions during crop production are needed to maintain/improve yield without deleterious environmental effects in the face of changing climate.  Although the effects of N application rates on yield and N₂O emission are fairly well documented, the potential for integrated N rate and nitrification inhibitors to simultaneously improve NUE and reduce N₂O emissions remain relatively unknown.  Much less known is the effect of this management system on the relationship between N₂O emissions, N uptake, recovery (NRE) and use efficiency (NUE).  Research was conducted in 2012 and 2013 in West Lafayette, Indiana, with the objectives to determine effects of N application rates, with and without nitrification inhibitor on (i) corn yield, N uptake, NRE, and NUE (ii) seasonal N₂O emissions, and the relationship between emissions and N rate, uptake, NRE, NUE in rainfed corn.  Nitrogen (urea ammonium-nitrate, UAN) was sidedressed to corn at 0, 90, 135, 180, and 225 kg N ha^-1, with and without nitrapyrin (Instinct^TM).  Nitrous oxide emission was measured weekly using the vented chamber procedure, and cumulative N₂O was then estimated by linearly interpolating fluxes between sampling dates. At physiological maturity, corn grain and biomass were harvested, N concentration determined, and N uptake, NRE and NUE were calculated.  Averaged across years, yield, N use efficiency, and N₂O emission were not affected by Instinct^TM application.  In contrast, yield, N uptake, NRE, and NUE were significantly affected by N rate.  Similarly, cumulative N₂O emission was significantly affected by N rate; N₂O increased non-linearly as N rate was increased.  Linear regression models indicated significant functional relationship between N₂O emission and N rate, NRE, and NUE.  In 2012, 28% of total variability of N₂O emission was explained by N rate (r² = 0.21) and NUE (r² = 0.08), and by NRE (r² = 0.22) in 2013.  Across years, 62% of the total variability associated with N₂O emission was accounted for by NUE (r² = 0.46), N rate (r₂ = 0.13), and N uptake (r² = 0.02).