Nitrous Oxide Emissions From Corn As Affected by Rate, Timing and History of Nitrogen Fertilizer Application.

This study examines the effect of timing, rate and history of urea-ammonium nitrate application on nitrous oxide (N2O) emissions in corn in a 10-yr trial starting in 2009 at Elora, ON, Canada. The three nitrogen (N) rates were 30, 145 and 218 kg N ha-1; and the two timings were N banded in mid-row at planting and N side-dressed in mid-row at 6-leaf stage. The two histories consisted of applying (i) the current year's N rates on plots that received 115 kg N ha-1 in the previous year, and (ii) the same N rate to a given plot over the duration of the trial. From May 13 through October 17, 2011, N2O emissions were measured on 28 days using non-flow-through non-steady-state chambers. Total N2O emissions during the growing season and corn yields increased significantly with increasing N application rates (0.50, 2.92 and 4.21 kg N2O ha-1 and 6.29, 10.19 and 10.82 Mg grain ha-1 for 30, 145 and 218 kg N ha-1, respectively). Total N2O emissions were significantly lower when N was applied at 6-leaf stage (1.71 kg N2O ha-1) compared to at planting (3.37 kg N2O ha-1), with no significant impact on corn grain yield (9.09 vs. 9.11 Mg ha-1 for application at planting and 6-leaf stage, respectively). N2O intensities for the two higher N-rates were not significantly different (0.285 vs. 0.389 g N2O kg-1 grain for 145 and 218 kg N ha-1 respectively, but were statistically higher than the lowest N-rate (0.080 g N2O kg-1 grain ). When N was applied at 6-leaf stage, N2O intensity was significantly lower (0.171 g N2O kg-1 grain) compared to when N was applied at planting (0.332 g N2O kg-1 grain). This study provides evidence that N-applied at 6-leaf stage compared to at planting for corn may result in reduced N2O emissions without affecting grain yield for the conditions in this study. Additional measurements are being taken in the summer of 2012.