Nitrous oxide (N 2O) emissions resulting from application of nitrogen (N) fertilizer contribute to the greenhouse gas footprint of corn production. In eastern Canada, corn is a major crop with most N fertilizer applied pre- or at planting. This timing of application results in a lack of synchrony of soil N supply and crop N demand. Matching the amount and timing of application to crop uptake has been suggested as a mitigation measure to reduce N losses, and is an integral part of the 4R Nutrient Stewardship program. This study examined the effect of timing, rate and history of urea-ammonium nitrate application on N 2O emissions in corn in 2011 and 2012 at Elora, ON, Canada. Treatments were three N rates (30, 145 and 218 kg N ha -1); two timings (N injected in mid-row at planting and at the 8th leaf stage, V8); two histories (short-term: applying N rate treatments on plots that had received 145 kg N ha -1 in the previous year, and long-term: applying the same N rate to a given plot over the duration of the trial). N 2O emissions were measured using static chambers. History of N application did not have an effect on N 2O emissions or grain yield. In both years, cumulative N 2O emissions during the growing season and corn yields increased significantly with increasing N application rates. In 2011, cumulative N 2O emissions were significantly lower when N was applied as side-dress at V8 (0.88 kg N ha -1) compared with planting (2.12 kg N ha -1), with no significant impact on corn grain yield (average 9.1 Mg ha -1). In contrast, in 2012, limited rainfall reduced both N 2O emissions and corn grain yield, and neither N 2O emission (average 0.17 kg N ha -1) nor grain yield (average 6.7 Mg ha -1) was affected by timing of N application. Applying N as side-dress at V8 instead of at planting and using the recommended N rate were shown to be effective N 2O emission mitigation practices without affecting corn yield during a typical wet spring in Ontario.
