A Matter of Source and Timing: Nitrous Oxide Emissions from Nitrogen Fertilizer Additions to Spring Wheat in Manitoba.

The application of synthetic nitrogen fertilizers to cropland is a major factor impeding nitrous oxide (N₂O) gas reductions for the Canadian agricultural sector. One solution to mitigate N₂O emissions is with enhanced efficiency fertilizers (EEF) of nitrogen which are designed to reduce nitrogen loses to the environment and better time availability of the nutrient with crop demand. Using the static-vented chamber technique, both fall and spring applications of urea and anhydrous ammonia using urease inhibitor, nitrification inhibitor, and controlled release EEF products were examined in two replicated plot trials in each of two years (2015 and 2016) in the Red River Valley of Manitoba. Urea nitrogen products were applied mid-row banded and anhydrous ammonia knifed in. Nitrogen rates were similar for all treatments at a trial based on fall nitrogen test and yield goal of hard red spring wheat (variety AAC Brandon). Fluxes were determined for approximately 20 days per site and linear interpolated between sampling dates to determine area-scaled cumulative emissions (ΣN₂O kg N ha^-1). For the 2015 and 2016 growing season, the EEF granular urea products SuperU and eNtrench had the lowest cumulative N₂O emissions. Conversely, in 2015 and 2016, LIMUS and anhydrous ammonia treatments had the highest N₂O fluxes, respectively. Nitrogen addition treatments across all sources was higher for fall than spring addition in only one of four sites in 2015 and 2016. Specifically, N-Serve application in the spring and LIMUS application in the fall produced the greatest cumulative N₂O emissions across all site years. Each plot trial had different N₂O flux magnitudes due to varying soil and agro-climatic conditions across the Red River Valley. Thus, relation of soil extractable nitrogen and environmental conditions for treatments combinations to nitrous oxide emissions will be discussed.