Greenhouse Gas Emission Reductions Associated with 4R Nitrogen Management in Irrigated Canola.

Nitrous oxide (N₂O) is an important ozone depleting and greenhouse gas, and substantial fertilizer induced emissions can result when rates of nitrogen fertilizer exceed crop requirements. It has been suggested that irrigated cropping systems may contribute to disproportionately high fertilizer induced emissions of N₂O. However, because yields are generally higher in irrigated systems, the greenhouse gas intensity (i.e., N₂O-N emitted per unit of yield) of irrigated cropping may be similar to, or lower than that of dryland cropping. Data for irrigated cropping systems in the semi-arid prairies is lacking, thus the objectives of this research are to increase our knowledge of how N₂O emissions are effected by nitrogen fertilizer management and determine the agri-environmental optimum rate of fertilizer N—the rate that maximizes yield while minimizing greenhouse gas intensity—for irrigated canola. A small-plot study is being conducted at the Canada-Saskatchewan Irrigation Diversification Centre (CSIDC) in Outlook, SK. There are four nitrogen rates applied in broadcast, banded, and split-broadcast applications and the greenhouse gas fluxes are monitored from spring thaw through fall freeze-up. Data from the 2014 and 2015 seasons show that cumulative N₂O emissions were significantly impacted by (i) N rate, with emissions increasing as the N rate increased—especially at the highest N rate (220 kg N ha^-1); and (ii) timing of the fertilizer application, with lower emissions from the split N application compared to a single application of the same N rate. The effect of fertilizer placement was variable, with emissions from the broadcast applications lower than the side-band application in 2014, but the reverse being true in 2015. Although N management had no significant effect on canola yields in either year, the lowest greenhouse gas intensity was associated with the split application.