USING 4R NUTRIENT MANAGEMENT TO REDUCE N2O EMISSIONS AND DETERMINE THE AGRI-ENVIRONMENTAL OPTIMUM NITROGEN APPLICATION FOR IRRIGATED CANOLA IN SASKATCHEWAN

Abstract

Saskatchewan has substantial potential to increase the number of irrigated acres in the province which could increase food production. An environmental consideration is the increased greenhouse gas (GHG) emissions often seen from irrigated land compared to dryland cropping. The yield-scaled emission factor (YsEF) can be similar to, or lower than that of dryland systems, however, due to increased yields associated with irrigation. The principles of 4R nutrient stewardship—the Right source, Right rate, Right time, and Right placement of fertilizer—were developed to minimize nutrient losses while still reaching yield targets. In a three-year field plot study, the effects of the 4Rs on GHG emissions were observed. It was found that (i) the highest rates of N fertilizer (165 and 220 kg N ha-1) resulted in greater N2O emissions; (ii) splitting the fertilizer over two applications instead of one reduced N2O emissions, but only at high application rates; and (iii) side-banded N fertilizer resulted in greater emissions in two of three years compared to broadcast and incorporated treatments. Soil moisture and N availability were found to be key factors that influenced N2O emissions, with large fluxes occurring after fertilizer applications— especially if closely followed by a precipitation or irrigation event—and small fluxes occurring later in the growing season when the crop would have used the available N. The greatest YsEF was consistently from the side-banded (SB) treatment at a rate of 220 kg N ha-1, however in 2015 the broadcast and incorporated (BCI-O) treatment at the same rate had a similarly high value. This research examined potential mitigation opportunities for irrigated canola in the semi-arid prairies and concluded that reducing N rates, splitting fertilizer applications and avoiding side-banding N at high rates may be effective in reducing N2O emissions in this area.