4R Nitrogen Management and Nitrous Oxide (N2O) Emissions for Irrigated Potato Production in Manitoba.

Irrigated potatoes are one of the most intensively managed crops in Manitoba, requiring substantial inputs of fertilizer and supplemental irrigation to maximize yield potential.  However, the influence of irrigation and 4R nitrogen practices on nitrous oxide (N₂O) emissions is not well understood. Existing studies indicate potatoes may be characterized by exceptionally high crop-specific emissions of N₂O.  In this study N₂O emissions were monitored for nitrogen fertilizer practices modifying N rate, source and placement at the Canada Manitoba Crop Diversification Centre (CMCDC) near Carberry, MB over the 2011 and 2012 growing seasons. In the first set of field trials conducted on site at CMCDC, factorial treatments of nitrogen rate (100, 200 kg ha^-1), source (urea, Environmentally Smart Nitrogen or ESN) and placement (banding, broadcast incorporated) were evaluated.  For this study increasing application rates of urea or ESN from 100 to 200 kg N ha^-1 consistently elevated cumulative N₂O emissions without impacting tuber yield.  Across both growing seasons banding of urea or ESN also reduced cumulative N₂O emissions relative to broadcast incorporation of these same N sources.  In a second set of field trials conducted off site pre-plant, at-hilling and fertigation strategies were combined to alter the proportion of N applied during the growing season.  Six fertility treatments were designed to apply a fixed rate of nitrogen (180 kg N ha^-1) at different time points throughout the growing season.  From this work split applications of nitrogen delivered at hilling or through irrigation water held greater potential for reducing cumulative N₂O emission from irrigated potatoes than did applying all urea or ESN at planting.  Averaged across field trials and site years cumulative and fertilizer-induced N₂O emissions consistently fell below current IPCC Tier II values for N₂O, suggesting emission factors for irrigated cropland in Canada may require modification.