Nitrous oxide emissions in response to ESN and urea, herbicide management and canola cultivar in a no-till cropping system
Abstract Environmentally Smart Nitrogen (ESN), a type of polymer-coated urea, synchronizes N release with crop demand to increase N use efficiency and potentially reduce N2O emissions. This study investigated the effects of ESN and weed management on N2O emissions from soil under a canola (Brassica napus L.) no-till cropping system. The experiment was conducted from 2005 to 2008 at three sites: Lethbridge, Lacombe, and Beaverlodge, located in southern, central and northern Alberta, Canada. Treatments included a hybrid and an open-pollinated canola cultivar, with ESN and urea applied at 1 and 1.5 times (×) the recommended rate, and herbicide at 50 and 100% of registered in-crop application rates. Canola was grown in rotation with barley (Hordeum vulgare L.) and both phases of crop rotation were present each year. The N2O fluxes from soil were measured using vented static chambers at 2-week intervals during the growing season from 2006 to 2008. Except for a few occasions with higher fluxes from urea than ESN earlier in the growing season and higher fluxes from ESN than urea later on, N2O fluxes were similar among all treatments for all three years and three sites. The N2O fluxes also varied over the growing season, and peak flux occurred in response to rainfall events. Similarly, cumulative N2O emissions, expressed as either per land area or per canola seed yield, over the three growing seasons were low (0.15–2.97 kg N ha−1 yr−1 or 0.05–1.19 g N kg−1 seed) for all treatments and sites, and unaffected by weed management or crop variety (P > 0.05). The N2O emission across the three sites from ESN averaged 20% lower (P = 0.040) than from urea although the differences between fertilizer types or application rates were not significant (P > 0.05) at each site. Elevated N2O emissions (72% higher; P = 0.028) from 1.5 × ESN (0.83 kg N ha−1 yr−1 or 0.33 g N kg−1 seed) relative to 1 × ESN (0.26 kg N ha−1 yr−1 or 0.16 g N kg−1 seed) were only observed at Beaverlodge while emissions were similar (P > 0.05) at the other two sites. The higher N2O emissions at 1.5 × ESN at Beaverlodge were due to excess N accumulation in soil caused by unfavourable weather conditions that reduced canola N uptake and yield. Our results suggest that ESN fertilizer could reduce N2O emissions in Alberta, Canada, but reductions will depend on rainfall events and canola N utilization.