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 N 2O emissions. This study investigated the effects of ESN and weed management on N 2O 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 N 2O 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, N 2O fluxes were similar among all treatments for all three years and three sites. The N 2O fluxes also varied over the growing season, and peak flux occurred in response to rainfall events. Similarly, cumulative N 2O 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 N 2O 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 N 2O 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 N 2O 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 N 2O emissions in Alberta, Canada, but reductions will depend on rainfall events and canola N utilization.