An evaluation of the N2O emission reduction potential of enhanced efficiency nitrogen fertilizers and application timing in a semi-arid cereal cropping system.

Efforts to cut fertilizer-related nitrous oxide (N2O) emissions require sustainable nitrogen (N) management that maintains crop productivity while reducing emissions. Technologies such as enhanced efficiency N fertilizers (EENFs) have potential to support best management practices by improving N use efficiency and lowering N2O emissions. This study (i) evaluated the effects of spring versus fall application of conventional urea and EENFs, including a polymer-coated urea (PCU; ESN), a nitrification inhibitor (NI; eNtrench), a dual urease inhibitor (Limus), and a urease and nitrification inhibitor (UNI; SuperU), on N2O emissions from spring wheat over two growing seasons in central Saskatchewan and (ii) compared soil nutrient supply rates among conventional urea and the EENFs to determine whether soil N dynamics reflected their differing modes of action. Results indicate that significant N2O emissions reductions can be achieved in rainfed cropping systems by using a urea-based EENF without crop yield penalties. In general, the greatest emissions reductions were achieved using EENF products that employ an NI; both the NI and the UNI reduced annual cumulative N2O emissions relative to urea by 8%-54% and 36%-64%, respectively (p < 0.05). Conversely, emissions from the PCU trended higher by 17%-41% relative to conventional urea, except when spring-applied in Year 1, when PCU reduced N2O emissions relative to urea. Across all treatments, spring N fertilizer applications led to the greatest N2O emissions reductions with EENFs compared to fall N fertilizer applications. Overall, NI-based EENFs show potential for reducing N2O emissions while maintaining wheat yields in Saskatchewan.