Performance Story: Can enhanced efficiency N fertilizers mitigate against N losses in single-pass seeding operations?
Results from this study indicate that significant N2O emissions reductions can be achieved in both rainfed (nonirrigated) and irrigated cropping systems by using a urea-based EENF. In general, the greatest emissions reductions were achieved using stabilized N products that employ a nitrification inhibitor to delay the oxidation of NH4 + to NO2 – by inhibiting the activity of nitrifying bacteria in the soil. Indeed, products employing a nitrification inhibitor either alone (eNtrench) or in combination or with a urease inhibitor (SuperU) yielded the most consistent results; i.e., they produced the greatest emissions reductions regardless of application timing (fall vs. spring) or cropping system (rainfed vs. irrigated). Product that employed a urease inhibitor alone (Limus) yielded significant emissions reductions, but only when applied in the spring. The polymer-coated urea (ESN) was the least effective at reducing N2O emissions, though significant emissions reductions were observed with ESN following the spring application in 2016—with emissions reductions at both the rainfed and irrigated sites, which suggests that this was not a “random” effect. Regardless of absolute magnitude, N2O emissions reductions were greatest when the EENFs were applied in the spring.
Total and fertilizer-induced N2O emissions were greater at the irrigated site than at the non-irrigated site. Emissions from the check (non-fertilized) plots also were greater at the irrigated site—indicating that differences between the site were not just a function of the higher N rates applied at the irrigated sites. That is, when taking Page 35 of 39 these differences into account, fertilizer-induced emissions—both total and as a percentage of the applied N—for the conventional N products (i.e., urea and anhydrous ammonia) were greater under irrigation than under rainfed conditions. This suggests that long-term irrigation may “prime” the soil for enhanced N2O production; i.e., over the long term, irrigated fields receive more water, nutrients, and residue inputs than non-irrigated fields, which is likely to alter the soil microbial community structure and activity and, in turn, the rates and magnitudes of N transformations—including nitrification and denitrification potential. Given the greater potential for N2O production/emission at the irrigated sites, it was not surprising that the EENFs tended to be more effective (i.e., produce larger emissions reductions) at these sites.
Current climate models predict a warming and more variable climate in Prairie Canada, which could increase the frequency, duration, and spatial extent of freeze-thaw events in cold climate regions such as Saskatchewan. Nevertheless, given the economics and convenience of fall applications, producers are likely to continue the practice. Data from the present study, together with our previous research, strongly suggests that N2O losses associated with fall N applications are dependent on antecedent (fall) soil moisture conditions. However, our data also demonstrate that there are real opportunities to significantly reduce N2O emissions from a fall N application by replacing conventional granular urea (or anhydrous ammonia) with an enhanced efficiency product-and specifically, one that employs a nitrification inhibitor. As well, it remains to be seen whether the use of an EENF can extend the safe application window for a fall N application.