There is an ever increasing need to identify practical tools that Saskatchewan producers can employ to help them to maintain or improve yields while simultaneously reducing nitrous oxide (N₂O) emissions; and to be able to quantify those benefits in a credible, verifiable manner. Urea impregnated with a Dual-Inhibitor (urease plus nitrification inhibitors) has been shown to have excellent potential for reducing fertilizer-induced N₂O emissions compared to urea and has also been promoted as having “enhanced efficiency” attributes, suggest that it could be applied at lower rates than urea while achieving comparable yields greater N₂O emissions reductions. This project was intended to address three questions: 1) Can a dual-inhibitor nitrogen (N) product be applied at a reduced N-rate as compared to Urea while maintaining equivalent yield? 2) How much can the application rate of a Dual-Inhibitor N product be reduced before negatively impacting yield relative to a recommended application rate of Urea? 3) What is the maximum N₂O reduction that can be achieved with an Dual-Inhibitor N fertilizer while maintaining crop yields equivalent the recommended rate of urea?

A canola-wheat sequence was established with both phases being present each year at two study sites – Melfort and Saskatoon. The N-fertilizer products were banded at planting in the spring. Nitrogen application rates of Urea and the Dual-Inhibitor N fertilizer were calculated using the formula “fertilizer N to be applied = total N required – soil N available” where “total N required” was based on the amount of crop available N required to achieve a target yield and “soil available nitrogen” was determined from soil samples collected and analyzed prior to seeding. Four N application rates were established, one at 100% of the calculated “fertilizer N rate” or “recommended rate”, and three other rates calculated to be 90%, 80% and 70% of the recommended rate. The Dual-Inhibitor was applied at N rates that exactly matched the Urea application rates. Soil-emitted N₂O fluxes was measured using manually sampled non-steady state vented chambers. Other measurements included grain and straw yield, crop N uptake, and soil mineral N status. This allowed the calculation of fertilizer-N use efficiency metrics, per area cumulative N₂O emissions, fertilizer-induced N₂O emission coefficients, fertilizer-induced N₂O reduction coefficients, as well as yield-scaled N₂O emissions.

Reducing the N-application rate did not result in statistically significant seed yield decreases until the rate was reduced to 70% of recommended rate. Treatment responses of N uptake, whether assessed as seed-N, straw-N or total N (seed-N + straw-N) generally paralleled those of seed yield. Calculations of agronomic efficiency (AE) and fertilizer recovery efficiency (FRE) returned consistent results for treatments receiving Urea with best AE and FRE values occurring at the 70% application rate – regardless of crop, site or year, while best AE and FRE on treatments receiving the Dual-Inhibitor product were more or less equally distributed between the 70%, 80% and 90% application rates. In general, application of both N-sources significantly increased N₂O emissions compared to the check (no N applied), but emissions from the Urea treatments were significantly higher than emissions from the Dual-Inhibitor treatments. Comparing emissions from the 100% Urea application treatment to emissions on the Dual-Inhibitor treatments showed reductions of between 13% and 80%, with the greatest reductions typically realized at the 70% N application rate. The best yield-scaled values (unit of emissions per unit grain produced) were most frequently realized at the 70% or 80% application rate for both Urea and the Dual-Inhibitor treatments. Based on results from this study, we would conclude that a 20% reduction in application rate with a dual-inhibitor N fertilizer could achieve maximum N₂O emissions reductions, ranging from at least 30% to as high as 79%, without incurring a statistically significant seed yield penalty.

• Greenhouse gas (GHG) emissions have become a key sustainability metric for agricultural products and an important consideration in the marketplace. Thus, there is an ever increasing need to identify sustainable fertilization practices that Saskatchewan producers can employ to help them to maintain or improve yields while simultaneously reducing N₂O emissions; and to be able to quantify those benefits in a credible, verifiable manner.
• The results of this study confirmed that nitrous oxide emissions from fertilizer use can be substantially reduced by employing a product that combines urea with a dual-inhibitor (urease and nitrification inhibitors) compared to urea at equivalent rates of N application.
• Further nitrous oxide emissions reductions can be achieved by reducing the application rate of a dual-inhibitor product. Deepest reductions, up to 80% lower than emissions from urea at the recommended rate, were achieved when the dual-inhibitor application rate was reduced by 30% compared to the recommended rate. However, although infrequent, statistically significant seed yield reductions were observed at the 30% N application rate.

Based on results from this study, we would conclude that a 20% reduction in application rate with a dual-inhibitor product could achieve maximum emissions reductions, ranging from at least 30% to as high as 79%, without incurring a statistically significant seed yield penalty