Impacts of enhanced efficiency nitrogen fertilizer type and application timing on N2O emission reductions in irrigated wheat fields

Abstract

Context Irrigation increases crop productivity but may also increase emissions of nitrous oxide (N 2 O), a potent greenhouse gas and stratospheric ozone-depleting substance, partly due to the higher nitrogen (N) fertilizer inputs often required. However, there is a paucity of field data from the Canadian Prairies evaluating the effectiveness of enhanced efficiency nitrogen fertilizers (EENFs) under irrigated conditions, despite the importance of this region to Canadian agriculture. Here we evaluated the efficacy of several EENFs and application timing (fall vs . spring) for mitigating N 2 O emissions in a semi-arid irrigated spring wheat cropping system, with the goal of generating field-based evidence to support mitigation recommendations and to contribute to the development of regionally relevant EFs. Methods The study was conducted over 2.5 years in the Dark Brown Soil Zone of Saskatchewan using a randomized complete block design. Conventional granular urea was compared to a controlled release polymer-coated urea (PCU), urea with a nitrification inhibitor (NI; nitrapyrin), urea with dual action urease inhibitors (UI; N-(butyl) thiophosphoric triamide [NBPT] + N-(propyl) thiophosphoric triamide [NPPT]), and urea with both a urease inhibitor (NBPT) and an NI (UNI; dicyandiamide [DCD]). Emissions of N 2 O were measured using non-steady state vented chambers and soil N dynamics were monitored using Plant Root Simulator (PRS)® probes. Results PRS® probe measurements of nitrate (NO 3 ⁻) and ammonium (NH 4 ⁺) supply rates confirmed the expected effects of EENFs on soil N transformations. The PCU, UNI, and UI modulated NH 4 + supply compared to urea, whereas the EENFs with an NI (NI and UNI) modulated NO 3 - supply. Both NI-containing EENFs reduced cumulative and fertilizer-induced N 2 O emissions by 50–80% and 77–83%, respectively, with the greatest reductions occurring when spring-applied. The UI showed inconsistent effects, reducing N 2 O by 43–74% only when spring-applied. No yield differences were observed among treatments. Conclusions Applying a urea-based fertilizer with an NI substantially reduced N 2 O emissions from a semi-aridirrigated spring wheat cropping system regardless of application timing, without increases in crop yield. Thus, mitigating N losses as N 2 O and modifying soil mineral N dynamics did not translate into greater crop productivity. Implications These findings underscore the importance of integrating regionally-tailored fertilizer source and timing within the 4 R Nutrient Stewardship framework best management practices (BMPs) and demonstrate the potential of EENFs to mitigate N 2 O emissions in irrigated cropping systems in semi-arid cereal cropping systems.

The authors' abstract, as published at the source. Field Crops Research, 2026 · DOI ↗