Nitrous oxide emissions and nitrogen use efficiency in wheat: Nitrogen fertilization timing and formulation, soil nitrogen, and weather effects

Improving N fertilization in croplands could minimize soil emissions of nitrous oxide (N2O) and mitigate climate change. This study investigated the effects of spring vs. fall N applications of conventional vs. enhanced-efficiency N fertilizers (EENFs) on N2O emissions and N use efficiency in spring wheat (Triticum aestivum L.) over 2.5 yr in Alberta, Canada. Fertilizers were anhydrous ammonia and urea and the EENF formulations included urease and nitrification inhibitors and a polymer coating. We measured a fertilizer N2O emission factor of 0.31 +/- 0.04%. Irrespective of N fertilizer and timing options peak N2O emissions were evident following soil thawing and major rainfalls. Because most of the annual N2O emissions were associated with soil thawing, spring-applied N emitted half the N2O of the fall-applied N during the second study year (P < .001). Conversely, the opposite was observed for the first study year when overall N2O emissions were 36% larger for spring- than fall-applied N (P = .031) as major rainfalls occurred shortly after the spring N fertilization. Nevertheless, within this first study year, EENFs significantly reduced N2O emissions (by 26% on average; P = .019), with a tendency for 11% higher grain yield across springtime EENFs than for conventional fertilizers. Concomitantly, spring-applied N doubled the fertilizer N recovery efficiency in the same year (P = .023). The soil at the study site inherently had high N availability (NH4 and NO3) and this probably moderated the beneficial effects of EENFs on N2O emissions and grain yields. Results suggest that spring EENFs can mitigate the risk for N2O emissions while sustaining high yields even under scenarios with high availability of native soil N.

Automated summary

Spring N fertilization reduced half of N2O emissions in the second year but increased 36% in the first year compared to fall application. Enhanced-efficiency N fertilizers significantly reduced N2O emissions and increased grain yield in the first year, with spring N application doubling the fertilizer N recovery efficiency.