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

Abstract Improving N fertilization in croplands could minimize soil emissions of nitrous oxide (N 2 O) and mitigate climate change. This study investigated the effects of spring vs. fall N applications of conventional vs. enhanced‐efficiency N fertilizers (EENFs) on N 2 O 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 N 2 O emission factor of 0.31 ± 0.04%. Irrespective of N fertilizer and timing options peak N 2 O emissions were evident following soil thawing and major rainfalls. Because most of the annual N 2 O emissions were associated with soil thawing, spring‐applied N emitted half the N 2 O of the fall‐applied N during the second study year ( P  < .001). Conversely, the opposite was observed for the first study year when overall N 2 O 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 N 2 O 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 (NH 4 and NO 3 ) and this probably moderated the beneficial effects of EENFs on N 2 O emissions and grain yields. Results suggest that spring EENFs can mitigate the risk for N 2 O emissions while sustaining high yields even under scenarios with high availability of native soil N.