Improved nitrogen fertilizer management reduces nitrous oxide emissions in a northern Prairie cropland

Arable croplands are a significant source of nitrous oxide (N₂O) emissions, largely due to nitrogen (N) fertilizer applications to support crop production. Nevertheless, there is limited research on the N₂O dynamics from canola-wheat rotations in the semi-arid northern Prairies, an important agricultural region. Here, we present micrometeorological N₂O fluxes measured from January 2021 to April 2024 in Saskatchewan, Canada, to evaluate the impact of N fertilizer management on the year-round N₂O emissions from a canola-wheat rotation. A combination of two 4R (Right Source, Right Rate, Right Time, Right Place) N management practices - a reduced N rate and an enhanced efficiency N fertilizer source - was compared to common fertilizer management practices for the region. Two periods at high risk for N₂O flux events were identified, after N fertilizer applications and the following spring thaw, with the magnitude of emissions varying over the multi-year period. As for cumulative emissions, the growing season (GS) N₂O emissions were 50 % of annual emissions, presenting an opportunity to mitigate N₂O emissions through improved N fertilizer management. Indeed, the improved 4R N management reduced N₂O emissions by 57 % over the entire study period without impacting yields. The reduction in GS N₂O emissions resulted from the 4R N management lowering mean N₂O flux at times of high WFPS (>50 %). The non-growing season (NGS) N₂O accounted for 11-67 % of annual emissions. Fall soil nitrate levels were a strong explanatory variable of NGS emissions (r² = 0.69, r² = 0.39), but the rate of change and magnitude of NGS emissions depended on thawing conditions - lower for drier thaws, higher for wetter thaws. Ultimately, better N fertilizer management reduces cumulative N₂O emissions from cropping systems when practiced for several years.