Placement and nitrogen source effects on N 2 O emissions for canola production in Manitoba

This study examined fertilizer nitrous oxide (N 2 O) emissions and canola ( Brassica napus L.) grain yield for two granular urea sources (conventional and a dual urease and nitrification inhibitor [SuperU]) and three at‐planting placement methods (broadcast‐incorporated, shallow banded, and deep banded) on commercial fields in Manitoba. Nitrogen (N) rates were 100% and 70% of what was recommended based on soil test and target yield, with the 100% treatments having N 2 O emissions monitored. SuperU fertilizer consistently reduced N 2 O emissions (area‐, N‐applied‐, and yield‐based) compared to urea. Significant reductions in N 2 O emissions with SuperU occurred in four of six site‐years and coincided with delayed nitrification. Compared to broadcast‐incorporated, subsurface banding of conventional urea reduced N 2 O emissions in drier site‐years but increased emissions when rainfall was higher (especially in shallow banded urea). Across all six site‐years, shallow banding of urea resulted in significantly higher emission intensities than all other treatments. Nitrogen placement did not affect the emission reduction benefit of SuperU. N source or placement did not greatly affect canola yield within either 100% or 70% N rates. Fertilizer N recovery efficiency was also not greatly impacted by either N source or placement. The results demonstrate that dual inhibited granular urea fairly consistently reduces N 2 O emissions in canola production in southern Manitoba, whereas nitrogen placement had variable effects depending on growing season rainfall. However, with little agronomic benefit, the added cost of enhanced efficiency fertilizers must be overcome for widespread adoption and to achieve greenhouse gas reduction targets for the Canadian agriculture sector. N 2 O emissions could have been reduced using a more realistic yield goal and thus lower N rates. SuperU fertilizer reduced N 2 O emissions compared to urea. Subsurface banding of urea reduced emissions in drier years but increased them in wetter years. Shallow subsurface banding urea tended to increase emissions. SuperU mitigated emissions with shallow banding.