Soil nitrous oxide emissions from wheat-based rotations with different types of pulse crops

Production of agricultural crops with a low greenhouse gas (GHG) footprint is essential to mitigate the adverse effects of climate change. The inclusion of pulse crops in cereal-based rotations can enhance environmental quality by providing biologically fixed N and thereby reducing the amount of synthetic N fertilizer required for the crop rotation. The inclusion of pulse crop has the potential to reduce N₂O emissions from the agricultural system in both the legume phase and the subsequent wheat phase of the rotation. However, long-term studies are necessary to thoroughly investigate N₂O emissions from rotations with pulse crops, particularly in the semiarid region where pulse crops are frequently grown. In the present study, we evaluated cumulative N₂O emissions and emission intensity during the rotation cycle. The assessment was conducted over 4 years, during two complete 2-yr cycles of an established rotation (years 9-12), under the climatological conditions of 2018-2021. Four rotations including wheat-wheat, pea-wheat, lentil-wheat, and chickpea-wheat were selected from a trial in Swift Current, Saskatchewan (semiarid prairies/Brown Chernozem). Our experiment was subjected to below normal precipitation, with interannual variations in climate and the last 2 years (2020-21) were drier than the first two years (2018-2019). Under such climate, PW and LW demonstrated to be environmentally sustainable, always exporting the highest N in grains (133 kg N ha^-1 averaged across PW and LW and cycles) and consistently achieving the lowest N₂O intensity (2.8 g N₂O-N per kg exported N averaged across PW and LW and cycles). Continuous wheat presented inconsistent results, with a significant reduction in exported N from years 9-10 to 11-12 (the driest cycle). Because WW also promoted the highest cumulative N₂O emissions, N₂O intensity over the 2-yr was always the highest for WW. The CW consistently promoted the lowest N exports and was not resilient to dry soil conditions, with 23% lower exported N in years 11-12 than in years 9-10. Hence including pulse crops with pea or lentil in the rotation reduced N₂O emissions and enhanced wheat yield resiliency.