RESUMO
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.