Plausible impacts of fall manuring on cover crop production and spring nitrous oxide emissions under climate change in southern Quebec, Canada

Abstract

Climate change is expected to intensify soil freeze-thaw events in cold humid temperate regions, increasing N2O emission from agricultural soils. Establishing a cover crop that absorbs reactive N compounds from soil could reduce N2O emissions, but adding manure that contains reactive N might increase the N2O emission. The objective of this study is to estimate soil N2O emissions in the spring freeze-thaw period from agricultural soils with cover crops and fall manuring, using the DeNitrification-DeComposition (DNDC) model forced by recent-past baseline conditions (1981–2010) and by two plausible future climate scenarios (for 2071–2100). The DNDC model was calibrated and validated with data from a two-year field study (September 2017 – April 2019) in Sainte-Anne-de-Bellevue, Quebec, Canada. Climatic conditions were set with nearby meteorological station data and two bias-adjusted simulations from the CRCM5/CanESM2 climate model (one for each of the Representative Concentration Pathways 4.5 and 8.5). After validation, the DNDC model could reliably simulate many environmental properties, cover crop biomass and the temporal pattern of N2O fluxes, but overestimated the spring N2O emissions. In the future warmer climate, there was more cover crop biomass (13–40 kg N ha−1 in the RCP8.5 scenario vs. 6–17 kg N ha−1 in the baseline scenario) without additional N2O emissions from soil in the spring freeze-thaw period (3–62 g N ha−1 in the RCP8.5 scenario vs. 4–50 g N ha−1 in the baseline scenario). However, bare soil could not buffer the reactive N supplied by fall-applied solid manure, leading to higher estimated N2O emission from soils with solid manure (57–62 g N ha−1) than with liquid manure (13–18 g N ha−1) or no manure (2.6 g N ha−1) in the two future climate scenarios. Cover crops were responsible for a 2.3–5.6-fold reduction in N2O emissions, which declined to 11–27 g N ha−1 when soil received solid manure and was planted with a cover crop, compared to bare, manured soil (62 g N ha−1) under the RCP8.5 scenario. In the future, planting more fall cover crops is recommended to prevent N2O loss from agricultural soils after manure application.