The role of conservation agriculture practices in mitigating N2O emissions: A meta-analysis

Authors: LI, YUE - Northwest Agriculture And Forestry University; CHEN, JI - Aarhus University; DRURY, CRAIG - Agriculture And Agri-Food Canada; Liebig, Mark; Johnson, Jane; WANG, ZHAOZHI - Agriculture And Agri-Food Canada; FENG, HAO - Northwest Agriculture And Forestry University; ABALOS, DIEGO - Aarhus University

Submitted to: Agronomy for Sustainable Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2023
Publication Date: 9/4/2023
Citation: Li, Y., Chen, J., Drury, C., Liebig, M.A., Johnson, J.M., Wang, Z., Feng, H., Abalos, D. 2023. The role of conservation agriculture practices in mitigating N2O emissions: A meta-analysis. Agronomy for Sustainable Development. 43,63. https://doi.org/10.1007/s13593-023-00911-x.
DOI: https://doi.org/10.1007/s13593-023-00911-x

Interpretive Summary: Conservation agriculture can improve environmental outcomes, including climate change mitigation through soil carbon storage. However, less is known concerning the effects of conservation agriculture on emissions of nitrous oxide, a powerful greenhouse gas. Results from published studies were compiled and summarized to better understand how nitrous oxide emissions varied in response to three conservation agriculture practices: cover crops, diversified crop rotations, and no-till and/or reduced tillage. Averaged across all comparisons, no-till and/or reduced tillage consistently decreased nitrous oxide emissions by 11% compared to conventional tillage. Adoption of cover crops and diversified crop rotations led to variable effects on nitrous oxide emissions. Cover crops were more likely to reduce nitrous oxide emissions at near-neutral soil pH and intermediate levels of soil total nitrogen and organic carbon. Diversified crop rotations tended to increase soil N2O emissions in temperate regions and neutral to alkaline soils. Results from this analysis provide a framework to better understand environmental tradeoffs associated with the adoption of conservation agriculture practices.

Technical Abstract: Conservation agriculture is often assumed to reduce soil N2O emissions. Yet, studies analyzing the specific effect of conservation agriculture practices on N2O emissions give contradictory results. Herein, we synthesized a comprehensive database on the three main conservation agriculture practices (cover crops, diversified crop rotations, and no-till and/or reduced tillage (NT/RT)) to elucidate the role of conservation practices on N2O emissions. Further, we used a random meta-forest approach to identify the most important predictors of the effects of these practices on soil N2O emissions. Averaged across all comparisons, NT/RT significantly decreased soil N2O emissions by 11% (95% CI: –19 to –1%) compared to conventional tillage. The reductions due to NT/RT were more commonly observed in humid climates and in soils with an initial carbon content < 20 g/kg. The implementation of cover crops and diversified crop rotations led to variable effects on soil N2O emissions. Cover crops were more likely to reduce soil N2O emissions at neutral soil pH, and in soils with intermediate carbon (~20 g/kg) and nitrogen (~3 g/kg) contents. Diversified crop rotations tended to increase soil N2O emissions in temperate regions and neutral to alkaline soils. Our results provide a comprehensive predictive framework to understand the conditions in which the adoption of various conservation agriculture practices can contribute to climate change mitigation. Combining these results with a similar mechanistic understanding of conservation agriculture impacts on ecosystem services and crop production will pave the way for a wider adoption globally of these management practices.