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

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^–1. 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^–1) and nitrogen (~3 g kg^–1) 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.