Soil-Atmosphere Exchange of Carbon, Nitrogen and Methane in Croplands: A Synthesis of Field Evidence

Abstract

Cropland soils are central to climate mitigation because they can store additional soil organic carbon while simultaneously emitting nitrous oxide and methane. Over the past decade, numerous field experiments and global syntheses have quantified how widely promoted practices—such as conservation tillage, residue retention, cover cropping, organic amendments and biochar, and water-saving irrigation in rice—shape these three components of the soil greenhouse-gas balance. This article presents a systematic tri-gas review, second-order meta-synthesis of recent field-based meta-analyses and large multi-site experiments to evaluate mitigation trade-offs and co-benefits across soil organic carbon stocks, nitrous oxide emissions, and methane fluxes in croplands. The compiled evidence shows that conservation tillage combined with residue retention frequently increases soil organic carbon in surface layers, but associated changes in nitrous oxide are small, inconsistent, or even positive in humid, fine-textured soils. Cover crops and diversified rotations generally deliver modest soil carbon gains and agronomic co-benefits, yet their effects on nitrous oxide range from mitigation to exacerbation, depending on climate, soil properties, species choice, and nitrogen management. In flooded rice systems, alternate wetting and drying and related water-saving regimes consistently reduce methane emissions and often maintain yields, but their impact on nitrous oxide is highly variable and sensitive to fertiliser timing and rate. Biochar and carefully managed organic amendments emerge as among the few interventions that frequently increase soil organic carbon while reducing nitrous oxide across a range of conditions, although their effects on methane are more context dependent. Overall, the synthesis confirms that no single practice provides universal “win–win” mitigation across all gases and regions. Rather, the greatest and most reliable climate benefits arise from management portfolios that combine carbon-building practices with explicit nitrogen management and, in flooded systems, tailored water control, thereby aligning soil-based mitigation with productivity and resilience objectives.