A meta-analysis of conservation tillage management effects on soil organic carbon sequestration and soil greenhouse gas flux.

Conservation tillage practices, including reduced tillage (RT), no-tillage (NT) and straw return (SR), have been widely adopted to enhance soil organic carbon density (PSOC) and improve the soil quality while mitigating the negative environmental impacts of intensive farming. However, current studies on the effects of these practices on SOC sequestration and NO flux show considerable variability, making it challenging to draw definitive conclusions about the individual and combined impacts of conservation tillage practices and introducing substantial uncertainty in estimating the agricultural sector's potential to mitigate climate change. To address this gap, we conducted a meta-analysis of 902 pairwise comparisons from 90 peer-reviewed publications to evaluate the effects of five conservation tillage practices (straw return (SR), reduced tillage (RT), no-tillage (NT), straw return combined with tillage reduction (SR + RT) and straw returning combined with no-tillage (SR + NT)) on C sequestration and NO emissions from agricultural soils. The results show that SR was the most effective practice for increasing SOC content (23.7 %), followed by RT + SR (5.5 %) and NT + SR (4.4 %). Additionally, RT (12.3 %) and NT (14.3 %) significantly reduced soil NO emissions. This study also identified key drivers, including climatic factors, soil properties, and agricultural management practices, that influence SOC content and NO emissions under different conservation tillage practices. For example, the mean annual precipitation, mean annual temperature, soil type, pH, soil total nitrogen content, N application rate, and experiment duration were identified as the key factors affecting SOC content and NO emissions Specifically, suitable temperature, lower rainfall and alkaline soil environment significantly enhanced the C sequestration efficiency of SR, while suitable climatic conditions and soil texture combined with an alkaline environment contributed to a significant reduction in long-term NT soil NO emissions. These results provide a robust scientific foundation for the strategic implementation of conservation tillage to reduce greenhouse gas emissions, mitigate global warming, and enhance soil C sequestration capacity.