UC Davis

Conservation tillage has been widely adopted in agricultural lands worldwide and is considered a potential strategy for climate change mitigation through enhanced carbon sequestration. However, conservation tillage may alter soil N2O emissions, which may diminish the potential climate change mitigation benefits. Based on 212 observations from 40 publications, a meta-analysis was conducted to quantitatively assess the effects of climate regimes, initial soil properties, and type/duration of agricultural practices on soil N2O emission following application of conservation tillage. Overall, conservation tillage significantly increased soil N2O emission by 17.8% compared to conventional tillage. The greatest increase in N2O emission was observed from soils in tropical climates (70.1%) experiencing short-term (29.3%) application of conservation tillage. Soil pH and clay content significantly influenced N2O emission, while overall soil texture and soil organic carbon (SOC) were not effective predictors of soil N2O emission following conservation tillage. According to the categorical meta-analysis, agricultural practices, including water, residue, and rotation managements and crop types, significantly affected soil N2O emission following conservation tillage. Conservation tillage induced N2O emissions were mitigated with rain-fed cropping systems, residue removal, crop rotation and cultivation of beans and some vegetables. Significant categorical variables affecting N2O emission were mainly attributed to soil aeration and substrate availability, which were important factors affecting nitrification and denitrification processes. Overall, the conservation tillage induced N2O emission factor (EFad) increased by 0.40%, suggesting an attenuation of climate change benefits from increased N2O emission. Our meta-analysis provides a scientific basis for assessing the effects of conservation tillage on N2O emissions and provides site-specific information to mitigate N2O emissions associated with conservation tillage practices.