OOS 12-4 - Effects of climate-smart agricultural practices on crop yield and greenhouse gas nitrous oxide emission: Meta-analyses

Croplands are considered biogeochemical hotspots of greenhouse gas N2O emissions. In order to increase crop yield while reducing greenhouse gas emissions, climate-smart agriculture practices such as no-tillage, cover crop, and biochar applications have been widely implemented. Meta-analysis has been used to synthesize the impacts of biochar application, cover crop, and no-tillage on crop yield and soil N2O emission, but the results among different meta-analyses are not conclusive. In this study, we evaluated these meta-analyses and conducted mega-analyses (meta-meta-analyses) to generate grand mean response ratios (RRs) of climate-smart agricultural practices. For biochar application, we found that 18 meta-analysis papers investigated its impact on soil N2O emission, four meta-analyses did not find a significant effect of biochar application on soil N2O emissions, and 14 meta-analyses reported reductions of soil N2O emissions from 10.5% to 54.8%. Results of this mega-analysis showed that biochar application overall reduced the soil N2O emissions by 38.8%. No-tillage systems tended to increase crop yield and soil N2O emission but reduce CO2 and CH4 emissions. Cover crop increased soil CO2 emission but had different impacts on soil N2O emission depending on management practices and soil texture. This study demonstrated that mega-analysis could be more accurate and representative than single meta-analysis. Potential benefits, limitations, and further research direction were discussed.