Global patterns and controls of soil greenhouse gas fluxes and crop yield under biochar application

Biochar application has been proven to be a viable technique in mitigating soil greenhouse gas (GHG) emissions and improving crop yield; however, the global patterns and responses of soil GHG fluxes, global warming potential (GWP), crop yield, and greenhouse gas intensity (GHGI) to biochar application, as well as the key drivers of biochar-induced changes, are not fully synthesized. Hence, we conducted a meta-analysis of 3883 paired observations from 220 studies. Overall, biochar application significantly increased carbon dioxide (CO2) emissions (7.4%) and yield (9.4%) and decreased soil methane (CH4, -13.0%) and nitrous oxide (N2O, -26.8%) emissions, as well as GWP (-7.7%) and GHGI (-14.3%). CH4 uptake was, however, not observed to change. The responses of soil GHG fluxes to the biochar application were more sensitive in the incubation and pot experiments compared to the field studies. In addition, increased CO2 emissions were mainly derived from incubation and pot experiments, whereas the biochar application did not significantly change CO2 emissions in the field studies. The climate, soil, and experimental conditions also affected the responses of soil GHG fluxes to biochar application, and the biochar-induced change in soil pH was the most essential factor associated with the variations in soil GHG fluxes. Globally, biochar application boosted the soil carbon (C) pool (38.1% in upland and 33.4% in paddy) and decreased soil GHGI (-18.7% in upland and -14.5% in paddy). Our study highlights the role of the reduced CH4 and N2O emissions in the biochar-induced mitigation of soil GHG emissions while exploring the relative importance of the influencing factors and providing crucial insights for the development of individualized biochar management measures.