Emission of CO2 from biochar‐amended soils and implications for soil organic carbon

Abstract Soil amendment with pyrogenic organic matter (Py OM ), also named biochar, is claimed to sequester carbon (C). However, possible interactions between Py OM and native soil organic carbon ( SOC ) may accelerate the loss of SOC , thus reducing Py OM 's C sequestration potential. We combined the results of 46 studies in a meta‐analysis to investigate changes in CO 2 emission of Py OM ‐amended soils and to identify the causes of these changes and the possible factors involved. Our results showed a statistically significant increase of 28% in CO 2 emission from Py OM ‐amended soils. When grouped by Py OM C (PyC): SOC ratios, the group of studies with a ratio >2 showed a significant increase in CO 2 emissions, but those with a ratio <2 showed no significant effect of Py OM application on CO 2 emission. Our data are consistent with the hypothesis that increased CO 2 emission after Py OM addition is additive and mainly derived from Py OM 's labile C fractions. The PyC: SOC ratio provided the best predictor of increases in CO 2 production after Py OM addition to soil. This meta‐analysis highlights the importance of taking into account the amount of applied PyC in relation to SOC for designing future decomposition experiments.