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

Soil amendment with pyrogenic organic matter (PyOM), also named biochar, is claimed to sequester carbon (C). However, possible interactions between PyOM and native soil organic carbon (SOC) may accelerate the loss of SOC, thus reducing PyOM?s C sequestration potential. We combined the results of 46 studies in a meta-analysis to investigate changes in CO2 emission of PyOM-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 CO2 emission from PyOM-amended soils. When grouped by PyOM C (PyC):SOC ratios, the group of studies with a ratio >2 showed a significant increase in CO2 emissions, but those with a ratio