Biochar-amended soil can further sorb atmospheric CO2 for more carbon sequestration

Input of biochar into soil is considered as an efficient technology for carbon sequestration. This work is aimed to explore if the extra sorption of carbon dioxide (CO2) exists in the biochar-amended soil, which has not yet received attention. Here we put biochar and mineral-rich biochar into soils to perform laboratory CO2 sorption experiments. Our results demonstrate that all biochars increased soil carbon storage and meanwhile further sorb CO2 for more carbon sequestration. The calcium or magnesium-rich biochar could react with more CO2 and eventually be converted into inorganic carbonate minerals in soils. Further, the country-level prediction showed that all cultivated topsoils with biochar application in China could achieve 7.38-12.5 billion tons of carbon sequestration and an additional 0.34-2.66 billion tons of CO₂ sorption. The results require us to take into consideration of both carbon sink and extra CO2 sorption in the assessment of biochar carbon sequestration potential in soil.