Biochar increased field soil inorganic carbon content five years after application

Soil inorganic carbon (SIC) plays an important role in terrestrial ecosystem carbon cycling, especially in arid and semi-arid areas. Biochar has becoming a great of interest as a mean for carbon sequestration, resulting from its high content of carbon and long-term persistence in soil. Moreover, there is abundance of information about the effect of biochar on the turnover of soil organic carbon; however, up to date, no study has been done on the impact of biochar on soil inorganic carbon pool despite biochar contains inorganic carbon. This study was conducted in a long-term field condition to investigate the effect of different biochar application rates (0, 30, 60 and 90 t ha^-1) on soil inorganic carbon content and composition in the soil profile (0-100 cm). Using stable δ¹³C isotope signatures, the SIC was distinguished into lithogenic and pedogenic inorganic carbon. The results showed that long-term biochar application, at 30, 60 and 90 t ha^-1, increased soil total inorganic carbon by 18.8, 42.4 and 62.3% and native soil inorganic carbon by 7.8, 20.2 and 28.3%, respectively, in the 0-20 cm soil layer. Biochar application at these rates also increased total inorganic carbon in the 20-40 cm soil layer by 13.4, 22.8 and 30.5%, respectively, but did not influence the total inorganic carbon content below the 40 cm soil depth. Moreover, as biochar application rate increased, δ¹³C of native soil inorganic carbon decreased, which indicated that pedogenic inorganic carbon was formed. Biochar application rates were positively related to the pedogenic inorganic carbon contents, however, it did not influence the lithogenic inorganic carbon contents. This is the first study about the effect of biochar application on native inorganic carbon content and its composition, which strengthens the understanding about the role of biochar in soil C sequestration.