Evaluation of long-term carbon sequestration of biochar in soil with biogeochemical field model

Return of biomass-derived biochar (BC) into soil has been considered as one of the carbon sequestration (CS) methods. It is important to evaluate the long-term biochar CS potential by integrating the complex physical interferences and biochemical reactions in real soil. This study incorporated biochar into a biogeochemical field model and established a daily-resolution simulator to assess 5-, 50-, 500-year CS potential upon Soil-Biochar-Plant interaction. Through the scenario simulation of burying 7.5-75 t/ha BC-C in a 50 cm-depth rainfed cropland soil with corn planted, we found biochar could retain 483-557 kg C/t BC-C after 500 years' natural decomposition, although soil pedoturbation and plant erosion accelerated its mineralization. Moreover, biochar provided labile-C to compensate microbial decom-position and modified long-term soil climate, resulting ina decrease in soil organic carbon degradation of 44-265 kg C/t BC-C. Furthermore, biochar promoted plant photosynthetic performance by offering exogenous nutrients, equiva-lent to capturing 66-1039 kg C/t BC-C over 50 years. But biochar limited endogenous nutrient release and inhibited plant growth after exogenous nutrients exhausted, so total CS decreases yearly after reaching an upper limit (1030-1722 kg C/t BC-C). A total of 651-725 kg C/t BC-C could be sequestered after 500 years. And biochar is more potential in infertile and arid soils. Overall, this study indicates the necessity of taking the biogeochemical reac-tions into consideration to assess biochar long-term CS, and it further demonstrates biochar soil implementation is a prospective carbon-negative strategy.