Abstract:Based on the long-term(18 years) field experiment in Zunyi of Guizhou Province, the effects of three different fertilization modes (no fertilization, chemical fertilizer alone, combined chemical and organic fertilizers) under two cropping systems (tobacco-maize rotation and continuous tobacco cultivation) on soil organic carbon (SOC) components, enzyme activities and carbon pool management index (CPMI) were investigated in order to explore carbon transformations in tobacco-planting soils and provide scientific management strategies for soil carbon. The results showed that under the same cropping system, combined chemical and organic fertilizers increased total soil organic carbon (TOC) content by 5.65%–12.13%, among them, light fraction organic carbon (LFOC), dissolved organic carbon (DOC) and readily oxidizable organic (ROC) increased by 23.33%–28.71%, 24.46%–25.54%, and 10.26%–18.99%, respectively. The CPMI also increased by 12.89%–23.34%. The activities of soil cellulase, β-glucosidase, amylase, peroxidase and invertase were significantly enhanced and were positively correlated with contents of SOC components and CPMI (0.59*–0.97**,n=18). Under the same fertilization conditions, SOC content, enzyme activities, and CPMI under the rotation were 6.14%–23.51%, 9.00%–37.92%, and 4.74%–14.44% higher than those under the continuous cropping system. In conclusion, tobacco-maize rotation with organic plus inorganic fertilizer application can not only significantly increase SOC and CPMI, but also enhance soil microbial biomass and labile organic carbon, which is of great importance for improving soil fertility and sustaining soil productivity.