Abstract:A long-term field experiment was conducted to study the effects of different combination proportions of organic and inorganic fertilizers on the contents of soil organic carbon fractions in tobacco-planting yellow soil. The results showed that compared with CK, long-term combined application of organic and inorganic fertilizers increased soil total carbon and active organic carbon pool, but did not reach significant level. Compared with the treatment with chemical fertilizer only, the treatment with organic fertilizer providing 70% nitrogen and chemical fertilizer providing 30% nitrogen increased significantly the contents of dissolved organic carbon, microbial biomass carbon, light fraction organic carbon and particulate organic carbon by 61.19%, 96.03%, 52.17% and 33.55%, respectively. The treatment with organic fertilizer providing 30% nitrogen and chemical fertilizer providing 70% nitrogen increased significantly the content of dissolved organic carbon, microbial biomass carbon, light fraction organic carbon and particulate organic carbon, but no significant increase was found in these active organic carbon fraction with continuous increasing organic fertilizer input. Therefore, the treatment with organic fertilizer providing 70% nitrogen and chemical fertilizer providing 30% nitrogen is the optimal to improve the fertility of tobacco-planting yellow soil and to promote the yield and quality of tobacco, which is also important to guarantee the sustainable development of tobacco production.