Abstract: Farming system plays an important role in soil organic carbon stability and accumulation. To study soil carbon dynamics of farming system evolution will contribute to farming technology selection and incentive policy making for carbon sequestration in agricultural soils. Therefore, some publisheddata from longterm field experiments were used to construct assessment model of the change in soil organic carbon density induced by conservational farming systems in paddy fields in Yangtze Delta Plain. In addition, soil carbon sequestration effects of conservational farming systems were primarily assessed based on the change of the farming system in the past 20 years in this region. Results showed that the increase in sown oilseed rape area,reducedtillage wheat area and straw application area had rises in organic carbon being about 0.94 Tg, 2.76 Tg and 3.95 Tg in surface soils (15 cm), respectively. The highest effect of carbon sequestration occurred under the transformation of wheatrice system to oilseed raperice system. Finally, the assessment method was discussed, and some recommendations were put forward for carbon sequestration research and to improve soil carbon sequestration potential.

Key words: Yangtze Delta Plain, conservational farming system, soil organic carbon, carbon sequestration, global change