Abstract: Based on the organic carbon data of 222 topsoil samples taken from 38 paddy field experiment sites in South China, calculations were made on the relative annual change of topsoil organic carbon content (RAC) and carbon sequestration duration in the paddy fields in South China under five fertilization modes (inorganic nitrogen fertilization, N; inorganic nitrogen and phosphorus fertilization, NP; inorganic nitrogen, phosphorus, and potassium fertilization, NPK; organic fertilization, O; and inorganic plus organic fertilization, OF). The RAC under the fertilizations was 0-0.4 g·kg^-1·a^-1, with an increment of 0.20 and 0.26 g·kg^-1·a^-1 in double and triple cropping systems, respectively. The RAC was higher in treatments O and OF than in treatments N, NP, and NPK, being the highest (0.32 g·kg^-1·a^-1) in treatment OF. The topsoil organic carbon accumulation rate decreased with increasing time, and the carbon sequestration duration in treatments N, NP, NPK, O, and OF was about 22, 28, 38, 57, and 54 years, respectively. Inorganic plus organic fertilization was the most effective practice for soil carbon sequestration in the paddy fields in South China.

Key words: paddy field, fertilization, soil organic carbon, carbon sequestration