Soil organic carbon (SOC) plays a crucial role in plant nutrient supply and soil physical, chemical, and biological function regulation. Factors such as climate change, human activities, and farm management practices can adversely affect SOC. Here, paddy soil in the double-cropping rice area of Hunan Province of China was cultured with eight kinds of organic materials, and the effects of organic fertilization on SOC content, humus content, and soil carbon sequestration efficiency were analyzed. The addition of straw, green fertilizer, and organic fertilizer had a positive influence on active SOC content. Straw addition had the most prolonged impact on soil microbial biomass carbon content, and green manure had the most rapid influence on soil dissolved organic carbon content. All organic materials enhanced the soil humus content
furthermore, the addition of organic fertilizers significantly improved the carbon sequestration efficiency among all treatments. The results of controlled culture experiments in paddy soils established that applying organic materials can increase SOC content, active carbon components, soil humus content, and the carbon fixation rate, thereby improving soil fertility. This study provides a theoretical basis for the optimal fertilization of paddy soil with organic material addition in China.