Long-term use of organic matter or rice straw with mineral fertilizer in rice fields can increase soil carbon and microbial biomass, improving soil quality and crop yields. This study compared different fertilization methods in a rice-growing area in China and found that adding organic matter or rice straw to mineral fertilizer led to higher levels of soil carbon and microbial biomass. These treatments also resulted in higher grain yields compared to using mineral fertilizer alone. This suggests that combining organic matter with mineral fertilizer can be a beneficial practice for enhancing soil health and crop productivity in double-cropping rice systems.