A study in subtropical China looked at how different fertilizers affect the amount and quality of carbon and nitrogen in paddy soil. They tested four types of fertilization over many years and found that using organic manure, with or without chemical fertilizers, increased the levels of organic carbon and nitrogen in the soil. This means that adding organic manure to the soil can help improve its health and fertility, which is important for growing crops like rice. Chemical fertilizers alone did not have the same positive effect on the soil's organic matter. Overall, the study showed that organic manure is the most effective way to boost the amount and quality of carbon and nitrogen in paddy soil.