Applying manure to crops in China can help increase soil fertility and grain yields. A study looked at nine long-term experiments with different crops like rice, wheat, and maize. They found that using manure regularly can boost soil organic carbon and grain yields in all the sites. Maize and wheat-maize systems showed bigger increases in soil organic carbon compared to rice-based systems. Manure tended to increase grain yields in maize and wheat-maize systems over time, while in rice-based systems, it boosted yields initially. Overall, manure can improve crop yields, especially in systems with lower initial yields.