The study looked at how different types of fertilizers affect soil fertility and rice yield over 18 years. They found that using organic manure along with chemical fertilizers increased nutrients in the soil the most. Farmers' fertilization practice and NPK had similar nutrient levels. Returning straw to the field and using NK fertilizer increased available potassium significantly. Soil organic matter increased with organic manure application. Soil organic matter was closely related to soil total nitrogen and CEC levels.