A 15-year study in China looked at how different fertilizers affect wheat and maize yields. They tested fertilizers with nitrogen (N), phosphorus (P), and potassium (K), with or without manure. The best yields came from using a mix of NPK fertilizer and manure. Soil fertility contributed to 37.9% of the highest yield, with the rest from fertilizers. Nitrogen had the biggest impact on yield, followed by phosphorus and potassium. Using a mix of chemical fertilizer and manure can help maintain good crop growth and increase soil organic matter.