Compound fertilizer refers to chemical fertilizers containing two or more nutrients. The compound fertilizer has the advantages of
high nutrient content, less auxiliary components and good physical properties. It is very important for alanced fertilization,
improving fertilizer utilization rate and promoting high yield and stable yield of crops. However, it also has some shortcomings,
such as its nutrient ratio is always fixed, and the types, quantities and proportions of nutrients required for different soils
and different crops are diverse. Therefore, it is best to conduct soil testing before use to understand the texture and
nutritional status of the soil in the field, and also pay attention to the application with unit fertilizer to get better results.