Compound fertilizers have advantages such as high nutrient content, minimal by-products, and favorable physical properties, playing a crucial role in balanced fertilization, improving fertilizer utilization efficiency, and promoting high and stable crop yields. However, they also have some drawbacks, such as fixed nutrient ratios, while the types, quantities, and proportions of nutrients required by different soils and crops vary. Therefore, it is essential to conduct soil testing before application to understand the texture and nutrient status of the field, and to combine them with single-element fertilizers for better results.   

1. Compound fertilizers have a long-lasting effect and are suitable for use as base fertilizer.   

Extensive trials have shown that both binary and ternary compound fertilizers are best applied as base fertilizers. This is because compound fertilizers contain multiple nutrients such as nitrogen, phosphorus, and potassium. Crops are particularly sensitive to phosphorus and potassium in their early growth stages, requiring these nutrients to be applied early as base fertilizers. Compound fertilizers should not be used for seedling-stage or mid-to-late growth-stage fertilization to prevent excessive vegetative growth. Since compound fertilizers decompose relatively slowly, crops treated with compound fertilizer as a base dressing should receive timely supplementary applications of quick-release nitrogen fertilizers during topdressing to meet their nutritional needs based on the specific nutrient requirements of different crops.   

2. The concentration of compound fertilizers varies significantly, so it is important to choose the appropriate concentration.   

Currently, most compound fertilizers are formulated based on the average nutrient content of specific soil types and the nutrient requirements of crops. There are high, medium, and low concentration series of compound fertilizers available on the market, typically with total nutrient content ranging from 25%-30% for low concentrations, 30%-40% for medium concentrations, and over 40% for high concentrations. The choice of economical and suitable compound fertilizers should be tailored to regional, soil, and crop conditions. Generally, high-concentration compound fertilizers are used for cash crops, offering superior quality, minimal residue, and high efficiency. Due to their high nutrient content, compound fertilizers must be kept away from direct contact with seeds. If seeds or seedling roots are exposed to compound fertilizers, it can affect germination or even cause seedling damage, root rot, and other issues. During sowing, seeds should be planted at least 5-10 centimeters away from compound fertilizers applied in pits or bands.   

3. Different raw materials for compound fertilizer formulations require attention to the application range of nutrient components.   

Different brands and concentrations of compound fertilizers use varying raw materials, and their application should be selected based on soil type and crop species in production.   

Fertilizers containing nitrate should not be used on leafy vegetables or paddy fields; those with ammonium ions are unsuitable for saline-alkali soils; fertilizers containing potassium chloride or chloride ions should not be applied to chloride-sensitive crops or saline-alkali soils; those with potassium sulfate are not recommended for paddy fields or acidic soils. Otherwise, their efficacy will be reduced, or even harm crops. Compound fertilizers contain two or more macronutrients. Surface application of nitrogen is prone to volatilization loss or leaching by rain, while phosphorus and potassium are easily fixed by soil—especially phosphorus, which has low mobility in soil. Surface application makes it difficult for crop roots to absorb and utilize these nutrients, and hinders deep root growth. Under drought conditions, the fertilizer may fail to dissolve, further reducing its effectiveness. Therefore, compound fertilizers should be applied deeply and covered with soil.