Compound fertilizers offer advantages such as high nutrient content, fewer secondary components, and good physical properties. They play a vital role in balancing fertilization, increasing fertilizer utilization rates, and promoting high and stable crop yields. However, they also have drawbacks; for instance, their nutrient ratios are fixed, while the types, quantities, and proportions of nutrients required by different soils and crops vary. Therefore, it is essential to conduct soil testing before use to understand the texture and nutritional status of the field. Additionally, attention should be paid to using them in coordination with single-nutrient fertilizers to achieve better results.
1. Compound fertilizers have long-lasting efficacy and are suitable as base fertilizers.
A large number of experiments 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 the early stages, requiring these to be applied early as base fertilizer. Compound fertilizers should not be used as seedling fertilizer or middle-to-late stage fertilizer to prevent “greedy green” (excessive vegetative growth) and delayed ripening. Compound fertilizers decompose slowly; for crops where compound fertilizer is used as the bottom fertilizer during sowing, quick-acting nitrogen fertilizer should be supplemented in a timely manner during top-dressing based on the nutrient requirements of different crops to meet their nutritional needs.
2. Compound fertilizers vary greatly in concentration; care should be taken to select the appropriate concentration.
Currently, most compound fertilizers are formulated according to the average soil nutrient status and crop fertilizer requirements of a specific region. There are high, medium, and low concentration series of compound fertilizers available on the market. Generally, low-concentration total nutrients range between 25% and 30%, medium-concentration between 30% and 40%, and high-concentration above 40%. It is necessary to choose an economical and effective compound fertilizer based on the region, soil, and crop. Generally, high-concentration compound fertilizers are used on economic crops for their superior quality, low residue, and high utilization rate.
As the concentration of compound fertilizer is high, direct contact between seeds and the fertilizer must be avoided. Compound fertilizers have high nutrient content; if they come into direct contact with seeds or seedling roots, it can affect emergence or even cause “burned seedlings” and root rot. During sowing, seeds should be kept 5–10 cm away from the compound fertilizer applied in holes or strips.
3. Different raw materials in compound fertilizer formulations require attention to their specific application range.
Different brands and concentrations of compound fertilizer utilize different raw materials. In production, selection must be made based on soil types and crop varieties.
Nitrate-based: Compound fertilizers containing nitrate should not be used on leafy vegetables or in paddy fields.
Ammonium-based: Compound fertilizers containing ammonium ions should not be applied to saline-alkali soils.
Chloride-based: Compound fertilizers containing potassium chloride or chloride ions must not be used on chlorine-sensitive crops or saline-alkali soils.
Sulfate-based: Compound fertilizers containing potassium sulfate are not suitable for paddy fields or acidic soils.
Failure to follow these guidelines will reduce fertilizer efficiency and may even poison the crops. Since compound fertilizer contains two or more macro-elements, surface application of nitrogen can lead to easy loss through volatilization or rainwater runoff. Furthermore, phosphorus and potassium are easily fixed by the soil. Phosphorus, in particular, has low mobility in soil; if applied to the surface, it is not easily absorbed by the root system, nor does it encourage roots to grow deep. In dry conditions, the fertilizer cannot dissolve, resulting in even poorer efficiency. Therefore, compound fertilizer should be applied deeply and covered with soil.