To effectively apply compound fertilizers, it's essential to first understand their characteristics and how they interact with the crop's nutritional needs throughout its growth cycle, as well as the soil's nutrient release capacity, moisture levels, and fertilizer retention. While this may seem complicated for some farmers, experienced growers take all these factors into account in their daily farming practices.
Compound fertilizers are made through secondary processing, where raw materials like urea, calcium sulfate, and potassium chloride are mixed and granulated with a small amount of binder. They appear as granules and contain nitrogen, phosphorus, and potassium, sometimes including trace elements like calcium, magnesium, sulfur, iron, or molybdenum. The nutrients in these fertilizers can be fully water-soluble, partially insoluble, or weakly acid-soluble—like in the case of ammonium phosphate, which has both water-soluble and weak acid-soluble forms. This means that compound fertilizers have several key features: they are granular with good compressive strength, they contain a mix of nutrients, and the nutrients come in various forms depending on the type of fertilizer used.
Because of their complex composition, compound fertilizers often cost more than single-nutrient fertilizers. Therefore, it’s important to use them correctly by considering the specific needs of the crop and soil. Combining the properties of the fertilizer with those of the soil and crop can lead to better yields and higher profits.
When applying compound fertilizers, they are best used as a base fertilizer. During soil preparation before planting, the fertilizer is applied at a certain depth—usually around 20 cm for grains and vegetables, and 30–40 cm for fruit trees. This ensures that nutrients are available during the later stages of growth. Most of the phosphorus and potassium needed for the growing season should be applied as a base fertilizer, while only part of the nitrogen is included in the compound fertilizer. The rest of the nitrogen should be applied as a top dressing during the plant’s active growth phase to avoid overloading the initial application.
The ratio of N-P-K in compound fertilizers is fixed, so when using them as a base fertilizer, the amount is usually calculated based on the P or K content. Half of the nitrogen should be applied separately as a top dressing. Compound fertilizers are generally not recommended for top dressing or foliar application, as phosphate doesn’t move much through the soil and may not be efficiently taken up by the roots. Although some farmers in Guangdong use 45% (15-15-15) compound fertilizer for leafy vegetables via irrigation, this method is inefficient and leads to wasted resources.
Low to medium concentration N-P binary compound fertilizers can be used as seed fertilizer, but care must be taken to keep the seeds and fertilizer separate. Organic-inorganic compound fertilizers can be applied in large quantities as a base fertilizer. It's also advisable to combine compound fertilizers with simple fertilizers to ensure balanced nutrition throughout the crop's growth. After applying compound fertilizer as a base, half of the nitrogen or a small amount of potash should be added as a top dressing to adjust the nutrient balance and support high-quality, high-yield production.
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