Different crops have different ratios of nitrogen, phosphorus, and potassium requirements during different growth stages such as germination, leaf growth, flowering, and fruiting. Compound fertilizers can be adjusted to meet specific needs and avoid "nutrient deficiency syndrome" (such as yellow leaves due to nitrogen deficiency, short stature due to phosphorus deficiency, and easy lodging due to potassium deficiency):

Promoting Nutritional Growth (Seedling Stage - Long Term): Compound fertilizers with high nitrogen content (such as N-P-K 20-10-10) can provide sufficient nitrogen for crop leaf and stem growth, promote chlorophyll synthesis, and make plants stronger. They are commonly used as topdressing during the seedling stage of wheat, corn, and rice, as well as during the leaf growth stage of vegetables such as cabbage and lettuce.

Assisted reproductive growth (flowering fruiting period): Compound fertilizers with high phosphorus and potassium content (such as 15-20-25) can promote flower bud differentiation, improve pollen vitality, reduce flower and fruit drop, and enhance fruit swelling, coloring, and sugar accumulation. They are typically used as topdressing during the flowering period of fruit trees (apples, citrus) and during the fruit expansion period of melons (tomatoes, watermelons).

Enhancing stress resistance (full cycle assistance): Compound fertilizers partially supplemented with trace elements such as calcium, magnesium, sulfur, and zinc can improve crop resistance to diseases, pests, cold, and drought. For example, zinc containing compound fertilizers can prevent corn "whitening seedlings", while calcium containing compound fertilizers can reduce tomato "navel rot", especially suitable for poor soil or continuous cropping plots.