In addition to absorbing nutrients through their roots, crops can also take up nutrients through their leaves and green stems. Spraying a nutrient-containing solution onto the above-ground parts of a crop (mainly the leaves) is known as foliar fertilization.
Foliar fertilization offers many advantages: fast nutrient uptake, high utilization efficiency, convenient application, noticeable results, and savings on fertilizer. It is a widely used method in agricultural production. However, foliar fertilization also requires proper technique to achieve the best results.
1. Choose the Right Fertilizer Types
Fertilizers that work well for foliar application include urea, monopotassium phosphate (MKP), potassium nitrate, potassium sulfate, ammonium sulfate, superphosphate extract, plant ash extract, ammonium metaphosphate, and most trace element fertilizers.
Note that highly volatile fertilizers (such as ammonia water and ammonium bicarbonate) and chloride-containing fertilizers (such as ammonium chloride and potassium chloride) are not suitable for foliar application - the former lead to significant nutrient loss, while the latter may adversely affect crops.
2. Use the Right Concentration and Volume
Typical concentrations for foliar fertilization are: urea 1%–2%, monopotassium phosphate 0.3%–0.5%, superphosphate extract 3%–5%, ammonium molybdate 0.01%–0.1%, ammonium metaphosphate 2%–3%, borax 0.1%–0.2%, and zinc sulfate 1%. The spray volume is generally 50–60 kg per mu.
Different crop types require different approaches. Broadleaf crops such as cotton, rapeseed, legumes, and vegetables have large leaf areas and thin cuticles, so nutrients are easily absorbed - spray concentrations should be appropriately lower. Monocot crops such as rice, wheat, and corn have relatively smaller leaf areas and more silicified leaves, making nutrient uptake slower - spray concentrations should be appropriately higher.
3. Determine the Right Spraying Frequency
Spraying frequency should be based on nutrient mobility within the plant:
Nitrogen and potassium fertilizers: Highly mobile within the plant; one spray during the key growth stage is sufficient.
Phosphorus fertilizers: Less mobile than nitrogen and potassium; spray 1–2 times depending on crop growth conditions.
Zinc, molybdenum, manganese, and copper fertilizers: Only partially mobile within the plant; generally require 2–3 consecutive sprays.
Boron and calcium fertilizers: Immobile within the plant; also require 2–3 consecutive sprays.
Foliar fertilization is effective, but only when the right fertilizer is chosen, the correct concentration is prepared, and spraying frequency is properly scheduled - this is how it truly delivers fertilizer savings, efficiency gains, and better crop yield and quality.
