Why is foliar feeding of crops so effective?
Foliar topdressing is simple and easy to do, saves fertilizer, shows results quickly, and also promotes leaf function - many benefits at once.
1. According to the characteristics of the fertilizer, choose the types of fertilizer suitable for foliar application.
Fertilizers that give good results when used for foliar topdressing include urea, potassium dihydrogen phosphate, potassium nitrate, potassium sulfate, ammonium sulfate, superphosphate and the extract of plant ash, ammonium metaphosphate, and most trace element fertilizers, etc. Some highly volatile fertilizers such as ammonia water and ammonium bicarbonate, as well as fertilizers containing chloride ions such as ammonium chloride and potassium chloride, are not suitable for foliar feeding, because some of them cause large fertilizer losses, and others have adverse effects on crops.
2. According to the crop type and growth stage, choose the amount and concentration of the fertilizer solution.
The suitable concentrations for foliar feeding of crops are generally: urea 1-2%, potassium dihydrogen phosphate 0.3-0.5%, superphosphate extract 3-5%, ammonium molybdate 0.01-0.1%, ammonium metaphosphate 2-3%, borax 0.1-0.2%, zinc sulfate 1%, and the amount of fertilizer solution used per mu is 50-60 kg. For dicotyledonous crops such as cotton, rapeseed, beans, and vegetables, the leaf area is large and the cuticle is thin, so the nutrients in the solution are easily absorbed; therefore, the concentration of the fertilizer solution sprayed on these crops should be appropriately lower. For monocotyledonous crops such as rice, wheat, and corn, the leaf area is relatively smaller and the degree of leaf silicification is high, so the nutrients are difficult for the leaves to absorb quickly; therefore, when spraying fertilizer, the concentration of the fertilizer solution must be appropriately increased (you can also add 800-1000 times of Xinguozhi film to the solution to increase adhesion for better results).
3. According to climatic conditions, choose the suitable time for spraying fertilizer.
Many experiments have proved that foliar feeding carried out in relatively humid weather, with the leaves kept moist for 30-60 minutes, can achieve better fertilizer efficiency. In order to extend the moisturizing time of the fertilizer solution on the plant leaf surface as much as possible, foliar feeding is best carried out in the morning and evening when the air is humid or there is dew. On windless cloudy days, it can be sprayed all day, but spraying in the evening gives the best results.
4. According to the mobility of the fertilizer within the crop plant, determine the number of sprayings.
According to relevant experimental reports, nitrogen and potassium fertilizers have very strong mobility within the crop plant, so during the key period of crop growth, spraying once is enough; the mobility of phosphate fertilizer is lower than that of nitrogen and potassium fertilizers, so it must be sprayed 1-2 times consecutively according to the growth condition of the crop; zinc, molybdenum, manganese, and copper fertilizers, which move only partially within the crop plant, and immobile trace fertilizers such as boron and calcium, should generally be sprayed 2-3 times consecutively.
5. According to the biological characteristics of the crop, choose the best part to spray fertilizer.
The green stems and leaves of crops are the reasonable part for spraying fertilizer, especially the young, tender, and vigorously growing green functional leaves, which receive the best fertilizer effect. It is worth noting that in the epidermal tissue on the upper surface of the leaves of dicotyledonous crops, there is a layer of closely arranged palisade tissue with small intercellular spaces. The nutrients in the fertilizer solution can hardly break through the "blockade" and penetrate; but the underside of the leaf is different - the epidermal tissue there is entirely made up of relatively loosely arranged spongy tissue with larger intercellular spaces, so the nutrients in the fertilizer solution can enter more easily and be absorbed quickly. Therefore, when spraying fertilizer on dicotyledonous crops, it should be sprayed evenly on both the upper and lower surfaces of the leaves, while for monocotyledonous crops it is enough to spray the fertilizer solution from top to bottom on the upper surface of the leaves.