The effect of fertilization outside the root of crops is good.

Topdressing outside roots is simple and easy, saving fertilizer and getting quick results, and can also promote leaf function.

1. According to the characteristics of fertilizer, select the fertilizer type suitable for extra-root application.

Urea, potassium dihydrogen phosphate, potassium nitrate, potassium sulfate, ammonium sulfate, calcium superphosphate and plant ash leaching solution, ammonium metaphosphate and most trace element fertilizers are used as topdressing fertilizer. Some highly volatile fertilizers such as ammonia, ammonium bicarbonate and fertilizers containing chloride ions such as ammonium chloride, potassium chloride, etc., should not be used as extra-root fertilization, because some of them cause large fertilizer losses, and some have adverse effects on crops.

2, according to crop types and growth period, select fertilizer dosage and concentration.

The suitable concentration of fertilizer applied outside roots of crops is generally: urea 1-2%, potassium dihydrogen phosphate 0.3-0.5%, calcium superphosphate leaching solution 3-5%, ammonium molybdate 0.01-0.1%, ammonium metaphosphate 2-3%, borax 0.1-0.2%, zinc sulfate 1%, fertilizer solution used per mu is 50-60 kg, dicotyledonous crops such as cotton, rape, beans, vegetables, etc. have large leaf areas and thin cuticle layers, nutrients in the solution are easily absorbed, Therefore, the concentration of fertilizer solution sprayed on such crops should be appropriately low; rice, wheat, corn and other monocotyledonous crops have relatively small leaf area, high silicification degree of leaves, and nutrient components are difficult to be rapidly absorbed by leaves, so the concentration of fertilizer solution must be appropriately increased when spraying fertilizer (800-1000 times of high lipid membrane can also be added to the solution to increase adhesion effect).

3, according to climatic conditions, choose the appropriate fertilizer spraying time.

Many experiments have proved that the best fertilizer efficiency can be obtained by applying fertilizer outside roots in humid weather and keeping leaves wet for 30-60 minutes. In order to prolong the moisturizing time of fertilizer solution on plant leaves as much as possible, it is best to apply fertilizer outside roots in the morning and evening when the air is humid or there is dew.

4. According to the mobility of fertilizer in crops, determine the number of fertilizer sprays.

According to relevant test reports, nitrogen and potassium fertilizers have strong mobility in crops, so they can be sprayed once during the critical period of crop growth; phosphorus fertilizers are second to nitrogen and potassium fertilizers in mobility, and they must be sprayed 1-2 times continuously according to the growth status of crops; zinc, molybdenum, manganese, copper fertilizers that only partially move in crops and boron, calcium and other trace fertilizers that do not move should generally be sprayed 2-3 times continuously.

5. According to the biological characteristics of crops, choose the best spraying position.

The green stems and leaves of crops are reasonable parts for spraying fertilizer, especially the green functional leaves with young and vigorous growth, which have the best fertilizer effect. It should be noted that the epidermis of dicotyledonous leaves is a layer of closely arranged palisade tissue with small intercellular spaces. Nutrients in the fertilizer solution are difficult to break through the "blockade" and penetrate; but the back of the leaf is different, the epidermis is all loosely arranged sponge tissue, the cell gap is larger, the nutrients in the fertilizer solution are easier to enter and be absorbed quickly. Therefore, when spraying fertilizer to dicotyledonous crops, it should be equally sprayed on the front and back of the leaves, while monocotyledonous crops only need to spray fertilizer solution from top to bottom on the front of the leaves.