Key Technical Points and Application Methods of Fruit Tree Foliar Fertilization

Fruit Tree Foliar Fertilization Technology

Foliar fertilization of fruit trees is an auxiliary and supplementary method to soil fertilization. It can promptly supply nutrient elements and plant growth regulators that fruit trees lack, and can rapidly promote or regulate the growth and development of fruit trees. It is a commonly used fertilization method in fruit tree production, with advantages such as avoiding the adverse effects of soil on applied substances, taking effect quickly, compensating for root function, being highly targeted, and being mixable with pesticides for spraying. The following introduces fruit tree foliar fertilization technology.

I. Selection of Foliar Fertilizers

Currently, foliar fertilizers commonly used in fruit tree production include: nutritional foliar fertilizers, regulatory foliar fertilizers, biological foliar fertilizers, amino acid foliar fertilizers, humic acid foliar fertilizers, compound foliar fertilizers, etc.

Appropriate foliar fertilizers should be selected according to the growth and development status of fruit trees, phenological period, natural environmental factors, types of nutrient deficiency diseases, etc.: When fruit trees grow excessively vigorously or are weakened, in addition to nutritional foliar fertilizers, regulatory foliar fertilizers should also be selected to control excessive growth or promote growth; for nutrient deficiency diseases in fruit trees, nutritional, compound, or amino acid foliar fertilizers containing the deficient element should be selected for spraying; in the early growth stage of fruit trees, foliar fertilizers mainly aimed at promoting growth should be selected for spraying; before and after flowering, foliar fertilizers that help improve fruit set rate should be sprayed more; in the late growth stage, foliar fertilizers that promote flower bud formation, improve fruit quality, and increase tree nutrient reserves should be selected for spraying; to prevent damage to fruit trees from disastrous weather (cold waves, frost, waterlogging, etc.), or to promote the growth and development of fruit trees after disasters and pest and disease damage, nutritional foliar fertilizers can be selected for spraying, combined with regulatory or compound foliar fertilizers, to restore growth and improve resistance. For regulatory or compound foliar fertilizers, Aiduoshou, brassinolide, amino acid and humic acid foliar fertilizers, etc. are often selected for spraying.

II. Application Concentration (Amount) of Foliar Fertilizers

When carrying out foliar fertilization, close attention must be paid to the spraying concentration. If the concentration is too low, it will not meet the fertilization requirements; if the concentration is too high, it is likely to cause damage or excessive promotion/control; the critical range for fruit trees from nutrient deficiency to excess is very narrow, especially when spraying growth regulator foliar fertilizers, the spraying concentration must be strictly controlled. The spraying concentration should be determined according to tree species (or even variety), tree age, tree vigor, type of nutrient deficiency, degree of nutrient deficiency, etc. For example, when spraying the plant growth inhibitor paclobutrazol on excessively vigorous fruit trees, if the concentration is too high, the inhibition will be excessive, causing tree dwarfing, smaller fruit, and decreased quality.

III. Fertilization Period

1. During the phenological period when fruit trees need fertilizer. Carry out targeted foliar fertilization according to the fertilizer requirements of each phenological period. For example, fruit trees need more boron fertilizer during the flowering period. During this phenological period, foliar fertilizers containing boron (such as borax, boric acid) can be sprayed, or foliar fertilizers containing plant growth regulators (such as gibberellin, fruit-setting hormone, etc.) can be sprayed or dipped, which can significantly increase the fruit set rate.

2. After fruit trees suffer from disastrous weather or pest and disease damage. After branches, leaves, flowers, fruits, or roots are damaged, foliar fertilizers can be promptly applied as a top dressing to help the affected fruit trees resume growth and development.

3. When nutrient deficiency symptoms appear. Based on observation and diagnosis, determine the type of nutrient element the fruit trees lack (determine the type of nutrient deficiency disease), and supplement exactly what is lacking. Preventive application can be carried out before the disease occurs, or the deficient element can be promptly applied in the early stage of the disease to achieve the purpose of prevention and treatment. For example, if it is determined to be yellow leaf disease of fruit trees (iron deficiency), foliar fertilizers such as ferrous sulfate and amino acid iron can be sprayed.

4. Predicting the types of deficient elements. ① Based on production experience, predict the types of deficient elements. According to the types of nutrient deficiency diseases that commonly occur in the orchard in the past, determine the deficient elements and prevention period, and formulate a fertilizer spraying plan. ② Based on scientific theory, predict the types of deficient elements. When fruit trees are planted on neutral soil, nutrient deficiency diseases generally rarely occur; when planted on acidic or alkaline soil, nutrient deficiency diseases often occur. In particular, when planted on alkaline soil with a pH value greater than 8, multiple nutrient deficiency diseases are likely to occur, such as yellow leaf disease, little leaf disease, and bitter pit disease caused by deficiencies of iron, zinc, calcium, and other elements. Based on this, formulate preventive measures. For example, if it is predicted that fruit will develop bitter pit disease, then in the young fruit stage, foliar fertilizers containing calcium, such as calcium nitrate and amino acid calcium, can be sprayed on young fruits and leaves, which can effectively prevent and control bitter pit disease.

5. Spraying time. After spraying foliar fertilizer, the longer the leaves remain moist, the more nutrients the leaves absorb and the better the effect. Therefore, spraying should be carried out on rainless days from early morning (after dew dries) to before 10 o'clock, and after 4 o'clock in the afternoon. On rainless cloudy days, spraying can be done all day. If rain occurs within 5 to 6 hours after spraying, it must be resprayed, and the concentration of the fertilizer solution for respraying should be appropriately reduced.

To extend the moist retention time of the foliar fertilizer solution on organs such as leaves and branch tips, and to enhance spreading and penetration, appropriate amounts of wetting agents, spreaders, and penetrants, such as Hailiping, Zhuxiaoling, neutral laundry detergent, etc., can be added when preparing foliar fertilizer.

IV. Number of Sprayings

The concentration of foliar fertilization is relatively low, and the amount applied each time is relatively small. Generally, spraying 1 to 2 times cannot meet the fertilizer requirement of fruit trees; moreover, the fertilizer effect period of foliar fertilization is short, generally only 6 to 7 days, especially when spraying nutritional foliar fertilizers, the applied amount is even more insufficient. Therefore, foliar fertilization should generally be no less than 2 times. For nutrient elements that do not easily move within the tree body (such as iron, boron, calcium, zinc, etc.), the number of sprayings can be appropriately increased. When spraying foliar fertilizers containing plant growth regulators (such as gibberellin, ethephon, forchlorfenuron, etc.), generally spray 1 to 2 times, with an interval of about 10 days each time, to prevent improper regulation and control from causing harm.

V. Application Methods

1. Spraying method. ① Growth period. After preparing the foliar fertilizer into a solution of a certain concentration, spray it on various organs of the tree canopy (mainly leaves). Nutrient elements or other substances are absorbed and penetrate into the tree body through stomata or intercellular spaces and are then utilized. Young leaves have stronger physiological activity than old leaves and also have stronger absorption and penetration capacity for nutrient elements, etc. When spraying foliar fertilizer, emphasis should be placed on spraying young leaves. When spraying foliar fertilizer, both the front and back of the leaves should be sprayed; the back of the leaf has a thinner cuticle and more stomata than the front, and has loose spongy tissue and larger intercellular spaces, which is conducive to the absorption and penetration of nutrients, so spraying should focus on the back of the leaves. When spraying nutrient elements that do not easily move within the fruit tree body, the foliar fertilizer solution can be sprayed directly onto the organs that need that element, so that it can quickly and effectively take effect. When spraying boron to increase the fruit set rate, the diluted boron-containing fertilizer solution can be sprayed directly onto flowers and young fruits. ② Dormant period. Generally, before fruit trees sprout, spray the foliar fertilizer solution onto the tree canopy. For example, to prevent and control little leaf disease caused by zinc deficiency in fruit trees, spray a 3% to 4% zinc sulfate solution before sprouting, and then spray a 0.3% to 0.5% zinc sulfate solution on the tree canopy after sprouting, with excellent results. When spraying branches and trunks, because the absorption and penetration capacity of branches and trunks is relatively poor, adding appropriate amounts of wetting agents, penetrants, etc. when preparing foliar fertilizer will produce better results.

2. Dipping method. Place the prepared foliar fertilizer solution in a wide-mouthed container (such as a large mug), put the fruit tree organs that need foliar fertilization into it and soak for 3 to 5 seconds to achieve the purpose of fertilization. This method is mostly used in grape flower and fruit management. For example, to increase the fruit set rate of grapes, 3 to 5 days before flowering, dip the inflorescences with 20 to 30 mg/L gibberellin.

3. Trunk injection method. This method is suitable for large trees with a trunk diameter greater than 10 cm. First drill a hole in the trunk, then inject the foliar fertilizer solution into the hole. After the fertilizer solution enters the conduit tissue of the xylem of the branches and trunk, it can be transported to various organs along with the movement of water within the tree body. The use of this method is less affected by the external natural environment, has high fertilizer utilization rate, and takes effect quickly. It is divided into the following two types:

① Infusion method. Similar to human infusion. At about 30 cm above the ground on the lower part of the trunk, drill a hole upward at an angle of about 45°, with the hole diameter matching the matching injection needle, drill depth 5 to 6 cm, clean out the wood chips, screw the matching injection needle into the injection hole, and tighten it so no liquid leaks; hang the commercial nutrient solution bag (bottle) or self-prepared nutrient solution bag (bottle) on the tree, and connect the injection needle for infusion. For self-prepared nutrient solution, use clean neutral water, preferably distilled water or purified water; the foliar fertilizer should be of high purity and have few impurities after dissolution. Simple infusion method: use medical infusion equipment, fill it with self-prepared foliar fertilizer solution, drill the hole and hang the foliar fertilizer solution bottle as above, and the hole can be slightly deeper; insert the needle into the hole, adjust the drip rate, and ensure that only a small amount of liquid remains in the hole without overflowing, then seal the opening with plasticine. Alternatively, after inserting the needle, plug the injection hole with a short branch segment of a thickness comparable to the diameter of the injection hole. For trees with a trunk diameter less than 10 cm, 1 hole can be drilled per tree; for trees with a trunk diameter greater than 10 cm, 2 to 3 holes per tree.

② High-pressure injection method. Use a special trunk injection machine for fruit trees and forest trees, generating pressure through a mechanical pump or hand pump, and inject the foliar fertilizer solution into the tree body through the needle tube. However, this method is currently used relatively little in fruit tree production.