The crown of fruit trees expands with the growth of tree age, and there are too many branches and leaves, which will inevitably lead to the consequences of dense outside and empty inside, premature aging of trees, serious years and low fruit yield and quality. Timely and reasonable pruning can play the following roles: ① Adjust the reasonable distribution of branches and leaves. That is, on the basis of reshaping, the density, distribution direction and leaf area coefficient of each part of the crown are adjusted to maximize the effective photosynthetic area of the crown. ② Regulating growth and fruiting. Make nutrition grow normally but not too much; Moderate flowering and fruiting without weakening the tree; At the same time, it can prevent fruit trees from aging ahead of time and renew and rejuvenate in time. ③ Adjust the proportion of branches. Short branches have short growth period, low consumption and early accumulation, but few leaves and low total photosynthesis; Vegetative branches have a long growth period and high consumption, but they also accumulate a lot in the later stage. Different tree species and tree ages need to have corresponding and appropriate branch proportions, so that the operation, distribution, consumption and accumulation of nutrients in a year's growth cycle can be coordinated according to the normal growth and reproduction rhythm. This can be achieved by pruning. (4) Pruning can also balance the growth potential among the population plants and between the main branches of the plants, so as to achieve a balanced yield and facilitate management. In addition, pruning is also a means to coordinate the growth of shoot and root system.
The regulation of mechanical pruning on the growth and development of branches, leaves and fruits is related to the change of apical dominance. Because the transport direction of cytokinin produced by roots is opposite to the direction of gravity, the more upright the branches are, the higher the position of buds is, and the more they get, so the faster the cells divide, the more prosperous they grow. However, the germination and growth of the lower bud of the terminal bud were inhibited. Once the branch is cut off, the top advantage is transferred to the cutting bud, and the growth potential of each bud under it is weakened in turn, so that it cannot germinate into a hidden bud, thus changing the original germination rate and branching ability, and changing the branch analogy and vegetative branch growth (Figure 1). In addition, the development and quality of buds on branches are also different, which is called bud heterogeneity. Generally speaking, the quality of buds is closely related to the size and function of leaves on nodes, the time of bud formation, the overall nutritional status of trees and environmental factors. Therefore, pruning also takes advantage of the heterogeneity of buds, and plays its regulatory role by choosing appropriate pruning buds. But pruning with similar branches and cut parts can not achieve the same effect. This is because different tree species and varieties have different germination and branching habits. Usually, the varieties with stout branches grow vigorously and bloom later than the varieties with high germination rate. Different tree species and varieties have different fruiting habits. In order to get the expected effect of pruning, it is necessary to know this in advance.
There are mainly the following pruning methods: ① Short cutting. That is, part of the tips and buds on the branches are cut off, so that nutrients are supplied centrally, and the cut buds are in an advantage, and strong branches are sprouted. Retraction of perennial branches is also a shortcut. If there are vegetative branches under the cutting section, which can be extended again, it is called "shrinking branches" and plays a role in renewal; Those who do not leave leading branches below the kerf are called "blocking", which is used to inhibit their growth and often force them to switch branches. Generally, the heavier the short cut, the stronger the local stimulation to the incision and its lower part, and the stronger the inhibition to the whole plant and even the root system. If young trees are pruned too much, the results will often be delayed. 2 choose the heart. That is to say, the tender part of the growing new bud is removed. The function is to inhibit the continuous growth of branches, promote nutrients to turn to their lower buds or their adjacent parts, and facilitate flower formation or fruit setting. ③ thinning. That is, thinning some branches and buds from the base. Because the nutrient area of the mother branch is reduced, it causes certain trauma, and the upper branch potential of thinning branches slows down and the lower branch strengthens. The influence of thinning on the whole depends on the type and quantity of thinning branches. Spare weak branches, dense branches or long branches, which can reduce useless consumption, increase effective photosynthetic area and be beneficial to comprehensive nutrition; However, thinning out too many vegetative branches will reduce nutrient accumulation and weaken the root system and tree potential. In the growing season, operations such as removing buds and wiping tips are also thinning branches, which are often used for evergreen fruit trees. 4. Sustained release. Let the vegetative branches extend naturally, without cutting, and use the weak terminal bud extension to gradually slow down and weaken its apical advantage, improve the bud germination rate, promote the growth of short branches and induce flowering. Slow release is usually combined with increasing the branching angle, and the effect is obvious when the branches grow nearly horizontally or obliquely. But it is generally not used for branches whose backs are too thick and upright. ⑤ Others, such as cutting, girdling, twisting or softening branches, damage some organs or transport tissues, temporarily change the transport direction or speed of nutrients, and also have a good effect on slowing down vigorous growth, promoting flowering and improving fruit setting. The application of various pruning methods should be different from tree to tree, taking into account the growth and fruiting characteristics of different tree species and varieties, rootstocks, tree age, tree vigor and other factors, as well as the characteristics of natural conditions and the level of cultivation management. Generally speaking, the main branches should maintain vigorous growth; For auxiliary branches, the growth potential should be slowed down in time to transform them into fruiting branches; For the old and weak branches, they should be pruned and updated in time. When pruning, try to use the lowest necessary pruning amount, especially young trees; At the same time, pay attention to the comprehensive application of various pruning methods and the cooperation between winter pruning and summer pruning.
And also pay attention to choose the right time for pruning. Normal pruning of deciduous fruit trees is carried out during the dormant period from defoliation to germination. The regular pruning period of evergreen fruit trees is after fruit picking in spring or before new buds germinate.