(1) The normal growth and fruiting of the balanced fruit trees are based on a certain dynamic balance. To a great extent, pruning fruit trees is to maintain this dynamic balance that is often disturbed by unexpected factors. By maintaining these balances, we can achieve high quality, high yield, health and longevity of fruit trees. The balance system directly related to fruit tree pruning technology mainly includes the following three aspects.
1. Maintain the balance between crown and root system: Because the above-ground crown and underground root system are in mutual supply and demand, they always maintain a certain relative balance. However, the life of fruit trees, like life, is sometimes forced to accept the test of some unfavorable environmental conditions in nature. Any damage to the crown and root system will weaken each other's normal growth. Therefore, it is necessary to maintain a certain root-shoot ratio balance by pruning. Pay special attention not to disturb this balance artificially when pruning. This is why trees that have not been pruned for many years are easy to peel off if they are pruned too much at one time, and it is more difficult to bear fruit.
2. Keep the balance between growth and fruiting: The growth and fruiting of fruit trees are in the relationship of unity of opposites, which are mutually utilized and influenced. When fruit trees are allowed to develop naturally, there will often be some uncoordinated contradictions in the formation and development of branches, leaves, flowers and fruits, which is the imbalance between tree growth and fruit. Fruit trees with this phenomenon will not grow and produce good fruit. For example, young trees grow too fast to blossom and bear fruit; Old trees have many flowers and fruits, which easily lead to weak trees, "big and small years", and so on. Therefore, in the annual and lifelong development of fruit trees, pruning measures such as adjusting branch angles and thinning flowers and fruits are often needed to maintain the balance between vegetative growth and reproductive growth.
3. Balance between tree potential and branch potential: tree potential and branch potential refer to the growth momentum of crown and branch respectively. The growth of trees that meet the requirements should be moderately balanced. The key to achieve this requirement is to maintain the balanced growth relationship between all kinds of backbone branches, especially the growth intensity of backbone branches at the same level in terms of branch length and branch diameter should be roughly the same. Therefore, pruning often uses the polar advantage, heterogeneity and damage effect of branch buds to "restrain the strong and help the weak, and promote the control reasonably" to achieve the purpose of maintaining the basic balance between tree potential and branch potential.
(2) Improving the relationship between fruit trees In a year and a lifetime, with the growth and development of branches, internal and external conditions often change to some extent, which leads to the continuous transformation of various contradictions and the emergence of new problems. Therefore, timely pruning is needed to improve the relationship between internal and external conditions of fruit trees.
1. Improve the relationship between fruit trees and the environment: As the saying goes, "fruit trees will not grow without fertilizer, branches and buds will not bear fruit without light", and "branches and leaves will flourish, and flowers and fruits will bloom with fragrance". Light, water and air in the environment of fruit trees are all necessary raw materials for leaf photosynthesis to produce organic nutrients, which in turn affects the formation of flower buds and the development and coloring of fruits. Therefore, it is very important to prune frequently to keep the canopy ventilated and transparent.
2. Improve the distribution and utilization of nutrients inside the tree: As mentioned above, no matter the inorganic nutrients and water absorbed by the roots from the soil or the organic nutrients produced by the photosynthesis of leaves, it is impossible for the fruit tree to meet the growth and development needs of branches, leaves, fruits and other organs at the same time, but first of all, it is necessary to ensure the supply of the current growth and development center. However, there are often unfavorable factors, which lead to interference and competition from non-growth and development centers. In this case, it is necessary to make local adjustment through pruning to ensure the timeliness, sequence, rhythm and quality of the growth and development of various organs.
(3) The optimal growth and development of various organs and the ability of flowering and fruiting of rejuvenating fruit trees have certain age stages. Beyond this age limit, physiological function will decline. Especially the fruiting ability of fruiting branches is very obvious. Branches that are too tender and too old are not conducive to flowering and fruiting. Young branches are difficult to blossom and bear fruit; Although the old branches can grow into flowers, it is difficult to bear fruit, which is often manifested as more flowers and less fruits and poor quality. Therefore, attention should be paid to the timely renewal and rejuvenation of aging and weak branches when pruning.