brief history
The record of pruning ancient fruit trees in China is very brief. In the 2nd century A.D., the Moon Order for Four People mentioned for the first time that "it is the first month (the first month), and the branches can be peeled off until February". In the Yuan Dynasty (13 14), it was pointed out that "cutting off small and messy branches will naturally make them fat". Later, the Complete Book of Agricultural Administration (1628) also clearly stated: "All fruit trees must be cut off from their numerous branches so that their strength will not be split ..." However, summer cutting techniques, such as girdling and longitudinal carving, were described as early as the 6th century in the Book of Qi Yaomin. Pruning in Europe began in the middle of17th century. In France, gardens are decorated with fruit trees, so the fruit trees are cut into various geometric figures by hand and stand against the wall. About19th century, fruit tree production developed greatly, and this forced pruning was replaced by natural pruning. About 18 10, natural pruning spread from America to Japan. At the same time, in the late19th century, the Frenchman Du Breyer systematically put forward the theory of fruit tree pruning. With the introduction of apple, pear, cherry and other fruit trees into China, pruning technology began to spread in China. After 1949, the pruning technology was combined with the traditional experience of China, and the theory was continuously improved and perfected. In practice, according to the biological characteristics of different tree species and varieties, combined with ecological and management conditions, different pruning measures are put forward.
The role of pruning
Fruit trees are perennial crops. If they are allowed to grow naturally, the top often grows vigorously, and the buds at the base are hidden and bare. Year after year, the branches are dense, the crown is closed, the inner chamber is empty, and the fruiting parts move out, which also leads to different years of fruit (see year), small fruit and poor quality. At the same time, due to the continuous extension of branches, the further the distance between branches and trunk, the advantages of the top will be offset, especially the branches that grow horizontally, which are more likely to weaken, leading to premature decline of trees and shortening economic achievements. Correct pruning can overcome the above shortcomings, and its main functions are:
Adjust the spatial position of branches and leaves
On the basis of modeling, according to the biological characteristics of different fruit trees and the requirements of trees, a certain number of branches with different sizes are arranged in space to cultivate leaf curtains that can effectively use space. Pruning in the young tree stage, except for cultivating the skeleton according to the requirements of the predetermined tree shape (see fruit tree shaping), the rest branches are lightly pruned to accelerate the vegetative growth, increase the amount of branches and leaves, make them form a crown as soon as possible, increase photosynthesis, accumulate nutrients and improve the flowering and fruiting ability. With the growth of tree age and the increase of branches, the light conditions inside and outside the crown began to differ. By pruning, too dense and redundant branches are removed, or branches are promoted. When the crown begins to hand over, the crown has reached its maximum. At this stage, we should control and delete the upper and outer flourishing branches and redundant branches, and enrich and maintain the internal branches and fruit branches. In addition, because the canopy is ventilated and transparent for a long time, it can also reduce the breeding of some pests and diseases.
Regulating vegetative growth and flowering and fruiting
Fruit tree branches can be divided into vegetative branches and fruiting branches according to their functions. And a considerable number of branches have both nutritional and fruiting functions, but in a certain period of time, they still focus on one function. Although vegetative growth is the basis of flowering and fruiting, excessive vegetative growth is not conducive to flowering and fruiting. On the other hand, if there are too many fruits, it will also weaken the vegetative growth and lead to the weakness of the tree. Usually in the young tree period, it often shows excessive growth, but after the full fruit period, it is easy to weaken. Correct pruning can adjust the balance between vegetative growth and flowering and fruiting, so that vegetative growth is vigorous and not wasteful, and moderate flowering and fruiting is not weak.
Regulate the distribution and operation of tree nutrition and water.
The growing point of vigorous branches can produce more auxin and gibberellin, making it a "reservoir" for absorbing tree nutrients; Leaves with good light conditions are the "source" of photosynthetic products. In the process of developing branches and long branches, the consumption is large and the accumulation is late; However, the fruiting branches and short branches stop growing early, and the construction consumption is less, but the accumulation is less. By pruning and adjusting the branch ratio of a tree, the distribution center of nutrients in the tree and the relationship between consumption and accumulation can be adjusted, so as to achieve the consumption necessary for building vegetative organs and promote the accumulation of substances necessary for flowering and fruiting. Coordinate the contradiction between consumption and accumulation to conform to the rhythm of the development law of various organs in the annual growth cycle of fruit trees. For trees with many flowers or older trees, pruning can moderately reduce the amount of flowers and branches and buds, so that storage nutrients can be supplied centrally, leaving fewer flower buds after pruning, and improving fruit setting rate and fruit quality.
Regulate the growth potential between populations and individuals
Due to the influence of internal and external factors, the growth potential of trees will be different in any orchard or between the main branches of the same tree, resulting in uneven growth of plants in different parts of an orchard or a tree, which is not conducive to cultivation management. Therefore, pruning is needed to balance the tree potential and adjust the growth space between trees.
The basis of pruning
The biological characteristics, external conditions and cultivation techniques of fruit trees are the main basis for pruning.
Apical dominance
Like any higher plant, fruit trees have apical phototaxis. Because cytokinins needed for germination and bamboo shoots are transported in the opposite direction to gravity, the more tops of the upper upright branches, the more favorable it is for germination, bamboo shoots and growth, while the lower buds are inhibited. Once the branch is trimmed, the advantage of the top is transferred to the bud below the incision. If the branches are leveled, the inhibitory effect of the terminal buds on the lower buds is weakened or disappeared. Using or changing apical dominance can regulate bud germination, balance the force between branches and plants, and even turn developing branches into fruiting branches, and vice versa. When the fruit tree is young, it has few branches, vigorous and upright growth, and obvious top advantage, so pruning should be light and leave as many branches as possible, and the opening angle will weaken its top advantage; Mature trees have many branches and few long branches, and the advantages of open branches and top are obviously weakened. Therefore, the pruning amount should be heavy, the short branches should be more, and the weak branches should be sparse.
Heterogeneity of buds
The quality of buds at different nodes on branches is different because of their different positions, time and nutritional status (see buds). Usually, the buds at the base of branches develop early and have poor nutrition, so they are small but not full. In most cases, it cannot germinate into a latent bud in the second year. From bottom to top, the leaves of each node are enlarged, the development conditions of axillary buds are improved, the buds formed are fuller, and the intra-bud differentiation is more perfect. They are strongest in the middle and upper branches, and then the leaves formed are smaller, the development time of buds is also reduced, and the quality of buds is poor. As for the tip, according to the different types of branches, either leaf buds or flower buds are formed. Taking autumn shoots as an example, the terminal buds often cannot fully develop into buds; At the junction of spring shoots and autumn shoots, flower buds often cannot be formed, forming a "blind knot". When pruning, the cut falls on the full bud, which can promote the branches to be strong; Cutting at the base can force the latent buds to sprout branches and play a role in regeneration; When the cuttings fall on the blind nodes, more weak buds in the lower part can germinate to form short branches, so as to alleviate the tree vigor or make the vegetative growth become flowers and fruits.
Diversified habits
Under the same pruning degree, the branching status of different tree species and varieties is also obviously different. For example, after pruning in the middle of the branch, some branches can grow a few flourishing branches, but no short branches occur below; Some only draw a long branch from above, and some short branches can be drawn from below; In addition, the fruiting branches of some varieties can produce fruiting branches every year, while some varieties often blossom and bear fruit every other year, and the life span of the same type of fruiting branches is also inconsistent. Pruning should also pay attention to the influence of rootstocks on plants. For example, rootstocks have developed roots, which can absorb more fertilizer and water, promote the overground foliage, and react strongly to pruning, while dwarfing rootstocks are the opposite. Even if the above-ground parts are cut off again, the growth is often still very small. In addition, the difference of management level and soil quality will also affect the tree potential, vegetative growth and fruiting ability of fruit trees, and these factors should also be considered when pruning.
ecological factor
Because the same fruit tree is cultivated under different ecological conditions, its annual growth rhythm is very different. Usually, in a warm and rainy environment, nutrient growth tends to be vigorous, the growth period is prolonged, and more nutrients are accumulated in the later stage of growth, which is sensitive to pruning. The pruning amount should be light, more sparse and less pruning, and vigorous growth should be controlled. On the contrary, in cold and arid areas, the growth potential is often weak and the pruning reaction is moderate. The same amount of cutting, the local stimulation is often lighter than that in warm and humid areas, and you can cut more or less. Excessive water and nitrogen fertilizer have similar effects to warm and humid areas, which is more obvious in young trees. Therefore, when pruning, we should pay attention to local conditions and make it suitable for trees.
Pruning method
The main methods are:
short cut
Cut off some branches (Figure 1). After the branches are cut short, the growth potential of cutting buds can be enhanced. Light and short cuttings have little stimulation to the original branches, and the cuttings will not have strong branches, but the lower buds are slightly inhibited and germinate more. Generally used to cultivate medium branchlets or slow down the growth potential; The medium and short cut cuttings are full buds, which can promote the growth of branches. A small number of medium and short branches are generally used for the extension of backbone branches, the guiding branches of medium and large branches, and when filling space; Heavy and short cutting can often promote several vigorous branches or long branches and strengthen local growth potential, which is similar to adding nitrogen fertilizer. Therefore, it is only used when controlling branches or balancing tree potential. Although heavy and short cutting can promote the growth of strong branches, because the cut branches are also longer, the crown is relatively smaller, and the nutrients stored in the branches are also lost, which weakens the whole plant. The shorter the weight of young and strong trees is cut, the more obvious the promotion of bud cutting, but the total growth and total leaf number of the whole tree decrease. The weakening of the whole tree potential is also obvious; If the old and weak trees are properly felled again, the storage nutrition will be concentrated because of the increase of root-shoot ratio, which will promote the germination of new shoots and revitalize the trees.
Figure 1 refinement
Also called thinning, it is to cut off annual or perennial branches from the base. When the upper branches become thinner, the top advantage is transferred to the lower branches to enhance the growth potential; If the drained branch is in the lower part, the wound during draining is a kind of injury and resistance to the upper branch, which will slow down the upper branch. Keeping strong branches can reduce competition, alleviate the contradiction between growth and fruiting, and thinning weak branches can concentrate nutrition, which is helpful to rejuvenate and regenerate the retained branches and improve the ability of flowering and fruit setting. Thinning is also used to reduce the number of branches of a tree, or to improve the scenery conditions in the parts where the branches and leaves are too dense, without affecting the major local stimulation.
eldest branch of a family
Also known as slow release. That is to let the branches grow naturally. At the top of long branches, the growth potential decreases year by year. Many branches are short, which is beneficial to relax tree vigor, increase accumulation and promote flowering. Young and prosperous trees, throwing some flat long branches and thick branches properly, are conducive to early flowering and fruiting. Standing branches for a long time, because of the large leaf area and strong top advantage, will make the stems thicker and faster, and the growth will continue to be too strong, so long-term placement should be combined with pulling branches.
Shrinkage shear
Also called retraction (Figure 2). It is often used to change the head of the backbone branch or update the result branch group. The reaction of cutting is related to the size of cutting section, cutting quantity and the quality of cut branches and buds. The shrinking branches are very irritating to the cutting section, so a certain amount of developing branches should be left in the cutting section to disperse their strength and achieve the purpose of easing, which is generally used to support branches with large layers; Shrinking the back of weak branches has a good rejuvenation effect and is usually used for weak fruit branches.
Figure 2. incision
Also called eye injury. Before the branches germinate, cut a knife horizontally about 2 ~ 3 mm above the buds and reach the xylem. Because of the stimulation of the wound and the retention of nutrients, buds can be forced to germinate, and they can be used when they want to fill the gap. Applying BA (benzyl adenine) to buds has a similar effect.
Internal bud external pedal
When pruning, the buds are cut upward or toward the center of the tree, and the secondary buds are outward (Figure 3). Mainly used in the extension branches of tall and straight main branches. After sprouting, the cuttings tend to stand upright, and when the branches below them sprout, the branch angles spread outward. At the end of the first growing season, cut off the upward growing branches (together with the biennial branches). The branch with that second branch as the backbone extend outward. Some pear and apple varieties with strong uprightness can be used for several years, or the 2-3-year-old upright branches can be cut off, and the outward branches can be selected to replace the original backbone branches, and the branches can be extended, that is, "the back branches can be changed."
Fig. 3 Big branch saw
When the crown grows gradually and the dense branches are removed, it needs to be sawed. Used for large auxiliary branch or redundant transition main branch of interlayer. When thinning, first saw a wound below the base of the branch, about 1 ~ 2 cm deep, and then saw it from above the branch to avoid tearing the big branch. Incision should be 0.5 ~ 1.0 cm higher than the branch base, nearly vertical and with a certain slope to avoid water accumulation and facilitate healing. After sawing, cut the incision flat with a knife and coat it with protective agent.
In addition, there are methods such as coring, sprouting, bare branches, and twisting tips (see summer pruning).
Pruning period
Usually it can be divided into dormancy pruning (winter pruning) and growth pruning (summer pruning). Different results can be obtained by the same pruning method in different periods. Before dormancy of deciduous fruit trees, leaves return most of the non-structural nutrients to branches, branches, stems and roots, and finally store them in branches. There is less nutrient loss during pruning in winter, and the stored nutrients can be supplied to the cut buds after pruning. Therefore, the effect of pruning is concentrated near the kerf; Pruning in growth period not only cuts off the grown leaves, but also reduces the photosynthetic function of new leaves, so pruning has obvious effect on weakening the tree potential. At the same time, after the new shoots are cut off, the lower buds regenerate, delaying the growth period, breaking the top advantage, promoting more germination of the lower buds and dispersing the branching force, so the impact on the whole is more obvious than that on the part. Therefore, young trees of apple, peach and other fruit trees are often pruned in summer to quickly adjust the contradiction between their growth and flowering.
Deciduous fruit trees have the least nutrients in their branches from deciduous to severe winter. After the severe winter, nutrition began to pick up. In severe winter, the wound is not easy to heal, and it is threatened by drainage and frostbite, and it is not cold-resistant. Fruit trees with large pith should be pruned immediately after defoliation, and fruit trees with strong cold tolerance, such as apples and pears, can be pruned later; Grape and walnut branches have large pith, so if the cut can't heal immediately, it will easily cause bleeding, so it should be trimmed when the leaves just fall or unfold. Evergreen fruit trees such as citrus do not shed leaves in winter, so they should be pruned after winter and before germination. In warm regions such as Guangdong, Guangxi and Taiwan Province, pruning should be done after harvest or just after dormancy.
Pruning promotes and stimulates the local area; On the whole, it is a kind of loss and weakening. The more pruning, the heavier pruning, the stronger stimulation and the heavier overall weakening. In practice, the amount of pruning should be reduced every year, and only necessary pruning should be carried out to avoid killing; Secondly, the effect of pruning is a gradual process, and the leafy trees need to be pruned slowly for 2 ~ 3 years before they can be alleviated or weakened; Judging from the number of branches, it is also a trend from less to more, and then to too dense. Therefore, the method and degree of pruning should be carefully selected. Once selected, it should not be changed easily, but should be changed slightly due to the change of tree potential in the continuous process. Thirdly, the adjustment function of pruning must be closely coordinated with other soil, fertilizer and water management measures, and the difference of external environmental conditions should be considered in order to give full play to the role of pruning.
Pruning technology has become more and more complex and precise, and even tends to be cumbersome. In order to speed up popularization and save labor, countries such as Europe and America tend to adopt mechanized pruning on the basis of predetermined crown, but it is not suitable for the biological characteristics of fruit trees and can not give full play to the production potential of fruit trees, so manual pruning is necessary. China, on the other hand, gives priority to manual work, combines winter and summer, speeds up plastic surgery, moderately cuts lightly, pays attention to renewal, gives priority to overall balance, simplifies the tree structure, and no longer emphasizes the pruning of twigs and branches, so as to achieve simplicity and improve efficiency.