Walnut is a high-quality tree species with the characteristics of poor adaptability, large yield, long growth life and outstanding ecological and economic benefits. Walnut, as an economic tree species, needs pruning in order to achieve high and stable yield. Correct pruning is conducive to creating a good tree structure, ensuring the grouping and even distribution of fruiting branches, solving the contradiction between vegetative growth and reproductive growth branches, and realizing premature delivery, stable production, high yield and high quality. Based on many years' working experience, this paper analyzes the pruning techniques of walnut trees, hoping that this research can be helpful to growers.

Walnut tree is an important economic tree species in Xinjiang, with developed root system, fast growth and long life. After planting branches for 6-8 years, it gradually enters the fruiting period. Proper shaping and pruning of walnut trees can effectively inhibit the bad growth of trees, adjust the internal structure of the crown, ensure good ventilation and sufficient sunlight, save nutrients, and promote walnut trees to bear more fruits early, thus achieving the goal of high yield.

Pruning principle of walnut tree

1. 1 pruning season selection

Walnut trees are very different from other economic fruit trees. The pruning of walnut trees must choose the season scientifically. If the season is wrong, it is likely to cause bleeding. Hemorrhage is the transparent liquid flowing from the wound when the walnut branch is bumped, trimmed or injured. This liquid is called blood. The bleeding period usually starts from 1 1 month after the leaves of walnut fall to the end of dormancy in late March of the following year, whether it is young fruit trees or fruit trees in fruiting period. Usually, the best pruning period of walnuts is from long summer to small branches, during which the branches are abundant. Choosing the right fruiting branch group and removing the useless branches will make the tree grow vigorously, which can accelerate wound healing, avoid cracking and consume less nutrients. After picking branches in autumn, pests and dead branches on fruit trees should be removed in time.

1.2 Pruning principle

In the process of pruning walnut trees, we should adjust measures to local conditions according to the age, growth state and actual situation of the planting area, and the number of fruiting branches of different walnut trees is different, so as to ensure adequate nutrient supply and ensure that pruning will not affect the growth and development of walnut trees in that year.

1.3 pruning method

Pruning walnut trees mainly includes several processes, such as cutting short, retracting, thinning branches, removing cores and smearing buds. Short cutting is mainly aimed at annual lignified branches, which means that more new branches grow from short cutting parts after removing the upper branches of branches. The purpose of short cutting is to accelerate the germination of new branches through local stimulation, promote the robust growth of backbone branches, ensure the outward growth of the whole crown, expand the crown and improve fruit yield. The retraction method is the same as that of the nipple. Mainly aimed at the perennial branches of walnut trees, the purpose is to prevent the fruiting branches from extending outward, accelerate the growth of fruit trees, and make the fruiting branches of fruit trees more concentrated and the nutrient supply more concentrated.

The purpose of thinning branches is to remove invalid and redundant branches in the crown, increase the ventilation and light transmission of fruit trees and strengthen photosynthesis. Branching is mainly to remove too dense branches, pests and diseases, dry branches, clustered branches, overlapping branches and crossed branches. For branches that grow too vigorously, the top of the branch can be cut off together with that part. The purpose of this is to eliminate the growth advantage of the top of the branch and prevent the branch from growing vigorously without complete lignification. This process is called coring. When the fruit tree enters the germination stage, the extra buds on the branches can be erased, which can ensure the reasonable layout of the whole resin, prevent excessive consumption of nutrients and avoid new wounds. Through reasonable pruning and shaping of fruit trees, the light intensity inside the crown of fruit trees can be adjusted, the tree potential can be balanced, and the fruiting branches can be cultivated to achieve the goal of stable and high yield.

Pruning technology of walnut tree

2. 1 Pruning of Young Walnut Forest

For walnut trees that have not reached the fixed dry height in the first year of planting, do not prune them, let them grow and form strong branches. In the second year, when the height of the walnut tree grows to more than 1.5m, the stem is fixed, and the branches are cut at the position 1- 1.2m from the ground, and the lateral buds below the fixed stem height are erased. Walnut trees are planted at a slow seedling stage, and their growth rate is relatively slow. After entering the second year, it will enter the rapid growth period, when a large number of branches will germinate, and it is necessary to prune and retain the branches in time. The walnut trees planted in the second year are mainly for cultivating branches.

Choose upright and strong branches as the central trunk. After the backbone branch is cultivated and branched, the lateral branch on one side of the backbone branch is reserved, a high-yield tree shape is cultivated, and insertion selection is carried out. Generally, three branches with similar growth are selected as 1 layer to avoid overlapping branches. The horizontal angle is about 120 degrees, and the interlayer distance is 20cm. After the branch of 1 layer is selected, select the second layer to ensure that the branch spacing between 1 layer and the second layer is controlled at 1.5-2m. After the main branch is selected, the lateral branch should be selected, which is the key to ensure the stable and high yield of walnut. The selection method of lateral branches is the same as that of branch group. The lateral branches should be reasonably distributed on each branch group. 1 Each branch group should have two lateral branches. 1 Branches should keep a distance of 40-60cm from the second branch, and the spacing between branches should be 40-60cm, so as to ensure the subordinate relationship between the lateral branches and the central trunk. In the process of pruning, competitive branches and excessive branches should be removed in time, and more auxiliary branches should be left appropriately.

2.2 Pruning of Walnut Forest at Early Fruiting Stage

Generally, walnut trees gradually enter the fruiting period after 6-8 years of planting. If you choose grafted seedlings, you can bear fruit 2-3 years in advance. On the basis of continuing to cultivate branches, ensuring uniform distribution of branches and reasonable crown structure, make full use of auxiliary branches to create fruiting branches to ensure premature and stable fruit trees. When the walnut tree enters the initial stage of fruiting and grows to a certain height, the top branches of the walnut tree should be removed in time to control the height of the walnut tree. By lowering the head and removing the top, the contradiction of branch growth in the crown can be effectively solved, and the nutrient supply can be ensured to be more adequate. In addition, it is necessary to choose the fruit branch owner and continue to expand the crown. Juglans regia has a large amount of germination in the fruiting period, which easily affects the ventilation and light transmission of the crown, so all branches that hinder the growth of branches and side branches should be shrunk inward, and branches that grow too densely should be thinned out. In the process of pruning and shaping fruit trees, in addition to arranging the branches of backbone branches at all levels, the branches threatened by pests and diseases should be pulled out in time and taken out of the orchard for centralized treatment.

2.4 Pruning of Walnut Forest in Full Fruit Period

Walnut trees have been planted for about 15 years, and gradually enter the full fruit stage. At this time, only scientific management is needed to ensure that the result is about 50- 100 years. After the walnut tree enters the full fruit period, it should slowly expand its crown and remove the branches that grow outside in time. With the increase of yield, the height of walnut trees should be controlled between 8- 10m branches, and when the branches reach the height, they should be turned around in time to remove the top. Entering the life stage, the peripheral branches gradually become fruiting branches, and the fruiting parts gradually extend outward. At this time, the growth contradiction inside and outside the crown is prominent. Once improperly managed, the external branches of the crown will be too dense, and the internal branches will overlap and affect each other, which is not conducive to improving the yield and quality of walnut trees. At this time, it should be properly thinned to improve the ventilation and lighting conditions inside the crown, so as to achieve the purpose of high and stable yield.