Detailed Explanation of Common Walnut Tree Shapes and Training Techniques

  A rational tree shape is the framework of the tree, the foundation for bearing yield, and the basic condition for high yield, quality and efficiency. The purpose of training is to create a solid tree framework, ensuring the leaf canopy can intercept light energy to the maximum extent and bear a relatively high yield. A rational tree shape should meet the requirements of early fruiting, high quality, high yield, easy management and high efficiency. The specific tree shape should be determined according to site conditions, management level, cultivar characteristics and cultivation methods.

  With the current trends in fruit tree production of trees changing from tall to short, density increasing from low to high, and tree shapes changing from complex to simple, the tree structure of fruit trees has undergone considerable changes, with smaller individual trees and simple structures replacing the various tree shapes used under the previous large-canopy, sparse-planting conditions. The goal is to fully and rationally utilize space, obtain the best population benefit, cultivate a rational and robust structure, maintain a stable tree vigor, and enable it to bear a relatively high yield.

  The heterogeneity of walnut branches and buds is very strong, and if left to grow naturally it is difficult to form a good tree shape. This is especially true for early-fruiting walnuts, which, because of their strong branching ability, early fruiting and tendency to produce secondary shoots, more easily develop disordered tree shapes. Therefore, in walnut cultivation and management, attention must be paid to the training of young trees.

  At present, walnut tree shapes in China mainly fall into two categories: the central-leader form represented by the scattered stratified shape, and the open-center form represented by the natural open-center shape. The scattered stratified shape has an obvious central leader, generally with 6-7 main branches arranged in 2-3 layers in a spiral on the central leader, forming a semicircular or conical crown. This tree shape is suitable for sparse planting in places with better conditions and strong trunk dominance. The natural open-center shape has no central leader, generally with 2-4 main branches. Its characteristics are quick formation, early fruiting, relatively flexible arrangement of scaffold branches at all levels, easy training and easy mastery. Young trees are relatively upright in shape and gradually spread after entering the fruiting stage, with good ventilation and light penetration and easy management. This tree shape is suitable for early-fruiting walnut cultivars planted in areas with thinner soil layers, poorer soil quality and poorer fertilizer and water conditions. According to the number of main branches, the open-center shape can be divided into two-main-branch, three-main-branch and multi-main-branch open-center shapes, among which the three-main-branch open-center shape is more common; and according to the size of the opening angle, it can be divided into multi-trunk shape, upright shape and open-center shape.

  In actual production, an appropriate training method can be selected according to cultivar characteristics, planting method, site conditions and management level. In general, early-fruiting walnuts have weak trunk dominance and are suitable for the open-center shape, while late-fruiting walnuts have strong trunk dominance and are suitable for the central-leader shape; for sparse planting the central-leader shape can be used, and for dense planting the open-center shape can be used; in mountain cultivation growth is weak and it is easy to train into the open-center shape, while on flat land and under conditions of relatively high management level, growth vigor is relatively strong and it can be trained into the central-leader shape. The general principle of walnut tree training is: "Have a shape but do not be bound by it, have no fixed shape but do not let it become disordered; prune according to the tree, and shape according to the branches."