Spring is the active period of life activities of fruit trees. From the beginning of liquid flow, to leaf spreading and branching, to flowering and fruiting, the nutrients stored in the tree gradually decrease, and it was not until late spring and early summer that the new leaves began to manufacture and accumulate nutrients. At the same time, the rapid growth of new shoots and roots, the expansion and development of fruits and so on. It consumes a lot of nutrients, so the accumulation of nutrients is very small at this time; In late summer and early autumn, the growth rate of branches, leaves and fruits on the ground began to slow down or stop, while the photosynthetic efficiency of leaves was high, which could accumulate a lot of nutrients and was beneficial to the formation of flower buds. In some years, flower buds can even form on the autumn tips. After entering late autumn and before defoliation, fruit trees accumulate the most nutrients, so at this time, fruit tree pruning is only a partial adjustment, not a comprehensive pruning.
Different kinds of fruit trees have different growth and development laws, but they all go through a series of phenological periods in turn, such as root activity period, bud expansion period, germination period, new shoot growth period, flowering period, physiological fruit drop period, fruit rapid expansion period, fruit maturity period, flower bud differentiation period, defoliation period, dormancy period and so on. Different kinds of fruit trees have different phenological periods: stone fruit trees such as peaches, plums and apricots bloom earlier than stone fruit trees such as apples and pears, and bloom first and then spread their leaves; Grapes, persimmons, dates, chestnuts, walnuts and other fruit trees spread their leaves first, branch and then bloom. Although the phenology of fruit trees has a certain order, the length, order and starting and ending time are different due to tree species, environmental conditions, management technology level and human influence. On the same tree, each phenology is often staggered, connected or shows several phenology at the same time. Therefore, the plastic trimming work must also be adapted to it to avoid mistakes. Generally speaking, the life course of deciduous fruit trees in one year can be divided into four periods. Namely vegetative growth period, growth dormancy period, relative dormancy period and dormant growth period.
(1) During vegetative growth, fruit trees form many new organs, such as leaves, new shoots, flowers and fruits. The pruning work should take corresponding measures according to the changes of phenology and tree nutrition, such as twisting the tip, girdling or girdling before the flower bud differentiation stage to promote the formation of flower buds; In order to increase the number of branches and quickly form a crown, coring in summer should be carried out at the early stage of rapid growth of new shoots; In order to promote the formation and plumpness of flower buds, nuclear twisting should be carried out in the slow growth period of new shoots.
(2) Growth dormancy is the preparation stage for fruit trees to enter dormancy in the later period of vegetative growth. At this time, a large amount of starch is accumulated in the tree, and the branches are lignified and fully mature. Later, when starch was converted into sugar, soluble fat, tannin and nitride also increased, and the concentration of cell fluid increased, so did the cold resistance. Leaves fall off too early or too late, indicating that there is little nutrition on the tree and insufficient preparation for wintering. Of course, abnormal climatic conditions will also lead to early leaf fall. Under normal circumstances, when the branches stop growing in autumn and prepare to enter the dormant period, the root system will have another growth peak, which will last until winter. Therefore, after autumn, the branches and leaves are too sparse, which is not conducive to the nutrient return and root growth of trees.
(3) Dormancy of deciduous fruit trees in relative dormancy period is a characteristic formed in the process of system development to adapt to unfavorable external environmental conditions. Deciduous fruit trees actually have two dormancy periods: one is natural dormancy and the other is forced dormancy. Natural dormancy is determined by genetic characteristics. At this time, even if the external environmental conditions are suitable, it cannot continue to grow. The length of natural dormancy period is related to the place of origin, and there are differences among different tree species and varieties, which are formed under the long-term ecological conditions of fruit trees in their place of origin and are adapted to unfavorable external environmental conditions such as low temperature. For example, the natural dormancy of almonds requires a short period of low temperature; Peach, apricot, persimmon, chestnut, pear, etc. , need a long time of low temperature; Walnut, jujube and grape. , the longest time requires the lowest temperature. Forced dormancy is due to inappropriate external environmental conditions, such as sudden cooling and water shortage. Once the external conditions are right, it can continue to grow. The cold resistance of fruit trees after natural dormancy is obviously reduced, so flower buds or flowers are most vulnerable to late frost. Therefore, when pruning in winter and spring, the number of flower buds left is more than the expected yield, that is, a certain safety factor should be left, generally 10% ~ 20%, so as not to affect the yield.
After the fruit trees enter dormancy, the physiological activities are weakened at low temperature, and the respiration and transpiration are kept to a minimum to reduce the consumption of stored nutrients. But at this time, a series of material transformations are still going on inside the tree, such as the growing points of embryos, roots and buds. With the increase of pH value, the activity of lipolytic enzyme increases, starch is converted into sugar, and protein is converted into amino acids. Therefore, dormant fruit trees are still carrying out physiological activities and consuming nutrients, but the number is small. The dormancy of different parts of trees is inconsistent in the morning and evening. Branchlets enter dormancy earlier, big branches and main branches later, and root neck enters dormancy at the latest. Wake up from hibernation in the opposite order. Therefore, the root neck at the base of the trunk is the most vulnerable part to freezing injury, which needs to be protected. When pruning, the wound should be reduced as much as possible to avoid injury.
(4) The period from dormancy to growth and from dormancy to growth. In deciduous fruit trees, this period is mostly around germination. At this time, if the external temperature and water conditions are suitable, the fruit trees will begin to sprout. But the germination time varies with tree species and varieties: peaches and pears germinate earlier than apples, apples germinate earlier than grapes and chestnuts, and jujube trees germinate at the latest; Among peach trees, plum blossoms germinate the earliest; Among apple varieties, Indian and Zhuguang germinated the earliest, while Guoguang germinated the latest. Different types of buds have different germination dates: flower buds are earlier than leaf buds, and terminal buds are earlier than axillary buds. All these physiological activities are closely related to pruning, especially in spring.
All the life activities of fruit trees in early spring are maintained by the nutrients stored in the trees. The richer the stored nutrients, the more orderly the germination and the more vigorous the growth. On the contrary, the germination is irregular and the quality of flower buds is poor. Therefore, when pruning fruit trees in autumn and winter, especially when smearing grape buds, we should cut off the extra buds and shoots that consume nutrients in time, and pay attention to the opening angle of main branches to save the consumption of reserved nutrients.