Key Technical Points for Cultivation and Management of Walnut Trees During the Growth Period
Based on the significant changes in tree growth and development characteristics throughout the life of a walnut tree, the growth period of the fruit tree can be roughly divided into: juvenile stage, initial fruiting stage, full fruiting stage, and senescence stage. In production, corresponding cultivation and management technical measures can be adopted according to the characteristics of each growth and development stage to regulate their growth and development status and meet production requirements.
I. Juvenile Stage
The period from seedling planting to the first flowering and fruiting is called the juvenile stage. The length of this period varies greatly depending on the walnut variety or type. Generally, early-fruiting walnuts have only 1-3 years, late-fruiting seedling walnuts about 7-10 years, iron walnut (Juglans sigillata) seedling trees about 10-15 years, and grafted seedlings of the latter two also require 5-8 years.
Basic characteristics: The tree body has vigorous centrifugal growth, upright branch posture, and 2-3 growth periods per year. Sometimes due to late growth cessation, shoots are prone to winter injury. During the juvenile stage, early-fruiting walnuts reach a tree height of 0.5-1.0 m, with only 1-2 vigorous vegetative branches, but medium and short branches form earlier. During the juvenile stage, late-fruiting walnuts reach a tree height of about 3.0 m, with new shoots reaching over 100, among which the proportion of short branches is relatively small. Grafted seedlings of late-fruiting walnuts have smaller crowns and more branches than seedling trees.
Management key points: In cultivation and management, it is necessary to strengthen vegetative growth as a whole, pay attention to training and shaping so that a firm and balanced framework is formed as soon as possible and the crown is expanded; at the same time, non-skeletal branches should be controlled or left unpruned to promote early flowering and fruiting.
II. Initial Fruiting Stage
The period from the first flowering and fruiting of walnut to before heavy fruiting is called the initial fruiting stage.
Basic characteristics: The tree body grows vigorously, and branches increase greatly. With the increase in fruit set, the branching angle gradually opens until centrifugal growth gradually slows and the tree body basically stabilizes. For early-fruiting walnuts, this is 2-4 years; for late-fruiting walnuts, about 7-20 years; for iron walnut, about 12-24 years, or even later. Late-fruiting walnut mother branches average 2 branches, while early-fruiting walnut mother branches average 1-3 branches. Fruit yield increases by 0.5-2.0 times each year. At this time, the crown diameter of late-fruiting walnuts can reach 5-6 m, while that of early-fruiting walnuts is only 3-4 m. The per-plant yield of early-fruiting walnut varieties is 5-8 kg, and that of late-fruiting walnut varieties is 5-10 kg. Early-fruiting walnuts have a strong ability to produce secondary shoots at this stage, especially during the first 2-3 years of fruiting. Investigations by Wang Hantao et al. showed that late-fruiting walnut trees grew rapidly in crown width within 15 years, belonging to the vigorous period of vegetative growth; investigations by Fang Wenliang et al. showed that while the fruit yield of iron walnut increased year by year, vegetative growth was still very vigorous and centrifugal growth was enhanced. Observations by Liu Wansheng et al. showed that the number of branches of early-fruiting walnuts before 6 years of age roughly increased in multiples, and then the growth rate gradually decreased, but the absolute number of fruiting branches increased significantly.
Management key points: The main task of cultivation at this stage is to strengthen comprehensive management, promote tree formation and increase fruit yield.
III. Full Fruiting Stage
The full fruiting stage refers to the period from when walnut enters the peak fruiting stage to before the beginning of senescence. The length of this period is greatly related to site conditions and cultivation management levels. Under normal circumstances, it is 50-100 years; late-fruiting walnuts are longer, and early-fruiting walnuts are shorter. Wang Hantao and Luo Xiujun of the Henan Academy of Forestry investigated 630 walnut trees in Anyang, Luoyang, Zhengzhou, Xinxiang, Sanmenxia Lushi and other places, showing that walnut trees begin to increase rapidly in yield at 16 years of age, reach the peak fruiting period at 40-90 years of age, and enter a high and stable yield period after 60 years of age.
Basic characteristics: The main characteristics of the tree body during this period are that both crown and root extension reach their maximum, and phenomena such as drying of inner canopy branches, outward movement of fruiting sites, and obvious local alternate bearing begin to appear. Early-fruiting walnuts enter the full fruiting stage at 8-12 years of age, late-fruiting walnuts at 15-20 years of age, and iron walnut (cultivated type) at about 25 years of age. During this period, vegetative growth and reproductive growth are relatively stable. The number of female flowers borne on walnut fruiting branches during the full fruiting stage and the yield level vary by variety. During the peak fruiting stage, the fruiting range of walnut is mostly concentrated in the outer part of the crown. According to a survey of 60-year-old large trees, fruit in the outer crown accounts for about 70%, in the middle about 26%, and in the inner canopy about 4%.
Management key points: This period is when walnut trees produce the greatest economic benefits in their lifetime. Walnut operators should attach importance to scientific management during this period, extend the peak fruiting stage, and obtain higher economic returns. The main task of cultivation is to strengthen comprehensive management, keep the tree body healthy, prevent the fruiting sites from moving outward excessively, timely cultivate and renew fruiting branch groups, and even renew some weakened secondary skeletal branches, so as to maintain high and stable yield and extend the duration of the full fruiting stage.
IV. Senescence Stage
This stage is from when the plant begins to enter senescence until complete death. The timing of the beginning of this period is related to site and cultivation conditions. Late-fruiting walnut and iron walnut begin at about 80-100 years, while early-fruiting walnut enters the senescence and renewal period earlier.
Basic characteristics: Fruit yield declines significantly, skeletal branches begin to die, and renewal branches emerge from the rear, indicating entry into the senescence and renewal period. In the early stage, the ends of main branches and lateral branches begin to die, the crown volume shrinks, more water sprouts emerge in the inner canopy, centripetal growth appears, and yield generally declines. In the later stage, a large number of renewal branches emerge from skeletal branches. After repeated renewal, tree vigor is significantly weakened, yield also drops sharply, and it may even lose economic cultivation value.
Management key points: The main task of cultivation and management during this age period is, on the basis of strengthening soil, fertilizer, and water management and tree protection, to carry out planned renewal of skeletal branches, form a new crown, restore tree vigor, maintain a certain yield, and extend its economic life. The timing of the beginning of the senescence and renewal period of walnut trees and the length of its duration vary greatly depending on variety, site conditions, and management level.
The above briefly describes the growth and development characteristics of walnut throughout its life in 4 stages. The stages are organically linked and develop and change. In order to obtain high and stable yields, reasonable cultivation technical measures must be adopted according to the characteristics of individual walnut development, so as to promote the early arrival of the peak fruiting stage and delay its end.