Walnut is an important oil-bearing fruit tree with high economic value. Walnut kernel is not only rich in fat, but also high in protein, vitamins and various minerals. Often used as a senior tonic, it has a certain medical effect. Walnut kernels in China are of good quality and high oil content, which are well received by the international market. Walnut and walnut kernel are both important traditional export raw materials.
Walnut is a fruit tree with strong tree property, strong adaptability, less pests and diseases, labor-saving management, convenient storage and transportation and long life, which is very suitable for mountain development.
Main types
Walnut belongs to the genus Juglans, and there are two kinds of economic cultivation: common walnut and iron walnut. Most of the varieties cultivated in the north and south of China belong to common walnuts. Iron walnut, also known as Yangbi walnut, is mainly distributed in Yunnan, Sichuan and Guizhou. This kind of walnut likes damp heat but is not cold-resistant, which is another ecotype different from ordinary walnut. In addition, there are wild Juglans mandshurica and wild walnut, both of which belong to the same genus.
It is worth mentioning that Carya cathayensis, another genus of Juglandaceae, also has a nut-producing fruit tree called Carya cathayensis, also called Carya cathayensis or Carya cathayensis. /kloc-was introduced to China at the end of 0/9, and is now cultivated sporadically in Jiangsu, Zhejiang, Fujian, Jiangxi and other provinces. Sex is warm and moist, nuts are big, rectangular, shells are thin and kind, and tastes good. It has great development value in the Yangtze River basin and its south area.
Walnut has always been propagated by seeds, most of which are local seedling types, and few varieties are formed by asexual propagation. Juglans regia can be divided into early fruiting walnut (fruiting 2-4 years after sowing) and late fruiting walnut (fruiting 5- 10 years after sowing) according to the date of fruiting and the thickness of core shell.
Growth and fruiting habits
Walnut is a tall deciduous tree with deep and wide roots and strong dryness, especially the dominance of branches and tops. Most of the middle and lower lateral buds are dormant or dry, and fall off after germination, so the branches in the crown are sparse.
Dormant annual branches can be divided into growth techniques, fruiting mother branches and male flower branches according to bud types. Any branch with only leaf buds (occasionally male flower buds) is a growing branch. Among them, what is located at the periphery of the crown and grows vigorously is the basis for expanding the crown and forming the fruiting mother branch. Branches with top 1 ~ 3 nodes (some varieties can be more) all bear mixed buds (female flower buds), and those that can bear new branches, blossom and bear fruit in the next year are the bearing mother branches. Results Besides mixed buds, there were leaf buds and male flower buds under the mother branch. Where only male flower buds and leaf buds are born on the branches, only male inflorescences are born in the second year, and male flower branches cannot bear fruit. This kind of branches generally grow short and weak, and many of them are in closed places in old and weak trees and crowns. After the male inflorescence falls off, it is bare below the terminal bud.
The lateral buds in the middle and upper parts of walnut branches are often compound buds, which are arranged in an overlapping manner. There are many forms such as female flower buds overlapping leaf buds, leaf buds overlapping male flower buds, male and female flower buds overlapping, male and female flower buds overlapping, double leaf buds overlapping and so on. Buds at the base of branches often become hidden buds.
Branches can have two growth peaks a year, forming spring shoots and autumn shoots. The branch angle is large and the crown is open. The weak branches in the upper part of adult trees tend to grow horizontally, forming strong back branches and disturbing the tree shape.
The age of first fruit of walnut is related to varieties and propagation methods. The early-fruiting walnut propagated by grafting can bear fruit in 2 ~ 3 years after planting, and the late-fruiting walnut propagated by seedling needs to bear fruit in 5 ~ 10 years, and grafting can advance the bearing age. Generally, it enters the full fruit period in 20 ~ 30 years, and its economic life is very long.
Walnut is monoecious. Wind media. Female flowers are inserted at the top of new branches, solitary or clustered with 2 ~ 3 flowers. The male flowers are clustered together. The flowering periods of female and male flowers on the same plant are often inconsistent, which affects pollination. Pollen viability is often low and effective pollination time is short, which is one of the reasons for low yield. The growth period of fruit is long, and the volume increases mainly in the early stage, and the middle and late stage is the period when the shell becomes hard and the grain is full. The fruit is wrapped in fleshy involucre and naturally cracks when it matures. Individual varieties have certain parthenogenetic ability.
The physiological fruit drop weight of most varieties began at 10 ~ 15 days after anthesis and basically ended at the hard shell stage. The fruiting branches extracted from the terminal buds of strong fruiting mother branches have high fruit-setting rate and can bear fruit for many years. The fruiting rate of fruiting branches extracted from short and weak fruiting mother branches or side mixed buds is low. However, at present, varieties with lateral bud setting rate as high as 60% have been cultivated in China.
Key points of cultivation techniques
1. The seeds planted are simple to propagate and raise seedlings, but the fruits are late and easy to mutate, which affects the commercialization of fruits. Grafting propagation should be gradually popularized in the future.
Grafting propagation of common rootstocks or wild walnuts. Sow in autumn or spring after sand storage. The sand storage time needs 60 ~ 90 days. If it is spring sowing in dry storage, the seeds should be soaked in warm water for 5-7 days before sowing, and the water should be changed every day 1 time, so as to promote seed imbibition and shell cracking and improve the emergence rate. The grafting method is mainly spring grafting (subcutaneous grafting or split grafting). Walnut trees have bleeding during dormancy, and the phenological adaptation period of grafting is delayed compared with other fruit trees, otherwise it will affect their survival. It usually takes about 10 days from rootstock germination to leaf development. However, the scion should be cut in advance and stored with moisture at a low temperature of 0 ~ 5 degrees. Bud grafting is carried out from July to September, and the square bud grafting method is commonly used. There are many tannins in the bark of walnut branches, which are easy to form an isolation layer at the interface. Therefore, the grafting operation is rapid and the section is smooth, which is beneficial to improve the grafting survival rate.
The row spacing of planting plants depends on the variety characteristics and soil fertility. When the planting area is (4 ~ 5)m×5 ~ 8)m, the row spacing of fruit grains can be expanded to 25 ~ 30 m ... It is required that the soil layer in the planting area is deep, and too barren land is easy to form "small old trees", which is not suitable for planting. Pay attention to planting pollinated trees when planting. Walnut seedlings have few lateral roots and are not resistant to transplanting, so they should be planted quickly after emergence, and the roots should not be exposed for too long, so attention should be paid to moisturizing before planting and after planting.
2. Pruned walnut is a light-loving tree species, especially after entering the fruiting period, it needs sufficient light. Trees are generally in the form of evacuation and layering or natural happiness. Varieties with strong dryness and good site conditions adopt vacuum layered modeling, and their specific requirements and operation procedures can refer to apples. Walnut has the characteristics of late branching, vigorous tree body and strong back branches. Therefore, during plastic surgery, we should also master the requirements of the height of high stem (1 m ~ 1.5 m) and the growth period of late stem, appropriately expand the layer spacing and the distance between the first main branch (that is, the side branch) and the central trunk, and it is not appropriate to choose the back branch as the back branch, which is a variety with weak crown and site conditions.
The pruning of young trees mainly deals with some branches that interfere with the tree shape. For example, early-bearing walnuts are prone to produce a large number of secondary branches and male flowers, and sometimes they are easy to grow branches. The secondary branches and long branches that need to be preserved should be picked or chopped in time and cultivated into fruiting branches; The rest should be removed as soon as possible. For the back branches that are easy to usurp the host's role, the branches located on the first layer of main branches and auxiliary main branches are all thinned from the base; Those located on the main branches and auxiliary branches on the second and third floors shall decide whether to stay or not according to their needs and growth strength. When the remaining branches grow vigorously, they can be removed from the core or shrunk back to be transformed into branches.
In order to improve the lighting conditions in the crown, adult trees should remove dense branches and drooping branches in time, and shrink the auxiliary branches that occupy a large space. When the proportion of short branches and male flowers in the crown increases, it shows that the tree has gradually weakened and should be renewed and rejuvenated in time. For the fruiting branch group, we can remove the weak and retain the strong, retract and update, make full use of the over-flourishing branches in the crown, carry out transformation and increase the proportion of strong and prosperous branches. When the scorched tip, big branch and middle branch die, it means that the tree has aged. Backbone branches at all levels can be retracted and renewed year by year, and the fruit-recovering ability of COVID-19 can be re-formed by using the long life of hidden buds of walnut.
Pruning of walnut during dormancy often leads to bleeding due to poor wound healing, which seriously affects the tree vigor. The suitable pruning period is after fruit picking in autumn and before leaves turn yellow. In addition, it can also be pruned after germination.
3. Soil, fertilizer and water management and sparse male walnut have deep roots and great demand for fertilizer and water. After defoliation, plough deeply ~ times a year, enlarge the tree tray and apply base fertilizer. Weeds are deeply planed during the growing period and ploughed after the rain. Topdressing should be carried out 2 ~ 3 times before germination, after flowering and during hard core stage. In the early stage, nitrogen fertilizer was mainly used to promote the growth of spring shoots and young fruits. In the later stage, nitrogen, phosphorus and potassium cooperated to promote flower bud differentiation, enrich nucleolus and improve nucleolus quality. After each fertilization, irrigation can be combined. Walnut is sensitive to drought, and areas lacking water can be covered with soil moisture. In the rainy season, it is necessary to drain the water in the field. After the spring shoots stop growing and before the autumn shoots stop growing, attention should be paid to water control to control the later growth of new shoots. In areas where freezing drought often occurs in winter and spring, frozen water should be poured once in early winter.
The number of male flowers in adult walnut trees is very large, which consumes the nutrients of the tree. When the male flower buds begin to swell, it is beneficial to increase production to take measures to sparse males (75% ~ 80% in full fruit stage).
Main pests and diseases and their control
1. The main diseases are walnut black spot and walnut anthracnose. Black spot of walnut is a bacterial disease, which harms fruit, leaves and branches, causes fruit rot and early fruit drop, and reduces kernel rate. Prevention and control methods: spray lime-sulfur mixture with Baume degree of 3 ~ 5 once before germination, spray Bordeaux solution with lime amount of 200 times before and after flowering, and spray it continuously for 2 ~ 3 times every 20 days thereafter. Walnut anthracnose is a fungal disease, which mainly harms fruits and can infect apple anthracnose. The control method can refer to apple anthracnose.
2. Pests mainly include walnut, small walnut, inchworm and Anoplophora versicolor. Walnut, also known as black walnut, occurs seriously in North China, with 1 ~ 2 generations per year. The larvae eat green husk, which makes the involucre black and rotten, the young fruit falls off, the nucleolus shrinks, and the mature larvae overwinter in the soil. Prevention and control methods: combined with deep planing of trees, 50% phoxim 300 times solution is sprayed on the ground for poisoning; Spraying 50% chlorpyrifos 1000 times solution or 20% metronidazole EC 5000 times solution before adults lay eggs and eat fruits; When the damage is slight, the fruit of the insect is removed and buried deep before the larva loses the fruit.
Harvest and storage
The best harvest time of walnut fruit is when the involucre turns from green to yellow and some of it naturally cracks. Harvesting too early, the involucre is not easy to peel off, and the kernel yield and oil yield decrease. The harvested involucre must be blanched and peeled. That is, pile walnuts on the site with a height of 30 cm ~ 50 cm and cover them with wet mats. After 3 ~ 5 days, the green husk can fall off with a stick. You can also soak peeled walnuts with 40% ethephon 500 ~ 1000 times solution, then pile them up for 24 hours and beat them with a stick. Green husk is easy to fall off, and the core-shell is clean and pollution-free.
Wash the peeled wet walnuts with clear water in time and bleach them immediately. Walnuts exported must be bleached to improve their appearance. Firstly, the bleaching powder is made into 80 times solution, then the walnut is put in, stirred constantly, taken out after 8 ~ 10 minutes, rinsed with clear water, spread on the foil pad and dried. When drying, the Qin Ying should be rotated to avoid the yellowing of the backlight surface and affect the quality. When the nucleolus becomes brittle, the cross section is white and the diaphragm is easily broken, it can be stored in a freeze-dried and ventilated place. Always check when storing, and pay attention to moisture and rats. If there are some moldy deterioration, take them out and dry them.
Key points of walnut grafting technology
Walnut grafting is one of the effective ways to improve the existing varieties, increase the commodity of walnuts and improve the economic benefits of walnut planting. Through walnut grafting, young trees can bear fruit early, old trees can be rejuvenated, fruit-bearing life can be prolonged and quality can be improved.
First, the preparation work before grafting
1. The grafted scion is taken from the annual fruiting branch of the superior tree, and its length is 15 ~ 20 cm. After collection, it was divided into 50 varieties and preserved in time by wax sealing. Scions were collected in1~ February. Stored in an ice room, the air temperature is controlled below 5℃, the humidity is about 70%, and the water content of wet sand is about 30%.
2. The rootstock is ready and suitable for beginners to graft. It is best to select 3 ~ 10 young trees for grafting.
3. Preparation of grafting materials ① Waxing: rosin, mineral wax, animal oil and alcohol. ② Binding materials: polyamide fiber rope and thickened plastic film. (3) Waste newspapers. ④ Plastic pipe: diameter 10 ~ 15cm, length 20 ~ 30cm. ⑤ A bamboo stick with a width of 2 cm.
Second, the grafting method is half-joking grafting.
Third, the grafting time is half a month before and after Qingming.
Fourthly, the grafting step
1. Remove miscellaneous irrigation, weeds and shade trees around the rootstock before grafting.
2. The bleeding of walnut tree is serious, which seriously affects the wound healing after grafting. If the bleeding is not handled properly, the survival rate is very low. Therefore, water must be drained before grafting to reduce bleeding. The method is: after cleaning the rootstock, use a hand saw to cut the cortex symmetrically from 10 cm above the ground, and then reach the xylem to make water flow out, resulting in 5 ~ 10 wounds. If possible, cut off a big root and drain water.
graft
(1) Cut off the trunk at a distance of 1.2 ~ 1.5 meters from the ground, flatten the section with a knife, and let the larger trees graft multiple heads.
(2) Selection of scions: select more than three scions with full buds, small pith, no germination, no water loss and no mildew, cut them into oblique sections, the length of which is 3-5cm, and peel off the wood and cortex.
③ Select the smooth side of the tree trunk on the cutting surface of the rootstock, cut it into crescent shape with a knife, and gently peel off the rough epidermis on the cortex of the rootstock with a knife to expose the green skin. The crescent is 0.8 ~ 1cm in width and 3 ~ 5cm in length. Insert the bamboo stick between the wood and the cortex to a depth of 3 ~ 5 cm. After pulling out, peel off the cut scion, insert it into the wooden part, press the scion cortex on the rootstock, then tie it firmly with polyamide fiber rope from bottom to top, and evenly wax the joint.
④ Bandage: There are two situations. One is to wrap it with thick plastic film from bottom to top until it is wrapped on the top of the scion. The other is to tie the plastic film wrapped in waste newspaper into a tube, and tie the lower part tightly. The length of the tube is 5 ~ 10 cm longer than that of the scion. Fill the cylinder with wet soil and tamp it gently. The height of soil is 3 ~ 5cm higher than that of scion, and the humidity should be pinched by hand. It is advisable to loosen it, tie the upper part tightly and put on a plastic bag.
Due to the unfavorable factors such as large bleeding, crooked scion and large pith, the survival rate will be improved only if the tools are sharp and the operation is accurate and standardized in the grafting process.
Verb (abbreviation for verb) management after grafting
1. Clean the roots and sprout. Because the upper branches of the rootstock have been removed and the scions have not been picked, the hidden buds on the rootstock are easily pulled out. If it is not removed in time, it will consume nutrients and water and affect survival and growth. Therefore, the buds on the rootstock must be wiped early and cleaned small.
2. Put fresh air on the grafted walnut tree for bagging and topdressing. Half a month after grafting, after the scion germinates, before the sun comes out every morning, gently open the bagging to reveal a bud and gradually open the bagging. Don't be too hasty in outdoor activities. Be diligent and focus on small things to prevent the sun from burning.
3. Wind damage Because the leaves of walnut branches are large and the wound has not completely healed, it is necessary to prevent wind damage. After the new tip is about 20 cm, the bracket should be tied in time to prevent wind damage.
4. After the new tip is 30cm long, untie the polyamide fiber rope.
5. After the new buds grow, use 40% omethoate 1000 times solution to control pests in the middle and late May.