Detailed Explanation of Key Cultivation Techniques for Pecan
As an important and highly valuable plant, pecan cultivation techniques should begin with an analysis of its basic characteristics, combined with various propagation techniques, and then through advanced cultivation methods, ultimately new varieties can be obtained for efficient production. First, one should study its phenological phases, propagation methods and steps, planting process, management methods, and pest and disease control methods to ensure that problems can be overcome during the cultivation process.
Phenological Phases
In Kunming, Yunnan, late March to early April is the budbreak period, early to mid-April is the leaf expansion period, early April to late August is the period of rapid new shoot growth, and mid-November is the leaf fall period.
Propagation
Sowing is the main method, but root-sucker seedlings can also be used for propagation. Seeds used for sowing must be fully mature nuts. After the seeds are harvested and water-selected, they are sown in autumn, and the seeds must be placed horizontally when sowing. If not sown in autumn, they must be stored in stratified moist sand. Seedlings generally must be cultivated for 2 years before they can be lifted from the nursery for planting. They can also be propagated in spring by grafting with the branch grafting method.
Sowing
After the fruits are harvested, spread them in a ventilated place indoors. Wait until most of the outer husks have split open, then remove the seeds; the seed yield rate is 50%-75%. The 1000-seed weight is 4500 g, and the germination rate is 75%-85%. Sowing can be done in both spring and autumn, but autumn sowing is less safe than spring sowing because the seeds are easily gnawed by rats and birds. Sometimes drought in winter causes the seeds to lose water and results in a low emergence rate. Autumn sowing can usually be completed before the soil freezes in autumn, while spring sowing should be done early, and can be sown in mid-March. If sowing in spring, the seeds must undergo sand storage treatment. That is, in winter mix them with sand and store them in a trench (at a temperature of 0-5 degrees C), and keep them in sand storage for 70-80 d. The ratio of sand to seeds is 3:1. During stratification, the seeds should be kept in thin layers to prevent the seeds from heating up and becoming moldy. When the temperature rises in early spring, check and turn them frequently. For seeds that have not undergone sand storage, soaking to promote germination can be done before sowing by soaking the seeds in cold water. Soaking is best done 2 times in succession; the first soaking should be longer, soaking for 36-48 h, then removing and draining for 24 h, then soaking again in cold water for 24 h. During the second soaking, adding potassium bromide solution (at a concentration of 300 ppm) gives better results. After the second soaking, they can be sown. For autumn sowing, it is best to use high-ridge sowing, with a ridge spacing of 60-70 cm and a seed spacing of 8-10 cm. When sowing, the hilum should face downward, or the seed suture line should be placed vertically. The covering soil thickness is 4-5 cm. It is best not to irrigate before the seeds germinate. They sprout and emerge 40 d after sowing, and ordinary management after germination is sufficient. The seedling survival rate reaches more than 80%, and the seedling yield is 10,000-15,000 plants/667 sq m.
Grafting
The rootstock used for grafting is generally walnut. In the cold regions of North China, Manchurian walnut is used; in the Yangtze River basin, wild walnut is mostly used; in Shandong and Shaanxi, Chinese wingnut is used. Collect scions from superior individual plants, and select plump and vigorous developmental branches from the outer part of the canopy, 30-40 cm long and 1-1.5 cm thick. Use the plump and full buds in the middle and lower parts of the scion as the graft buds. Immediately after the scions are collected, cut off the leaves, leaving only a 1-1.5 cm long petiole to reduce water evaporation. After removing the leaves, immediately place them in a bucket, cover them with a wet cloth, or place them in wet sand to prevent water evaporation. It is best to use scions collected the same day on the same day; if they cannot all be used the same day, they should be buried in wet sand or moist sawdust, and not placed in a bucket, so as not to affect the grafting survival rate. This is especially true for bud grafting; graft buds soaked in water have an extremely low survival rate. Walnut, Chinese wingnut, and Manchurian walnut used as rootstocks all have bleeding during the dormant period, and bleeding affects callus tissue formation; the scions are easily rotted by the bleeding and cannot heal and survive. Therefore, grafting should be done when there is very little or no bleeding. Branch grafting is carried out after budbreak. The bark-flap tongue grafting is most suitable from walnut leaf expansion to the end of male flowering.
Cuttings
Select vigorous 1-year-old branches; the cuttings are 17-20 cm long. With ordinary cutting methods, the survival rate is more than 90%.
Root Cuttings
Collect roots in conjunction with lifting seedlings from the nursery, then heel them in, and carry out cuttings in spring. The root pieces are 1 cm in diameter and 10 cm long. Root cuttings are best done in beds, and the upper cut end of the root must be buried 0.5-1 cm below the bed surface.
Layering
During the dormant period, bend vigorous branches from the base of the mother plant into the soil. After a period of time they will root, then separate the branch from the mother plant, transplant it, and cultivate it further.
Planting
Choose plots with deep, loose soil, sufficient water sources, and shelter from the wind and facing the sun for planting. A plant spacing and row spacing of 4 m x 5 m to 7 m x 8 m is suitable. The planting hole should be 1-1.5 m in diameter and 1-1.2 m deep; keep the topsoil and subsoil separate, first place a layer of straw at the bottom of the pit, then cover with topsoil to 20 cm; add 50 kg of organic fertilizer, 20 g of Jiadi powder, and 500 g of superphosphate, and mix thoroughly with the soil. Plant seedlings from December to January. After planting, firm the tree basin and water thoroughly to settle the roots. Direct sowing to establish an orchard is also possible. The sowing time is from October in winter to March of the following year, and it can be done except during freezing weather. When transplanting, it is best to keep a soil ball for short-distance transport; for long-distance transport, after the seedlings are dug up, the roots should immediately be dipped in mud slurry, which can provide protection.
Orchard Establishment
Transplant after leaf fall or before germination. Large seedlings should be moved with a mud ball, and 1-2a-old small seedlings must retain more lateral roots and fibrous roots and be promptly dipped in mud slurry to avoid root water loss that would affect survival. A plant spacing and row spacing of 5 m x 7 m or 6 m x 8 m is more suitable. In the young tree stage of walnut, especially before the first winter after planting, attention should be paid to measures such as burying the soil and building soil mounds to protect young trees from cold and from shoot dieback. Especially in the cold winter regions of North China and Northwest China, whitewashing the trunks of large trees (with lime) helps prevent trunk frost damage. Common tree forms of walnut include the open-center stratified form, the natural open-center form, and the upright cylindrical form, with the open-center stratified form being the most common. Because walnut has bleeding, pruning is mostly carried out from after harvest to before leaf fall. Late-fruiting walnut bears fruit on terminal buds or the top 1-3 buds, so the fruiting branches should not be excessively short-cut. Most types of early-fruiting walnut have a high proportion of lateral flower buds, so short cutting can be carried out. Because the branching angle is large and growth on the back side is vigorous and easily inhibits the extension shoot, the trunk of walnut should be headed higher. In order to achieve internal and external and three-dimensional fruiting in the tree body, fruiting branch groups should be developed on the scaffold branches. The specific method is to use the measures of “release first, then retract” or summer pinching of vigorous shoots. Planting density and varieties should be determined according to the site conditions of the orchard. The plant spacing and row spacing are generally 3-6 m x 4-8 m. In areas with deep soil, good soil texture, and high fertility, the plant spacing and row spacing should be larger, and vice versa smaller. When planting, pay attention to variety matching. More than 3 varieties with strong mutual pollination compatibility should be planted in the same plot to help increase the fruit-setting rate.
Training and Pruning
Early pruning should be light, and appropriately more scaffold branches should be retained so that they bear fruit early. When pruning, the inner canopy of the tree crown should be kept ventilated and light-transmitting. In the early stage, shoots in the upper part of the crown should be retained as much as possible, while the lower part of the crown can be gradually thinned, and overly dense large branches can be sawed off when necessary. Saw cuts must be smoothed and coated with a protective agent to prevent decay. After hickory enters the aging stage, all parts above the point where renewal shoots occur in the crown can be sawed off, and the already sprouted renewal shoots should be cultivated; all dead parts of the main branches of the aging crown should be cut off. While carrying out branch renewal by cutting back, it is best to combine this with deep plowing and fertilization.
Fertilization and Management
High-yield orchards produce more than 500 kg per 667 sq m. Within 1-3 years of orchard establishment, crops such as soybean, corn, and Atractylodes macrocephala can be intercropped. During intercropping, the orchard should be cultivated and weeded, and appropriate amounts of organic fertilizers such as burnt mud ash, cake fertilizer, and barnyard manure should be applied. In addition, 1-2 times each year from July to August, cut down woodland weeds, shrubs, thorns, vines, and so on, and cover the woodland with the cut weeds. In winter, plow the mulch into the soil to increase soil fertility. Each year before spring germination, apply about 30 kg of urea per 667 sq m, apply 80 kg of special fruit tree fertilizer during the fruit swelling period, and apply 3000 kg of base fertilizer in autumn. After entering the fruiting period, increase fertilizer application according to the fruiting situation. Combined with pesticide spraying, foliar fertilizer can be applied once about every 15 days; spray 0.3% urea in the early and late growth stages, and spray 0.3% monopotassium phosphate in June-July. In winter, water thoroughly for overwintering and for budbreak. In the rainy season, drain promptly to prevent waterlogging. Fruiting trees are fertilized 2 times each year. In February, open radial trenches along the tree basin, and apply 20 kg of corn stalks and 5 kg of manure per plant. In July, fertilization is mainly with ternary compound fertilizer, applied at 0.2 kg per sq m.