Detailed Explanation of Key Management Techniques for Walnut Seedlings After Planting
After planting, a thorough watering must be given once, and another thorough watering should be given two weeks later, which can improve the survival rate of planting. Thereafter, if high temperatures or drought occur, timely irrigation should also be carried out. In areas with insufficient water sources, after planting and watering, immediately cover the tree disk with straw or plastic film to reduce soil moisture evaporation. In spring and summer, in combination with irrigation, an appropriate amount of chemical fertilizer can be applied as a top dressing. In the early stage, nitrogen fertilizer should be the main top dressing, and in the later stage, phosphorus and potassium fertilizer should be the main top dressing. Foliar spraying of fertilizer can also be carried out.
1. Checking survival and replanting. Under normal circumstances, after spring planting, young trees can begin to sprout after 1 month, with budding starting above ground and root growth also beginning underground. However, due to various reasons, a small number of plants do not sprout, the stems lose water severely, and they eventually die. For some trees planted in autumn, when the growing season arrives, although they do not sprout temporarily, the stems are still fresh and contain moisture, so they cannot be judged as dead. These trees may still sprout after a period of time. Trees that have already been judged as dead should be replanted in a timely manner.
2. Trunk heading. For young trees that have survived planting, if the tree height reaches more than 1 m, trunk heading should be carried out in a timely manner according to shaping requirements. When determining the trunk heading height, consideration should be given simultaneously to variety characteristics, cultivation methods, and soil and environmental conditions. The crown of early-bearing walnuts is relatively small, and the trunk heading height is preferably 1.0-1.2 m; the crown of late-bearing walnuts is relatively large, and the trunk heading height is generally 1.2-1.5 m; when there are intercropped crops, the trunk heading height is 1.5-2.0 m. For late-bearing walnuts planted on mountainous or sloping land, because the soil layer is relatively thin and fertility is relatively poor, the trunk heading height can be 1.0-1.2 m.
On northern spring hillside land, during the period when vegetation sprouts, large numbers of black velvet chafer beetles often gnaw on the tender buds of walnut trees, affecting walnut growth. Plastic film can be used to make, or ready-made long bags 50-60 cm long and 4-5 cm wide can be purchased and placed over the seedling trunks for protection. After the seedlings sprout and grow, ventilation openings should be cut in a timely manner at the top and bottom of the plastic bags, and the long bags should be removed after leaf expansion.
3. Strengthening tree body protection
(1) Preventing and controlling pest and disease damage. After young trees sprout and expand leaves, they are often susceptible to damage by aphids, red spiders, chafer beetles, and leaf miners, and corresponding measures should be taken in a timely manner for prevention and control.
(2) Cold protection for young trees. In North China and Northwest China, winter temperatures are relatively low, and walnut young trees 2-3 years after planting often develop the phenomenon of "stem dieback," and the farther north the geographical latitude, the more severe the "stem dieback." The main reason for the occurrence of "stem dieback" is insufficient preparation for overwintering of the tree body, relatively low winter temperatures, freezing of soil moisture, difficulty for the walnut root system to absorb water, while in early spring the temperature rises relatively quickly, the air is dry and windy, and the amount of water transpiration from branches is large, resulting in an imbalance in water income and expenditure in the aboveground part of the tree body, causing physiological drought and "stem dieback." The "stem dieback" phenomenon mostly occurs in February and March. For newly established walnut orchards, in spring planting areas, after planting, various protective measures can be taken to prevent severe water loss from the stems. Spraying paraffin emulsion on the trunks is best, 107 glue (polyvinyl alcohol) also has a good effect, or water-based adhesive clay antifreeze, or placing slender plastic bags over the stems, all have certain effects. If it is an autumn planting area, before freezing, the seedlings should be buried with soil for overwintering, and the soil covering thickness should be about 20 cm. When the spring temperature rises to about 15°C, uncover them in a timely manner, and pay attention to watering the seedlings to retain water, so as to improve the survival rate of field planting.
For walnut young trees that have already formed an orchard, the fundamental measures to prevent "stem dieback": First, improve the tree body's own cold resistance and resistance to "stem dieback." According to the principle of promoting early and controlling later, pay attention to strengthening fertilizer and water management. Before July, nitrogen fertilizer should be the main fertilizer, and after July, phosphorus fertilizer should be the main fertilizer, and irrigation should be controlled appropriately. Starting in mid-August, measures such as multiple pinching of growing new shoots and controlling the opening angle should be taken, and in early to mid-September, spraying 0.5% potassium dihydrogen phosphate twice can effectively control excessive branch growth, increase branch fullness, increase stored nutrients and resistance of the tree body. At this stage, timely prevention should be taken against large green leafhoppers laying eggs on branches and trunks for damage. In early November, giving one thorough watering can effectively increase soil water content and reduce the occurrence of "stem dieback."