(1) Seed collection and storage
Seed collection is the key link of seedling propagation. Because chestnut is a cross-pollinated plant, its offspring are influenced by both maternal and paternal inheritance, so it is best to take into account the genetic characteristics of parents when collecting seeds, and pay attention to the selection of selection areas, plants and seeds. In production, some chestnut trees with high yield, good quality and vigorous growth are usually selected as seed collection areas, because most chestnut trees in these areas have high yield and good quality, and a good population is formed through mutual pollination; When Castanopsis carlesii ripens and cracks fruit, choose a single plant with strong growth, high and stable yield, good quality and strong stress resistance as the mother plant, and it is not suitable to use a single-seed chestnut tree as the mother plant; After the chestnut tree matures, the chestnut with big head, thin skin, full skin, fresh and tender skin, luster and no pests and diseases is picked from the mother plant as seeds.
Chestnut seeds have strict storage requirements, and chestnut fruits are afraid of dryness, dampness, heat, freezing and peeling. High temperature and high humidity are easy to make chestnut fruit moldy, while low temperature and freezing damage will make the fruit deteriorate. If air-drying loses moisture, the germination rate will be greatly reduced, and even the seeds will lose vitality. Therefore, from harvesting, storage to sowing, we should pay attention to moisturizing, heat protection and antifreeze. Seeds should be stored in the sand immediately after collection. Choose leeward slope with good drainage to dig ditches for water storage. The ditch is 80 ~ 100 cm deep and 60 ~ 100 cm wide, depending on the number of seeds. Spread 5 ~ 10 cm of wet sand on the bottom of the ditch, then mix the seeds and wet sand evenly according to the ratio of 1: 3 ~ 5 times and put them in the ditch until they are 20 cm away from the mouth of the ditch. The sowing amount can be about 1 m, and a bundle of straw can be erected with the thickness of 10 ~ 15 cm, which is convenient for ventilation. After the seeds are put away, cover them with wet sand 10 cm, and finally fill them with soil to prevent water accumulation. The storage temperature should be between 0 ~ 5℃. After storage, it should be checked regularly. If abnormal temperature and humidity or animal damage is found, it should be handled in time to prevent loss. Those with cold storage conditions can be stored at 1 ~ 4℃, and the seeds must be stored at low temperature. Pay attention to moisture and ventilation during storage, and the temperature shall not be lower than 0℃.
(2) sowing
Nursery should be sandy loam or light loam plot. Plots with heavy soil and poor water permeability are not suitable for nursery. Chestnut likes acidic soil. In alkaline soil (above 7.5), the seedling growth is poor, which leads to seedling death. We should pay attention to this when choosing nursery land.
Sowing time is divided into autumn sowing and spring sowing. Sow in autumn when the temperature drops to about 5 ~ 10℃ in late autumn and early winter. Its advantage is that it does not need to store seeds, and it can complete the dormancy period by using the free time after autumn. Disadvantages are inconvenient management, great changes in external conditions, too high or too low humidity, easy to cause seed rot, reduce germination rate, and vulnerable to pikas and pests.
Spring sowing, from mid-March to early April in the northern province (autonomous region) and from mid-February to early April in the south. Because chestnut seeds are easy to germinate during storage, they should be sown early in general. If seeds can be stored at low temperature to inhibit germination, it is better to sow them later, which is beneficial to raise soil temperature, shorten the time of burying seeds, reduce losses and make seedlings neat and consistent.
Nurseries usually sow in flat beds. When the sowing amount is about 100kg/667 m2, seedlings can emerge 1000 ~ 10000. When sowing, the seeds must be placed flat or horizontally, and the seed tips should not be up or down, otherwise the young roots and buds will be difficult to grow (Figure 37). Germination can be accelerated before sowing, and the root tips of young roots can be properly cut off after germination, which can stimulate the development of lateral roots and form a robust lateral root system, which is convenient for seedlings to leave the nursery and is also beneficial to the growth and development of seedlings after planting. Because of the strong dependence of seedlings on cotyledons, we must be careful not to break the petiole when cutting root tips. If both sides of the petiole are broken, the seedlings can't survive. Irrigation should be carried out before sowing, and sowing should be carried out 2-4 days after the soil is wet and loose. After sowing, cover the soil for 2 ~ 3 cm and slightly suppress it to promote the water rise and ensure the water needed for seed germination. After pressing, plow the topsoil with a flat rake. Don't water the plastic film after sowing, so as to avoid the hardening of the topsoil and the difficulty of seedling emergence.
Fig. 37 sowing posture and germination state of chestnut
1, 2. Seeding postures 3 and 4 are incorrect. Correct sowing posture
(3) Key points of seedling management
When the conditions are suitable, the seedlings will emerge within 1 ~ 2 weeks after sowing, and the seedlings should be interplanted, replenished and fixed in time after emergence. Chestnuts have twins. If one species produces two seedlings, it is necessary to remove the weak and retain the strong, concentrate nutrients and promote the growth of seedlings. At this time, if it is dry, we can irrigate it properly.
Chestnut seedlings can be topdressed with about 5 kg of urea in mid-June and August, and watered after fertilization. After the seedlings stop growing in autumn, organic fertilizer can be applied and frozen water poured to help the seedlings overwinter.
During seedling stage, intertillage and weeding should be done many times, and drainage and waterlogging prevention should be paid attention to during rainy season. The growth standard of seedlings in that year is: the thickness of stem base is more than 0.6 cm, the height of seedlings is more than 60 cm, and the diameter of base reaches 1.5 ~ 2 cm. For plots whose growth is not up to nursery or grafting standards, stubble should be leveled at the end of autumn, cut off from the height of 4 ~ 5 cm above the ground, and wound cultivation should be carried out in the next year to promote seedling growth. After germination in the second year, one seedling should be selected and the rest should be wiped off.
The main pests at seedling stage are grubs, golden needle worms, scarabs and so on. The main diseases are damping-off and powdery mildew, which should be prevented in time.