Key Technical Points for Seedling Raising and Nursery Stock Management in Chinese Mahogany (Toona sinensis) Cultivation
Toona sinensis belongs to the Meliaceae family and is known as red Toona in Henan. It is a deciduous tree species and a fast-growing timber tree unique to China. Its tender buds and young leaves are rich in nutrients, pleasant in fragrance, and high in edible value, and it has become a good economic tree species for urban and rural "four-side" greening and for increasing farmers' income. Through years of production practice, relatively in-depth research has been conducted on Toona sinensis seedling raising and nursery stock management, aiming to provide reference for high-quality and high-yield Toona sinensis.
I. Seedling raising techniques. Toona sinensis seedling raising usually adopts sowing and root burying.
1. Sowing and seedling raising
(1) Seed collection: Toona sinensis generally begins to bear fruit at 7-8 years. For seed collection, select excellent mother trees 15-30 years old that are robust in growth and free of pests and diseases. When the capsules change from green to yellow-brown, pick them promptly. After picking, spread them on a mat to dry in the shade for several days. When the capsules split and the seeds scatter out, winnow out impurities and place them in gunny bags for dry storage. The germination rate of newly collected seeds of the current year can reach more than 80%.
(2) Select a good nursery site and prepare the land and make beds. Choose sandy loam and loam soil with good drainage and a groundwater level of 1.5-2.5 m. In early spring, rake level and make beds. The beds are 1 m wide and 10-20 m long, and the bed ridges are 30 cm wide. Apply 750 kg of decomposed farmyard manure and 25 kg of phosphate fertilizer per mu, and at the same time spray 1.5% dimethoate powder and 90% crystal trichlorfon, 1-1.5 kg per mu. After spraying, immediately shallow-turn once to turn the fertilizer and pesticide into the soil, then rake level. Irrigate once 5-7 days before sowing.
(3) Seed germination promotion treatment. 3-5 days before sowing, pour clean seeds into warm water and stir for 5 minutes, soak the seeds for 12-24 hours, take them out and rinse several times with clean water, put the seeds into a wet gunny bag, and place them in a warm place to promote germination. Rinse once a day with clean water. When 1/3 of the seeds have cracked and exposed white sprout tips, they can be taken out for sowing.
(4) Sowing. Generally in mid-to-late March, sowing must be done before Grain Rain at the latest. For drilling, open several sowing strips on the bed surface, each 10 cm wide and about 3 cm deep, with a row spacing of 35 cm. Pour a small amount of water into the furrows. After the water has soaked through, evenly scatter the germinated seeds into the furrows and cover with 1-1.5 cm of fine soil. The seeding rate is 2.25 kg per mu, and the seedling output is 6,000 plants. When the seedlings grow 4-6 true leaves, thin or transplant seedlings where they are too dense.
2. Root burying and seedling raising
(1) Collect root cuttings. Generally at the end of November or between March and April, open ditches 1-2 m from the main trunk and dig out 1-2-year-old roots. The thickness is required to be between 0.5-1.5 cm, with fibrous roots. Cut them into root segments 15-20 cm long, with the upper end cut flat and the lower end cut obliquely. Tie the root segments into bundles of 30 or 50.
(2) Germination promotion treatment of root cuttings. Dig a pit in a higher terrain, 80 cm deep and 100 cm wide, with the length depending on the number of root cuttings. Spread 25 cm of clean, moist fine sand on the bottom of the pit, then stand the root cuttings bundle by bundle upright in the pit, leaving 2-3 cm gaps between bundles, and fill with moist fine sand. Then place one layer of sand and one layer of root segments until reaching 10-20 cm below the pit opening. Every 1 m in the pit, stand a bundle of sorghum stalks upright to facilitate ventilation. Finally, cover the pit opening level with sand, then cover with 1-2 cm of fine soil, dig drainage ditches around it, and before freezing, pile the pit opening into a mound of soil and periodically dig into the pit to inspect. For root cuttings collected in early spring, bury them in a pit sheltered from the wind and facing the sun, 60 cm deep, with 10 cm of fine sand laid on the bottom layer. Dip the roots in 500 ppm naphthalene acetic acid solution, stand them in bundles on the sand layer, fill with fine sand until level with the pit opening, then cover with plastic film. Germination promotion is completed quickly. When tender buds 0.2-0.3 cm long grow on the roots, they can be cuttings.
(3) Cutting. After land preparation and fertilization in the nursery, build soil ridges 20-25 cm high and 35 cm wide at the base, with the distance between ridge centerlines 40-50 cm. Insert the root cuttings obliquely into the middle-lower part of the sunny side of the soil ridge, with a plant spacing of 25-30 cm. Cover the upper part of the root cuttings with 1-2 cm of soil, and water thoroughly once along the ridge furrow. If conditions permit, cover with plastic mulch. After cutting, if dry, irrigate with a small amount of water along the furrow.
(4) Management after cutting. When the root cuttings sprout and emerge from the soil, poke a hole in the plastic mulch to facilitate the growth of young buds. For those not covered with plastic mulch, cover with 2-3 cm of soil and water thoroughly once along the ridge furrow, but do not let the water submerge the inserted root parts.
II. Nursery stock management techniques
1. Fertilizer and water management. Because Toona sinensis nursery stock tends to grow late and luxuriantly in autumn, the degree of lignification at the top of new shoots is low and cold resistance is weak. Therefore, scientifically apply fertilizer and water to control autumn growth. In arid areas of the north, generally water 2-3 times in May-June. In July there is more rain, so whether to water can be decided according to rainfall conditions. After mid-August, strictly control moisture to prevent late luxuriant growth of nursery stock. Toona sinensis nursery stock is afraid of waterlogging, so drain promptly during the rainy season. At the same time, apply fertilizer scientifically. In addition to applying sufficient base fertilizer during land preparation, June is exactly the rapid growth period of nursery stock. Nursery stock of all specifications must be topdressed once with chemical fertilizer, applying 5 kg of urea per mu. In mid-July, except for nursery stock used in plastic greenhouses, which is no longer topdressed, nursery stock of other specifications needs another topdressing of chemical fertilizer, applying 5 kg of urea, 8 kg of phosphate fertilizer, and 6.5 kg of potassium fertilizer per mu. Fertilization should be combined with clear water. After early August, stop fertilizing and watering to control nursery stock growth and improve the degree of lignification of nursery stock.
2. Cultivate nursery stock with short trunks and side branches. Nursery stock required for dense planting orchards, open fields, field edges, and fast-growing high-yield forests should be cultivated into nursery stock with short trunks and many side branches. However, for protected cultivation of Toona sinensis, nursery stock with many side branches is not needed for dense planting. The key technical points for cultivating nursery stock with short trunks and many side branches are as follows.
(1) Cut the main branch during the seedling stage. That is, in mid-to-late June during the vigorous growth of nursery stock, when the seedling height reaches about 40 cm, use a shovel to dig about 30 cm deep in the ground and cut off the main root of the nursery stock, inhibiting vertical root growth, promoting side branch differentiation, inhibiting aboveground growth, and making the nursery stock stem low, short, and thick.
(2) Remove the terminal bud. In mid-to-late June, remove the terminal bud of the nursery stock, and apply 80×10-6 glycerol gibberellin (CGA) to the wound of the terminal bud. Buds below the terminal bud can then germinate.
(3) Spray growth regulators. In mid-to-late June, spray nursery stock with triiodobenzoic acid (TIBA), 20 g per mu once every half month, spraying continuously 2-3 times. This can inhibit apical dominance, promote plant dwarfing, and increase the number of side branches.
3. Loosen soil and weed. Loosening soil and weeding in time can reduce water evaporation, prevent surface crusting, promote gas exchange, improve the utilization rate of available soil nutrients, and at the same time eliminate weeds, reduce competition between weeds and nursery stock for water and nutrients, and eliminate parasitic sites for pests and diseases. Loosening soil and weeding should be carried out in combination, 5-10 times a year, with a loosening depth of 3-6 cm, deepening as the nursery stock grows. Weeding should achieve "weed early, weed small, weed completely".