Detailed Explanation of Key Techniques for Directional Cultivation of Amur Maple Seedlings

Amur maple (Acer ginnala) is a deciduous large shrub or small tree of the genus Acer in the family Aceraceae. Its leaves and fruits are ornamental, and the leaf shape is beautiful. In autumn the leaf color turns brilliant red, particularly eye-catching; in summer the newly formed samaras are pink, very delicate and distinctive. It is an excellent ornamental greening tree species in northern regions, suitable for specimen planting, row planting, group planting, or pruning into hedges and topiary trees. In Heilongjiang Province it is mainly produced in the Xiaoxing'anling Mountains and the mountainous areas to the south; it is distributed in the northeastern, northern and northwestern provinces and regions of China; in addition, it is also distributed in Japan, Korea, eastern Siberia of Russia and Mongolia.

1 Botanical characteristics

Deciduous large shrub or small tree, up to 6 m tall. Bark grayish brown. Young branches green or purplish brown, old branches grayish yellow. Simple leaves opposite, ovate or oblong-ovate-elliptic, 5-9 cm long and 3-6 cm wide, usually 3-lobed or indistinctly 5-lobed, or not lobed, the middle lobe extra large and long, base rounded or nearly cordate, margin irregularly sparsely doubly serrate, nearly entire near the base; petiole slender, 1.5-4 cm. Flowers polygamous-monoecious, in terminal corymbs, many-flowered, pale green or tinged with yellow. Samaras dark brown, 2.5-3 cm long; nutlets flat, oblong, with fine vein lines, hairy when young; wing about 2 cm long, sometimes purplish red, the two wings upright, spreading at an acute angle or nearly parallel and overlapping. Flowering period May-June. Fruit ripening period September.

2 Biological characteristics

A sun-loving tree species, tolerant of shade, cold-resistant, fond of moist soil, but tolerant of dry and barren conditions, with strong disease resistance and strong adaptability. It often grows on sunny slopes, riverbanks or wet grasslands below 800 m altitude, scattered or forming thickets, and is also commonly seen on semi-sunny slopes or at the edges of mixed forests on semi-shady slopes.

3 Seedling cultivation

3.1 Seed collection

The seeds can be harvested when the samaras develop and mature and the fruit coat turns yellowish brown. Seeds can be collected from September each year to March of the following year, and the fruits do not fall off. After the fruits are harvested, spread them out to dry, rub off the fruit wings, and after winnowing and removing impurities, oblong fruit grains are obtained, which are called seeds in production, and are bagged and stored in a cold room. Thousand-grain weight 95 g, germination rate 60%.

3.2 Seed treatment (germination promotion)

30-40 days before spring sowing, soak the seeds in a 30°C 1% sodium bicarbonate aqueous solution for 2 hours, then let them cool naturally; at the same time, rub the seeds with your hands, then soak the seeds in clean cold water for 3-5 days, changing the water once a day; after 3-5 days, soak the seeds again in a 0.5% potassium permanganate solution for disinfection for 3-4 hours, then remove the seeds. After washing off the liquid with clean water, mix the seeds into 3 times their volume of clean wet river sand, place the seed-sand mixture at a low temperature of 5-10°C, maintain 60% humidity, and after 30 days the seeds begin to crack; when 1/3 of the seeds have cracked, they can be sown.

3.3 Sowing

The sowing site should be selected as loam or sandy loam plots with fertile soil and good drainage, and autumn land preparation should be carried out in advance. About 10 days before spring sowing, apply fertilizer and harrow the land, then make the beds. The seedbed is 20-30 m long, 110 cm wide, 15 cm high, and the path is 50 cm wide. Rake the bed surface fine and level, then water once thoroughly, and when the water has seeped in and the bed surface is slightly dry, sowing can begin. Use the method of strip sowing on the bed surface, sowing rate 50 g/sq m, 18 kg/mu (667 sq m), covering soil 1.5 cm thick, watering after pressing, then covering the bed surface with fine grass scraps or wood shavings and other mulch to keep the bed surface moist.

3.4 Seedling stage management

About 15 days after sowing, the seeds can germinate and emerge. When the seedlings grow to 2 cm high, the first thinning can be carried out, leaving 200 plants/sq m; when the seedlings grow to 4-5 cm high, final thinning is carried out, leaving 150 plants/sq m. After final thinning, water promptly, and 2-3 days later apply a topdressing of nitrogen fertilizer once, and thereafter weed and loosen the soil at the appropriate time. In the same year the seedlings reach 60-90 cm high, with a seedling yield of 150 plants/sq m, 54,000 plants/mu (667 sq m). One-year-old seedlings can also, as needed, remain in the bed for another 1-2 years of growth; during the period when the seedlings remain growing in the bed, apply topdressing of nitrogen fertilizer twice, and weed and loosen the soil at the appropriate time. Two-year-old seedlings are 90-140 cm high, and three-year-old seedlings are 130-170 cm high.

4 Directional cultivation

4.1 For hedges and pattern planting

Seedlings used for establishing hedges and pattern planting require many branches, a low branching point, uniform branch thickness, and consistent branch length, and 1-year-old seedlings are commonly used for planting. For this reason, during seedling cultivation, when the seedlings grow to 4-5 cm high, final thinning is carried out, and at the same time the seedlings should be pinched, leaving 100 plants/sq m, and managed as general seedlings. In the same year the seedlings are 30-50 cm high, with 3-5 branches, and a seedling yield of 36,000 plants/mu.

4.2 For topiary trees

During seedling cultivation, the seedlings are not pinched, and as needed they remain in the bed for 1-2 years of growth, leaving 100 plants/sq m, and managed as general seedlings. For the cultivation of seedlings used for topiary trees, loam or sandy loam plots with fertile soil and good drainage should also be selected, and land preparation and fertilization should be carried out before planting. In spring, 2-3-year-old seedlings remaining in the bed are used for ridge-style cultivation, with ridge width 60-70 cm and plant spacing 100 cm, and the seedlings should be set upright and firmed by treading. Before planting, prune the seedling root system, keeping root length 12-15 cm. Starting from the 2nd year after planting, the seedlings are trained for trunk height, with the trunk-training height at 60-120 cm. In the 2nd year after trunk training, the seedlings are pruned and shaped; after 2-3 years of shaping treatment, the seedling shape is basically fixed, and they can be lifted from the nursery and planted in the autumn of that year or the spring of the following year. For topiary tree seedlings that do not need branch-free trunk height, seedlings that have been pinched can also be cultivated on ridges; starting from the 2nd year after planting, the seedlings are pruned and shaped, and after 4-5 years from planting they can be lifted from the nursery and planted.

4.3 Ornamental shrubs

In spring, 1-year-old seedlings that have not been pinched are cultivated on ridges, with plant spacing 60 cm; after planting, cut back to the base, with stubble height 10 cm. In June, when the side branches grow to 10-20 cm, select 3 robust side branches to keep, and cut off all the rest; the 3 retained side branches should be distributed as evenly as possible. Weed and loosen the soil at the appropriate time, apply nitrogen fertilizer topdressing once a year, and after 3 years from planting the seedlings can be lifted from the nursery and planted, at which time the seedlings are 120-150 cm high.

4.4 For ornamental trees and road greening

In spring, 2-3-year-old seedlings remaining in the bed that have not been pinched are planted on alternate ridges, with plant spacing 80 cm; the empty ridges can be used to plant seedlings of evergreen tree species such as Picea koraiensis and Picea wilsonii, with seedling height 20-30 cm and plant spacing 50 cm; they can also be used to plant seedlings of low-growing flowering shrubs such as Ligustrum obtusifolium and Syringa oblata, with plant spacing 40 cm, so as to make full use of land resources. After the seedlings are planted, weeding, soil loosening and nitrogen fertilizer topdressing should be carried out twice each year in May-July to promote healthy growth of the seedlings. Starting from the 2nd year after planting, the seedlings should also be properly pruned each year, mainly by shortening the large side branches that affect the growth of the main trunk of the seedling and cutting off all side branches and sprouting branches within the lower 1/3 of the seedling. For those whose main branch growth is weak or whose main branch is damaged, 1 strong-growing large side branch can be selected to replace the main branch. As needed, starting from the 2nd year after planting, the seedlings can also be trained for trunk height, with the trunk-training height at 120-160 cm. After 3-4 years from planting, the seedlings can be lifted from the nursery and planted; at this time the ground diameter of the seedlings can reach 3-4 cm, and for landscape greening they should be transplanted with soil.