Key Technical Points for Raising Seedlings of Dioscorea nipponica from True Seed

The propagation methods of Dioscorea nipponica include seed propagation, seedling raising and transplanting, and rhizome section propagation. Rhizome propagation is fast and produces finished products early, but the amount of seed rhizomes used per unit area is large and the propagation coefficient is low. The greatest feature of seed propagation is its high propagation coefficient, which is conducive to rapidly expanding the area and forming large-scale production. Every 500 grams of seed produces 30,000 seedlings. In the year of seedling raising, no trellis needs to be set up. The main rhizome reaches 10 cm long and 1 cm thick, and the lateral rhizomes are 3—5 cm long, forming 5—8 overwintering buds and 4—5 rhizome growth points, easily forming a massive root mass. The specific techniques for seed seedling raising are described below.

1. Seed collection and treatment. From late September to early October, collect the fruit spikes from the plants and place them in a ventilated spot, with a placement thickness not exceeding 10 cm. Water thoroughly once a day and turn them once at noon, persevering for 10—15 days, after which the seeds will fall off. From late October to mid-November, soak the dry seeds in clean water for 24—30 hours, then drain off the water. Mix fine sand equal to 2 times the seed volume with the seeds, stir thoroughly, put the mixture into a breathable woven bag, and seal the bag opening. Then choose a shaded spot with higher terrain that does not accumulate water, lay the seed bag flat on the ground surface, take soil from both sides of the seed bag and cover it completely, with a soil cover thickness of more than 10 cm. After the seed bag and the covering soil freeze, spread another 30 cm thick layer of rice straw on top to prolong the freezing time. Ten days before sowing, remove the covering rice straw.

2. Land selection and preparation. The seedling-raising land should preferably be sandy loam with higher terrain and a slope of more than 5 degrees. Before land preparation, apply 2000 kg of decomposed farmyard manure per 667 sq m, or 15 kg of compound fertilizer. Then plow the soil 15 cm deep so that the fertilizer is evenly mixed into the soil. Following the slope, make beds 1.2 m wide, 10 cm high and no more than 30 cm long, with operation paths 30 cm wide, to facilitate management activities such as weeding and watering.

3. Sowing. The sowing time is from May 15 to 30. Before sowing, dress the seeds with Dexon, using 2.5 kg of seed and 400 g of Dexon per 667 sq m. Level the bed surface, broadcast the seed, sowing about 100 seeds per linear meter. Cover the seeds with 1.5 cm of soil and press once with a wooden roller. On the bed surface after sowing, cover with a 1 cm thick layer of larch leaves. Sprinkle a little sand on top of the larch leaves to prevent them from being blown away by wind or washed away by heavy rain. Then water the sown bed thoroughly in one application. Check the moisture in the bed promptly and keep the soil in the seed layer moist; when water is lacking, water immediately after sunset. Seedlings can only emerge when the ground temperature is above 22°C. The first germination produces 1 true leaf, with a seedling height of 1.5 cm; after 12—15 days, a bolting individual plant germinates, and when the seedling height reaches 15 cm it twines around other plants to grow. In the same year, the seedling height can reach about 1 m.

4. Field management. Before and after seedling emergence, when weeds grow 2 true leaves, pull them out promptly; otherwise, if the weeds are too large, they easily pull out the seeds or small seedlings. Later, if monocotyledonous weeds are too numerous, sethoxydim can be used for weed control. From late July to early August, when the rainy season arrives, air humidity is high and the plants are prone to leaf rot, wilting in patches in a water-soaked manner. The control method is to spray Daminlv or Zhuangduoshou once every 10 days starting from the unfolding of the first true leaf, for 3 consecutive sprays. In late July, spray Tuzet twice. The main pests harming the seedlings are red hairy caterpillars and locusts, which mostly cause damage at night; pesticides such as Decis can be sprayed from 3—5 p.m.

5. Overwintering management. The plants grow until late September and wither after frost; they must not be transplanted before the soil freezes. If there is no rain before the soil freezes, water must be applied as winterizing water to prevent soil drought in winter due to lack of snow from killing the overwintering buds. After watering, once the bed soil freezes, cover the bed surface with a 10 cm thick layer of rice straw to ensure bed soil moisture and delay the germination of the overwintering buds until the spring of the second year, because seedlings in bare ground germinate in mid-April and are killed by late frost before May 20. Promoting delayed germination is conducive to early-spring transplanting and ensures the survival rate.