Chinese Yam Cultivation Methods
[Alternative Names]: Yam, White Yam, Dioscorea, and more.
[Botanical Name]: Genus Dioscorea.
[Growth Habits]: Yam is a deep-rooted plant that thrives in deep, loose, well-drained sandy soil. It has high environmental requirements but shows strong adaptability. For optimal growth, it prefers warm and sunny conditions. However, it does not do well in overly heavy or sandy soils with poor water retention. Continuous planting in the same area should be avoided to prevent soil exhaustion and disease buildup.
[Propagation Methods]: Propagation is typically done through rhizomes (reeds) and bulbous buds.
1. Rhizome Propagation: In late October, when the stems and leaves of yam turn yellow, the underground roots are carefully dug up. The rhizome head (the part with buds on top) is selected as propagation material. Choose heads that are short-stemmed, plump, and free from pests, measuring about 15–20 cm in length. After drying for 5–6 days in a ventilated indoor space, they are bundled with straw rope, stored in a dry cellar, or layered with river sand on a clean mud floor. Stacking is done in layers, approximately 80–100 cm high, and covered with moist cloth and straw for insulation. Storage temperature should be between 0°C and 10°C. Below 0°C, the buds may freeze; above 10°C, premature sprouting or rotting can occur. These rhizomes are kept until spring of the following year for planting.
2. Bulbous Bud Propagation: During harvest, the bulbous buds between the leaves are collected. Select large, round, and pest-free buds, dry them indoors, and store them in wooden barrels or bamboo baskets in a cool, dry, and well-ventilated place. Maintain temperatures above 5°C during winter. They are ready for sowing in the following spring.
Seedlings are usually raised using this method and transplanted the next year. By mid-March in northern regions, seedbeds are prepared with 25–30 cm spacing, and shallow trenches 5–7 cm deep are made. One bulbous bud is placed every 10 cm, covered with fine manure soil, compacted, and then leveled. Watering is done after planting. Seedlings typically emerge within 20–25 days. Proper management is essential during this period. When seedlings begin to wither in early winter, the thick, straight roots are dug up and stored using the same method as before.
In practice, both propagation methods are alternated to maintain variety quality. Long-term use of rhizome propagation may lead to genetic degradation, so bulbous bud cultivation is recommended for rejuvenation and improved yield and quality. However, this should not be used continuously, as it may reduce yields over time.
[Cultivation Techniques]
1. Soil Preparation: In autumn, the soil is deeply tilled to a depth of at least 60 cm. After the spring thaw, well-decomposed manure (5000 kg per acre) and cake fertilizer (100 kg per acre) are applied, followed by plowing to a depth of about 30 cm. The field is then leveled, and raised beds of 1.3 meters wide are created, with 30 cm drainage ditches on either side. To control underground pests, 15 grams of 40% phoxim per acre is applied for soil disinfection.
2. Planting: In early April, when temperatures reach around 15°C, rhizomes or previously grown tubers (from bulbous buds) are taken out of storage and planted. A horizontal furrow 30 cm apart, 10 cm deep and 20 cm wide, is made. The rhizomes are placed with the buds facing upward, spaced 16–20 cm apart. After covering with 5 cm of soil, a layer of compost is added, followed by a thin layer of manure and livestock waste water. Approximately 5500–8000 plants are planted per acre.
[Field Management]
1. Weeding and Soil Loosening: This is done three times. The first time is in April–May, when seedlings emerge, and the soil is lightly loosened without damaging the rhizomes. The second time is in June, and the third is from late July to early August, when vines are manually lifted and weeded.
2. Fertilization: When seedlings reach 30 cm, apply 2500 kg of human and animal manure water per mu. In summer, an additional 2500–3000 kg of manure water is applied.
3. Support Structures: Once seedlings grow over 30 cm, bamboo poles or branches are set up between rows to form supports. These are two meters high, with 4–5 pillars per row, tied together with plastic ropes. Vines are then guided onto the structures to reduce pest damage and increase productivity.
4. Drainage and Irrigation: During rainy seasons, excess water must be drained to prevent root rot. In dry periods, irrigation is necessary, and it should be combined with fertilization.
[Pests and Diseases & Control]
1. Major Diseases:
(1) Anthracnose: Appears from July to August, with brown spots on stems and leaves, forming irregular rings and black spots. Severe cases result in leaf fall and stem drying.
Control: Soak seeds in 1:1:50 Bordeaux mixture for 10 minutes before planting. Spray 1:10 Bordeaux mixture every 10 days, or use 65% Zinc Oxide 500 times or 50% Eubacteria 800–1000 times.
(2) White Rust: Occurs in rainy summers, causing pale yellow spots that become milky white ridges. Eventually, the epidermis ruptures, releasing white powder.
Control: Avoid waterlogging, rotate crops with crucifers, and spray 1:1:100 Bordeaux mixture or 65% Dexamethasone 500 times.
(3) Nematode Disease: Affects underground roots, causing galls and stunted growth.
Control: Apply 40% Phoxim or 3% Methyl Isothiophos during site preparation, avoid infected plants, and soak rhizomes in 1:1:150 Bordeaux mixture for 10 minutes.
2. Major Pests:
(1) Root-knot Nematodes: Damage tuber roots, reducing yield and quality.
Control: Use 90% Trichlorfon 1000–1500 times diluted, or 3% Carbofuran granules mixed with wet soil.
(2) Leaf Bees: Larvae feed on leaves, causing severe damage from May to June.
Control: Spray 90% Trichlorfon 1000 times.
(3) Ground Beetles: Eat underground roots.
Control: Apply 90% Trichlorfon 1000–1500 times diluted.
[Harvesting and Processing]
1. Harvesting: Early spring, just before the first frost, is the best time. When stems and leaves turn yellow in late October, dig up the bulbs first, remove the stems, cut the vines, and carefully excavate the underground roots. Ensure the roots are not damaged during digging. After harvesting, trim the tops for storage and process the roots for medicinal use.
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