How to grow Isatis indigotica (woad) for high yields? Detailed cultivation methods

Isatis indigotica is a biennial plant of the Brassicaceae family. Both its roots and leaves can be used medicinally, and it is a commonly used bulk traditional Chinese medicinal herb, as well as one of the preferred traditional Chinese medicinal herbs for antiviral use. This plant has strong adaptability, prefers a warm, sunny environment, and is cold-tolerant. Except for low-lying waterlogged land and heavy clay soil, it can be grown in both northern and southern China. The high-yield cultivation techniques for this medicinal herb are described below:

I. Land preparation and fertilization

Because Isatis indigotica is a deep-rooted plant, it is best to choose flat, well-drained, fertile, loose sandy loam. During land preparation, apply 2000-3000 kg of decomposed compost or barnyard manure, 100 kg of plant ash, and 20-30 kg of superphosphate per mu, or apply 50 kg of compound fertilizer, then deep plow more than 30 cm, followed by one shallow plowing, rake fine and level, and make flat beds 1-1.5 m wide. If drought occurs, water before sowing to build up soil moisture.

II. Timely sowing

There are spring sowing and summer sowing. Spring sowing is in early to mid-April, and summer sowing is in late May. Spring sowing should not be too early, because after the seeds emerge, affected by early spring cold, the plants will go through vernalization, bolt and flower prematurely, and complete their growth cycle in the same year, causing planting failure. Before sowing, soak the seeds in warm water at 30°C-40°C for 4 hours. Remove and air-dry. Both drilling and hole sowing can be used, but drilling is mostly adopted. Open furrows in the bed at a row spacing of 20-30 cm, with a furrow depth of 1.5-2 cm. Mix the seeds with fine sandy soil and evenly sow them into the furrows, cover with 0.5-1 cm of soil, then press down. Keep the bed soil moist. At an air temperature of 18°C-20°C, seedlings can emerge in 7-10 days; for hole sowing, the hole, row, and plant spacing can all be 25 cm; the germination rate of Isatis indigotica seeds is 80%, and 4 kg of seeds are used per mu. Broadcasting results in poorer seedling emergence, thereby affecting yield.

III. Field management

1. Thinning. Thin seedlings when the seedlings are 5-7 cm tall, and final thinning when the seedlings are 10-15 cm tall. During thinning and final thinning, remove weak plants and keep strong ones, and replant missing spots in time. During this stage, keep the soil moist.

2. Cultivation and weeding. After full emergence, cultivate and weed once in time, then about once every half a month. After the plants close the rows, stop cultivation and weeding.

3. Topdressing. Carry out from May to July. Apply 500-1000 kg of human excrement and urine per mu in furrows, or 10 kg of urea, and add 10 kg of superphosphate, then water after application. After each leaf harvest, apply 5-7 kg of ammonium sulfate per mu (never use ammonium bicarbonate).

4. Watering and drainage. Water in time when the weather is dry in summer, and pay attention to clearing ditches and draining water during the rainy season to prevent root rot.

5. Propagation method. Propagate by seed. Isatis indigotica harvested for roots in the same year does not set seed. In late October, when digging and harvesting the roots, select roots that are free of pests and diseases, with thick, robust main roots and no branching, and transplant them to fertile seed-production fields at a row spacing of 50 cm × 30 cm. Water promptly after planting and strengthen field management; in May-June of the second year, when the seeds mature, harvest them in stages, sun-dry, and thresh, then store in a ventilated, dry place for later use. The roots of Isatis indigotica that have produced seeds become lignified and can no longer be used as medicinal material.

IV. Pest and disease control

1. Diseases. Mainly downy mildew and root rot. In downy mildew, the leaves show pale green lesions, and when the disease occurs, white or grayish-white mold-like substances appear on the underside of the leaves; in severe cases, the leaves wither and die. Root rot mostly occurs in the rainy season, causing the roots to rot and leading to the death of the whole plant. Control methods: mainly agricultural control, rational crop rotation with grasses and legumes, rational close planting, improving ventilation and light conditions, and promptly removing diseased leaves and plants from the field and deeply burying them in a centralized manner; 65% zineb or 77% copper hydroxide wettable powder can also be used for spraying or root drenching.

2. Insect pests. Mainly cabbage caterpillars and diamondback moths. Cabbage caterpillars bite and eat the leaves, causing holes and notches, and in severe cases only the leaf veins remain; diamondback moths bite and eat the leaves, initially causing "window-pane" damage, and later causing notches and holes, leaving only a net-like leaf vein structure. Use diflubenzuron No. 3, BT emulsion, or 90% trichlorfon 1000-fold spray for control.

V. Harvesting and processing

1. Daqingye (Isatis leaf). For spring-sown plants, harvest 2-3 times each year. The first time is in early June; the second time is in early August, but harvesting is not suitable during the hot midsummer period, so as to avoid causing large-scale death of the plants; the third time is from mid-October until before root digging. When harvesting, choose a sunny day, cut 1-2 cm above the ground, and after cutting, remove withered yellow leaves and impurities, then sun-dry immediately. During drying, never pile them up, so as to prevent the leaves from heating, blackening, and deteriorating. The yield is about 200 kg of dried leaves per mu. After sun-drying, place in a ventilated, dry place to prevent mildew.

2. Isatis root. Dig the roots in late October. Because the roots go deep into the soil, when harvesting, first dig a deep furrow at one end of the bed and dig along the furrow to avoid breaking the roots. Remove the aboveground stems and leaves and soil, sun-dry until 70-80% dry, tie into small bundles, then sun-dry until completely dry, and place in a dry place to prevent mildew. The yield is 200-250 kg of finished Isatis root per mu.