Detailed Explanation of Key Techniques for High-Yield Cultivation of Isatis Root

Isatis root, commonly known by other names: indigo root, blue indigo root, Daqing root, is a traditional Chinese medicinal herb. It is produced throughout China. Isatis root is divided into northern isatis root and southern isatis root. Northern isatis root comes from the roots of Isatis indigotica and Isatis costata, plants of the Brassicaceae family; southern isatis root comes from the rhizomes and roots of Baphicacanthus cusia, a plant of the Acanthaceae family. It has the effects of clearing heat and detoxifying, cooling blood and reducing swelling, and soothing the throat.

Isatis root is not suitable for planting in low-temperature waterlogged land, as waterlogging easily causes root rot. To reduce the occurrence of diseases and pests, it should be ridge-cultivated with gramineous and leguminous plants; if the soil is fertile, it can also be planted as a catch crop.

Land Preparation and Fertilization

Isatis root is a deep-rooted plant. Apply 4-5 cubic meters of decomposed organic fertilizer per 667 sq m. Before application, crush it finely first, then spread it evenly on the ground. Deep plow 20-30 cm, harrow finely and level, and make flat beds 1 m wide. When the ground is dry, water thoroughly, and sow again after the surface soil is slightly dry and loose.

Sowing

There are spring sowing and summer sowing. Spring sowing is around Qingming, no later than the Grain Rain solar term. Summer sowing is around Mangzhong. When sowing, in the prepared bed, draw furrows 1.5 cm deep at a row spacing of 20 cm, spread the seeds evenly into the furrows, then cover with soil, level it, press lightly, and water immediately. Generally, seedlings emerge in 7-10 days, using 1.5-2 kg of seed per 667 sq m. In some production areas, isatis is intercropped with grain crops or vegetables, which can make full use of the land and achieve increased income.

Field Management

After sowing, keep the soil moist. When the seedlings are 6-10 cm tall, thin to a final stand (you can also thin to a final stand in one go, or first thin and then establish the final stand), removing the weak and keeping the strong; if there are gaps, transplant in time to fill them. The focus of management is hoeing and weeding. After the seedlings emerge, hoe shallowly to prevent crushing the seedlings; after the final stand is established, loosen the soil and weed, keeping the surface loose at all times and keeping the field free of weeds. For those mainly harvesting Daqing leaves, topdress 3 times a year. The first topdressing is after the final stand is established, applying 10-12 kg of urea per 667 sq m, applied in furrows between rows, and watered in case of drought; the second and third times are both topdressed immediately after harvesting the leaves. For those mainly harvesting isatis root, do not cut the leaves during the vigorous growth period, and apply less nitrogen fertilizer; 30-40 kg of cake fertilizer may be applied.

Management of Seed-Production Fields

Spring-sown isatis cannot flower and set seed in the same year. In order to harvest seeds, it must undergo low temperatures. There are the following two methods: First, when digging and harvesting isatis root in late October, select the main roots that are free of diseases and pests and thick and straight, transplant them to the seed-collection nursery and strengthen management, cover with horse manure in November to protect against the cold, and the seeds mature from late May to early June of the following year; select and keep plump, full seeds for propagation the next year. Second, sow in August on a sunny, fertile plot, and the seedlings can reach about 30 cm tall in the same year. Before winter, fertilize and water fully to promote seedling growth; after greening up the following year, thin the seedlings twice, keeping plants at a row spacing of 30-40 cm. They bloom in mid-to-late April, and seeds can be harvested in May-June. For any isatis from which seeds have been harvested, its roots should no longer be used for medicinal purposes.

Pest and Disease Control

The main disease of isatis root is downy mildew. This disease harms the leaves. When it occurs, white or grayish-white mold-like substances are produced on the underside of the leaves, with no obvious lesions; in severe cases, the leaf sheaths turn brown and even wither. The control method is mainly agricultural control: rational close planting to reduce soil moisture; reasonable rotation with gramineous crops when arranging cropping sequences; when diseased plants are found, remove them promptly in the early stage of disease onset. Chemical control can also be used. In the early stage of disease onset, spray with 1:1:100 Bordeaux mixture. Spray evenly on the leaf surface and underside, once every 7-10 days, for 3 consecutive sprayings; 65% zineb wettable powder at 500 times dilution can also be sprayed for control. The main pest harming isatis root is the cabbage caterpillar, which damages tender leaves. During the larval stage, spray 90% trichlorfon at 800 times dilution for control.

Harvesting and Processing

For those mainly harvesting Daqing leaves, 2-3 cuttings can be taken per year. The first cutting is during the vigorous growth season around Mangzhong, the second before the Beginning of Autumn, and the third between the End of Heat and White Dew. When cutting the leaves, choose a sunny day to harvest and dry them immediately; those that remain green are of better quality. If rainy weather occurs, dry them promptly. For those mainly harvesting isatis root, do not cut the leaves during the growth period, or cut the leaves only once; dig and harvest in late October when the aboveground parts wither, avoiding breaking the main root. Spread the dug isatis root to dry until 60-70% dry, remove the soil, tie into small bundles, and then continue drying until fully dry, at which point it is commercial isatis root.