Which variety of biennial herbaceous Isatis indigotica is good, and when is the suitable time to plant it?

Isatis indigotica, also known as Indigo root, Blue indigo root and Daqing root, is a relatively common biennial herbaceous plant in China. Because it has the effects of clearing heat and detoxifying, cooling blood and soothing the throat, it is widely used as medicine. So what varieties of Isatis indigotica are there? Which variety is good? When is the best time to plant?

Introduction to Isatis indigotica varieties:

1. Isatis root: It is the dried root of the plant Isatis indigotica, slender and cylindrical, with a light grayish yellow surface, rough, with longitudinal wrinkles and transverse marks, and rootlet scars. The root head is slightly swollen, with a depression at the top and dark green petiole remains around it. Thicker roots also show dense wart-like protrusions and grayish brown petiole scars arranged in a ring. The texture is solid and brittle; the fracture shows a yellow-white to light brown bark and a yellow xylem. Those with straight, thick and strong roots, solid texture and high powderiness are considered better.

2. Baphicacanthus root: It is the dried rhizome and root of the plant Baphicacanthus cusia, grayish brown. The rhizome is cylindrical, with a short aerial stem at the upper part. The aerial stem has opposite branches. The rhizome has swollen nodes, and from the nodes grow slightly thicker rhizomes and slender fibrous roots. The roots are slender and slightly curved, with fine wrinkles on the surface. The rhizome and aerial stem are brittle and easy to break, with an uneven fracture, slightly fibrous, and a large pith in the center; the root is relatively flexible. Those with long strips and uniform thickness are considered better.

The above two varieties of Isatis indigotica both have good effects and functions. Generally, pharmaceutical factories use these two for medicine production, so when planting, either one can be chosen.

Planting time:

Because Isatis indigotica is sown in different seasons, the harvested products are also different. According to the sowing time of Isatis indigotica, it can be divided into 4 stages: autumn sowing, early spring sowing, spring sowing and summer sowing. Autumn sowing and early spring sowing are mostly aimed at harvesting seeds; the roots of Isatis indigotica planted in these two periods cannot be used as medicinal material. Summer sowing is suitable for areas in the south with a relatively long plum rain season. This method can reduce pests and diseases, but the yield is relatively low. Spring-sown Isatis indigotica can harvest both leaves and roots, and the yield is relatively high, so it is the most commonly used method.

Planting techniques:

Seedling raising

Generally, perennial root transplanting or autumn sowing for seed reservation is used. Seeds harvested in May and June are sown in early April of the following year. The nursery should be selected as fertile, loose sandy loam, with a bed width of 3.33 m and a height of 16.7 cm; the length is unlimited. The bed surface should be soft and flat, and either broadcast sowing or drill sowing can be used. Apply 1500-2000 kg of farmyard manure per 667 sq m (1 mu) as base fertilizer. For drill sowing, open shallow furrows 0.33-0.67 cm deep at a row spacing of 10-13 cm. Before sowing, first place the seeds in 10% salt water, remove the floating sclerotia and shriveled grains, then take them out and soak them in warm water at 25°C for 24 hours for sealed seed treatment and germination acceleration. Sow after the seeds show white, then cover with soil and press firm. Sow about 2.5 kg per 667 sq m. After sowing, cover with a thin layer of rice straw to prevent sun exposure, spray water once in the morning and once in the evening each day, and keep the seedbed moist. Seedlings can emerge after 6-7 days. After emergence, the covering should be removed immediately. When the seedlings are 1.5-2 cm high, thin them, removing the weak and keeping the strong. When the seedlings are 3-5 cm high, keep one strong seedling per 3-4 cm square, and apply one topdressing of dilute human feces and urine, spray Bordeaux mixture at 100 times to control downy mildew, and at the same time use zineb at 500 times to control sclerotinia. If damping-off is found, also spray 50% thiophanate-methyl or carbendazim at 800 times, and pull out diseased plants and burn them centrally to prevent spread.

Generally, after about 30 days of cultivation, they can leave the nursery. Perennial root transplanting is preferably carried out in spring and autumn, because the temperature and humidity are suitable for transplanting into field planting or replanting for seedling cultivation.

Field planting

Isatis indigotica is a taproot plant with a long main root, generally able to penetrate more than 30 cm into the soil. Therefore, it is best to choose dry land or sloping land with deep soil, fertility, looseness, and shelter from wind and facing the sun for planting, but it should not be planted in low-lying waterlogged places or paddy fields. The time for transplanting seedlings for field planting is preferably autumn or spring. In early spring, when frost and snow are gone, the temperature rises and there is more rain, so the survival rate after planting is high; in autumn, the temperature gradually drops and the climate is cool, so survival is also easy, but attention should be paid to preventing drought. Spring sowing and transplanting are for producing commercial products, while autumn sowing is for seed reservation. In commercial fields of Isatis indigotica, seedlings are transplanted in early to mid-May, generally by hole planting. If planting in contiguous plots, first remove weeds, loosen the soil, then prepare the land and make beds, with a bed width of 1.5-2 m, an interval width of 33.3 cm, and a bed height of 16-20 cm. Apply 1500-2000 kg of decomposed farmyard organic fertilizer per 667 sq m, rake fine and level, dig holes at a plant spacing of 35-40 cm and a row spacing of 60-70 cm, and plant 2 plants per hole. When transplanting, plant as the seedlings are lifted, pay attention to spreading the root system, press firm, and water thoroughly for seedling establishment.

Management

After the transplanted seedlings survive, check the seedlings and fill gaps to achieve balanced growth, and apply one topdressing of dilute human feces and urine to promote rapid seedling growth. When the seedlings are about 20 cm high, carry out shallow hoeing to remove weeds and apply a seedling-growth fertilizer, applying 8-10 kg of urea, 20 kg of superphosphate and 40 kg of cake fertilizer per 667 sq m. In early to mid-June, when the seedlings are more than 25 cm high, the first leaf harvest should be carried out in time. After cutting the leaves, apply 500 kg of quick-acting human feces and urine or 5-6 kg of urea per 667 sq m (applied with water) to promote rapid leaf regrowth. In late July and mid-September, the leaves can be cut once more respectively. After each leaf cutting, quick-acting nitrogen fertilizer should be applied, combined with intertillage and soil loosening. If dry weather occurs, irrigate in time to preserve soil moisture and moisten the soil, so as to ensure a high yield.