The Brassica rapa is an annual fast-growing herbaceous plant that belongs to the Brassicaceae family. It is native to Iran and was introduced to Egypt, Rome, Greece, India, and other countries in ancient times. It has been widely cultivated in European countries. In China, it is mainly grown in the Yanbian area of Jilin Province and used as the main ingredient for pickled spicy vegetables. In other regions, it is only cultivated in small quantities as a specialty vegetable or sprout. The wild resources of Brassica rapa in China are abundant, mainly distributed in Northeast, North China, Northwest, Southwest, and other regions, growing along the roadside ditches.
I. Botanical Characteristics
The cotyledons of Brassica rapa are deeply divided into three distinct shapes. The stem is covered with papillate short hairs. The basal leaves are narrowly spatulate and pinnately lobed. The stem leaves are linear with serrated or entire margins, and the petioles gradually shorten from the bottom to the top. It branches extensively. The inflorescence is longer than the branches. The flowers are very small, with early falling petals, filiform and degenerate petals, and 2-4 stamens. The short horned fruit is nearly round or elliptical, flat, with a slightly indented apex and narrow wings on the upper part. The seeds are elliptical and reddish-brown. The thousand grain weight is 2.2 grams, and the germination capacity can be maintained for 5 years when stored in a dry place at room temperature.
II. Environmental Requirements
Brassica rapa prefers a cool and mild climate. It grows weak and short when exposed to high temperatures and drought, and quickly bolts and flowers. After fruiting, the plants wither and die. The growth cycle is about 60 days. In temperate and subtropical regions, early spring and autumn are the best growing seasons. The optimal germination temperature is around 16℃. It has a wide adaptability to different types of soil.
III. Cultivation Management
(1) Varieties
- Narrow-leaf Brassica rapa or common Brassica rapa: The leaves are slender, early-maturing, with a growth period of 40-45 days, and a strong spicy taste with tender and soft texture.
- "Normandy" wrinkled leaf Brassica rapa: Imported from France, its pinnate compound leaves are curled, with a beautiful appearance and pleasant flavor.
- Dwarf wrinkled leaf Brassica rapa: The pinnate leaves are highly curled, and the leaf blades grow open. It is resistant to cold, does not easily bolt, and has a growth period of about 60 days.
- Broad-leaf Brassica rapa: The leaves are wide, shallowly lobed, elongated oval-shaped, with slender petioles and uneven appearance. It has a growth period of about 50 days and a milder flavor.
(2) Cultivation Season
Brassica rapa is a fast-growing vegetable, taking 15-20 days from sowing to harvest. It can be produced throughout the year. It is suitable to be sown in stages and batches in open fields during the appropriate temperature seasons. It can be cultivated with shade structures to reduce heat in hot summer, and with insulation facilities in cold winter. In the main production area of Yanbian, Jilin Province, it is used as raw material for pickled spicy vegetables. It is sown in late August and harvested in early to mid-October.
(3) Cultivation Methods
- Cultivation of seedlings: Prepare the field, apply base fertilizer, and rake it finely. Broadcast or drill the seeds, with a seeding rate of 37.5-45 kg per hectare. After sowing, cover the seeds with fine soil and slightly press them down, then water to keep the soil moist. Generally, it can be harvested 2 weeks after emergence.
- Cultivation for pickling: Sow in autumn, with row spacing of 15-20 cm. Broadcast the seeds in shallow furrows, with a seeding rate of 15-22.5 kg per hectare. Cover the seeds with soil about 1-1.5 cm thick. After the appearance of the first true leaves, thin the seedlings and remove weeds. When the seedlings reach a height of 6-10 cm, apply quick-acting nitrogen fertilizer 1-2 times, with a rate of 225 kg urea per hectare, and keep the soil moist. Harvest when the plants reach a height of 15-20 cm in mid-October.
- Sprout cultivation: Use containers such as plates or seedling trays, line the bottom with filter paper, and evenly sprinkle the seeds (soak the seeds in warm water for half a day before sowing to remove the mucilage). Place them indoors at a temperature of 20-23℃ and cover them with black plastic film. Spray water 1-2 times a day. After one week, remove the black film to promote greening. The sprouts can be harvested in about 10 days.
- Seed production: Use the land that was plowed and exposed in the previous autumn or plow it early in spring, apply base fertilizer, and form ridges or beds. Increase the application of phosphorus and potassium fertilizers, with a rate of 300 kg diammonium phosphate and 225 kg potassium chloride per hectare. Sow in rows with a row spacing of 10-15 cm, and a seeding rate of 7.5-15 kg per hectare. Cover the seeds with soil about 1-1.5 cm thick. After the appearance of true leaves, thin the seedlings 1-2 times, with a spacing of 5-6 cm between plants. Remove weeds and prevent aphids, diamondback moths, and flea beetles. Apply additional fertilizers 1-2 times after bolting, with a rate of 300 kg diammonium phosphate and 225 kg potassium chloride per hectare, to promote the growth of lateral branches and increase the number of pods per plant. Generally, sow in mid to late April and complete harvesting from late June to mid-July. The seed yield is about 750 kg per hectare. After drying, store the seeds in a cool and dry place.
IV. Nutritional Value and Utilization
Every 100 grams of fresh Brassica rapa leaves contain 55 mg of vitamin C, 0.23 mg of vitamin E, 3.93 mg of beta-carotene, 1.61 grams of fiber, 334.9 mg of potassium, 120.8 mg of sodium, 187.8 mg of calcium, 42.48 mg of magnesium, 123.6 mg of phosphorus, 0.06 mg of copper, 4.703 mg of iron, 0.899 mg of zinc, 0.355 mg of manganese, and 0.082 mg of strontium. The seeds mainly contain protein, sugar, glucosinolates, fatty acids, etc.
(1) Medicinal use: Brassica rapa has a pungent, bitter, and cold taste, and is non-toxic. The seeds contain cardiac glycosides and fatty acids. It has the effects of eliminating phlegm, relieving asthma, promoting diuresis, and relieving water retention. It is suitable for cough with excessive phlegm, chest stuffiness, and difficulty in urination. It is known as "Tingli Zi" in traditional Chinese medicine. When lightly fried until slightly purple, ground into powder, and boiled in water, it can be used to treat lung congestion, cough with pus and blood. Ground dried seeds can be boiled and used to wash the hair to treat alopecia in children. In recent years, research has found that Brassica rapa has particularly strong anti-cancer and anti-promoting activity.
(2) Culinary use: The stems and leaves of Brassica rapa have a unique fragrance, slightly pungent and spicy, with a soft texture. People in Europe and America often use it as a salad ingredient or as a seasoning in fish, meat, and soup. It is also a traditional component of sandwiches. Wrinkled leaf varieties are often used as decorative vegetables. In the main production area of Jilin Province, China, it is mainly used for pickling. It is mixed with 3%-6% salt, 2%-8% garlic, and 1%-5% chili powder. After being mixed well, it is added to sliced or shredded apples, pears, and basil powder. It is then stored in a cool place for about half a month before consumption.
