Botanical and biological features
Daikon is a representative of the Raphanus sativus L. species belonging to the Cruciferae family. The root system is vertical (is represented by a tap root(s)), penetrating deep into the soil – to a depth of more than 2 m (deep-root system) – and measuring more than 1,5 m in diameter. The storage organ is a storage root having a complex structure and consisting of epicotyl (the portion of the axis of a young seedling above the point where the cotyledon(s) is attached, a modified shortened shoot with rosette leaves), hypocotyl (the portion of a seedling below the cotyledon(s), a modified shoot) and the root proper. In some Japanese and Chinese daikon varieties, the sale root can, under adequate ecological conditions, be as long as 1 m and 2 to 25 cm in diameter, depending on the variety. At economic maturity, the root weight is 1-1,5 kg, reaching 16 kg in some varieties. The degree to which the roots are embedded in soil varies according to variety. Under the long-day conditions, the plants form no roots and proceed to the reproductive stage (flowering).
Throughout the more than a thousand-year-long history of daikon in Japan, over 400 varieties and hybrids exhibiting a great variety of shapes and colors have been developed. The roots of most daikon varieties and hybrids have superior eating qualities. They are more succulent, tender and almost free of pungent radish flavor characteristic of European radish varieties. Daikon is rich in potassium and calcium salts, fiber, pectins, vitamin C and a digestive enzyme. It also exhibits healing properties due to the presence in its roots of glycosides, phytoncides and unique bacteriostatic protein substances of complex structure. Among all the vegetable crops, only radish, daikon and horse radish are capable of cleansing liver and kidneys and having a litholytic effect.
The crop management practice
Spring and autumn is the best time for daikon production. Particular attention should be given to preparation of soil – deep plowing (to a depth of no less than 30 cm) in autumn and deep loosening before winter period. In spring (early April), sowing is carried out with depth of seed placement varying between 2 and 2,5 cm. For autumn harvest, the sowing is performed in the latter half of July. The planting pattern for the Late Spring Star F1 RS hybrid is 30 x 20 cm. A planting pattern like this ensures that the plants will not shade one another and provides optimum growing conditions. On a 1,8 m-wide planting bed, 4 rows are arranged with a row spacing of 27-30 cm and plant spacing of 20 cm, resulting in a plant density of 100,000-110,000 plants/ha. With an average root weight of 1-1,2 kg, the crop yield is 100-120 ton/ha (10-12 kg/m2). The growing season varies between 50 and 70 days, depending on sowing time, growing area and growing conditions.Fertilizers are applied at a rate of 300 g ammonium nitrate, 500 g superphosphate and 250 g potassium salt per 10 m2 (NPK 100 kg of active substance each per hectare). The phosphate-potassium fertilizers are applied with autumn digging and the nitrogenous ones as presowing and supplementary fertilizing.
Systematic irrigation is an important factor in daikon production. Normally, 2-6 irrigations are given to the crop in the course of the growing season with a water application rate of 350 l per 10 m2. The best irrigation technique is drip irrigation. Major pests: blue fleas, the cabbage root fly and other soil-inhabiting pests. Control measures: strict adherence to the crop sequence, seed dressing and treatment of plants with insecticides during the flight of the cabbage root fly and at first signs of infestation by other pests. By the time of harvesting, the roots protrude from soil to 2/3 of their length and are lifted very easily. The harvested roots are handled as follows: the soil is shaken off, the tops are cut and the roots are washed, where necessary, then packed and marketed. In summer, daikon roots packed in stretch film can be stored in a cool place for as long as 2 to 3 weeks. Intact autumn-harvested daikon roots can keep until February at 0°С and relative humidity of 90-95%.