Introduction
Radish is a popular vegetable in both tropical as well as temperate regions. It is cultivated under glass house conditions for i early market, but large scale cultivation in the field is more I common. Being a quick growing crop it can be easily planted as a companion crop or intercrop between the rows of the other vegetables. It can also be planted on ridges, separating one plot from another. It is cultivated all over India, especially near the city markets. Radish originated probably in China. In India, it seems to have been cultivated from ancient times. It was popular among the ancient Egyptians and Greeks. The botanical name of radish is Raphanus sativus. The enlarged edible roots are fusiform and differ in colour from white to red. There are two distinct genetical groups in radish. The Asiatic varieties, which are primarily for tropical climates, produce edible roots in the first season and seed in the second season as a biennial crop. On the other hand, the exotic or European varieties produce roots in the plains of tropical and subtropical climate and seeds in the hills of temperate climate.
Climate
Commonly radish is a cool season crop but the Asiatic varieties can resist more heat than the European or temperate varieties. It attains best flavour, texture and size at 10 to 15°C. Long days as well as high temperature lead to bolting without adequate root formation. During the hot weather, the root becomes tough and pungent before reaching the edible size and, therefore, crop should be harvested while young and small in size. The radish is more pungent at higher tempcrature. Pungency decreases with cooler temperature
Soil
Radish can be grown on nearly all types of soils, but the best results are obtained on light friable loam soil that contains ample humus. Heavy soils produce rough, mis-shapen roots with a number of small fibrous laterals and, therefore, such soils should be avoided.
Land Preparations
The soil for radish is thoroughly prepared so that there are no clods to interfere with root development. The soil should not contain any undecomposed organic matter because that may result into forking of roots or mis-shapen roots. Generally first ploughing, about 30 cm deep, is done with soil turning plough and remaining 4-5 ploughings are done with desi plough. Each ploughing should be followed by planking. Application of well decomposed farmyard manure should preferably be done at the time of first ploughing.
Sowing of Seed:
Since radish is a cool season crop, its cultivation is prepared during winter season in the plains. It can be sown at any time between September and January in northern plains as it is not affected either by frost or by extreme cold weather condition. It is grown from March to August in the hills. In the regions where summer is mild, it can be grown throughout the year, except few months of summer. In Bangalore, radish roots are available for 8-10 months of the year but the best edible roots are available during November-December only. The temperate types are generally not planted till October.
Seed rate and Seed Treatment
Radish seeds count about l00-125seeds per gram. About 9-12 kg seed will be sufficient for sowing in one hectare of land. It has been found that soaking radish seeds in naphthaline acetic acid (NAA) at. 10-20 ppm before sowing is effective in stimulating germination of radish seeds.
Method of Sowing
Radish is usually grown on ridges to facilitate good root production. It is grown, as a single crop or as a companion crop. The plant rows or ridges about 22 cm high are kept about 45 cm apart, whereas the plants within the rows are kept 8 cm apart. The European or temperate types, as they need closer spacing, can be sown 20 -30 cm apart. Generally the seed sowing is done 1.15 cm deep. Seed is sown by any of the two methods namely line sowing and broadcasting.
- Line sowing
Seed is mixed with sand or soil in the ratio of 1:4 and placed in a row by hand, over the ridges and then covered with Soil.
- Broadcasting
Seed is mixed with sand or soil in ratio of 1:4 and scattered over the field, as even as possible, followed by planking. Plants are spaced after germination while hoeing.
Manuring:
Radish is a quick growing crop, hence the soil should be highly rich in plant nutrients. Add farmyard manure 25-40 tonnes, nitrogcn 18-50 kg in the form of ammonium sulphate, phosphorus 50 kg in the form of superphosphate and potash 50 kg in the form of muriate of potash for one hectare of the field. The farmyard manure should be mixed up thoroughly at the time of field preparation, whereas the complete doses of potassic phosphatic and one half dose of nitrogenous fertilizers can be applied in the rows before sowing. The remaining half dose of nitrogenous fertilizers should be applied as a top dressing along with irrigation when the plants start growing vigrously.
Irrigation
It is necessary that enough of soil moisture is available to help uniform seed germination and growth of the plant. If sufficient soil moisture is not available at the time of sowing, the first irrigation is given immediately after sowing. It is advantageous in case of light soils but it hinders the germination in heavy soils. In such soils, the surface becomes dry with hard film formation before the seed sprouts. In this case it is always safer if the sowing is done when already enough of soil moisture is available for germination. Depending upon the season and the soil moisture availability, radish may be irrigated once or twice a week. It should not be irrigated very frequently, but care should be taken that field does not become dry and compact and the root development is not checked.
Interculture
Regular weeding is necessary to check the growth of the weeds. During rainy season, two weedings will be required to keep the growth of weeds under check. Tok E -25 (Nitrofan 25%) applied as pre-emergence, controls both monocot as well as dicot weeds in radish field. One earthing up and one weeding during the early stages of growth are necessary for proper development of roots. Radish has a tendency to bulge out of soil as it grows in size. Therefore, thorough covering by earthing up is recommended to produce quality roots. For seed crop, a second earthing up during flowering and fruiting is advocated to prevent lodging of the plants.
Harvesting and Yield
Depending upon the cultivars, the roots become ready for harvesting in about 25-35 days after sowing. Early and rapid maturing European cultivars reach harvest maturity in 25-30 days after sowing. They become bitter and pithy if the harvesting is delayed. In India, harvesting is done manually. A light irrigation may be given before harvesting to facilitate lifting of roots. In advanced f countries, commercial radish growers use a single row harvester that pulls the plants from the soil, cuts the roots from the tops, then places them in bags for transportation to a picking shed. The Asiatic improved varieties produce 150-250 quintals roots per hectare in 40-60 days, whereas the European or temperate varieties produce 80 -100 quintals roots per hectare in 25 -30 days
Storage and Marketing
After harvesting, the roots are properly washed, graded and tied in bundles. They can be put in wooden baskets and sent to markets early in the morning. Radish roots cannot be stored for more than 2 -3 days under room temperature. However, they can be stored for about two months in, cold storage at 0oC temperature with 90 -95% relative humidity.