Introduction
Knol-khol (Brassica oleracea var. gongylodes) is known by several names in India. This crop originated from wild species, B. oleracea var. sylvestris through mutation, human selection, and adaptation along with other brassica vegetables like cabbage, cauliflower, and broccoli. The species is supposed to be from the Eastern Mediterranean region. The edible part is characterized by the formation of a knob (tuber), which arises from a thickening of the stem tissue above the cotyledons. The fleshy turnip-like enlargement of the stem develops entirely above the ground. This knob is harvested for human consumption as a raw or cooked vegetable, though in some parts particularly Kashmir, young leaves are also used. It is produced on a small scale in Kashmir, West Bengal, Maharashtra, Assam, Uttar Pradesh, Punjab, and some parts of south India.
Table of Contents (toc)
Climate and Soil Requirement for Knol-khol
It is a temperate vegetable crop. However, early maturing varieties of knol-khol cultivated in India require a relatively cool, moist climate. In temperate regions, the early varieties are sensitive to early bolting but under subtropical conditions, this problem is not much since the vernalization effect of low night temperature is counteracted by high temperatures during the day with the result that means temperature hardly goes below 10°C. The high temperature after planting delays the bolting of plants that have vernalized on the seedbed. It grows well with a monthly average temperature of 15-20°C, maximum and minimum average being 24° and 4.5°C. In late varieties, low temperature does not have a stimulating effect on bolting at early stages. It is vernalized in the later stages only as other biennial cole crops when the plant has made some growth. It can withstand extreme cold and frost better than other cool-season crops.
Varieties that are susceptible to bolting lack a juvenile phase and become generative without producing knobs if exposed after germination to low temperature. When the low temperature occurs at the knob formation stage, the round and flat round varieties produce long oval-shaped knobs. The low temperature or frost conditions sometimes develop anthocyanin pigment on knobs or plant parts. These pigments are intensified, if there is lack of N and P in soil, deteriorating the quality of knobs, especially of green types.
Knol-khol can be grown on all types of soils. However, a rich soil produces excellent knobs. Sandy loam is ideal for an early crop and clay or silt loam for higher yield and late crop. It does not grow well in highly acidic soil. The optimum pH is 5.5-6.8.
Varieties of Knol-Khol
Some of the promising varieties available in India are Sutton’s Earliest Purple (Sutton), Golith White (Sadashiv), Early White Vienna, King of the Market and Early Purple Vienna (Verma, Pocha). Although research station and some private seed companies are engaged in testing and maintenance of varieties, no serious attempt has been made for the improvement of the crop as the available introductions are well suited to our conditions. All the exotic varieties available in India are early type and become ready for harvesting within 60-70 days after planting. In Europe, Wiesmoor Forcing White and Gaugels Forcing White are resistant to bolting and mature 30-45 days after planting. These are early varieties characterized by the horizontal position of the lower leaves. The late varieties mature 70-100 days after planting. The earliest variety in this group is Purple Speck white Goliath.
Pusa Virat, developed at IARI, Regional Station, Katrain, is suitable for cultivation under Indian conditions. The recommended varieties are given here.
Early Purple Vienna: An early strain of Purple Vienna which has purple leaves; globular-round large knobs with purple skin and light green flesh. It takes 55-60 days after transplanting for knob formation. Average yield is 20-25 tonnes/ha.
Early White Vienna: An early strain of White Vienna takes 50-55 days after planting to form knobs. Knobs are globular-round and green with fewer leaves. Flesh is creamy white, tender and crisp with an average yield of 20 tonnes/ha.
King of North: Plant height, 20-30 cm; foliage, dark green; knob, flattish-round; leaf sheath, large and well spread over the knob. It matures 60-65 days after transplanting.
Large Green: Green round large-size knobs with small tops; knobs tender, delicately flavored with white flesh; ready for harvesting in 76 days with an average yield potential of 22-25 tonnes/ha; and is recommended for mid and high hills of the western Himalayas.
Palam Tender: This variety, developed by CSKHPKV, Palampur, Himachal Pradesh, has light green globular round knobs with green leaves. It takes around 55 to 60 days after planting to form knobs. It has tender creamish flesh. The knobs are smaller than Pusa Virat with an average yield of 15-20 tonnes/ha.
Purple Vienna: This is sown about 1 week later than White Vienna. Knob of purplish-blue with greenish-white flesh; purple leaves; requires 55-65 days for knob formation. It has slightly better yield potential than White Vienna. The purple color is mainly due to the presence of anthocyanin pigments.
Pusa Virat: The variety has dwarf plant type and semi-spreading habit. The individual knob weighs around 800 g and the average yield is 23 tonnes/ha. Harvesting can be done from 50-60 days after transplanting. Both knobs and leaves are edible. It can withstand high frost and cold conditions. Seed sowing may be done from April to October under hilly regions and October to December in the north Indian plains. There is little or no fiber development at maturity.
White Vienna: An early variety with globular, light green, smooth, tender, medium size knobs having creamy white tender flesh with delicate flavor; dwarf plants; short tops; leaves and stems, medium green; yield potential 15-20 tonnes/ha; and matures 55-65 days after transplanting. It takes 50-60 days for knob formation.
Cultivation of Knol-Khol
Nursery preparation in Cultivation of Knol-Khol
Knol-khol is usually propagated by seed, and seed rate (1-1.5 kg/ha) is almost double as compared to cabbage. Seed should be given a hot water treatment at 50°C for half an hour against black rot, and Captan against downy mildew before sowing in disease-prone areas. The seedlings are raised in the nursery beds. About 4 to 6 week-old seedlings are ready for transplanting.
Generally, 60 cm wide and 2.5 m long nursery beds are prepared. For 1 m² nursery, 100 g of fertilizer mixture containing 15 g each N, P, and K, and 2.5-4 kg farmyard manure mixed well in soil and raised nursery beds must be prepared with 30 cm channel along with the nursery. On light and drought-sensitive soils, sunken nursery beds are preferred. Acidic soils should be limed. Seeds are sown in rows at a distance of 5-6 cm for ease in manual hoeing, weeding, and thinning. In too close spacing, the seedlings are liable to be attacked by damping off disease and become lanky. Proper spacing results in stocky and vigorous seedlings. A depth of 1.5-2 cm is optimum since deeper sowing delays germination. The nursery bed is covered with grass to conserve moisture for uniform germination and watering is given as and when required. The mulch is removed just before the seed germination to control damping-off and drenching with dithane M-45 (0.2%) is recommended. Seedlings are hardened in the nursery by restricting the water supply for about a week before transplanting in the field to enable them to withstand the shock of transplanting.
Planting of Knol-Khol
In the plains of north India, planting may be done in September, while in the milder winter regions, October is the best time for planting. In the hills, of northern India seeds are sown from March April to August. About 5-6 week-old seedlings are transplanted for summer and autumn crops. The growing of seedlings in March-April needs protection from cold and frost for which low-cost polyhouses may be used.
Preparation of land is done by 2-3 ploughings to get fine tilth. The beds and channels are prepared to facilitate irrigation. Transplanting of seedlings is done in the evening and/or on cloudy days. The soil around the plants should be well pressed to establish contact with the roots. This process should be followed by a light irrigation. The dead plants should be replaced and gaps are filled 5-6 days after transplanting. The transplanting is done at a close spacing of 25 cm x 25 cm, 25 cm x 30 cm, 25 cm x 40 cm, 30 cm x 45 cm depending on climatic conditions and fertility of the soil. The yield is more in close spacing but the size of the knobs is reduced. The early varieties may be planted at closer spacing while the late ones require wider spacing.
Nutrition Requirement for Knol-Khol
Knol-khol responds well to manuring as it is a heavy feeder. A yield of 20 tonnes/ha removes about 100 kg N, 85 kg P, and 170 kg K. Excess of N may cause abundant leafy growth and a delayed crop. Split application of N is more beneficial. Half of N along with the full quantity P and K are applied at the same time of transplanting and the other at the knob development stage. The farmyard manure is added to soil 4-6 weeks before transplanting. In general, an NPK dose of 80:60:100 kg/ha is recommended for optimum yield.
The deficiency of B, Mo, and N may induce physiological disorders such as browning, whiptail, and buttoning. Foliar application of urea (1-2%) to correct the N deficiency is useful and economical. To correct boron deficiency 10-15 kg/ha of borax as a soil application or two sprays of 0.3% borax on the crop are beneficial. In highly acidic soils, Mo deficiency can be overcome by liming the soil which ammonium molybdate @ 200 g/ ha at a concentration of 0.01-0.1%. The plants should be supplied with B and Zn each @of 15 kg/ha for a higher yield. Application of B and Zn also enhances growth, yield, and quality traits. The knob quality in respect of TSS and ascorbic acid content also gets enhanced with the application of B and Zn.
Irrigation in Knol-Khol
Knol-khol requires a continuous supply of moisture for uniform growth and development of knobs. First irrigation is done immediately after transplanting and thereafter as and when needed, depending on soil and weather conditions. Irrigation at 15 days intervals is adequate. Heavy irrigation should be avoided. Irrigation should be applied when the moisture content of the soil has dropped below 50% of field capacity. At the time of maturity of knobs, irrigation is detrimental.
Aftercare in Cultivation of Knol-Khol
Steady growth is of utmost importance. Any check-in the growth causes knobs to be fibrous and woody. On the other hand, too rapid growth after slow initial growth may result in the cracking of knobs though a lot of varietal variation exists. The knobs may become elongated in close spacing due to lack of light as in knobs growing in the shade. The production of elongated knobs may also be caused by high temperature and excess of N. Cracking of knobs also occurs if the long dry spell is followed by moist conditions or irrigation, because of increased root pressure.
The intercultural operations are performed mainly to check the weed growth to make the soil loose and to maintain proper moisture conditions. Since its root system is shallow, hoeing is done to keep the crop weed-free. The presence of weeds in the early stages reduces the yield due to the poor growth of the plants. Timely hoeing helps check the weed population. As soon as the weeds start appearing, shallow hoeing should be done. Once the weeds are well established, their removal disturbs the root system of plants resulting in weak growth. No sooner than the soil is covered with foliage, hoeing is stopped. Hoeing during the knob development stage is discouraged and weeds if any removed by hand.
Besides manual weeding, some of the herbicides can be used for effective weed management. Pre-emergence herbicides like trifluralin, pendimethaline, DCPA are very effective for weed control. Few post-emergence selective herbicides like sethoxydim and clethodim are also suitable for knol-khol. Treflan (trifluralin @ 0.5 litre/ha) and Semeron (desmetrayne @ 1kg/ha) applied before transplanting control both monocot and dicot weeds. The use of black polythene mulch for controlling weeds can also be made. Recently the effectiveness of Stomp (Pendimethalin @ 1-2 kg/ha) in controlling weeds has been recommended. The practice of a weedicide application supplemented with 1 or 2 hand hoeing is useful and economical.
Quality improvement in Knol-Khol
Size and nutritional quality of knol-khol improve with the application of organic manures in the form of FYM, vermicompost, biofertilizers. Growth attributes such as stem diameter, plant height, number of leaves/plant, and spread of plant are significantly improved under the application of organic fertilizers. Yield/ha and maximum nutritional contents were found in organic fertilizer-treated plots. The application of vermicompost is found to be the most beneficial in increasing the yield and nutritional quality of knol-khol. Vermicompost application significantly increases the percentage of dry matter, protein, carbohydrate, vitamin C, and calcium contents of curd of all the cole crops including knol-khol.
Diseases and Pests In Knol-Khol
The occurrence of diseases and pests is less in knol khol as compared to other cole crops. If precautions are taken at right time these can be managed effectively and not become a major problem in the cultivation of knol-khol. However commonly reported diseases to include damping off, downy mildew, and black rot.
Harvesting and Post-Harvest Management in Knol-Khol
 The knobs are harvested by cutting the stem just below it with a sharp knife or sickle before they are fully grown. After that, they become tough and woody. The demand is fairly high for knobs of smaller sizes of about 5-8 cm diameter. In preparing the produce for the market, the root portion is removed and the plants are tied in bunches along with tender leaves. It is also marketed after removing both leaves and roots.
The knobs of early varieties may have an average weight of 200-500 g while those of late ones weigh up to 1 kg. Generally, the yield may vary from 12-30 tonnes/ ha.
