Mean per hectare yield was 18.53 tonnes. The agro-climatic conditions in the province are suitable for onion bulb and seed production. Major growing districts are Chagai, Mastung, Kalat, Turbat, Nasirabad, Kuzdar, Kharan, Quetta and K.S. Ullah.
Onion is a cool season plant, with optimum temperature for seed germination ranging from 20-25C. The early growth stages before bulbing require 13-20C and bulb development needs 16-25C.
The photoperiod plays a critical role in bulb development and determines the suitability of a cultivar for a particular region. Varieties adapted to tropics form bulbs when grown in areas with 10 to 12 hours of daylight (short day types onion). But the varieties adapted to the sub-tropics require 13 to 14 hours (intermediate day types onion). The long day types require above 16 hours for bulb formation and are not suitable in our environment. Only short to intermediate day length types respond well. Therefore, for successful production it is imperative to select the suitable varieties for each agro-ecological region.
Onion can be grown on a wide range of soils preferably sandy rich loam, well drained and contain sufficient organic material to retain soil moisture for proper growth. Soil with pH from 6 to 7 is suitable for optimum crop growth. Hard soils induce the bulbs to be small and irregular in shape. Adequate quantity of manure and fertilizer is necessary for successful onion production.
Its varieties vary in colour, shape, flavour and quality. Saryab Red and Chiltan-89 are commercially grown varieties. These red pungent are good for storage, and can also be used as green bunching onion if harvested at the proper stage. Both have good yield potential, if improved agronomic practices are followed.
The soil should be ploughed as deep as 15-20cm, and one or two plankings are sufficient to get good tilth and levelled seedbed. Seed is sown in seedbeds 8-10 weeks before transplanting. Raised beds of about 2.5m long, 1.25m wide and 10-15cm above the ground level are prepared. Seed rate varies per acre according to method of sowing i.e. 2-3kg seed for nursery raising, and 6-9kg per acre for direct sowing. Nursery beds are kept weed-free and drenched with copper fungicides @ 25-30 gram per 10 litres of water. Seed treatment with Thiram @ 2-3 gram per kg of seed is effective to control damping off. Onions are usually transplanted in the field at 10cm plant-to-plant spacing and 20-25cm apart in rows on flat beds. However, transplanting on ridges is better to harvest more yields of higher grade.
Direct seeding necessitates timely thinning of seedlings, otherwise it leads to under-sized bulbs. It is advisable to transplant onion seedlings early on to ensure good stand and to gain time in areas with a short growing season. This is practised in Balochistan, where onion crops take 9-10 months for the bulbs to mature. Its sowing begins from the 4th week of February to 4th week of March. Though onion has limited root system, but is responsive to manures and commercial fertilizers. A well-rotten farmyard manure @ 10 tonnes per acre should be ploughed down at the time of land preparation at least one month before land preparation.
The first irrigation is given immediately after sowing and transplanting. Thereafter, every week in summer. Irrigation must be discontinued before neck fall, so as to allow the bulbs to ripen off.
Onion plant grows slowly during early stages therefore, fast growing weeds affect crop very badly. As soon as young plants emerge these should be hoed to control weeds. It should be hoed lightly, as it is a shallow rooted crop.
Onion bulbs should be harvested at appropriate stage of maturity. After 50 per cent of the crop showing neck fall, the onions may be lifted out of the soil. Bulbs should be left on the surface of the ground for field curing until tops are fully dry. Direct sunlight can cause scalding. One to two centimetres of the top is usually left on the bulbs to prevent entrance of disease organisms and bulbs are placed in open sheds for curing. Good ventilation is essential.
Onion requires cool weather during inflorescence initiation and seed stalk development. A moderately high temperature and dry weather conditions are favourable for seed maturation. Onion seed loses 50 per cent of viability after one year and has to be produced every year. It is a highly cross-pollinated crop.
Generally, the pungent varieties perform better than the mild varieties during storage. These should be stored at a temperature as near 00C, and the relative humidity should be maintained at 65 per cent with good air circulation through the piles. These should not be allowed to get damp. The crop intended for storage can be sprayed with a sprout suppressant to reduce the incidence of sprouting in store. After treatment, the crop must be left in field at least for four days before harvesting.
Onion thrips (thrips tabaci) are small, yellowish sucking insects which feed on the foliage of onion plants. The tender central leaves become curled and deformed and the outer leaves turn brown at the tips. Thrips are most injurious during dry weather. The pest is very injurious at the time of flowering and impairs seed production. Spraying malathion at weekly interval as soon as thrips appear on the plants has given excellent control.
The neck rot (botrytis alii) is a disease of mature bulbs found in all regions where onions are stored. The fungus only attacks onions that have been injured or wounded during harvesting, therefore, bruising during harvest should be avoided. Thick-necked onions should not be stored since they are slow to cure and succumb quickly to neck rot.
The downy mildew of onion (peronospora destructor) is a fungal disease grown in cool moist conditions. The systemic infection occurs when the plants are grown from a diseased bulb. In this case the plants remain stunted, become distorted and pale green. In humid weather fungus develops as white or purplish downy growth over the leaf surface but in dry weather only white spots are seen. The precautionary measures include crop rotation with a four-year break in cultivation, planting onion at appropriate site, weed control and removal of infected plants from the field.
Purple blotch (alternaria porri) is a fungal disease that occurs at temperatures ranging between 25-30C with 70-90 per cent relative humidity. The leaves and flower stalks show whitish flecks with purple colour centre, which on further development form dead patches.