Onion is cultivated on a vast area of the country. During 2005 it was cultivated over an area of about 127,000 ha with a production of about 1.76 million tones. The vegetable is used as an ingredient in many dishes. The unique flavour and odour of onion has made it an excellent food source. Moreover, the numerous ways in which onion is prepared from boiling, frying, stewing, baking, pickling, to eating raw, make them a versatile food source.
Nutritionally, onion is low in calories. Compounds from onion have a range of health benefits which include anti-carcinogenic properties, anti-platelet activity, anti-thrombotic activity, anti-asthmatic and antibiotic effects.
Onion seed production is a highly remunerative business. During the growing season, prices of its seed escalate to Rs1000-1500 per kilogramme. There are some professional onion seed producers. Through improved seed production technology both the yield and quality can be improved which can fetch higher prices in the market.
Soil requirement: Onion is shallow rooted and can be grown in almost all types of soils from sandy loam to heavy clay. The clay should be well supplied with humus to lighten them. The soil should be free from perennial weeds and soil borne diseases. It should be friable, fertile and well drained. Loamy soil is the best for onion seed production. The soil pH should preferably be 6.0-6.8.
Tillage and fertilisation: The soil should be ploughed to a depth of 15 to 20 cm, harrowed, and worked until a uniform firm seedbed 10 to 15 cm deep is established. Ten to 15 tones of well rotten farm yard manure per acre should be mixed in soil followed by watering. When land comes in condition ridges should be made followed by two gobal ploughings and one rotavator. For better seed production one bag each of DAP and SOP (sulphate of potash) per acre should be drilled on both sides of ridges. These fertilisers develop immunity against attack of insect pests and diseases. One bag of Nitrophos (NP) should be applied followed by each weeding.
Planting time: Suitable time for growing seed crop is from November to December, which is ready by end of March and end of April respectively.
Method of production: Onion seed is generally produced by growing onion bulbs. Mature bulbs of equal size are selected from the freshly harvested crop. For one acre 20 gunny bags or 50 maunds bulbs are required. The bulbs should be lifted when 75 per cent plant show neck fall/top die down. The bulbs should be dried under naturally ventilated place. The storage temperature also influences seed yield. The temperature ranging from 4.5 to 140C with an optimum of about 120C is the best for storage of mother bulbs that are to be planted for seed production.
The roots of the bulbs should be left intact after harvest. The damaged; twin bulbs and long necked bulbs if any should be discarded. Medium size bulbs weighing (50-80 g) are selected and stored. The increase in bulb weight increases the seed yield. Although increase in weight and size of bulb results in higher seed yield, very large size bulbs if used will need a very high seed rate.
The one-third part of the bulb is cut with sharp knife before planting. To avoid rotting due to fungal infection of the bulb in field, bulbs should be dipped in suitable seed dressing fungicide at the rate of 10 grams in 10 liters of water before planting. Bulbs should be transplanted on both sides of ridges in such a manner that they may not face each other and distance be maintained one and half foot apart. Field should be irrigated before transplanting of bulbs.
Irrigation: Onions require frequent irrigations. They extract very little water from depths beyond 24 inches; most of the water is from the top 12 inches of soil. Thus upper soil areas must be kept moist to stimulate root growth and provide adequate water for the plant.
Weed control: Onion is a poor competitor against weeds because of its slow growth, small stature, shallow roots, and lack of dense foliage. Weeds interfere with harvest and other field operations and also contaminate the seed. The most effective weed control measures include proper land preparation, crop rotations, weeding, and use of selective herbicides.
Insect pest management: Onion seed crop is most commonly attacked by thrips. Onion thrips (Thrips tabaci) feed on leaf surfaces during warm, dry weather causing the leaves to turn white or silver. They also feed on flowers causing reduced seed set and smaller seeds. When thrips damage is suspected, it is best to examine the angles of leaves since this is a common hiding place for small insects. Control of thrips is difficult in seed crops because use of insecticides can simultaneously harm pollinating bees. Since onion seed production requires insect pollinators, any insect pest control measure should be applied before flowering. Insecticides must be avoided or used with extreme care during the pollination period.
Diseases management: Onions are subject to attack by many of fungal diseases which reduce seed yields. Application of preventive fungicides, crop rotation, cultural practices that promote leaf drying and avoidance of sprinkler irrigation are the most suitable management practices
Pollination: Pollination in onion occurs through bees, flies and other insects. It is essential to ensure that there is sufficient population of pollinating insects to achieve the full potential of onion seed. Bee hives can be used to make the pollination process more effective. Optimum seed production occurs when 12 to 24 hives per hectare (five to 10 hives per acre) are moved to the edge of seed fields. The most effective concentration and configuration of beehives depends on several factors: neighbouring crop and weed competition for bees, bee colony strength, onion variety, and field placement.
Harvesting and threshing: Determining the harvesting time is the critical decision in onion seed production. Two objectives are in conflict-- to allow maximum seed maturity, and to minimise the loss of seed from umbels shattered during harvest. Too early a harvest will minimise the loss to shattering, but some harvested seeds will be immature, light weight, poor vigour, or non-viable. If harvesting is delayed until all seeds reach optimal maturity, much of the earlier maturing seeds can fall to the ground or shatter from the umbels during cutting and transport. Harvest is generally initiated when about 10 per cent of the black seeds are visibly exposed in the umbel.
Storage: The onion seed generally has relatively short storage life, and viability decreases rapidly at higher temperatures or high humidity. They quickly loose complete viability in less than a year when stored under hot, humid conditions. If properly stored, however, viability of onion seed can be retained for long periods and low seed moisture content and low storage temperature favour longer storage life. Of these two parameters, seed moisture content is the easiest to adjust. Onion seeds stored at six per cent moisture content have retained viability up to three years.