The onion is one of the most important commercial vegetable crops grown in India: The demand for onion is worldwide. It is used both in raw and mature bulb stage as vegetable and spices. The pungency in onion is due to a volatile oil known as ally-proopyldisulphide. The bulb of onion consists of swollen bases of green foliage leaves and fleshy scales. Maharashtra, Tamil Nadu, A.P., Bihar and Punjab are the important onion producing states.
Climate:
Onion is a cool season crop. It is grown during winter and harvested before the real hot season begins. Onion can be grown under a wide range of climatic condition. But it succeeds best in mild season without extremes of heat and cold. According to Rao and Purewal (1954), it can be grown as a rained crop even at elevation of 1500 to 2000 m between April and August, Onion produce bulbs more rapidly at warm (210C to 260C) that at cool 150C to 210C) temperature.
Soil and its Preparation:
Onion can be grown on various soils. But sandy loam, silly loam and deep friable soils are best suited for onion crop. The land is prepared by giving 5-6 ploughings. The optimum pH range is between 5.8 and 6.5.
Seed rate & Time of Sowing:
In onion 10 to 12 kg seeds require/ha..For kharif it is sown in June & for rabi sown in October-November.
Layout & Spacing:
Ridges & furrow type of layout is follow15x10 cm. spacing is given.
In case of onion preferably flat beds are use because
- As in flat beds plants accommodate are more than ridges & furrow so we get more yield.
- In flat bed (leveled) there is equal distribution of water & fertilizers. So we get uniform size & compact bulb of onion which have good keeping quality in storage & transport.
- In percentage of twines is less in flat beds than ridges & furrow.
Manures & Fertilizers:
25 to 30 cart loads of well rotten FYM or compost applied at the time soil preparation per hectare. For onion 50 kg N, 25 kg P^Os & 25 kg Potash should be applied, as .usual method.
Intercultural, Weeding and Other Operations:
Cultural Operation keeps the field absolutely free from weeds to produce a good crop of onion. Weeds if not controlled in early stage but removed later on, will injure the onion bulbs and the out-turn will be poor. 2-3 hoeing and weedings are enough for the crop. After 2 to 3 irrigations, earth up the poor plants. According to Mehta (1959), if the mature bulbs are to be stored for any length of time care should be taken to cut away the seed stalks as soon as they come out, otherwise they will develop thickness will not be cured properly and, therefore,, they will also fail to keep well in storage. Though no work has been done on the usefulness of crushing or bending over the leaf tops to hasten maturity yet the results of experiments done in U.S.A. indicate that it is an ineffective measure.
Irrigation:
The root system of onion is restricted io top 8 cm and roots penetrate seldom deeper than 15 cm. Water requirement of the crop at the Initial growth period is less. Irrigation should be stopped 15-20 days before attaining maturity for improving the keeping quality of bulbs. Frequent irrigation delays maturity. In kharif season, depending upon the rains and time of planting 6-10 irrigations are enough. In rabi, 10-15 irrigations are given at bulb formation, irrigation is necessary and moisture stress at this stage results in low yield.
Harvesting, Curing, Yield and Storage:
Follow harvesting of onion bulbs at right stage of maturity. It is important in deciding storage life of onion as bulbs may be stored for about six months.
The onion bulbs, reach maturity when the plants cease to produce new leaves and roots. In onion, neck fall is the indication of maturity. Time of harvesting depends on several factors tike planting season, cultivar, market price and condition of the crop. In general, when about 50 percent neck fall is seen crop is harvested. Onion for storage should be fully developed. Thick-neck bulbs which result due to premature harvesting do not store well. Late harvesting leads to increased respiration, subsequent susceptibility to diseases and excessive sprouting during prolonged storage and left in field sunburn is also noticed. Bulbs are harvested by hand pulling if soil is light; they are also harvested by hand implements. Kharif crop, since the growth continues forced toppling should be taken up to stop growth 15 days before harvesting. Onion along with tops are kept in field for 2-3 days, curing for 3-4 days is necessary to remove excess moisture from outer skin and neck to reduce shrinkage and development of colour in storage. In rabi season, yield of onion is around 25-30 tons per hectare, while in kharif season it is comparatively low. Yield : In onion we get 150 to 250 quintals of yield/ha
source : http://agriinfo.in/default.aspx?page=topic&superid=2&topicid=935
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