Onion (Allium cepa) is one of the important commercial vegetable crops grown in India. It is widely grown in different parts of the country mainly by small and marginal farmers. India produces around 20 million tons of onion annually and exports around 1-5-2.0 million tons. Annual domestic consumption varies between 13.5- 14.5 million tons, depending upon prices and availability. The domestic consumption is based on NSSO- per capita consumption of 0.89 kg/month and current population of 1.34 billion. Post-harvest losses, varies between 15-25%, are more in onion as it contains approximately 85% water during harvest.

(Source: NHRDF)

(Source: NHRDF)

In Maharashtra, Gujarat, Haryana, Madhya Pradesh and Western Uttar Pradesh large-scale storage of onions is taken in conventionally-designed structures. In other states, the storage is taken only on small scale but now showing increasing trend after the post-harvest technology and improved storage structures have been popularized by NHRDF.

Traditional storage practices result in substantial losses in stored onions, hence use of improved storage structures as well as use of good storer varieties, judicious use of fertilizers, timely irrigation and post-harvest technology are essential to reduce the losses in stored onions.

Storage temperature and humidity affect loss in weight, respiration rate, sprouting, rotting and quality of bulbs in storage. The dormancy in onion bulbs is the main factor to determine as how long the bulbs can be stored. Inherent characters of dormancy based on equilibrium of inhibitors in onion bulbs also gets affected by temperature where lower (00C) and higher (300C) temperature increase the dormant state of onion bulbs and moderate (10-150C) temperature enhance the sprouting losses by breaking dormancy. Higher temperature, however, increases the rottage if accompanied with high humidity and desiccation/water loss is reduced at higher humidity but it increase the rooting and rotting. Hence equilibrium of temperature and relative humidity by providing sufficient aeration/ventilation is needed in improved onion store houses. The improved storage godown designed by NHRDF is based on the above factors.

Salient features of improved storage structures
• Construction of structure on raised platform to prevent moisture contact and dampness.
• Use of Mangalore tiled roof or other suitable material to prevent build-up, high temperature inside.
• Providing bottom ventilation for free and faster air circulation to avoid formation of hot and humid pockets between the onion layers.
• Avoid direct sunlight on onion bulbs to reduce sunscald, fading of colour and quality deterioration.
• Restriction on width of each stack to 60-75 cm for hot and humid weather, 75 - 90 cm for mild and humid weather and 90-120 cm for mild and dry weather conditions.
• Maintenance of stacking height to 100 cm for small and multiplier onions and hot weather and 120 cm for mild weather and for big onions to avoid pressure bruising.
• Providing cubicles instead of continuous stack and sufficient space for ventilation from all sides.
• One cubic meter area of store accommodates about 750 kg onions. Accordingly construction of godown for required capacity and construction of more units instead of single big structure and in zigzag manner when constructed in more rows to have better aeration.
• Providing 2-tier if space available is insufficient.
• Periodical disinfection of structures and premises to check rottage. The cost-efficient structures is based on locally - available materials and labour.

(Source: NHRDF)

Harvesting takes in 45-90 days from field setting for green onions and 65-150 days for bulb depending upon variety / types. Bulbs are considered to be mature when the neck tissues begin to soften and tops are about to abscise and decolourise. Development of red pigment and characteristic pungency of variety are also important harvesting indices of onion.

Onion for sale as dried bulbs or for storage should be harvested after tops have started falling over. Best time to harvest rabi onion is one week after 50% tops have fallen over. In kharif season since tops do not fall, soon after the colour of leaves changes to slightly yellow and tops start drying, red pigmentation on bulbs develop and also true shape and size develop, bulbs are harvested and kept in windrow for drying the tops. Small pickling and multiplier onions are harvested when 50% - 75% of tops have fallen over. The leaves are cut leaving about 2-2.5 cm tops above the bulb after complete drying. Leaving the tops intact until complete drying increases dry-matter content which might be due to greater loss of water from the bulbs with intact foliage or due to movement of materials from the tops to the bulbs.

If tops are cut too close, the neck does not close well and decay organisms have easy access to the bulb. Early harvesting results in sprouting of bulbs while late harvesting results in formation of secondary roots during storage. In kharif season late harvesting results in doubles and bolting.

(Source: NHRDF)

Onion is a cool season crop, hardy to frost but less sensitive to heat. It is adopted to a temperature range of 13-24ºC. For good vegetative growth 15-21ºC temperature before bulbing and 20-25ºC for bulb development are suitable. The optimum temperature for seedling growth is 20-25ºC. Growth starts declining at temperatures higher than 27ºC.

The requirement of day length of different varieties may differ. Kharif onion varieties require day length of 10-11 hours, whereas rabi varieties require relatively higher temperature and 12-13 hours day length.

Onions can be grown in all types of soils. Sandy soil needs more and frequent irrigation and favour early maturity, whereas heavy soils give rise to irregular bulbs size causing problem in digging of bulbs. For high yield and quality bulbs, cool soils are ideal. In general, sandy loam to clay loam soil is recommended. The optimum pH range is between 5.8 and 6.5. Highly alkaline and saline soils are not suitable for onion cultivation. Salt concentration above 4 mmhos/cm² inhibits vegetative growth of most of its cultivars. Good drainage is essential. Waterlogging can result in failure of crop. Onions are very much sensitive to the effects of high water table.

(Source: NHRDF)

Raising seedlings
Onion seeds are sown in nursery beds to raise seedlings. Best time for sowing early-kharif crop is February-April in South, May-June in Maharashtra and other parts, August-September for late-kharif and October-November for rabi in plains all over the country. In hills (higher altitudes), March-April is ideal sowing time. Raised beds of about 3 m long, 0.6 meter wide and 20-30 cm high are prepared. About 70cm distance is kept between 2 beds to carry out operations of watering, weeding etc. The surface of beds should be smooth and well-levelled. Raised beds are necessary to avoid problem of waterlogging in heavy soils. In sandy soils, however, sowing can be taken up in flat beds. Sowing should be done in lines spaced at 5-7 cm distance.

Before sowing, seed should be treated with thiram @ 2 g/kg of seed to avoid damage from damping off disease. The soil of nursery should also be treated with thiram or captan @ 4-5 g/ m² area. The nursery beds should be irrigated 15-20 days before sowing and covered with 250 gauge transparent polythene for soil solarization. Application of Trichodermaviride @ 1,250 g / ha is also recommended to manage damping off and raise healthy seedlings. The seeds after sowing should be covered with fine powdered farmyard manure or compost followed by light watering. The beds should then be covered with dry straw or grass or sugarcane leaves to maintain optimum temperature and moisture. Watering should be done by a water can as per the need till germination is completed. Dry straw or grass is removed immediately after germination is completed. Delay in removal of dry straw and grass may result in lanky seedlings.

Raising small bulblets
For getting early kharif crop small bulblets of kharif onion varieties like Agrifound Dark Red, Baswant 780, N53 and ArkaKalyan raised in previous season are used for planting. Seeds @ 15 g/m² are sown on raised beds or in flat beds. Carbofuran @ 1 kg ai/ha should be mixed in soil for managing thrips insects. Best time for sowing of seeds for getting quality bulblets is mid-January to early February depending upon the area. All other operations for raising of bulblets are the same as that of nursery for transplanting. The plants are left in the nursery bed up to April-May till there is top fall. Harvesting is done along with the tops. Selected bulblets (1.5 - 2.00 cm) are stored by hanging method till August in a well- ventilated house. Bulblets below 1.5 cm if planted do not establish and sprout but rot. Large sized bulblet result in more doubles and bolters, increasing cost of production.

Broadcasting in beds or sowing in rows
Seeds of big onion varieties are sown directly in rows 30 cm apart in parts of Chitradurga, Bellary and Dharwad districts of Karnataka and Satara district in Maharashtra. They are thinned later to give proper spacing for development of bulbs. Seeds of small onion ( Bangalore Rose, Agrifound Rose and ArkaBindu ) are broadcasted in small flat beds which are thinned later. After sowing, hoeing is done by hand-hoes to allow seeds to reach to a depth of 2.5-3 cm. Light irrigation is given immediately after covering the seeds. Weeding is recommended at 10 days interval for healthy and stout seedlings.

Planting of bulblets in multiplier onion.
In multiplier onion ( Agrifound Red, Co-3 and Co-4 ), bulblets are separated and planted. The bigger-sized bulblets should be selected for planting to get higher yield of bigger size bulbs.

(Source: NHRDF)

For common big onions, 8-10 kg seed is sufficient for raising seedlings for one hectare, accomodating 100-110 beds of 3m X 0.6m size each. For broadcasting directly in the field or sowing in the rows, 20-25 kg seeds is enough for a hectare. For multiplier onions 10-12 quintal bulblets are required for planting one hectare.

(Source: NHRDF)

In general,soil for onion growing should be liberally manured and fertilized. About 20-25 tonnes of farmyard/ha adequate. The requirement of nutrients depends on soil type, region of growing, varieties and removal of major nutrients. Onion crop yielding 300 q/ha removes 73 kg nitrogen, 36 kg phosphorus and 68 kg potassium. As it depends on the variety, season etc. soil analysis for application of fertilizers is preferred.

Farmyard manure should be applied one month before transplanting / planting or sowing and mixed well in the soil. Whole quantity of phosphorus, potassium and half of nitrogen should be mixed in the soil before transplanting. Remaining half of nitrogen should be given as topdressing in single dose in bulblet method of planting in big onions and bulblet method of planting in multiplier onion at 20-25 days after planting. In transplanting method, topdressing is taken up in 2 split doses and first dose should be applied at 30 days after transplanting whereas second dose at 45 days after transplanting. The topdressing must be completed before initiation of bulbing. Delayed application results in thick neck or doubles.

In addition to fertilizer, application of micronutrients is beneficial in improving the quality of bulbs. Application of zinc copper and boron increases the yield and enhances quality of bulbs by increasing TSS, sugar and ascorbic acid.

(Source: NHRDF)

The field should be ploughed to a fine tilth by 4 -5 times with a sufficient interval between two ploughings. The ploughings should be done by tractor-drawn implements or deshi plough. The ploughing should be shallow as most of the onion roots penetrate to a depth of not more than 5-6 cm. The planking should be done for proper leveling. The field is then divided into beds and channels. The normal width of a bed should be about 1.8 m.The length may, however, vary according to level of land but it is better to have small-sized beds for proper irrigation and other cultural operations. For onion grown on drip or sprinkler system, this width is kept on 1.2m and length can be taken up to 40-45 m for better drip operation.

(Source: NHRDF)

Seedlings are usually transplanted in flat beds. Transplanting on raised beds or on both sides of ridges is, however, better for kharif or rainy season crops. Flat beds of 1.8 m wide and 7.2 m length depending upon level of land, soil type and irrigation method, are prepared. Seedlings of (6-7 weeks old age) are ideal for transplanting in kharifseason, while 8-9 weeks old seedlings are recommended for rabi crop. Over-aged seedlings if planted , bolting increases. In case of younger seedlings, establishment is poor.

In Maharashtra, best time of transplanting for kharif onion is July-August. In North, it is mid or end of August. In other parts too, August is best time for transplanting. In Tamil Nadu and Andhra Pradesh, kharif crop is raised by planting early. Transplanting is done in April-May in Tamil Nadu whereas in Andhra Pradesh, it is done in May-June. Late kharif crop in Maharashtra is sown in August-September and transplanted in October-November. For rabi the best time of transplanting in Northern and Eastern India, is December-end to first week of January. In other parts mid December is the best time. In Eastern states, where onion is raised after paddy, the transplanting is done in October-November. In Nashik and Karnalmid December planting of Agrifound Light Red and Pusa Red gives higher yield. In Northern mid-hills,onion is transplanted during November and April. Dipping of seedling roots in fungicide and insecticide solution before transplanting helps in better establishment of seedlings. Small pickling onion is planted 3 times in a year in Karnataka, i.e. March-April, June-July and September-October. In Andhra Pradesh,onion is planted in July-August

(Source: NHRDF)

The spacing depends upon the variety and size of bulbs. In common big onions an spacing of 15 cm from line-to-line and 10 cm from plant to plant is ideal. For small pickling onion, 8 cm x 5 cm spacing has been recommended if crop is raised by transplanting method. If bulblets are used for raising big onion crop, ridges are prepared at 30- 45 cm distance and bulblets of kharif onion and multiplier onion bulblets are planted at 10-12 cm distance . For getting quality bulbs, 1.5-2 cm sized bulblets are considered best for planting. Establishment is, however, a problem in smaller-sized bulblets, 2-2.5 cm sized bulblets have been recommended for getting highyer yield.

(Source: NHRDF)

Onion is shallow-rooted crop. Its root system is normally restricted to top 3 cm and roots penetrate seldom deeper (15 cm). The water requirement of its crop at initial growth is less. It depends on crop growth, soil type and planting season.

One irrigation is necessary immediately after transplanting particularly in rainy season in Northern India where temperature at the time of transplanting is very high. Wherever, there is erratic power supply in rainy season, transplanting is recommended 8 hours after irrigation particularly in Karnal area. In kharif season depending upon the rains 8-10 irrigations are enough. Late-kharif crop requires 12-15 irrigations while in rabi seasons 15-20 irrigations are given. At bulb formation, irrigation is necessary and moisture stress at this stage results in low yield. The field should not be kept dry for long which otherwise results in splitting and also force maturity. Frequent and light irrigation at weekly intervals in general (2 acre inch per irrigation) results in good bulb development and increase in yield. Sprinkler and drip irrigation methods increase onion yield significantly.

Irrigation with drip/sprinkler for one hour daily or 2-3 hours at alternate days gave higher yield, irrigation after long per (5 or more) reduced the yield. Irrigation should be stopped when tops mature and start falling in rabi season. In kharif season it should be stopped 10 days before harvesting. Last irrigation at 10-15 days before harvesting gives lower storage losses.

(Source: NHRDF)

Weeds are to be kept down to get a good yield of onion. Stomp @ 3.5 litres/ha applied 3days after transplanting plus 1 hand weeding at 45 days in rabi onion. While in kharif onion Stomp @ 2.5 lit/ha with 1 hand-weeding is very effective. Oxyflurofen @ 150-250 g/ha with one hand-weeding is also effective. Other weedicides used in onion are Lasso, Ronstar, Dual,Treflan and Raft etc.

(Source: NHRDF)

Use of Cytozyme @ 0.2% as root dipping for 20 minutes before transplanting and foliar sprays at 15 and 45 DAT are found more effective in bulbs development and higher yield of kharif onion at Nashik and Karnal. Use of MH @ 2000 ppm applied at 75 DAP in kharif onion and @ 2500 ppm just before neck fall in rabi onion are recommended to cheek premature bolting and sprouting.

(Source: NHRDF)