AGRO-TECHNIQUES



CLIMATE AND SOIL

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

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. Long day varieties do not bulb under short day whereas short day varieties, if planted under long day, develop bulbs.

Healthy onion nursery

Soil for onion should be deep friable and highly fertile. Onions can, however, be grown in all types of soils. Sandy soil needs more and frequent irrigation and favour early maturity, whereas heavy soils give rise to mis-shapen bulbs 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/cm 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.

PROPAGATION

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/ m area. The nursery beds should be irrigated 15-20 days before sowing and covered with 250 gauge transparent polythene for soil solarization. Application of Trichoderma viride @ 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.

In case there is still problem of damping off disease the drenching with thiram @ 2-3 g/ litre of water should be undertaken. Weeding and hoeings are carried out to manage weeds. Stomp ( Pendimethalin 30 EC) @ 2.5 litres/ha can be applied even before sowing to manage weeds economically during rainy season wherever there is labour scarcity. About 6-7 and 8-9 weeks old seedlings are suitable for transplanting in kharif and rabi seasons respectively. If lower aged seedlings are transplanted establishment is poor and if over-aged seedlings are planted there is a problem of premature bolting.

Onion seed

Raising small bulblets

For getting early kharif crop small bulblets of kharif onion varieties like Agrifound Dark Red, Baswant 780, N53 and Arka Kalyan raised in previous season are used for planting. Seeds @ 15 g/m 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 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 Arka Bindu ) are broadcast 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.

Seed sowing in rows

 

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 yields of bigger sized bulbs.

SEED RATE

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.

MANURES AND FERTILIZERS

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 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 45 days after transplanting. The topdressing must be completed before initiation of bulbing. Delayed application results in thick neck or doubles.

Top dressing onion crop

 

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.

LAND PREPARATION

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.

TRANSPLANTING

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 (6-7 weeks old) are ideal for transplanting in kharif season, 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.

Transplanting seedlings

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. Nashik and Karnal mid 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

SPACING

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. At Karnal 150 kg N and 15 cm x 10cm spacing while at Nashik 100 kg N and 15cm x 10cm spacing give higher yields. 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.

IRRIGATION

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 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 10-15 days before harvesting gives lower storage losses.

Top falling in onion
 

 

WEED MANAGEMENT

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.

GROWTH REGULATORS

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


HARVESTING

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.

Cutting of tops
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 picking 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.

Onion bulbs

YIELD

Common big onions give 25-30 tonnes/ha yield, small pickling onions give 16-20 tonnes/ha and multiplier onions 15-18 tonnes/ha.

SEED PRODUCTION TECHNOLOGY

Agrifound Dark Red variety is grown during kharif and thus seed can be produced within one year. The seeds are sown in may-June for harvesting of bulbs in October-November. Selected bulbs are planted in November-December to produce seed in April-may for use in the next season. The production technology has been standardized.

Crop ready for harvesting

Selection of bulbs, land preparation and planting

Medium-sized bulbs (4.5-6.5 cm for big onion and 2.5-3 cm for small onion) should be selected for planting. Last week of October to first fortnight of November is recommended for planting of bulbs. Kharif onion since is available in November-end or December beginning, bulbs could be planted by 15th December from the same crops and this way seed production can be taken within an year. Maharashtra, Madhya Pradesh, Gujarat and Rajasthan are ideal for higher seed production without much damage from diseases. Seed should never be produced in plains of Tamil Nadu because bulbs do not get conditioning thereby number of sprouts are 2-3 as also whatever seeds are formed these are not of good quality. Big-sized bulbs increase in number of sprouts/scapes and thereby produce more seed yield per ha. It is, however, better to select medium-sized bulbs for economic seed production. The main objection in small size is that they do not express the true character of the varieties, making it difficult to rogue off types. The best planting time is October-end or November. If planting is done early, the crop gets damaged from rain which comes in March/April. If late planting is done, vegetative growth is less and due to this there are lesser number of flowers and also the seeds in umbel. Attack of the thrips is also more. Selected bulbs of 4.5 - 6.5 cm size are planted in well-prepared field at 45 x 30cm distance in normal loam to clay loam soil. If spacing is kept closer because of less ventilation, drying of field is slow after irrigation, thus heavy dew and rains favour disease. In sandy soils, spacing may, however, be reduced to even 30cm x 30cm. The depth is kept 7.5 cm. Irrigation is given immediately after transplanting.About 25 to 30 quintal bulbs for big onions and 15-18 quintal bulbs for small onions are enough to plant one ha/area. Seed crop also needs to be fertilized each with 80-100 kg of N, 60 kg of P2O5 and 50 kg K/ha. If soil is low in nitrogen, 120 kg N/ha should be applied. 50% N and full dose of P and K should be applied as basal dressing and rest half of N should be applied as topdressing 45 days after planting. Weedicides like pendimethalin at 2.5-3.5 lit/ha or oxyflorofen at 0.15-0.25 litres ha with 1 handweeding at 45 days given good control of weeds.

Irrigation and aftercare

Irrigation is given at 7-10 days interval depending on types of soil and season. Earthing is done 2 months after transplanting to avoid lodging. Weeding and hoeing are done as per requirement. Specific precautions are taken to irrigate the crop more frequently during flowering and seed setting stages. Saturating soil surface and keeping it wet, however, should be avoided as this facilitates in the development of rots and other diseases which cause seed stalks to die prematurely.

Isolation

Since onion is highly cross-pollinated crop, an isolation distance of 500 m is kept between 2 varieties. This is necessary in case of pedigree or certified seed production. For stock or foundation seed production, isolation distance should be kept 1000 m.

Roguing

Diseased and off type plants are rogued out before flowering for quality seed production. Because onion is a highly cross-pollinated that too by bees, it is necessary to have good number of bees for better pollination and seed setting. Following points should be taken care of for improving the pollination.

  • Bee colonies should be kept in field.
  • Irrigation should be given more frequently at the time of flowering and seed setting.
  • Only safer insecticides should be sprayed during flowering.
  • In case of high wind, sometimes bees do not sit on the flowers. To avoid this plant wind breakers all round the field.

Harvesting and post-harvest management

All seed heads do not mature simultaneously, therefore, harvesting is done in installments. When seed inside capsules become black and 20 - 25% black seeds are exposed, the umbels are cut with 10 - 15 cm of stems attached. The heads are spread on ground or canvas to avoid attack of mould and obtain uniform drying.

Threshing and cleaning

Seed is threshed when the capsules are brittle and break readily. Threshing is done by flairing methods. Cleaning is done by air screen machine by using 1/14 x as grading screen. Cleaning is also done by water dipping. For this seeds are dipped in water for 2 - 3 minutes. The heavier seeds at bottom are taken out and spread on screen bottom trays for immediate drying. Dipping in no case is done for more than 2-3 minutes as otherwise the germination is affected adversely. Upgrading is further done on gravity separator if required.

Drying, packing and storage

For safe storage, seeds are dried to a level of about 6% moisture and then packed in aluminium foils or tins. Then it is stored in air conditioned and dehumidified store having a temperature of 20-250C and relative humidity of 30-40%. In hot and humid climate, viability of onion seed is lost within an year. Onion seed if dried to 6.0% moisture level and stored in sealed containers, its life may be prolonged to 3-4 years without evident loss in seed germination.

Seed yield

Generally 6-8 q/ha of seed yield is obtained.If weather is favourable,it may go upto 12 q/ha.

Seed certification

The purpose of seed certification does not differ from other crops. It is taken up to maintain and make available to public, through certification high quality seed and propogating material of superior varieties so grown and distributed to ensure genetic identity and genetic purity.Different steps / requirements of certification are :

Field Inspection : For assurance of quality, the field inspections are very much essential. The stages of inspection are mentioned below.

  • Mother bulb production stage :A Minimum of two inspections should be made.

  • The first inspections should be made after transplanting of seedlings in order to determine isolation, volunteer plants, off types including bolter and other relevant factors.

  • The second and third inspections should be made during flowering to check isolation, pollen shedding umbels, off types and other relevant factors.

  • The fourth inspection should be made at maturity to verify the true nature of umbels and other relevent factors.

Field Standards :

The field standards are :

General requirements

Onion seed fields offered for certification should be isolated from the contaminants by the distances.

Table1 : Contaminants and isolation distances.

Contaminants   

Minimum distance ( m. ) 

   Mother bulb production stage

Seed production stage

Foundation   Certified  Foundation   Certified 
Field of other varieties 5 5 1000 500
Fields of the same variety not conforming to varietal purity requirements for certification 5 5 1000 500

Specific Requirements

Factor

 Maximum permitted  
Foundation Certified
*Bulbs not conforming to varietal characteristics    0.10% (by number) 0.20% (by number)
* Off types

0.10%

0.20%

*Maximum permitted at second inspection at mother bulb production stage.
**Maximum permitted at and after flowering at seed production stage.

  Seed Standards : Seed standards are as given below

Factor

Maximum permitted  

Foundation Certified
Pure seed ( minimum ) ( Physical )  98 %   98 %
Genetic purity ( minimum )  98 %   98 %
Inert matter ( maximum )  2.0 %  2.0 %
Other crop Seeds ( maximum )  5 / kg 10 / kg
Weed seeds (maximum)  5 / kg 10 / kg
Germination ( minimum )  70 %    70 %
Moisture (maximum) 8.0 %   8.0 %
Moisture for vapour - proof containers (maximum) 6.0 %   6.0 %