Following varieties are recommended for Sri Lankan conditions considering factors such as high yield, seed setting ability, storage adaptability, pungency and colour etc.
Variety was developed at IARI, New Delhi, India. It is well adapted to dry zone of Sri Lanka. 90- 100 days to mature the crop. Average yield is about 20- 25 mt/ha. High pungency, Light rose in colour
Originated from India. Well adapted to dry zone in Sri Lanka . Takes 85- 90 days to mature the crop. The yield is about 15-20 mt/ha with better storability. light rose in colour, High pungency
Variety developed at India by mass selection well adapted to dry zone to cultivate as a yala cropn under irrigation. Pink in colour and it takes about 90-100 days to mature. average yield is about 15-20 mt/ha with good storability.
Bulb colour is slightly rose medium pungency. 85-90 days takes for maturity, Light rose colour, Medium pungency
mainly cultivate as vegetable. Dark red in colour poor storability.
To cultivate one ha of land it is required 7.5 - 8.5 kg of true seeds. If use proper nursery techniques with high quality seeds it can be reduced up to 6-7 kg/ha.
To destroy the causal agents (Pythium, Phytopthora, Rhizoctonia, Sclerotium, Fusarium spp )of damping off. Sterilization is essential using any of the recommended method as mention below.
Turning the soil once a week and expose to direct sun light about 3 times
Burning ( using rice straw and rice husk)
Well prepared nursery beds
Apply the fungicide as mentioned below
In -corporate the following mixture to the surface of the bed
Tripple super phosphate 30 g
Mureate of Potash 15g
To control the spread of disease through seed add 4-6 g from the one of above fungicides to 1 kg of seeds and mix thoroughly
a) Apply seeds at the rate of 40-50 g/bed to the depth of 1 cm in rows and 10 -15 cm apart. Cover with straw mulch after seeding.
b) Daily apply water after covering and until germination
a) Usually completed in 8 - 10 days
b) Remove mulch after germination
Cover the beds using white poly- ethylene to protect from rains and sun light during initial stage of seedlings
Increase the exposure time and watering interval should be increased.
The seedlings, which have 3-4 leaves, 15-18 cm height, slightly bulbs is marked and with the age of about 35-40 days are better to transplant.
It is very essential to select the seedlings prior to planting to achieve good bulb yield
Onion crop can be successfully produced on most fertile soils. soil pH in the range 6-7 is usually recommended . But on organic soils a lower pH is satisfactory. Suitable soil types ( Reddish Brown Earth and Regosols ) are available in the dry zone of sri lanka
Crop need longer day length ( > 12 hours) because it is a long day plant. However, some varieties which can be cultivated in the tropics are need 11-12 hours day length period. Only this type of varieties can produce good bulbs under Sri Lankan condition during yala season.
There should be lower rain fall ( less than 750 mm ) through out the cropping period. At the harvesting period ( last 1 month) need to be dry and hot for better crop.
Less than 70 % RH is favorable.
It is very important to decide the proper time of nursery application because it decides the time of planting. In Sri Lanka it is recommended from early April to early May for nursery application. The climatic requirement of the crop is in the country prevailed during Yala season (May to September). Therefore, it is essential to transplant by mid May - mid June to achieve good yields.
Crop establishment using dry sets is practiced during late Maha (December to February)
However, climatic conditions are not favorable to the crop during this period. Therefore, set planting is not much popular.
Well-drained land selection is essential. Cropping site is very critical factor to decide the yield. Primary weed control is needed prior to land preparation. This can be done by manually or using none selective weed killer
eg. Glyposate( 2-4 liter/ha) apply when weeds are actively growing and 10-14 day before land preparation
Plough the land at the depth of 8 inch and prepare the soil smoothly
According to the irrigation facility better to decide the bed width and length. Normally recommend (1m x 3 m x 15cm beds) Prior to planting it is essential to apply any kind of well-decomposed organic manure at least at the rate of 10 mt/ha.
Fertilizer N,P and K should be incorporated into the soil 2-3 days before planting. For better yield 100-156 plants/m2 is preferable. One cm depth of planting is encourage better bulbing. Deep planting is not suitable for good bulb development. Selected and pre treated seedlings must be used for planting
TSP- Tripple Super Phosphate MOP-Mutreate Of Potash
At the initial stages of the crop water requirement is high. Therefore, it is necessary to irrigate about 3-day intervals and later it can be increased. This intervals may be depend on the soil type. However, after irrigation drainage improving is very essential unless the crop may fail due to ill drainage condition. Two weeks before harvesting water supply should be stopped to increase the quality of the harvest.
Technology for Pest and disease control
Thrips ( Thrips tabaci)
Most damaging pest in Sri Lanka. Warmer and windy climate at July, Augustpromote to increase the pest population . Rasp and pierce the leaf cells and sap release. Insect active when at the poor sunlight in the morning and evening.
Leaf eating caterpillar (Spodoptera exigua)
Root eating ants ( Dorylus spp)
Purple blotch ( Alternaria porri)
Initially irregular white spots can be seen on leaves. Later become large and brown, oval shaped spots with pink colour margins. Finally become black patches.
Anthracnose ( Colletotrichum gleospordes)
Downy mildew ( Peronospora destructor)
(Fungi : Fusarium spp, Phythium spp, Sclerotium spp, Rhizoctonia spp)
True Seed Production
Technology for true seed production
* Select medium size uniform ( 60-70 g/bulb) mother bulbs from recommended variety with related characters and store up to December. Vernalized ( store bulbs under 8-15 c0 for two weeks just before planting ) bulbs treat well from the recommended fungicide . Apply basal chemical fertilizer 2 days before planting ( TSP- 100kg/ha, MOP- 50 kg/ha 1st top dressing at one week after planting ( Urea- 65kg/ha) 2nd top dressing at flower bud initiation ( Urea -65,kg/ha MOP - 25kg/ha). Plant mother bulbs on raised beds with the spacing of 22.5 x 22.5 cm. Suitable time of planting is early January and the crop should be covered with white polythene at the height of about 3ft. at the rains and night. Better to cultivate crops like sunhemp around the crop to attract the insect to increase the pollination. Mature seed can harvest about 3 months after planting. Seed must be well dried unless germination may be loss quickly.
* Pest and disease control
Bulb rot, purple blotch and anthracnose are the major diseases in maha season due to unfavorable weather during period. Control of diseases are similar as in the crop. Chemical application at flowering must be done carefully , because the insects attraction may be restrict.
Identified suitable areas for true seed production during maha season
Because of the higher disease incidences it was needed to find favorable areas for true seed production. In Bandarawela (IM3) area it has given higher seed yield compared to DL1 areas with low disease incidences. Planting time and cultural practices are similar to DI1 region. However it takes longer period ( more than 30 days compared to DL1) for crop maturity.
True seed production under poly tunnels during maha season
Rainy weather condition during December to April cause to fail the seed crop due to high disease incidences. Therefore, it recommend true seed production under poly tunnels in which side opening are allowed to ventilation . All the agronomic practices are similar to maha season true seed production. Higher true seed yield can be obtained from the poly tunnels compared to normal crop with low disease incidences.
Medium size ( 60-70g/bulb ) mother bulbs which are produced in previous Yala season need to be stored up to May. These mother bulbs need to plant at early May to mid May with the spacing of 15 x 15 cm on raised beds. Bulb treatment, fertilizer and cultural practices are similar to maha crop and not necessary to cover the crop . Disease incidences are very low compared to maha season and higher seed yield could be obtained compared to maha season.
Harvesting & Post-harvest Technology
The crop matures about 100 days from transplanting. It is depending on the cultivar and the weather condition. At the 50 % neck fold stage other plant must be bent or press using plank. Thereafter water supply must be stopped. After 14 days crop can uproot and need to shade dry to improve the quality and storability. Then bulb can be seen covered with dry scales. Later, the harvest suitable for storage.
* Suitable varieties for storage Agrifound Light Red, Pusa Red, Kalpitiya selection, and Pampure
* Application of 75- 150 kg N/ha is adequate to obtain good quality bulbs for storage. Application of over doses
drastically reduce the storage
* Malic hydracide sprayed at 50% leaf fall stage reduced the sprouting losses especially when when stored at low
temperature and Carbendazim sprayed to the crop ( 8g/10 l ) two weeks before harvesting decreased rotting
losses in storage
* Bulbs could be stored up to 10 cm thickness without affecting the storability . Due to high high relative humidity
during the storage period ( maha) prevents any futher increase in pile thickness
* Midium size ( 50-60 g) bulbs are the most suitable bulbs for storage
* Environments with low RH ( <80%) and moderate temperature ( 20-300C ) are suitable for big onion storage
© 2006 Department of Agriculture, Sri Lanka (DOASL), All rights reserved-Developed in association with ICTA.