प्याज की जैविक खेती के लिए उत्पादन तकनीक
Onion is a bulbous herbaceous biennial plant (Allium cepa) of the lily family cultivated as a rounded edible bulb composed of fleshy, tight, concentric leaf bases having a pungent odor and taste. They can be eaten in fresh, frozen, canned, pickled, powdered, chopped, and in dehydrated forms.
Onion varieties are classified mainly according to pungency (mild or pungent) and use (dry bulbs or green bunching). Onions are pungent; because they contain a sulfur-rich volatile oil. Onions vary in size, shape, colour, and pungency.
Bulbs may be white, red, or yellow. Varieties differ markedly in their keeping quality and in their response to length of day. Hybrid varieties must have increased disease resistance, longer storage life, and improved quality.
Onions bear a cluster of small, greenish white flowers on one or more leafless stalks. The leaf base swells to form the underground mature edible onion. Though low in standard nutrients, they are valued for their flavor. Onions cure colds, earaches, and laryngitis and have been used to treat animal bites, powder burns and warts.
Research studies for the organic cultivation of Onion by CRT have resulted in standardization of practices in the cultivation of Onion.
Season of onion cultivation:
Onion is a cool season crop, hardy to frost but less sensitive to heat. It grows well under mild climate without extreme heat or cold or excessive rainfall. A temperature range of 15-21ºC is congenial to vegetative growth prior to bulbing and bulb development is favored in a temp of 20-25ºC.
The optimum temperature for seedling growth is 20-25ºC. Growth is adversely affected 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 a day length of 12-13 hours. Long day varieties do not bulb under short day whereas short day varieties, if planted under long day, develop bulbs.
Soil for Onion crop:
Soil for onion should be deep, well drained friable and rich in organic matter. Sandy soil needs frequent irrigations and crops mature early whereas in heavy deformed bulbs are formed. For high yield and quality bulbs, cool soils are ideal. It cannot be grown in low lying and clay soils.
The optimum pH range is between 5.8 and 6.5. Highly alkaline and saline soils are unsuited and inhibit vegetative growth. Soil aeration and drainage is critical. Water-logging leads to crop failure.
Varieties for organic cultivation of Onion
Dark Red varities: N-53, Agri found Dark Red
Light Red Varities: Pusa red,N,2-4-1, Agrifound light red
Yelllow varities: Tana F1, Granex etc
Rose onion: Bangalore Rose
Stage I of Organic cultivation
Land preparation
Plough soil thoroughly and till to make soil friable, deep and workable. Level and make raised beds with a width of 1.8m. Finally, level the field to a fine tilth. Add 5 tons of compost with about 2 kg Trichoderma/Pseudomonas, 100 kg neem cake, 50 kg groundnut cake, 500 kg Bokashi, 2 kg Azotobacter, 2 kg PSB and 2 kg K mobiliser and prepare fields.
Stage II of Organic cultivation
Seeds and sowing
Seed rate:
Big onion- 5-8 kg/ha, Multiplier onion-10-12 Q bulblets per ha.
Seed treatment:
Soak seeds in panchakavya 3 % and Pseudomonas 5% prior to sowing
Onion Nursery:
Seedlings are raised in nursery beds or plastic trays. Fill with coir pith compost and drench with Trichoderma and Azotobacter@3 gm/litre of water. Seeds can be sown in late march to April for kharif and Oct-Nov for rabi crop
Transplanting
can be done when seedlings are 6-7 weeks old in Kharif and 8-9 weeks old in rabi season. Transplanting young seedlings leads to poor growth and vigor while planting older seedlings leads to premature bolting.
Bed preparation:
Transplanting must be done on raised beds for better yields and good growth. Unfavorable beds leads to doubles, bolters and deformity. Transplanting must be completed by May-early June for kharif and late Nov- Dec for Rabi.
Spacing:
Adopt a spacing of 15X10 cm for a good crop.
Stage III of organic cultivation of Onion
Manuring
Mix a quantity of 2 tons of Compost+3 Kg VAM+1 L Pseudomonas at the time of bed prepration. Add sufficient quantity of water to moisten the heap and set aside for 3 days.
At the time of top dressing, mix bio fertilizer – Azotobacter(250 ml)+PSB (250 ml) in good quality compost (200 kg) and 1 kg of Trichoderma with about 1 ton compost and 150 Kg groundnut cake and apply at the time of earthing up about 30 days from transplanting. Second earthing up and weeding should be done at 45 days after transplanting
If having drip irrigation add EM @ 1L in 250 Litres of water. Give EM water twice a week in the drip water. Add bio fertilizer – Phosphorous Solubilising Bacteria (250 ml) + Potash Mobiliser (250 ml) to the irrigation water twice a week. Give EM and the bio-fertiliser mix on separate days.
Spray crop with Panchakavya or Amrit Pani on 30th and 45th day for better yields. Stop giving Effective Micro-organisms ( E.M.) after 45 days.
Stage IV of organic cultivation of Onion
Irrigation
Onion is a shallow rooted crop and very sensitive to water logging . Initial water requirement is low and is influenced by crop growth, soil type and planting season. Give good copious irrigation immediately after transplanting.
Water is critical at bulb formation and any water stress at this time leads low yields and adverse production. Bi-weekly irrigations with drip facilitate good growth and yields. Stop irrigation about 10 days before harvesting.
Stage V of organic cultivation of Onion
Weeding
Two-three weedings followed by one earthing up and a second if necessary a fortnight later is sufficient for the Onion crop.
Stage VI of organic cultivation of Onion
Plant protection (Disease and insect control, Spray schedule)
| Name of pest/disease | Symptoms | Control measures |
|
Thrips (Thrips tabaci) |
Leaves have shining silver streaks or brown spots. Many minute yellow or white insect moving near base or middle of leaves |
Use predators like Lacewing and Minute pirate bugPlant sunflower, cosmos, and dill are companion crops that divert the attention of thrips. Keep plants well irrigated. Lack of water increases the susceptibility of plants to thrips damage. Prune off and remove heavily infested plant parts.Remove weeds as the thrips population builds-up on them. Garlic – Crush 500 gm garlic and mix in 5 litre of water. Filter and spray extract @ 5ml in 1 litre of water. Neem- Spray 3 % neem seed kernel extract. Use bright blue or royal blue sticky traps: spread petroleum jelly or used motor oil on a blue shade of painted plywood, 6 cm ´ 15 cm or up in size. Place traps near the plants but not touching the leaves. The traps when hung should be positioned at a 60-75 cm zone above the plants |
|
Mites (Aceria tulipae) |
Infested leaves show yellow patches. |
Coriander Decoction-Crush 500gms coriander leaves and 500 gms mint leaves. Pound coarsely. Add 5 liters of water. Filter after 2 days and spray @ 5ml/liter. Spraying Neem seed kernel extract @ 5ml /liter.Furoflavone in Pungam oil acts both as miticide and ovaricide. Spray 5-8 ml/litre of water. Spray Paecilomyces fumosoroseus (1X 10 8 CFU’s/gm) @ 5gm/litre of water. Spray when temperatures are between 220 C and 300 C and high humidity prevails. Repeat sprays once every 10-15 days for four times. Sulfur - Dust with sulfur powder or spray 2 % Wettable sulfur to control mites |
|
Onion Fly (Delia antiqua) |
Maggots are small white legless and feed on developing bulb underground through roots. Infested plant turns yellowish and dry. Secondary infection by fungus causes soft rot. | Spray NSKE @ 3ml per litre of water followed by Verticillium lecanii @ 5ml per litre of water |
|
Cut worm (Agrotis epsilon) Head Borer (Heliothis armigera) |
Seedlings are cut from the base at night |
BT: Spray BT at 12-15 days @ 6-10 ml/litre of water twice a week on second larval instar. NPV: Spray a solution of NPV @ 100ml+0.5ml/litre of khadhi soap+0.5ml of clothes blue. The dosage of NPV is about 100-200 ml/acre. Spray Beauvaria bassiana (1X 10 8 CFU’s/gm) @ 5g/litre of water. Drench or dust in root zone either manually or by watering. Beauvaria enters host pest by contact and then mobilize and kill it in 7-10 days |
|
Groundnut earwig (Euborellia annulipes) |
Bores into onion bulbs | Spray Metaarhizium anisopliae @ 5 gm/ litre twice a week to control pest |
|
Purple Blotch disease (Alternaria app) |
Small sunken whitish flecks with purple centres develop on leaves and flower-stalks, These lead to dead patches and fall from point of attack. |
Proper seed selection and warm seed treatmentRemove and destroy infected leaves but do not put them to compost pit. Improve airflow among plants. Practice wider spacing to have higher light penetration and airflow.Remove tall weeds around the plants to increase air movement and lower humidity levels. HOT WATER DIP -Soak seed in hot water (122°F; 50°C) for 25 minutes. Do not soak longer or seed could be damaged. |
|
Blight disease (Stemphylium) |
Infections occur on radical leaves of transplanted seedlings at 3-4 leaf stage. Small yellow to pale orange streaks in middle of leaves/flower stalk appear to one side and lead to toppling of plant. |
Proper selection of seeds for sowing/planting. Make sure that these are disease-free and not taken from plants that were previously infested by blight disease. Plow all the crop residues after harvest to physically remove the spore source from the top soil Practice crop rotation. Fields should not be planted with onion for at least 2 cropping seasons.Remove weeds as these may serve as alternate hosts. Practice the recommended plant spacing to promote good air circulation. Harvest bulbs when the soil is not wet and when the leaves are dry. Minimize injury to the bulbsSpray Marigold extract |
|
Basal Rot (Fusarium oxysporum var cepae) |
Wilting and rapid dying back of leaves from tip as plants approach maturity and roots turn pinkish. The roots start rotting, bulb becomes soft and when cut a semi-watery decay advances from base of the scales upward. |
Five year rotation with unrelated crop.Plant wilt-resistant cultivars whenever possible. Practice a proper crop rotation.Remove and destroy infested plant materials after harvest. Do not use it in the compost pit . Compost from such materials will contain the fungi. Grow healthy plants with appropriate fertilization, irrigation, and weed control. Spray Trichoderma /Pseudomonas @ 5ml/litre of water at weekly interval. |
|
Downy mildew (Pernospora destructor) |
Violet fungal growth on surface of leaves and flower stalk, turns pale green yellow leading to leaves and seed collapse. Bulbs become soft, shriveled in storage. |
Select and use only diseased-free seeds for sowing.Transplant only healthy seedlingsEnsure that soil is well drained and aerated. Adopt appropriate spacing to ensure ventilation and circulation. Practice crop rotation. Rotate susceptible crops with resistant ones. Avoid overhead watering. |
|
Onion Smut (Urocystis cepulae) |
The disease appears as dark elongated thickened areas at base of seedlings and on young cotyledon as plant emerges. The leaves bend down abnormally with raised blisters. The lesions burst to expose a black powdery mass of spores. |
Use of disease-free seeds Control insect pests Removal and proper disposal of infected plant debrisAvoid field activities when the plants are wet |
|
Bacterial Soft Rot (Erwinia carotovora) |
Common in storage, bulbs rot starting at the neck, giving an offensive smell |
Proper curing and rapid drying at harvest. Discard damaged bulbs before storageCure green bulbs properly. |
| Yellow dwarf | Severe stunting, dwarfing, twisting of flower stalk is followed by colour change in leaves to yellow, crinkling and bending over. | Control spread and attack of thrips |
Stage VI of organic cultivation of Onion
Harvesting:
- Bulbs are ready for harvest 65-150 days.
- Green onions can be harvested in 45-90 days.
- Bulbs can be harvested when neck tissues begin to soften and tops are about to abscise and decolorize.
- Proper colour development with characteristic pungency is also an important index for harvesting.
- Harvest bulbs for sale as dried bulbs after tops start falling over. Alternatively when leaves change colour to yellow and tops start drying and red pigmentation commences bulbs can be harvested.
- Harvest rose and multiplier onions when 50% - 75% tops have fallen over.
- Cut leaves leaving 2-2.5 cm at the top until it has dried completely. This increases dry matter due to greater water loss with intact foliage and material movement from tops to bulbs. If cut to close it serves as entry point for fungal and other pathogens leading to decay and rotting.
- Early harvests lead to sprouting while late harvesting induces secondary root formation. Late harvesting may also induce doubles and bolting.
Yields:
- Big onions: 25-30 tons/ha in rabi and lower in kharif season
- Pickling and rose onions-16-20 tons/ha
- Mulitplier-15-18 tons/Ha
Authors:
Bindumathi Mohan
T.S. Srinivasan Centre For Rural Training
SIPCOT II, Bethalapalli, Hosur, Tamil Nadu 635109
Mail Id-