The onions are bulk stored in special houses with thatched roof and side walls are made up with bamboo sticks or wire mesh for good air circulation. In North India, the sides are also covered with gunny cloth. Onions are stored in these sheds by spreading them on dry and damp proof floor or racks. Periodical turning of bulbs or removal of rotten, damaged and sprouted bulbs should be done. Well-ventilated improved storage structures with racks or tiers having two or three layers of bulbs would be desirable for proper storage.

The salient features of improved storage structures are as below

• Construction of storage godown on raised platform helps in reduction of moisture and dampness

• Use of Mangalore tiles roof or other suitable material prevents built up of high temperature inside.

• Increased centre height and more slope is better for air circulation and preventing humid microclimate inside godown.

• Bottom ventilation provides 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 60-70 cm for cool humid weather, 75-90 cm for mild and humid weather and 90-120 cm for mild and dry weather conditions

• Restriction of stacking height to 100 cm for small and multiplier onion and hot weather and 120 cm for mild weather and for big onion to avoid pressure bruising.

• Cubicles should be made instead of continuous stack leaving sufficient space for ventilation from all the sides.

One cubic metre area of store accommodates about 750 kg onions.

Transport

Onion stocks are transported in bullock carts, tractor trolleys and trucks as also railway wagons are used for longer distance movement within the country. Onions are transported in ventilated ships as well as sailing vessels / motorboats for export to Gulf and South-East Asian countries. It is also shipped in 3.5m containers or 7m containers by loading on ships. ………………………………………………………………………………………………

2.1 Pre-harvest Operations

The condition of onion leaves is a good indicator of the maturity and general state of the bulb. Bulb onions which are to be stored should be allowed to mature fully before harvest and this occurs when the leaves bend just above the top of the bulb and fall over. As a practical guide, farmers should conduct sample counts on the number of bulbs, which have fallen over in a field; and when the percentage of bulbs, which have fallen over, reaches about 70-80% then the entire crop should be harvested.

Harvesting could commence earlier when 50-80% of the tops have gone over, before it is possible to see split skins exposing onion flesh Storage losses at optimum maturity are normally lower than those harvested before the tops collapse.

Bulbs generally mature within 100-140 days from sowing, depending on the cultivar and the weather. Spring onions mature for harvesting after 35-45 days from sowing. Harvested crop should be allowed to dry or cure and ripen in the sun for several days after lifting. Onions can yield up to 5 t.ha-1 under good growing and management conditions.

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