DOWN TO EARTH: Drying onions will reduce losses

Tag : Dry Onion


PRODUCING ONIONS without any means of drying or storing them is a risky businessfor local farmers since the matured crop is exposed to the vagariesof the weather, which is often unpredictable. It has been shownthat in the wet season, losses of 37 per cent from rotting andweight loss are common during "windrowing" or natural drying ofbulbs in the field for 14 days.

However, there are farmers who have suffered total losses of cropsdue to persistent heavy rains at harvest time and the inability todry and store the bulbs.

When bulbs are left to windrow in the field, they are also exposedto losses from praedial larceny. Since crop insurance is notavailable, this means a heavy loss to the farmers.

Proper drying and curing of onion bulbs under protected conditionsis necessary to minimise disease development after harvest and toproduce a top-quality bulb for the market. The aim of the dryingprocess is to remove 4 to 5 per cent moisture to produce bulbs withtightly closed necks and dry outer scales which "rustle" whenhandled. Drying reduces further shrinkage due to water loss duringstorage and marketing.

It may not be feasible for every farmer to have his/her own dryingand storage facility, so a central facility owned by governmentwhich offers a drying and storage service to farmers for a fee isrecommended. This would allow farmers more flexibility in marketingtheir crops. A similar system is used in Trinidad where thegovernment-owned packhouse is used by exporters for a fee.

To avoid the problem of farmers not being sure that they receivetheir own onions after drying or storage, the facility could be setup as individual locked compartments where both the key of themanager and the key of the supplier are necessary to open thecompartment (similar to safe deposit boxes in banks).

In these times of high oil prices, the ideal facility is one whichuses solar energy to heat the air for the drying process. Thesimplest device would be a black painted corrugated metal rooffitted with an insulated drop-down ceiling to produce a plenum orchamber to collect the heated air which would then be extracted bya fan and forced through stacks of ventilated crates filled withonions. After drying and storage, the onions would be sorted,graded and bagged as required for the market.

In the absence of a central drying facility, farmers may have toconsider constructing simpler on-farm structures which, though notideal, would provide some measure of protection and drying andreduce their risk of losses. For very small farmers, stacked meshtrays with bulbs could be stored in a simple mesh-sided structurewith enough overhang to protect bulbs from rain. The floor shouldbe provided with a moisture barrier. The roof could be made ofclear fibreglass or plastic so as to allow the sun to penetrate andheat the air to some extent. After, the drying the roof could becovered with coconut leaves or other material like shade netting toprotect the bulbs from further exposure to the sun.

For slightly larger farms, a concrete or corrugated metal buildingwith metal roof, fitted with an extractor fan in the roof and ablower fan at floor level could be used to protect bulbs from theweather and to provide some additional heat and air movement. Bulbscould be placed in stacked ventilated field crates and placed onpallets on a floor fitted with a moisture barrier.

Disease rather than sprouting is the main cause of onion losses instorage in the Caribbean. Black mould ( Aspergillus niger ) and Soft Rot ( Erwinia spp ) account for a high percentage of storage losses. Both thesediseases may start in the field before harvest, so application ofchemicals like Benlate and Phyton is important before harvest toreduce later losses in storage. The storage of sound bulbs withthin, well closed necks under dry conditions with good air movementwill reduce storage losses.

Farmers are urged to pay close attention to disease control duringthe life of their onion crops as well as to the post-harvesthandling so as to reduce their losses and extend the availabilityof locally produced onions.

The Agrodoc has over 35 years experience in agriculture inBarbados, operating at different levels of the sector. Send anyquestions or comments to: The Agro-doc, C/o Nation Publishing Co.Ltd, Fontabelle, St Michael.