BY THE AGRODOC

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

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

When bulbs are left to windrow in the field, they are also exposed to losses from praedial larceny. Since crop insurance is not available, this means a heavy loss to the farmers.

Proper drying and curing of onion bulbs under protected conditions is necessary to minimise disease development after harvest and to produce a top-quality bulb for the market. The aim of the drying process is to remove 4 to 5 per cent moisture to produce bulbs with tightly closed necks and dry outer scales which "rustle" when handled. Drying reduces further shrinkage due to water loss during storage and marketing.

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

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

In these times of high oil prices, the ideal facility is one which uses solar energy to heat the air for the drying process. The simplest device would be a black painted corrugated metal roof fitted with an insulated drop-down ceiling to produce a plenum or chamber to collect the heated air which would then be extracted by a fan and forced through stacks of ventilated crates filled with onions. 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 to consider constructing simpler on-farm structures which, though not ideal, would provide some measure of protection and drying and reduce their risk of losses. For very small farmers, stacked mesh trays with bulbs could be stored in a simple mesh-sided structure with enough overhang to protect bulbs from rain. The floor should be provided with a moisture barrier. The roof could be made of clear fibreglass or plastic so as to allow the sun to penetrate and heat the air to some extent. After, the drying the roof could be covered with coconut leaves or other material like shade netting to protect the bulbs from further exposure to the sun.

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

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

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

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