Pakissan.com; Storage of grain

Storage of grain
By Dr Ali Muhammed Khushk and Bhugro Mal

THE storage of grain requires proper care and planning. It releases and absorbs heat and moisture from the surrounding. Insects infesting stored foods can be divided into primary and secondary grain feeders. Insects capable of infesting undamaged grains include moths, weevils, lesser grain borer and grain beetle.

Temperature and moisture are most important factors as these not only affect the quality, but also give rise to insect pests and fungi. The optimum temperature for most insect pests is around 28-32°c. They are able to develop and multiply between 15.5 to 18.3°c. Many can live long at low temperatures but their activity is reduced very much. These feed on dry materials need certain amount of moisture.

The moisture requirement varies from species to species but practically all of them need more than 10 per cent moisture with 14 per cent optimum. Therefore, grain with less than 10 per cent moisture is safe for storage. Micro-organisms also develop at high moisture content.

If wheat is stored at a moisture content of 14 to 18 per cent at 21.1°c, it will be attacked by Aspergillus restriculus. Grain in storage also undergoes chemical changes with a change in moisture. Increased respiration of stored grain under high temperature increases fatty acids and reduces sugar content.

At high moisture level, carbohydrate fermentation may occur with the production of alcohol or acetic acid resulting in a characteristic sour odour. Storage of grain above 16 per cent moisture may reduce seed viability to a great extent. High moisture content not only deteriorates quality, but also occupies more space as its bulk increases.

At the time of harvest, the grain should be dried until the moisture content is less than nine per cent. The storage of grain requires complete knowledge of all things involved.

In Pakistan, public sector agencies are involved in the procurement, handling, marketing, storage and supplies include the four provincial food departments and national public grain agency, the Pakistan Agricultural Services and Supplies Corporation (Passco).

The rated storage capacity with these agencies is 4.34 million tons out of which 2.45 million tons is with the Punjab Food department; 0.71 million tons with the Sindh Food Department; 0.16 million tons with the NWFP; 0.44 million tons with the Balochistan Food Department; 0.45 million tons with Passco; and about 0.13 million tons with other agencies.

Sindh and Punjab have surplus quantity which they supply to deficit provinces. Passco mostly operates in Punjab in areas not allocated to food department.

Storage structures at public level: The government has constructed large sheds commonly called house type godowns constructed with some variations to suit climatic and other conditions of the area.

In Karachi each unit measures 51.21m x 12.19m with a storage capacity for about 1,500 tons of wheat. Door and ventilation arrangements are made to provide aeration to stored grains. These types do not provide protection from insect infestation and are impossible to make gas-tight for fumigation.

Due to poor maintenance, the structures have deteriorated with the passage of time and considerable grain loss takes place in these godowns due to insect pests.

Binishells: These are dome-shaped structures. The height of the dome in the centre is about 10m with floor having diameter of about 32m. One binishell has the capacity of about 1,500 tons of grain. The structure gets heated up in summer, particularly in Sindh and Punjab resulting in rapid multiplication of insect pests. The structure is also difficult to make gas tight for fumigation.

Silos: There are two types of silos, concrete and metal. Each accommodates about 5,000 tons of grain. Most are not fully utilized due to operational difficulties.

Storage at village level: Major proportion of food grains is held in the houses, in villages and towns, in small but numerous types of receptacles for self consumption. The receptacles may be gunny bags, earthen and metallic bins and pots of various sizes, pallies, kharas, bakharies etc.

During handling and storage considerable quantity of food grain is lost between harvest and consumption. If safe measures are adopted, both quantitative and qualitative losses can be avoided at all levels.

Cleanliness is a primary prerequisite for preventing insect damage in stored products. Most of the insects and mites live in empty godowns or granaries as well as in stored food. Therefore, it is important to destroy them before the granaries are re-filled with grain.

Prior to storage, all bins, granaries and surrounding area should be thoroughly cleaned to get rid of insects and mites living in cracks and crevices. Floor, ceiling, walls and doors should be thoroughly swept, cleaned and the collected rubbish should be burned or removed far away from the storage area.

Empty godowns should also be spread with deltamethrin to kill the already available insects. All cracks, crevices and holes should be filled with cement plaster and made birds and rodent proof. Adequate ventilation is important.

Storage godowns should be waterproof and gas-tight to protect grain from moisture and leakages during fumigation. Walls should be whitewashed with white or light coloured emulsion paint. Grains having moisture less than 10 per cent should be stored. Bags should never be stored near the walls of godowns. Insect free transport should be used for shifting grain from one area to another. Already infested grains should never be stored.

As soon as the grain is brought into godowns, the already available insects begin their job of infesting. Therefore, fumigation just after storage is necessary. In case of house type godowns, spray with deltamethrin at recommended dose on all exposed surfaces of godown, fabric and periphery of stacks. Thereafter, fumigate twice with Aluminum phosphide (ALP) tablets at the rate of three tablets per cubic meter, in two equal doses i.e., 1.5 tablets on the first and fourth day, respectively.

Banishells due to their high leakage rate are difficult to be fumigated. In these godowns, spray with delta methrin as before and thereafter fumigate with phophine tablets using the multiple dose i.e., first dose at the rate of 1.5 tablets per cubic meter, followed by application of one tablet per cubic meter each on 3rd, 5th and 7th, day.

But after fumigation and spray godowns should be regularly inspected for insects, rodents, molds and heating spots. As insects mostly move at dusk, it is therefore, better to inspect for live insect pests in dim light in the evening with torch, but the damage should be worked out in daylight. Detailed examination of dust, cracks and crevices for sign of insects should be done.

Do not allow spoilage of grain in the godown. Always keep the godown tidy and occasionally give the walls, floor, ledges beam and doors a good brush out, discard rubbish and treat the infested goods promptly. Perform periodic check of roof, gutters, walls, floor and doors.

Ventilators and doors should be opened during dry weather and closed during the period of excessive humidity. In case if moisture content of grain exceeds 11 per cent, it should be dried at once, because high moisture is conducive for the attack of insects and formation of mold. Wet grains can be dried by spreading in one inch layer on cemented floor on hot sunny days and given 2-3 turnings during a day.

Courtesy: The DAWN

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