Grain storage techniques ... - Storage at farm/village level and in warehouses

'Improved' farm/village storage methods

Temporary Storage Methods

It is recognized that, although temporary storage methods are the least desirable, there are circumstances in which they are unavoidable. The following suggestions and recommendations for improving such storage methods are offered, on the understanding that more permanent solutions to problems should be sought wherever possible.

Little can be done to improve aerial storage except, perhaps, to suggest that the bundles of cereals may be safer if suspended in a well ventilated part of the house; or above a fireplace where insects may be deterred and the moisture content of the grain may be reduced.

As far as storage on the ground, or on floors is concerned, the grain is less exposed to risk if it is placed on wattle mats or the like laid on the ground or floor. Drying floors could be improved by making them of concrete; or by stabilising the earth chemically or with natural material such as néré juice. Larger animals are less likely to spoil the grain if such floors are constructed near the house, where they can be better guarded.

If the grain is stored on the floor in a part of the house, it is best to ensure that the floor is clean and stabilised. To prevent the translocation of moisture through the floor to the grain, a plastic sheet should be placed upon it first (or better, embedded in the floor during its construction). The room should be rodent proofed as far as possible (including wire mesh screens fitted to windows), and the grain should be treated with insecticide. Before each new harvest the room should be cleaned, to remove any residual insect infestation.

Open timber platforms may be improved by fitted rodent barriers around the supporting posts. Furthermore, the posts should be driven at least 60 cm into the ground, to withstand pressures caused by wind, uneven loads, or even animals leaning against them (some animals will rub against trees to relieve itches!). To protect them against termites, posts should be coated with bitumen or used engine oil, or superficially charred after having the bark removed. Alternatively, since termites do not attack fresh, healthy wood, green wood which will sprout and grow may be used as poles.

The central post of a conical-shaped platform should be at least 80 cm high to prevent rodent attack and, like the poles supporting the upper frame, should be fitted with a rodent barrier. The poles or large bamboos comprising the cone, while being sufficiently strong, must not fit so tight together as to impede the passage of air and retard drying. One solution is to cover the timbers with enough loosely woven wattle (sorghum stems for example), to prevent cobs falling between the timbers, to pass the weight of the grain to the wood and allow air to pass at the same time.

Long-term Storage Methods

The upright poles which support the platforms of traditional storage baskets (cribs) should be at least 80 cm high, and protected against termites as described above. They should also be fitted with rodent barriers in similar fashion (Figure 6.7). The poles should be as thick as possible, in order to reduce the number needed and therefore the amount of metal sheet which has to be purchased for making the rodent barriers.

Where it is customary to raise the roof (or part of it) when removing grain from the crib, then the possibility of incorporating a small framed door near the bottom of the wall should be considered. This will prevent damaging the roof and help maintaining its waterproofness. When the platform is conically shaped, an opening in the side of the cone could be practical. If the walls are woven, a trapdoor could be fitted into the platform for access from underneath the crib.

In a dramatic break-away from traditional crib design, while retaining the important principle of using locally available materials as much as possible, the African Rural Storage Centre (ARSC) based at IITA in Ibadan, Nigeria, has developed a crib which optimises both the drying and storage of maize under humid tropical conditions (FAO, 1987).

Such a crib consists basically of two parallel frames between which the grain, mainly cob maize, is stored. The supporting posts are driven 50 to 60 cm into the ground one metre apart and protected from termites with sump oil, tar or scorching. They are then fitted with rodent barriers.

The walls of the ARSC crib may be constructed of wire netting or local material, such as rafia, bamboo or wooden lattice, and should be 1.5 to 2 metres high. The floor, which should be fixed at least 80 cm above ground level, is made of straight poles; if possible removable to facilitate emptying. The roof may be covered with corrugated metal sheet or thatch, which should overhang a long way to protect the cobs from rain: an overhang of 0.6 to 1 metre is recommended.

The various components of the crib are nailed together, or can be bound together with lianas or bark string.

In very humid areas where maize is harvested at 30-35 % moisture content, the recommended width for the crib is 60 cm. In drier zones with a single rainy season, maize is harvested at about 25% moisture content and the width may be increased to 1 metre. In very dry places the crib could be 1.5 metres wide.

The length of the crib is a function of the quantity to be stored. Given that 500 kg of maize cobs with their sheaths removed, and a moisture content of 30%, (equivalent to 300 kg of shelled maize at 14% mc) occupy approximately one cubic metre: if a crib is 60 cm wide and 1.7 metres high, it will need to be 5 metres long to contain the cob equivalent of 1,500 kg of shelled maize at the quoted moisture contents.

If it is possible, the crib should be erected across the direction of the prevailing wind and, if this is strong, the supporting posts should be reinforced to resist it. The crib should be located in a ventilated area and not constructed along a wall or next to a windbreak of trees.

Calabashes, gourds, and earthenware pots can be rendered virtually airtight by treating the exterior surfaces with varnish or with dry oil such as linseed oil (McFarlane, 1970). The mouth may be carefully sealed with wax; or covered with a doubled plastic sheet tied firmly in position.

If an absolutely air-tight seal cannot be guaranteed, the grain should be treated with insecticide.

Jars should be treated like small containers (see above) to make them airtight. Very large and immobile jars could be provided with outlets in their bases, for the easy removal of grain. Such outlets could, for example, be metal tubes fitted with lockable caps for greater security. If the cap is well designed it would ensure both security and airtightness.

The following suggestions are made for improving traditional solid wall bins

Where the base consists of a layer of stones, these should be set in concrete or clay mixed with a hardener such as néré juice, to prevent the base becoming a hiding place for rodents (and snakes). An alternative is to make a hollow base with an opening, in which to house chickens (see Figure 6.5.). A solid concrete base could also be made, but the cost is often too high.
When clay is used alone, it is very friable and must therefore be protected. Rendering with pure cement is not recommended, because it resists movements of the walls (expansion, contraction, settling), cracks and becomes detached within a short time. It is preferable to use a mixture of earth and cement (one part cement to ten of earth) or earth mixed with lime (one part lime to five parts of earth) or earth stabilised with a natural product such as guava juice, karité butter, cow dung, opuntia (cactus), flour (in the form of a paste, made by mixing 15 litres of flour with 220 litres of water, which is added to the earth), euphorbia latex, néré juice, etc.
Traditional solid wall bins can be made more secure against thieves by providing each compartment with a lockable outlet at its base. If a mud-plastered ceiling (under the thatch roof) is also provided, with sealable entrance(s) for loading, such an improved bin can be made reasonably airtight.

Underground storage pits may be improved in a number of ways, several of which are already employed locally but are worth adopting elsewhere (Boxall, 1974).

In the first instance, it is very worth while extending the neck, or collar, of the pit above ground level - with clay or even a concrete slab - to minimise the risk of rainwater pentrating at this point. This risk can be further reduced by digging simple drainage trenches around and away from the pit, to remove rainwater from the area as quickly as possible. Such precautions may interfere with the security of the pit, by revealing its presence to potential thieves; so the fitting of a lockable lid should be considered. Alternatively, the pit can be located under a lockable shed, or even under the floor of a room in the house.
The floor of the pit may be strengthened with stones, stabilised earth or even concrete; and the walls may be solidified with cow dung, or chicken wire mesh plastered with cement. A double layer of concrete, each layer about 5 cm thick, with chicken wire (for strength) and bitumen (for waterproofness) sandwiched between, is probably the best type of lining that can be recommended.
Plastic sheeting could be applied to the walls and the floor, but this is not easy and it is probably more practical to put the grain into plastic sacks and stack these in the pit.

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