5.2.2 Improvement of storage in the south of Benin

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Maize is the principal food crop and dietary base for the people of southern and central Benin. Its cultivation extends to the north of the country where it constitutes the second cash crop after cotton. Maize is an important commodity traded commercially within the country and with neighbouring countries. Maize production was more than 271,000 tonnes in 1982 and reached nearly 460,000 tonnes in 1992 thanks to the efforts of agricultural development services.

Despite this dynamism in production and marketing, traditional storage practices remained unchanged and unadapted to the increased level of production. The appearance of new storage pests has aggravated this situation, leading to high losses (average loss rate rising from 10-15% to 30% for the first crop).

Improvement initiatives such as "Ditcher" silos, "Brooks" driers (1976) and "cribs" (1985) had little impact in rural situations. The project BEN/87/017, "Decentralized Storage Systems", executed with technical assistance from FAO has proposed some appropriate solutions (Afomasse, 1994). A base-line study was first carried out on the socio-economic environment of the "storage function" and a technical evaluation was made of the structures and methods of storage utilised. Subsequent improvements took into account the issues raised by the farmers, among which were:

• the quality of timber used in the construction of the floor;
• the strength and durability of the structure;
• protection of the supporting posts against rodent ingress;
• the maize harvest period;
• preparation of the product before storage; and
• the treatment of the maize in husk with pesticides recommended by the pest control service(5).

Parameters 2,4,5 and 6 were taken into account during trials on modified granaries.

Technical description of modified granaries

The circular granary of woven bamboo (BT) provided with a fixed straw roof and a window has been retained, to be modified in accordance with the needs of the peasant farmers. Two types of platform have been tested: the flat platform (height from ground to ceiling 0.80m) and the conical platform (height from ground to ceiling 1.20m and height from ground to base of cone 60cm) which permit good load spreading and better drying.

The three types of improved granary are:

• BT2 - Diameter: 2m, Height: 2m, Storage capacity: 2 tonnes of cobs in husk.
• BT3 - Diameter: 3m, Storage capacity: 6 tonnes, conical central chimney in wood (60cm base diameter, 1.6m high). Figure 5.7
• BT4 - Diameter: 4m, Storage capacity: 10 tonnes, fitted with three wooden chimneys (50cm diameter, 1.6m high) udesigned to favour drying (Figure 5.8).

Figure 5.7 - Adaptation of a chimney on the floor of a traditional granary (Source: Afomasse, 1994)

Figure 5.8 - Maize granary fitted with three conical chimneys in wood distributed evenly across the floor to improve air circulation (Source: Afomasse, 1994)

Technical results

It was observed that after three months the grain moisture content dropped to 15.3%, 15.8% and 15% respectively in granaries BT2, BT3 and the control granary (Table 5.1). At the end of six months, the grain moisture content was well below the safe storage level (about 1314%). On the other hand, in the 4m diameter granary (BT4) at the end of six months the grain moisture content was continually above 15%, despite the provision of cones to facilitate the passage of air. Increase of the diameter of improved granaries above 3m is therefore not to be advised.

Despite a systematic selection of cobs to discard those already mouldy, a significant level of moulding was observed due to storage for long periods at high moisture levels (Table 5.2). For the BT2, BT3 and traditional models the degree of moulding was small but could represent a considerable risk in the absence of monitoring and analysis. In the case of BT4 the level of moulding, above 10%, was definitely too high.

The evaluation of losses due to insects (Table 5.3) shows the significant effect of phytosanitary treatment associated with the preparation of cobs prior to storage in the improved granaries. Less than 1.5% loss in weight was found in the improved granaries compared with 6.2% in the traditional granary.

Table 5.1- Evolution of grain moisture content (%)

Table 5.2 - Loss to moulding (% of grain mouldy)

Table 5.3 - Loss in weight due to insects (%)

(Source: Afomasse, 1994)

Socio-economic results

The cost of storage comprises the costs of construction, phytosanitary treatment and handling into storage. The cost/benefit ratio is the greatest value achieved in differentiating the sales of maize (Table 5.4)

Table 5.4 - Storage costs

Losses due to pests are considerably reduced thanks to use of a storage structure which performs well associated with a timely harvest, preparation of cobs prior to storage and phytosanitary treatment. The unaided spread of techniques for construction of improved granaries has started to develop in the project zone, a sign of the interest generated by the technique. The peasant farmers trained by the project are offering their services to other farmers on a commercial basis.

5.3 Silos

Traditional small, closed grain stores are used by farmers all over Africa. They include underground silos, walled silos and above-ground structures made from clay, often mixed with a strengthening material, notably straw or cow manure. They are found in regions where the hydrometric air conditions, at harvest time, easily permit grain moisture content to be lowered to 12% (or less) for good silo storage (Figure 5.9).

For 25 years attempts have been made to introduce "improved" silos, either to modify part of a traditional silo (floor or walls), or to replace a straw silo (Figure 5.10). Aboveground silos in timber, brick or concrete and underground silos present characteristics, of airtightness for example, adequate for good control of insects by fumigation. Nevertheless, the rate of adoption of improved techniques has often been feeble for various reasons (see the beginning of Part 2 of the chapter), notably: poor availability of construction materials, insufficient technical knowledge and the need for supplemental drying.

Two successful experiences, the spread of metallic silos in Swaziland and the underground silo in Morocco are briefly described below.

5.3.1 The spread of metallic silos in Swaziland

Cultivated by all the farmers in the country, maize is the basic foodstuff of Swaziland. After drying in a crib or on house roofs, the whole crop is shelled before sale or storage on the farm, generally in metal silos. This constitutes a unique case in Africa, attempts to introduce this type of silo in other African countries having failed.

The first metal silos in Swaziland are described in reports of the Ministry of Agriculture in 1940 but their use did not develop until the 1950s. By the end of the 1960s they were made locally by small and medium-scale metalworking enterprises. It seems that no help in the form of training or subsidy has been given to these enterprises or to the farmers using the silos. It is perhaps worth noting that the rural communities are relatively wealthy and have easy access to materials such as galvanized sheeting. In 1971-72, 24.7% of farm holdings possessed an average of 1.3 metallic silos each, making a total of 12,400 silos in the country. in 1979, this estimate was increased to 15,000 silos. An inquiry in 1988-89 reported 30,000 silos (36% of holdings had 1.2 silos each). In 1990 70% of farmers possessed a silo. Today in 1994, the number of silos is approximately 45,500.

Technical description

The construction of the silo is similar to that of local water tanks. Sheets of galvanized steel, 0.63mm thickness, are rolled and rivetted in rings to form the walls of the silo. Two sheets per ring are needed for a silo holding 2 tonnes. The sheets are fastened at top and bottom to form a hermetically sealed enclosure. Joints and rivets should be sealed with solder.

The silo is installed on a solid, level base, raised above ground level (Figure 5.11). Farmers place their silos in the shade of large trees, under shelters or inside their houses to avoid condensation problems. Well maintained silos last more than 30 years. Nevertheless, they are not considered permanent structures. This factor is of primordial importance for the Swazi farmer who does not own of the land.

The grain is filled through an opening 38 to 50cm in diameter at the top of the silo. A metal cover, overlapping the edges of the opening by 5cm provides a hermetic seal. The extraction opening in the base is a descending tube, 15cm long and 14cm in diameter. The covers (filling and extraction) can be provided with security chains. The capacity of a silo varies between less than a tonne to 8 or 9 tonnes of maize grain. Those of one to three tonnes are most common.

Figure 5.11- Metallic silos in Swaziland

Grain fumigation

The major benefit of metallic silos is their resistance to rodent attack and the facility to control insects by fumigation. Farmers prefer fumigation to the use of insecticide powders. For fumigation, the filling and extraction openings are sealed with thick plastic sheet (an old fertiliser bag, for example) before fitting the metal covers. From the 1940s to the end of the 1960s, the fumigant used was carbon bisulphite in liquid form. Since 1972 phosphine has been adopted following a campaign of promotion and extension (Table 5.5). from 1972 to 1975 the Grain Storage Section has trained farmers in the safe, effective utilization of phosphine tablets. Moreover, in the absence of private enterprises in the market, it has established a distribution network and carried out demonstrations of the dosage and techniques for sealing the silos. This type of action associated with advice on the installation and maintenance of silos has considerably improved the conditions for use of metallic silos in Swaziland.

Table 5.5 - Quantity of phosphine used for fumigation in Swaziland

5.3.2 The underground silos in Morocco

Storage of grain in underground silos is an ancient technique practiced in many countries. In Morocco, many farmers prefer underground storage for conservation of their produce. It is estimated that storage capacity with this method totals about a million tonnes. This technique, used as well in Tunisia, in Egypt and in Sudan, is adapted to the rural context and to small holdings where soil conditions permit. The atmosphere, poor in oxygen, created inside the underground store, permits a reduction in insect attack. This constitutes a natural means of combatting pests as a substitute for pesticide products which are often difficult to procure (Bartali, 1994).

Technical description

Traditionally, the lining of the underground silo walls is of straw (Figure 5.12) or plastic (sheets simply stuck to one another). These practices can lead to penetration of soil water into the stored grain and considerable losses. In order to reduce these risks, classic straw linings have been compared with a lining formed manually from polythene sacks, closely following the shape of the store (Figure 5.13). The study, financed by the USAID PSTC programme was carried out on the storage of hard wheat in 1.5-tonne stores for a period of 16 months. During the project, the farmers were invited to take part in different phases of the study: filling and emptying the stores, measurement and evaluation of losses.

Figure 5.12 - Underground silo lined with straw (Source: Bratali, 1994)

Figure 5.13 - Underground silo lined with plastic (Source: Bartali, 1994)

Results

• The soil covering the silo protects the grain from fluctuations in the exterior air temperature. The temperature at the heart of the silo lined with plastic remained around 17°C while the exterior temperature reached 45°C. In the silos lined with straw the lack of air tightness led to greater biological activity within the mass of grain and the temperature could attain 30°C.
• The relative humidity of the air in the silo, which was 53% before filling, increased rapidly a few days after filling to stabilize around 73 % (hydroscopic airgrain equilibrium) three months later.
• The other parameters, CO₂ concentration, moisture content, volumetric weight and loss of dry weight are shown in the table below and highlight the better performance of the silo lined with plastic.

Parameters measured according to type of silo lining:

• Germination rate diminishes by 30% after 3 months in grain stored in straw-lined silos, while it remains at almost its initial value in grain stored in silos lined with plastic.

The cost of using plastic sacks rose in 1987 to $25 for a silo of 1.5 tonnes. This investment, equivalent in value to a quintal of wheat, may save the farmer the deterioration of several quintals of stock (moisture content, drop in germination capacity, nutritive and commercial values). Several farmers have already adopted the plastic lining. At each harvest the extension effort is continued: definition of the type of plastic to use, demonstration of the make up of the plastic sacks, techniques for filling and sealing the stores. Incentive measures have been adopted for decentralized storage on the farm such as negotiation with credit authorities to obtain flexibility in credit terms for crop finance.

5.3.3 Silos of clay reinforced with straw

Since 1987, another exercise, organized by the Department of Rural Engineering at the Hassan II Agronomic and Veterinary Institute in Rabat, has evaluated the performance of silos of clay reinforced with straw (Bartali, 1994). These silos are similar to storage structures used in China. In 1982, FAO highlighted the interest in such structures in countries with a tradition of construction in mud and straw for rural housing.

The structure is made from local materials. The wall is built from a mixture of clay and chopped straw in which are incorporated ropes of plaited straw arranged in a circle with the objective of countering the internal pressure of the contents against the wall. Farmers also use vertical silos of reeds lined with clay with a capacity of 1 to 2 tonnes. The advantages of these silos are the low cost, the simplicity of construction and the good thermal insulation offered by the walls. Two pilot silos of 15 tonne capacity have been constructed in one coastal region and one continental region.

Technical description

The circular storage enclosure has a wall 0.45m thick, a height of 2.9m and a diameter of 3m. The clay and straw store is raised on a circular plinth 2m high provided with a door to control emptying. The base of the silo is conical to facilitate emptying at a rate of 6 tonnes per hour. The roof, of earth, straw or plastic is conical in form to permit better aeration and to shed rain water. The silo is filled through an opening high in the wall. At this level there are also grilles to improve the natural ventilation of the grain.

Results

Research on these structures has centred on storage of barley and soft wheat over periods of one to two consecutive years. These silos, cheap and durable, provide good storage conditions as they lend themselves well to fumigation, are characterised by interior temperatures lower than the ambient air and have a low rate of dry weight loss (4%).

5.4 Cereal banks

The last 25 years are remarkable for the appearance of the concept of "cereal banks" and the development of these structures. Following the serious droughts at the beginning of the 1970s it seemed necessary to put in place village-level structures, controlled by the villagers, in order to limit the situation of food insecurity and to complement the actions of the Cereal Authorities or to compensate for their shortcomings. This idea was based on two observations: i) the seasonal fluctuation in cereal prices (low price at harvest and high price when these stocks run down) which intervenes just before the following harvest; ii) the liquidity requirements of farmers which lead them to sell at low prices or to sell more than their real excesses which later obliges them to repurchase when prices are high.

The " village community granary" provides a means to buy at harvest time, to store and to sell when household stocks run low with the objective of:

• maintaining a minimum stock at village level;
• provide a supply at lower cost in periods of shortage;
• offer a market for farmers wishing to sell produce at harvest time when prices are low.

The first cereal banks, established in Burkina Faso between 1979 and 1983 were essentially designed for the food security of the village. During the 1980s the rapid development of cereal banks was assisted by national programmes and projects financed by international institutions and non-governmental organizations. These actions, which mobilized substantial resources, achieved varying degrees of success. Table 5.6 presents an estimation of the number of banks which is lower than the number actually created because of a fairly high rate of failure.

Eventually, cereal banks progressively accumulated functions of produce disposal and market regulation, much as commercial outlets for the Cereal Authorities (Gergely et al., 1990). However, because new national cereal policies, defined in the context of structural adjustment, have largely eliminated, or considerably reduced, the interventionist role of the Cereal Authorities, the cereal banks have found themselves once more directly involved in the market without a privileged interlocutor. Despite this difficulty, cereal banks have provided, and always provide, groups of peasant farmers with the possibility of adapting themselves to new market conditions.

Table 5.6 - Cereal banks in sahelian countries (Gergely et al., 1990)

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