|Traditional Storage of Yams and Cassave and its Improvement (GTZ)|
|4.7 Measures to improve traditional yam storage|
In view of reducing losses and long storage, the yarn barn shows the best results in comparison to other storage systems widespread in West Africa. This is one of the reasons for the yam barn frequently being selected as the basis for improvement measures to traditional systems of storage on which this work is based. Without changing the type of storage some measures and extensions to the construction can be carried out and can lead to a considerable improvement of the barn.
Improved storage of fresh yam tubers begins during harvesting. Injuries should be avoided as much as possible as these constitute doors for rot viruses. For this reason, harvesting, transport and storage have to be carried out with as much care as possible (NWANKITI et al., 1989). When transporting over longer distances, the tubers should not be piled up too high or this will quickly lead to injury to the epidermis and the formation of bruises.
Immediately after harvesting, the tubers should be subjected to curing (cf. Chapter 4.7.2). Bruises and lesions on the tubers should be cut out as smooth wounds heal better. For hygienic reasons the soil clinging to the end of the tubers should be removed. In how far treatment of wounds with ash or other traditional means improves storage ability will have to be clarified by further experiments. Prior to storage, the remains of the previous year's harvest should be removed and burned as this can constitute a source of infection.
The traditional yam barn has some disadvantages. Consequently, the following improvements should be made.
- A roof construction similar to a hut and made out of local
materials like straw, palm leaves etc. should cover the barn. A roof made of
plant materials not only provides sufficient protection from sunlight or rain
but also regulates temperature fluctuations due to its insulation features. The
roof should have a height of at least 2.50 metres so that ventilation of the
barn is not restricted (FAO, 1990).
- The barn should be made safe from rodents and domestic animals. There are several possibilities here. It can be surrounded by a fence made of oil barrels which have been cut open. Possible would also be a wall which, however, would have to be at least one metre high. As rodents can easily overcome a wall (in contrast to an oil barrel barrier) the space between the top of the wall and the roof should be protected with fine wire mesh. It is important that the barn is fitted with a door which closes well and will also prevent theft.
- In the modified yam barn the tubers are stored on multi-level shelves. The shelves can be constructed of various locally available materials as far as these provide sufficient support. The lowest board should be about 50 cm above the ground so mat no moisture is taken up from the ground. The shelves should be arranged so that a visual control of the tubers is possible quickly and all around. This is facilitated by the tubers only being stored in two or three layers on each shelf. It will also prevent too much weight exerting pressure on individual tubers and thus reduces the risk of bruising.
- The selection of the site is very important in making use of the advantages for the system. This should be chosen so mat natural air movements can be used for ventilation. The store should be set sideways to the main wind direction so that the natural movement of the air can be used to its full effect. Existing natural sources of shade, e.g. evergreens, should also be taken into account during selection of the site as the temperature in the interior of the barn can be considerably reduced by these.
The natural shade and its temperature reducing effect can mean too strong ventilation during the day. Consequently it must be ascertained mat not too much hot air enters the store as ventilation during the day.
The size of the store can be adapted to individual needs. There is no documented experience on costs for construction and maintenance of the yam barn. As local materials are mostly used, the extra financial means necessary should be limited in comparison to the traditional yam barn.
Fig 11 Example of a rodent-proof fence for storage of yam tubers in the yam barn and in similar storage systems (Source: Wilson, undated)
Fig 12 Simple shelves made of local materials for the storage of yam tubers (Source: NIGERIAN STORED PRODUCTS RESEARCH INSTITUTE 1982)
The use of germination inhibiting agents like gibberellic acid, treating the tubes with fungicides and insecticides can be considered as complementary means of improving storage systems. The lack of practical experience in the application of these prevent any concrete recommendations on the use of such products at this stage.
Regular inspection of the stored products is important for the success of storage systems. Rotting tubers must be sorted out and removed. Germs have to be removed regularly. The INPT (1988) recommends removing germs when these are approx. 50 cm long. Removing the germs too frequently induces the tuber to produce more germs.
According to investigations by NWANKITI et al. (1988), the improved yam barn can contribute considerably to reducing losses. The weight losses observed after six months storage in the traditional yam barn were 41.7%, in the improved yam barn these were 13.3% and with the improved yam barn with extra protection from rodents, 10.8%.
The results of investigations by NWANKITI et al. (1988) indicate that even simple improvements to the traditional yam barn can substantially reduce losses. For this, not all of the improvements mentioned above have to be carried out. Also individual improvements can clearly reduce losses. This means that improvements can be oriented to particular local conditions and requirements of farmers.
Considered macroeconomically, the improved yam barn leads to an increase in the supply of foodstuffs which can be produced on the domestic market. A contribution can be made to the balance of trade if the foodstuffs produced substitute food imports.
For the farmer, improved storage means an increase in subsistence security. At the same time he gains larger scope for decisions on selling and is better able to take advantage of price movements to improve his income.
Fig. 13: Model of an improved yam barn with protective roof and walls (Source: NWANKITI and MAKURDI, 1989 (modified))