|Traditional Storage of Yams and Cassave and its Improvement (GTZ)|
The yam is a demanding plant in every respect. Its demands on the soil fertility mean that it is mostly the first member in crop rotation.
The preparation of the fields, ridging, vegetative propagation mulching, weed control and harvesting mean a great input of work. About 500 working days have to be calculated per hectare with a harvest yield of 10 tons of tubers (COURSEY, 1966) There is also little indication of relief through mechanization, even for parts of activities (ONWUEME, 1978).
According to the variety and sort of yam, the production potential to 20 - 50 tons per hectare. The average yield m Africa however. only amounts to around 10 tans per hectare (FAO, 1985). Of these, 2 tons per hectare have to be reserved for traditional propagation, leaving only 8 tons for consumption.
The output per unit area for the yam is very high However, it must be considered that yams can only be grown in primary locations. Labour productivity is low. This may be a reason why yam production is stagnating m many places or is even declining. In Togo between 1911 and 1986 yam production fell from 807,000 tons to 409,000 (INPT, 1988). This is mainly due to a shortage of manpower m rural regions. The stagnating production must also partly be seen as a result of an increasing concentration of the population. This effects a higher and higher production index for arable land and the cultivation of boundary locations Both restrict the cultivation of yams; but promote the cultivation of cassava (cf. Chapter 5.3) which is gradually replacing the yam in many places.