|Traditional Storage of Yams and Cassave and its Improvement (GTZ)|
The yam is a plant of tropical climates and does not tolerate. Temperatures below 20°C impede the growth of the plant which needs temperatures between 25 and 30°C to develop normally.
Most varieties of yam have a growing phase of 7 - 9 months up to maturity. The yam requires an annual precipitation of over 1,500 mm distributed evenly over the vegetation period to take full advantage of its production potential. For this reason, a long rainy season during the growth period has a positive effect on the yield of yams Off the other hand, the plant is able to survive longer dry periods which, however, reduce the yield considerably
The yam makes high demands on soil fertility. Soils with a high humic content correspond best to the requirements of the yam. On soils which are low in nutrients and which are predominant in the humid tropics, the yam is often the first member in crop rotation so that its high demand on nutrients can be fulfilled In addition to a high concentration of nutrients, the soils should have good water-bearing properties as yams are not able to tolerate stagnant water. They also need deep soil which is free of stones. Shallow or soils impede the formation of the tubers and or result in deformity.
Although not completely analysed, there are many indications of light intensity affecting growth - in particular of the tuber. Thus staking for the tendrils promotes the yield Semi-shade, e.g. in a greenhouse or under trees, leads to a noticeable loss in yield (ONWUEME, 1978).