|Traditional Storage of Yams and Cassave and its Improvement (GTZ)|
|2 Socio-cultural aspects involved in the production of roots and tubers|
|3 Basic comments on the storage properties of roots and tubers|
|4.1 The environmental requirements of yams|
|4.2 The yam tuber|
|4.3 Farm-economic aspects of yam production|
|4.4 Yam harvesting|
|4.5 Causes of storage losses for yams|
|4.5.5 Rot due to mould and bacteriosis|
|4.6 Traditional storage systems for fresh yams|
|4.6.1 Leaving the yam tubers in the ridges after maturity|
|4.6.2 Storing the yam tubers in trench silos|
|4.6.3 Storage of yam tubers in heaps on the ground|
|4.6.4 Storage of yam tubers in clamp silos|
|4.6.5 Storage of yam tubers under a conical protective roof made of maize or millet stalks|
|4.6.6 storage of yam tubers in mud huts|
|4.6.7 The storage of yam tubers in the yam barn.|
|4.7 Measures to improve traditional yam storage|
|4.7.1 Care in harvesting transport and storage|
|4.7.3 Influencing dormancy|
|4.7.4 Influencing the storage climate|
|4.7.5 control of rot|
|4.7.6 Control of nematodes|
|4.7.7 Control of insects damaging stored produce|
|4.7.8 Measures for protection from mammals|
|4.7.9 The improved traditional yam barn|
|5.1 The environmental requirements of cassava|
|5.2 The cassava root|
|5.3 Economic aspects of cassava production|
|5.4 Causes of limitations to storage for fresh cassava roots|
|5.5 Ways of and limits to. storing fresh cassava roots|
|5.5.1 Storing cassava roots in the soil after maturity|
|5.5.2 Traditional methods of storing fresh cassava roots|
|5.5.3 Storage of fresh cassava roots in clamp silos|
|5.5.4 Storing fresh cassava roots in crates|
|5.5.5 Storing fresh cassava roots in a dip|
|5.5.6 Storing fresh cassava roots in plastic bags|
|5.5.7 Use of modern methods to store fresh cassava roots|
|5.5.8 Measures to prepare fresh cassava roots for storage|
|5.5.9 Suitability of storage systems for fresh cassava roots on a small farmholder level|
|5.6 The processing of cassava roots|
|5.6.1 The purpose of processing|
|5.6.2 Hydrogen cyanide and its release|
|5.6.3 The production of cassava chips|
Cassava is a plant of the new world which originates in the northeast Brazil. Central America is assumed as another source (ONWUEME, 1978). Having begun with these two regions, cassava is now cultivated in all tropical regions of the world.
In contrast to yams, mere is only one species of cassava bearing the scientific name Manihot esculenta Crantz and belonging to the family of the Euphorbiaceae.
There is a wide range of cassava varieties. Individual varieties can be recognised by the leaf and root form, the duration of vegetation, the yield and the content of hydrogen cyanide. The latter constitutes the difference between the sweet and the bitter cassava.
The bitter varieties of cassava have a high hydrogen cyanide content which can amount to up to 250 mg pa kg fresh root (GRACE, 1977). To avoid poisoning, the roots have to be detoxified before consumption. The vegetation period for bitter cassava varieties lies between 12 and 18 months. After ripening, the roots can be left unharvested in the soil for a long period and will not spoil (ONWUEME, 1978).
The sweet cassava varieties only contain low quantities of hydrogen cyanide so mat detoxification prior to eating is normally not necessary. The vegetation period is relatively short at 6 - 9 months. The roots of this variety rot quickly if they are left in the soil after maturity.
The content of hydrogen cyanide is not constant according to the varieties, but is subject to fluctuation due to the environment. For this reason, the content of hydrogen cyanide is unsuitable as the only criterion in defining the varieties of cassava (ONWUEME, 1978).
Cassava is a perennial plant. Apart from for purposes of research and breeding, propagation is exclusively vegetative. In contrast to yams which are propagated via the tuber, the cassava can be reproduced by cuttings taken from the stalks of the plant. As the stalks, in contrast to the root, are used neither for consumption nor other economic purposes, the cost of propagating cassava where planting material is concerned, is practically zero.