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close this bookTraditional Storage of Yams and Cassave and its Improvement (GTZ)
View the document(introduction...)
View the documentPreface
View the document1 Introduction
View the document2 Socio-cultural aspects involved in the production of roots and tubers
View the document3 Basic comments on the storage properties of roots and tubers
close this folder4 Yams
View the document(introduction...)
View the document4.1 The environmental requirements of yams
View the document4.2 The yam tuber
View the document4.3 Farm-economic aspects of yam production
View the document4.4 Yam harvesting
close this folder4.5 Causes of storage losses for yams
View the document(introduction...)
View the document4.5.1 Dormancy
View the document4.5.2 Transpiration
View the document4.5.3 Respiration
View the document4.5.4 Germination
View the document4.5.5 Rot due to mould and bacteriosis
View the document4.5.6 Nematodes
View the document4.5.7 Insects
View the document4.5.8 Mammals
close this folder4.6 Traditional storage systems for fresh yams
View the document(introduction...)
View the document4.6.1 Leaving the yam tubers in the ridges after maturity
View the document4.6.2 Storing the yam tubers in trench silos
View the document4.6.3 Storage of yam tubers in heaps on the ground
View the document4.6.4 Storage of yam tubers in clamp silos
View the document4.6.5 Storage of yam tubers under a conical protective roof made of maize or millet stalks
View the document4.6.6 storage of yam tubers in mud huts
View the document4.6.7 The storage of yam tubers in the yam barn.
close this folder4.7 Measures to improve traditional yam storage
View the document(introduction...)
View the document4.7.1 Care in harvesting transport and storage
View the document4.7.2 Curing
View the document4.7.3 Influencing dormancy
View the document4.7.4 Influencing the storage climate
View the document4.7.5 control of rot
View the document4.7.6 Control of nematodes
View the document4.7.7 Control of insects damaging stored produce
View the document4.7.8 Measures for protection from mammals
View the document4.7.9 The improved traditional yam barn
close this folder5 Cassava
View the document(introduction...)
View the document5.1 The environmental requirements of cassava
View the document5.2 The cassava root
View the document5.3 Economic aspects of cassava production
View the document5.4 Causes of limitations to storage for fresh cassava roots
close this folder5.5 Ways of and limits to. storing fresh cassava roots
View the document(introduction...)
View the document5.5.1 Storing cassava roots in the soil after maturity
View the document5.5.2 Traditional methods of storing fresh cassava roots
View the document5.5.3 Storage of fresh cassava roots in clamp silos
View the document5.5.4 Storing fresh cassava roots in crates
View the document5.5.5 Storing fresh cassava roots in a dip
View the document5.5.6 Storing fresh cassava roots in plastic bags
View the document5.5.7 Use of modern methods to store fresh cassava roots
View the document5.5.8 Measures to prepare fresh cassava roots for storage
View the document5.5.9 Suitability of storage systems for fresh cassava roots on a small farmholder level
close this folder5.6 The processing of cassava roots
View the document5.6.1 The purpose of processing
View the document5.6.2 Hydrogen cyanide and its release
View the document5.6.3 The production of cassava chips
View the document6 Summary
View the document7 Bibliography


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.