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Losses in economic value are also high eg. Wastes come in various forms eg. Waste often has no economic value which can make processing a marginal business proposition.

Tropical root and tuber crops: cassava, sweet potato, yams and aroids.

The overall objective of Gratitude Gains from Losses of Root and Tuber Crops is to improve the post-harvest management of cassava and yams leading to reduced physical losses, reduced economic losses through value-added processing and valorization of waste products. Technologies and systems developed and validated within the Gratitude project will particularly benefit small-holder households, and will support small and medium scale enterprises to increase profitability, create new jobs and develop links to large-scale industry.

This project will help improve the livelihoods of people on low incomes and enhance the role that these crops play in food and income security. Go directly to: Content Search box Breadcrumb. Post harvest losses are significant and come in three forms: physical; economic through discounting, or processing into low value products ; from bio-wastes.

But the tuber lives on and grows a new stem during the next year.

Invasive Species Compendium

Yams climb by turning round a support. The stem itself is too weak to stand on its own. The leaves often have the shape of a heart and are compound leaves with three smaller leaves making up the total leaf. Yams are usually propagated vegetatively, i. Therefore, people do not pay much attention to yam flowers. However, the plants produce male and female flowers separately. But whereas in the case of maize the two types of flowers are on the same plant, in the case of yams they are on different plants.

They are only important when it comes to breeding improved varieties. This can best be done by crosspollinating plants with different characteristics. Origin: The origin of the yam is in Asia, Africa, and the Carribean islands. The yellow Guinea yam originated in West Africa, together with the white Guinea yam.

Roots & Tubers (Part 2) - Cassava

The three-leaved or bitter yam, also called cluster yam, likewise originates from Africa. The aerial yam or potato yam has its origins both in Africa and Asia, and the water yam, also called ten months yam, is an Asian plant. Farming is done according to traditional methods under the system of multiple cropping. For details see the section on Traditional Farming part I.


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Only on school farms are yams farmed in single cropping since they represent one of the most important school crops. Farming: Yams need a deep, well drained soil. The best soil is sandy loam. If the soil is too heavy, the tubers may start to rot in the ground. There are varieties adapted to dry conditions mm rainfall per year and to very wet conditions mm annual rainfall. Usually the varieties grown locally are adapted to the local climate unless they have been recently introduced.

The white yam needs an annual rainfall of to mm evenly distributed over 6 - 7 months. For planting small tubers seed yams or parts of larger tubers setts are used.

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If setts are used, tops are preferable. Most varieties grow on setts weighing to g. Setts are planted with the cut part pointing upwards and the eyes downwards.

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After planting, the setts should be covered or "capped" by a layer of dry grass about cm thick on top of the soil. This has the usual advantages of mulching. Planting holes should be 50 cm deep and 60 x 60 cm large. They should be filled with rich surface soil or manure. Yams are usually planted on mounds or ridges and only occasionally on the flat. Recommended distances are given in the table p. There are two planting times. Early planting is done in November if the soil has retained enough water to allow germination and growth during dry season. Late planting is done in February and March.

Staking allows the plant to develop more leaves than if no stakes are used. With more leaves the plant produces more starch and the tubers grow bigger. Stakes or "poles" should be put as near to the yam plant as possible.

Andean roots & tuber crops

A strong stake, Young vines are guided in the direction of the stake, usually along stalks of maize or dry grass. Cluster yams are not stakes. Hilling or earthing up becomes necessary when the upper part of the yam tuber is no longer covered with soil. Manuring depends very much on local soil characteristics. No general indications can be given. On old farms or on sandy soil it would be good to put some compost manure in the planting holes. Chemical fertilizer should be applied when the shoots are about half a meter tall, about six to seven weeks after germination.

Chemical fertilizer is applied in a ring around the plant and must not touch it directly, otherwise it might burn the yam. One or two matchboxes full for every plant would be about the right quantity. Harvesting can be done twice. About six months after planting, the yams may be tapped. The tuber is cut so that the top remains attached to the stem. When the top is put back into the soil, it usually produces a number of smaller tubers which can be used as seed yams.

The main harvest is done towards the end of the growth cycle, when the tubers are completely ripe. This is the case when the leaves begin to turn yellow. Storage: The following rules should be applied when storing yams for details see part IV on Tuber Preservation :. Pests and Diseases: The yam beetle attacks the tubers. No other serious pest is known. Wilting leaves or black-brown spots on leaves are caused by anthracnose. The affected leaves should be removed and destroyed as soon as possible. Plant Improvement: Improvement by breeding and-selection is difficult with yams because the flowers rarely produce seeds which germinate.

Cassava farming is on the increase in West Africa. In many areas it gradually replaces yam as the staple food.

Yet, it is extremely low in protein content and may lead to protein deficiencies if the daily food is not supplied with protein from other sources. The Plant: Cassava is a perennial plant growing to between 1 and 5 m tall. All its parts contain latex, a white liquid that forms an elastic cover when it dries. It has a relatively deep rooting system with feeder roots going down to a depth of 40 to 80 cm.

Gratitude - Gains from Losses of Root and Tuber Crops

Some of the adventitious roots start swelling and store starch. The stem shows very pronounced leaf scars.


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The leaves are divided and look vaguely like a hand with the fingers spread out. Cassava flowers are small and light green in colour. They produce seeds.