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Yam-Importance and production of yam

(Dioscorea species)

 Source: IITA

Yams are starchy staples in the form of large tubers produced by annual and perennial vines grown in Africa, the Americas, the Caribbean, South Pacific and Asia. There are hundreds of wild and domesticated Dioscorea species. White Guinea yam, D. rotundata, is the most important species especially in the dominant yam production zone in West and Central Africa. It is indigenous to West Africa, as is the Yellow yam, D. cayenensis. Water yam, D. alata, the second most cultivated species, originated from Asia and is the most widely distributed species in the world.


Importance

Yams are primary agricultural commodities and major staple crops in Africa, where yam cultivation began 11,000 years ago. In West Africa they are major sources of income and have high cultural value. They are used in fertility and marriage ceremonies, and a festival is held annually to celebrate its harvest.

Consumer demand for yam is generally very high in this sub-region and yam cultivation is very profitable despite high production costs.


Production

Worldwide yam production in 2007 amounted to 52 million tons, of which Africa produced 96%. Most of the world’s production comes from West Africa representing 94%, with Nigeria alone producing 71%, equalling more than 37 million tons. African countries imported more than 2,000 tons in 2002, and exported 15,500, of which Nigeria exported 12%.

Yam production is declining in some traditional producing areas due to declining soil fertility, increasing pest pressures and the high cost of labor. Smallholders therefore need access to innovations to reduce labor and improve productivity.

Yams are grown by planting pieces of tuber, or small whole tubers (‘seed yams’) saved from the previous season. Small-scale farmers, the majority of producers, often intercrop yams with cereals and vegetables.

The major pests that affect yams include insects such as leaf and tuber beetles, mealy bugs, and scales; parasitic nematodes; fungi causing anthracnose, leaf spot, leaf blight, and tuber rot; and viruses, especially the yam mosaic virus (YMV).


Harvesting

In terms of area harvested, 4.6 million hectares were planted worldwide in 2007, with about 4.3 million in Central and West Africa.

In West and Central Africa tubers are planted between February and April, depending on whether in humid forest or on the savanna, and are harvested 180 to 270 days later. Care is needed during harvesting to minimize damage to tubers that lead to rot and a decrease in market value. Harvested tubers normally stay dormant (do not develop sprouts) for 30 to 120 days depending on environmental conditions, the date of harvest, and the species. This means that only one crop cycle is possible per year, possibly restricting supply.


Consumption

Yam tubers consist of about 21% dietary fiber and are rich in carbohydrates, vitamin C and essential minerals. Worldwide annual consumption of yams is 18 million tons, with 15 million in West Africa. Annual consumption in West Africa is 61 kilograms per capita. Yams are boiled, roasted, baked or fried. In Africa they are also mashed into a sticky paste or dough after boiling.

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