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Nigeria is by far the world’s largest producer of yams, accounting for over 70–76 percent of the world production. According to the Food and Agricultural Organization report, in 1985, Nigeria produced 18.3 million tonnes of yam from 1.5 million hectares, representing 73.8 percent of total yam production in Africa. According to 2008 figures, yam production in Nigeria has nearly doubled since 1985, with Nigeria producing 35.017 million metric tonnes with value equivalent of US$5.654 billion. In perspective, the world's second and third largest producers of yams, Côte d'Ivoire and Ghana, only produced 6.9 and 4.8 million tonnes of yams in 2008 respectively. According to the International Institute of Tropical Agriculture, Nigeria accounted for about 70 percent of the world production amounting to 17 million tonnes from land area 2,837,000 hectares under yam cultivation. Yam, a tropical crop in the genus ''Dioscorea'', has as many as 600 species out of which six are economically important staple species. These are: ''Dioscorea rotundata'' (white guinea yam), ''Dioscorea alata'' (yellow yam), ''Dioscorea bulbifera'' (aerial yam),'' Dioscorea esculant'' (Chinese yam) and ''Dioscorea dumetorum'' (trifoliate yam). Out of these, ''Dioscorea rotundata'' (white yam) and ''Dioscorea alata'' (water yam) are the most common species in Nigeria. Yams are grown in the coastal region in rain forests, wood savanna and southern savanna habitats.〔 Yam is in the class of roots and tubers that is a staple of the Nigerian and West African diet, which provides some 200 calories of energy per capita daily. In Nigeria, in many yam-producing areas, it is said that "yam is food and food is yam". However, the production of yam in Nigeria is substantially short and cannot meet the growing demand at its present level of use. It also has an important social status in gatherings and religious functions, which is assessed by the size of yam holdings one possesses.〔 ==Geographic regions== The farmland production system in the Ekiti State consists of wetland (20% farms are under this category), upland (50% farms in this category) types and a combination of the two types (30% by the balance farms). A study carried out on the efficiency of the three systems to improve crop outputs to meet growing demands for this food crop, indicates that the "wetland yam based enterprises are the most economically efficient with mean economic efficiency of 0.80 followed by upland yam based enterprises with mean efficiency of 0.79."〔 The combination of wetland/upland yam based enterprises is assessed as the least economically efficient, with mean efficiency of 0.76. Hence, it has been recommended that more yams should be grown more on wetlands. Another recommendation made is to adopt the yam minisett technology developed by the International Institute for Tropical Agriculture (IITA) and the National Root Crops Research Institute (NRCRI).〔 Although it is grown widely in Nigeria, the area where it is grown most is the Benue State (land area of 802,295 km²) one of the states in Benue valley of Nigeria where the labour-intensive practices are still the norm and the land holdings are small. In this state especially among Tiv people, the size of the yam farm or the tonnage of yams produced becomes the social status of that farmer. Because of high level of yam production in the State of Benue, Benue State is crowned as the Nigerian Bread Basket. Yams are planted on mounds rather than flat slopes depending on the hydromorphic nature of the soils which are generally of loose soil suitable to grow roots and tuber crops.〔 While yam production issues have been stressed on agronomical practices, a research study carried out on the economic efficiency of this crop grown in this region with small farm holdings, which is labour-intensive, reveals that land, labour and material (fertilizers and chemicals), credit and extension services inputs have a significant bearing on the yield of yam in the region.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Yam production in Nigeria」の詳細全文を読む スポンサード リンク
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