There are about 600 species of Dioscoreaceae but a few are cultivated for food or medicine out of which only six are economically important staple species. Yams originated from tropical forests or savannas where there are sharply demarcated rainy and dry reasons. Yam remains the most preferred starchy staple for many people in yam belt of West Africa. The major edible species of African origin are white Guinea yam (D. rotundata Poir.), yellow Guinea yam (D. cayenensis Lam.), and trifoliate or bitter yam (D. dumetorum Kunth). Edible species from Asia include water or greater yam (D. alata L.); and lesser yam (D. esculenta Lour. Burkill). Nigeria is the largest producer of yams contributing 65.5% to global production. Yams provide essential nutrients for millions of people, contributing to food security but also deeply intertwined with socio-cultural practices, serving as special gifts, ritual objects, and centerpiece of vibrant New Yam Festivals in various regions of the word. Yam production has been on the decline in the world because it is constrained by limited availability of planting materials, high cost of farm operation, depletion of soil fertility, degradation of soil physical properties and inadequate use of fertilizers as well as poor funding for research. This review covers relevance and prevalence of cultivation, production areas, environment for good yam production, soils for good yam production, soil nutrient management techniques, fertilization and fertilizer requirements, fertilizer recommendations for individual yam species, plant population and sett weight, intercropping/mixed cropping, weed, pests and diseases and yam yield, processing/composition and storage, yam improvement, comparative economic analysis, and major constraints on yam production for purposes of providing relevant information for increased and sustainable production.
Asadu et al. (Wed,) studied this question.