Eruola, A.O., Bello, N. J., G.C. Ufoegbune, Makinde, A.A, Dr.. " Application of rainfall- potential evapotranspiration model for determining optimum planting date of yam (Dioscorea rotundata) in a tropical wet-and-dry climate" Global Journal of Science Frontier Research [Online], Volume 12 Number 5-D (5 May 2012)