This paper presents statistical analyses of effects and efficacies of NPK fertilizer levels on yield of four differentspecies of yam in three different locations of kwara state Nigeria. Four quantitative and equally spaced levels0kg/ha, 22.5kg/ha, 45kg/ha and 76kg/ha respectively, of the fertilizer type were considered in the experiment.Factorial design model was used in collecting data sets on yield variables of the plant, using fixed effects, in anexperiment conducted by the Kwara Agricultural Development Project (KWADP) Ilorin, in the year 2012. Thefour varieties of yam examined included white yam, water yam, aerial yam and bitter yam respectively.Observations were taken from Ekan-Meje, Omu-Aran and Omupo locations of the state on a number of responsevariables namely, number of yam plants, number of yam tubers and weight (kg) of yam tubers. Beforeconducting ANOVA, the data sets were inspected for homogeneity of error variances using Fligner-Killeen testin the R statistical package. The test revealed that homoscedasticity assumption was not violated and Shapiro-Wilk test of normality was further used to check normality of the residuals arising from the ANOVA model. Theresponse variables were modelled with orthogonal polynomials so as be able to predict response yield atintermediate factor levels. Fertilizer level of 22.5kg/ha was found to be the most effective and economical forgrowing yam with the corresponding optimum yield.Keywords: ANOVA, NPK, Factorial design, KWADP, Fligner-Killeen test, Shapiro-Wilk test and orthogonalpolynomia
