Effects of site and insecticide application on growth and grain yield of local and improved cowpea varieties in south-western Nigeria

Improved varieties of cowpea (Vigna unguiculata L. Walp) are not being widely adopted by farmers in south-western Nigeria. Seven varieties of cowpea were tested at the University of Agriculture at Abeokuta to determine if agronomic or economic factors could be linked to this slow adoption. Between 2004 and 2006 cowpea was tested in both wet and dry seasons to evaluate the effects of sites and insecticide application of local and improved varieties on upland and inland valley soils. The experimental design was a split-split-plot with sites as the main plot while insecticide application versus nil constituted the sub-plot and varieties: IT90K-76, IT90K-277-2 (improved), Drum, Olo, Oloyin, Mallam and Sokoto as sub-sub-plot. Biomass of the varieties was similar. Grain yields were similar on both sites but consistently higher in insecticide-treated plots. Grain yields of Oloyin which command the highest premium price was comparable to the improved varieties in both sites. When price discounts for improved varieties were assumed, Oloyin and Olo gave the highest grow margin and insecticide benefit-cost ratio on the inland valley site, while Oloyin and Sokoto had the best economic performance at the upland site. Only if quality differences were ignored and market prices of all varieties were assumed equal were the improved varieties economically competitive. This study indicates that the slow adoption of improved cowpea varieties in south-western Nigeria may be linked to the failure of those improved varieties to appeal to consumer preferences.