Competitiveness and persistence of commercial rhizobial soybean inoculants in central and western Kenya

Low effectiveness of native strains remains a limitation to soybean productivity in sub-Saharan Africa, while commercial rhizobial inoculants are widely and successfully used for soybean production in Latin America. The inoculants may become expensive to farmers who want to purchase them especially if the inoculation has to be repeated every season. To assess the competitiveness of effective rhizobial strains and their persistency in the field for two cropping seasons, it's very important to assist poor farmers targeted by the COMPRO project funded by BMGF with appropriated technologies. Field experiments were set up for two seasons (one with inoculation and the following one without) to evaluate the response of three promiscuous soybean varieties (a non-promiscuous and two promiscuous) to commercial rhizobial inoculants in a Nitisol (no soybean growing history) and a Ferralsol (with soybean growing history) in Central and Western Kenya respectively. High nodulation was observed in the Ferralsol while nodule occupancy showed indigenous strains occupied < 90 % of the nodules for all the varieties whatever the rhizobial inoculants. The Nitisol showed nodule occupancy variation depending on variety and inoculants. Legumefix was having the highest grain increases, showed competitiveness and hence better grain yield, nodule occupancy and biological nitrogen fixation. (Résumé d'auteur