Effect of selected bradyrhizobia and nutrients on cowpea biomass, biological nitrogen fixation and yield in Kilifi and Mbeere Regions of Kenya
Kimutai, Winnie Jelagat
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Cowpea cultivation in Kenya is practiced by smallholder farmers who use little or no inputs like microbial inoculants and fertilizer. This study was conducted to evaluate the effect of rhizobial inoculation and nutrient supplementation on different cowpea genotypes in two soils in Kenya. Four rhizobia strains and three cowpea genotypes were initially assessed for nodulation in a greenhouse experiment and the best strain- cultivar combination was selected to determine the effect of 5 nutrient levels which were applied in the form of sympal, a legume-specific fertilizer blend, in a second greenhouse experiment. The best rate from the findings was validated under field conditions, which were carried out in Kilifi in two different sites. Black-eyed pea genotype showed significantly high nodulation, shoot biomass and yield. Co-application of BR3267 and sympal at the rate of 60 kg ha-1 significantly enhanced nodule fresh weight, shoot dry biomass and nutrient uptake of Black- eyed pea genotype investigated (P≤0.05). The most promising strain among the four which were evaluated (i.e. BR3267) when co-applied with Sympal at the rate of 60 kg ha-1 increased black-eyed cowpea yield to 1110 kg ha-1 compared to 800 kg ha-1 generally obtained by smallholder farmers in both Kilifi sites, or 915 kg ha-1 obtained in the untreated control in this study. Selection of best bet combinations of rhizobia inoculants, legume-specific fertilizer blend, and cowpea genotypes adapted to local conditions would significantly reduce the current cowpea yield gap in sub-Saharan Africa, though the findings of this study have to be evaluated in various agro-ecological zones before large scale dissemination of the innovation.