Study of the Effect of Rhizobium Inoculation on Cowpea Nodulation and Yield in Niger State

Biological nitrogen fixation through Rhizobium inoculation reduces the dependency of cowpea on mineral nitrogen fertiliser and can improve soil nitrogen status, offering a sustainable and affordable productivity enhancement option for smallholder farmers in the Guinea savanna of Niger State. This study investigated the effect of Rhizobium inoculation on nodule development, nitrogen fixation, and grain yield of cowpea (Vigna unguiculata L. Walp.) at Bida, Niger State, North Central Nigeria. A randomised complete block design experiment with five treatments (uninoculated control, 20 kg N ha-1, 40 kg N ha-1, Rhizobium inoculant alone, and Rhizobium inoculant plus 20 kg N ha-1 starter nitrogen) and three replications was conducted during the 2023 rainy season using IAR1695-4 variety. Nodule number, nodule dry weight, above-ground dry matter, and grain yield were measured. Results showed that Rhizobium inoculation significantly increased nodule number and dry weight compared to the uninoculated unfertilised control (p < 0.05). Inoculation plus 20 kg N ha-1 starter nitrogen produced the highest grain yield (1.89 tonnes per hectare), followed by inoculant alone (1.74 t ha-1). The 40 kg N ha-1 treatment (1.71 t ha-1) was not significantly different from inoculant alone, suggesting effective biological nitrogen fixation. The study concludes that Rhizobium inoculation with 20 kg N ha-1 starter nitrogen is an effective and affordable strategy for cowpea production in Niger State and recommends its inclusion in state extension service recommendations. Keywords: Rhizobium inoculation, cowpea, biological nitrogen fixation, nodulation, Niger State