Abstract

The use of inoculants containing N₂-fixing bacteria increases every year in cowpea crop in the North and Northeast regions of Brazil. In this context, this study aimed to evaluate the effects of inoculation with Bradyrhizobium sp. and Azospirillum brasilense in association with phosphate fertilization on the vegetative development, nodulation and yield of cowpea genotypes grown in Southern Rondônia state, Brazil. The experiment was conducted from February to May 2018, in the municipality of Colorado do Oeste, RO. The experimental design was randomized blocks in 4 × 3 × 2 factorial scheme, corresponding to four dose of phosphorus (0, 80, 120 and 160 kg ha^-1 of P₂O₅); absence, inoculation and co-inoculation with rhizobacteria; two cowpea genotypes (White and Butter), with three replicates. Cowpea seeds were inoculated with the commercial inoculant TotalNitro Cowpea with strains of Bradyrhizobium sp. (Semia 6462 and Semia 6463); co-inoculation was performed using the commercial product, containing a combination of strains of Azospirillum brasilense, both in liquid formulation. Co-inoculation (Bradyrhizobium sp.+ Azospirillum brasilense) did not influence the production components of cowpea plants. Inoculation with Bradyrhizobium sp. associated with phosphate fertilization of 120 kg ha^-1 of P₂O₅ was sufficient to promote maximum growth and development of cowpea plants in Amazonian soil. The genotype White had higher capacity of nodulation, dry matter production and grain yield. Inoculation of Bradyrhizobium sp. increased N and P contents in the leaves. The genotype Butter was superior to the genotype White with respect to the accumulation of P, K, Ca and Mg in the leaves.

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