Nutritional Status of Cowpea Plants Inoculated with Bradyrhizobium and Azospirillum brasilense in Associated with Phosphate Fertilization in Soil Amazonian

Biological nitrogen fixation (BNF) plays an important role in cowpea cultivation. Thus, the present study aimed to evaluate the effects of inoculation and co-inoculation of rhizobacteria associated with phosphate fertilization on biometric parameters and absorption and use of nutrients by different cowpea genotypes. The experimental design was randomized blocks in a 4x3x2 factorial scheme, corresponding to four rates 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 four replicates. The results revealed variability between the cowpea genotypes with respect to efficiency and response to phosphorus application. Cowpea plants inoculated with Bradyrhizobium sp. showed increments of approximately 22.66%, 23.58%, 55.31%, 47.95%, 65.66% and 20%, respectively, in N contents in the roots, leaves, shoots and in the plant, N absorption efficiency and N use efficiency. Inoculation of Bradyrhizobium sp. associated with 120 and 160 kg ha-1 of P2O5 increases plant height and P and S contents in the shoots of cowpea plants. Increased P rates lead to increment in dry matter production and N, P and K contents in cowpea plants. Coinoculation of Bradyrhizobium sp. and Azospirillum brasilense did not positively influence any of the variables studied over the effects of Bradyrhizobium sp. alone. Cowpea has potential to be used as green fertilizer after a short period of cultivation, due to the accumulation of nutrients in its leaves and shoots.