Azospirillum brasilense associated with nitrogen fertilization in Urochloa humidicola pastures cultivated in the Amazonian savanna

Abstract The objective of this study was to assess the impact of Azospirillum brasilense in conjunction with nitrogen fertilization on structural, morphogenetic, yield-related, and chemical characteristics of Urochloa humidicola cultivated in the Amazon savannah. Treatments consisted of five nitrogen application rates (0, 50, 100, 150, and 200 kg ha-1), both with and without A. brasilense inoculation. The experiment was laid out in a completely randomized design with a 5×2 factorial arrangement, including four replications. The morphological composition of the pastures, morphogenetic and structural characteristics and chemical composition of the forage were evaluated. The utilization of A. brasilense, either alone or combined with nitrogen fertilization, did not influence the enhancement of forage yield. However, nitrogen fertilisation led to consistent increases in production, primarily through an increase in leaf and culm components and a reduction in the proportion of dead material in pastures. It also led to a linear increase in the proportions of NDF, ADF and CP in the forage. The use of A. brasilense does not alter the production and chemical composition of the forage, while nitrogen fertilization favors the management of pastures with U. humidicola grown in Amazonian savanna soil.