Reinoculação de doses de rizóbio em cobertura, sob presença ou não de Azospirillum em cultivares de feijão comum

Abstract

Bacteria of the Rhizobium group are able to fix atmospheric nitrogen and supply it to the bean crop; however, the results of using this technique are still questionable in the field by farmers. Thus, this study aimed to investigate the nodulation, growth, and yield of common bean cultivars under field conditions, subjected to Rhizobium re-inoculation in topdressing applied at different doses, mixed or not with Azospirillum. A randomized block design was used, in a 2 x 4 x 2 + 2 factorial scheme, with four replications. The treatments consisted of two common bean cultivars (BRS Estilo and BRS Esteio), reinoculated with R. trocipi in topdressing at the following doses: 0 (control), 1, 2, and 4 times the reference dose, mixed or not with Azospirillum in co-inoculation. As additional treatments, mineral nitrogen fertilization (20 and 50 kg ha-1 respectively in the sowing furrow and top dressing) was assessed for both cultivars. In the R6 stage, the nodulation (number of active nodules and dry mass of nodules), morphological traits of the plants (root length, root dry weight, plant height, shoot dry weight), and nitrogen content) were evaluated. The yield components (number of pods per plant, number of grains per pod, and 100-grain weight) and grain yield were assessed at harvest. The conduction of the study led to the following conclusions: Reinoculation involving the association of R. tropici with A. brasilense influenced the nodulation process and morphological traits of the common bean plants. The re-inoculation with R. tropici at a dose corresponding to 2.5 times the reference dose, equivalent to 375 L ha-1, associated with co-inoculation with A. brasilense at a dose of 100 L ha-1 performed at stage V4, provides obtaining higher yields of the bean crop, equivalent to the values obtained with mineral nitrogen fertilization The adoption of the re-inoculation with Rhizobium cells associated with Azospirillum, in addition to the inoculation carried out in the seeds, can replace the supply of mineral N in the common bean crop.