Reinoculação de rizóbio e co-inoculação de Azospirillum aplicado em cobertura em distintos estádios de crescimento do feijão

Abstract

Common beans can meet their nitrogen demand through Biological Nitrogen Fixation (BNF). However, for this to happen, it is necessary to overcome bottlenecks related to application technologies. This study aimed to investigate th e response capacity of common beans to the reinoculation of Rhizobium tropici as a sidedressing, with or without co inoculation of Azospirillum brasilense, at different stages of crop development. The experiments were conducted during the 2023 winter harve st and the 2023/2024 rainy season, using a randomized block design with 12 treatments and 4 replicates. The treatments included the application of an inoculant based on R. tropici alone and in co inoculation with Azospirillum, reinoculated as a sidedressin g at the V3, V4, R5 and R6 stages. Additional treatments were also tested: control without inoculation and without fertilization; inoculation with R. tropici via seed at the reference dose; co inoculation with R. tropici + Azospirillum via seed at the refe rence dose; and mineral nitrogen fertilization (16 and 64 kg ha⁻¹, respectively, at the base and as topdressing). The evaluated characteristics included: nodulation (number and dry mass of nodules), plant morphophysiology (length of the main root, dry mass of the root, dry mass of the aerial part and leaf N content), in addition to the productive components (number of pods per plant, number of grains per pod, average weight of one hundred grains, grain yield and final stand). The data were subjected to anal ysis of variance and the effect of the treatments was discriminated by the Scott Knott test at 5% probability. A principal component analysis (PCA) was also performed to identify the relationships between the studied characteristics. The results showed tha t the reinoculation technique with co inoculation of Azospirillum at the V4 stage resulted in significantly yields to topdressing with 80 kg ha⁻¹ of N. In addition, there was an 8.7% increase in common bean yield compared to the application of nitrogen fer tilizer, evidencing the benefits of the applied technique. The PCA analysis confirmed the variation in data between harvests, indicating the influence of water stress and thermal accumulation on bean yield