Interaction of the use of Azospirillum brasilense and herbicides in soybean crops

Abstract

The efficiency of nitrogen-fixing bacteria applied to crops can be influenced by the application of phytosanitary products, such as herbicides. This research aimed to evaluate the interaction between the application modalities of Azospirillum brasilense and the use of residual herbicides. The application of A. brasilense via seed treatment (TS), application in the planting furrow (AS) and foliar spray (PF) at the V3 stage of soybean were tested in the field, with treatments with diclosulam, pyroxasulfone + flumioxazin and the weeded control. The trial was conducted in randomized blocks with four replications and the treatments arranged in split plots (3x3), with the application modalities of A. brasiliense allocated in the plots. The doses of A. brasilense, at a concentration of the bacteria per mL of 2x108, were 100, 300 and 500 mL ha-1, respectively, for TS, AS and PF. The doses of diclosulam were 35.03 g ha-1 and pyroxasulfone + flumioxazin were 120 + 80 g ha-1, respectively. Weeding was done at 10 and 20 days after emergence (DAE). The most frequent weeds in evaluations made during the soybean harvest were Euphorbia heterophylla, Commelina benghalensis, Digitaria horizontalis, Eleusine indica and Panicum maximum. Higher densities and dry mass of the weed community were observed in the weeded plots, regardless of the inoculant application method. No effects of treatments, interactions or isolated effects were observed for the dry masses of leaves, stems and reproductive structures of soybean plants evaluated at crop flowering. At the soybean harvest, no effects of treatments were observed for plant population, yield components, grain yield and soybean harvest index.