Abstract

The competitiveness of Brazilian soybean in the international market is highly dependent on biological nitrogen fixation, whose efficiency is related to factors that affect the survival of the bacteria, such as the chemicals used in the treatment of seeds. The study objective was to evaluate Bradyrhizobium pre-inoculation (10 days before sowing) of soybean seeds treated with fungicides and insecticide compared to the standard inoculation performed on the planting day. Four experiments were conducted in two distinct ecosystems, two in Brazilian savanna (Cerrado) and two in Cerrado/forest transition areas of Roraima state. In each ecosystem, the experiments were performed in areas without and with soybean cultivation history. The treatments were in: 1- Control without inoculation; 2- inoculation on sowing day in untreated seeds; 3- treatment with carbendazim; 4- treatment with pyraclostrobin + methyl thiophanate + fipronil; 5- treatment with fludioxonil + metalaxyl-M. Groups 3, 4, and 5 were pre-inoculated 10 days before sowing. Viable cells in the seeds were recovered on the sowing day. Nodule number and dry mass, root, and aerial part dry mass were evaluated 35 days after emergence. Grain yield was evaluated at harvest. The number of viable cells was negatively affected by seed treatment. For all evaluated variables, treatments with pre-inoculation plus fungicides/insecticide were similar to the standard sowing-day inoculation. Pre-inoculation performed 10 days before planting, along with seed treatment with fungicides/insecticides, positively affected soybean crop productivity and could be used without compromising the nitrogen fixation.

Key words: Glycine max (L.) Merr., biological nitrogen fixation, Amazon.