Seed treatment with phytosanitary products and interaction with pre-inoculation in soybean

Pre-inoculation offers logistical advantages for soybean cultivation by eliminating on-farm inoculation, but little is known about its interaction with phytosanitary products. This study evaluated the effect of seed treatment with pesticides combined with pre-inoculation performed 10 days before sowing, without bacterial protectant, on soybean nodulation and yield. Field trials were conducted in six locations in Paraná and Mato Grosso do Sul states using a randomized block design with five treatments: (1) absolute control (no inoculation or nitrogen fertilization); (2) mineral nitrogen control (200 kg N ha-1); (3) standard inoculation with Bradyrhizobium spp. at sowing; (4) pre-inoculation with Bradyrhizobium japonicum + insecticides (imidacloprid + thiodicarb); and (5) pre-inoculation with B. japonicum + fungicide (fludioxonil + metalaxyl-M) + insecticide (thiamethoxam). Parameters assessed included nodulation, plant biomass, nitrogen accumulation in shoots and grains, and yield. Pre-inoculation with pesticides promoted nodulation and productivity comparable or superior to standard inoculation. Across all sites, pre-inoculated treatments outperformed the absolute control, and in most sites they also surpassed mineral nitrogen fertilization. The results demonstrate that pre-inoculation carried out 10 days before sowing, in combination with chemical seed treatment, is an effective strategy to enhance nodulation and yield in soybean cultivation.