Abstract

The inoculation of nitrogen-fixing bacteria in soybean crops allows the achievement of high crop yield by reducing or eliminating the application of nitrogen fertilizers. Pre-inoculation of seeds can reduce costs and increase the efficacy of this agricultural practice. The objective of this study was to assess the efficacy of pre-inoculation of soybean seeds with a commercial inoculant of Bradyrhizobium (RIZOLIQ LLI^® manufactured by Rizobacter do Brasil) at 60, 45, and 30 days before sowing using a cell protector and different chemical treatments. The study was conducted in four municipalities in the state of Paraná (Londrina, Pato Branco, Ponta Grossa, and Santa Tereza do Oeste) and included 14 treatments, a negative control, standard inoculation of the recommended bacterial strains on the day of sowing, and pre-inoculation at 30, 45, and 60 days before sowing using the commercial inoculant RIZOLIQ LLI^® together with the cell protector and chemical treatment of seeds with Imidacloprid (Rocks^®), Fipronil+Thiophanate-methyl+Pyraclostrobin+ (Standack^®Top), Metalaxyl-M+Fludioxonil (Maxim^®XL), and Metalaxyl-M+Fludioxonil+Thiabendazole with Thiamethoxam (Maxim^®Advanced+Cruiser^®). The nodulation, plant biomass, nitrogen concentration in shoot and grain, and grain yield were evaluated. The cell protector was efficient in maintaining the bacterial inoculant viable in the seed for up to 60 days. All treatments of pre-inoculation of soybean chemically-treated seeds up to 60 days before sowing could be performed without impairment of nodulation, plant biomass, nitrogen concentration in shoot and grain, and grain yield. Therefore, pre-inoculation of soybean seeds up to 60 days before sowing is an efficient and practical inoculation strategy for sowing soybean crops.

Key words: Inocula, pre-sowing inoculation, rhizobia, symbiosis.