Fernanda Barros - Federal University of Uberlândia (ICIAG - UFU), Minas Gerais state, Brazil
Reginaldo de Camargo - Federal University of Uberlândia (ICIAG - UFU), Minas Gerais state, Brazil
Regina Maria Lana - Federal University of Uberlândia (ICIAG - UFU), Minas Gerais state, Brazil
Miguel Henrique Franco - Federal University of Uberlândia (ICIAG - UFU), Minas Gerais state, Brazil
Mayara Cristiana Stanger - Federal University of Uberlândia (ICIAG - UFU), Minas Gerais state, Brazil
Vanderley José Pereira - Federal University of Uberlândia (ICIAG - UFU), Minas Gerais state, Brazil
Ernane Lemes - Federal University of Uberlândia (ICIAG - UFU), Minas Gerais state, Brazil

Purpose Nitrogen-fixing bacteria (NFB) are essential for biologically fixing nitrogen in natural and soybean crop systems. The use of organomineral fertilizers is a promising crop management tool made from the mixing of an organic source and mineral fertilizers. This study evaluated the efficacy of an organomineral fertilizer (sewage sludge-based) as a carrier for the Azospirillum brasilense inoculation and the influence of A. brasilense plus Bradyrhizobium japonicum on the soybean antioxidant metabolism.Method The experiment was performed under greenhouse conditions. The soybean cultivar (AS ۳۶۸۰ IPRO) was evaluated in a ۴×۲(+۱) factorial scheme, corresponding to four doses of A. brasilense [۰, ۱۰۰, ۲۰۰, ۳۰۰ mL ha-۱ (۲x۱۰۸ viable cells mL-۱) per ۵۰ kg-۱ of soybean seeds], with or without B. japonicum [۱۰۰ mL ha-۱ (۵x۱۰۹ viable cells mL-۱) per ۵۰ kg-۱ of soybean seeds], and a control treatment (without inoculants or fertilizers). Soybean antioxidant metabolism (enzymes, oxidative processes, proline amino acid) was evaluated in different plant stages.Results The seed inoculation with A. brasilense via organomineral fertilizer enhanced the soybean plant protection factors. Plant protection to stresses happened mainly by reductions in the superoxide dismutase activity, lipid peroxidation, and hydrogen peroxide concentration. The co-inoculation of A. brasilense with B. japonicum enhanced the proline activity at the V۳ and R۵ soybean phenological stage compared to A. brasilense inoculated alone.Conclusion The studied organomineral fertilizer is an efficient inoculant carrier for A. brasilense in soybean plants via seed treatment. The protective results observed for A. brasilense were improved when co-inoculated with B. japonicum.

Glycine max, biological nitrogen fixation, growth-promoting bacteria, Joint inoculation, Antioxidant enzymes