Highlighting the benefits of biological nitrogen fixation on agronomic, physiological, and nutritive value traits of brachiariagrass

The search for efficiency in forage-based systems has intensified in recent years, increasing the need to reduce environmental impacts of animal agriculture. Reducing the dependence on fossil fuels for nitrogen (N) input with the use of microorganisms (e.g., biological nitrogen fixation, BNF) and grass-legume mixed stands has become an important practice. The objective of this study was to evaluate N input strategies that affect the agronomic, physiological, and nutritive value traits of Ipyporã brachiariagrass (Brachiaria hybrid ‘BRS RB331 Ipyporã’) based on the use of mineral N fertilization (ammonium sulfate), bacterial inoculation (Azospirillum brasilense strains Ab-V5 and Ab-V6; CNPSo), and mixed stands with forage peanut (Arachis pintoi Krapov. & W.C. Greg. cv. BRS Mandobi) in the Amazon biome. The treatments were six N-input strategies: 1. pastures with no nitrogen fertilization (control); 2. fertilized with 80 kg N ha-1 season-1 (N); 3. inoculated with A. brasilense (Az); 4. fertilized with 80 kg N ha-1 season-1 + A. brasilense (N + Az); 5. mixed stand of Ipyporã brachiariagrass and forage peanut (Mix) and 6. mixed stand + A. brasilense (Mix+Az). The experimental period was from 20 January 2015–21 March 2017, covering three summer growing seasons. Forage was cut to a 12-cm stubble when average canopy height reached 25 cm. Annual forage accumulation (FA) was greater in N, Az, N + Az, and Mix+Az (averaged 7760 kg DM ha-1) than in Control and Mix (averaged 6485 kg DM ha-1). The FA measured in Az and Mix+Az was equivalent to applying 58 and 86 kg of N ha-1, respectively when compared with Control. The greatest leaf mass was measured in N, Az, N + Az, and Mix+Az (averaged 1475 kg DM ha-1). The Az and Mix+Az can be options to improve the sustainability of forage systems and maintain forage production while using renewable sources for nitrogen.