Biological nitrogen fixation in sorghum: a basis for reduction of synthetic nitrogen dependence

• Ano de defesa: 2022
• Autor(a) principal: Paula, Thiago de Almeida
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa; Fitotecnia
• Palavras-chave em Português: Sorgo; Nitrogênio - Fixação; Biotecnologia agrícola; Rhizobium; Sphingomonas; Fitotecnia
• Link de acesso: https://locus.ufv.br//handle/123456789/31899; https://doi.org/10.47328/ufvbbt.2023.113

The increasing population and its demands require intensifying the current agricultural model to boost productivity. Chemical fertilizers, especially nitrogen fertilizers, play a crucial role in improving agriculture in Brazil, making it a major importer. However, excessive use of chemical fertilizers raises production costs, causes environmental damage, and impacts soil microbial ecology and dynamics, which could pose long-term problems as plant-microbe interactions are considered a solution for sustainable agriculture. Hence, the agricultural model must be reassessed to reduce the demand for synthetic fertilizers and increase the use of microorganisms that enhance production sustainability. The study aimed to examine the impact of nitrogen fertilization on the diazotrophic community associated with sorghum plants and evaluate the feasibility of using pre-selected bacteria in combination with different levels of nitrogen fertilization to improve sorghum productivity and reduce chemical N fertilization dependence. The study consisted of several experiments, including: isolation of N-fixing and plant growth-promoting bacteria, selection of bacteria with biotechnological potential, evaluation of the impact of nitrogen fertilization on diazotrophic microbiota during sorghum sowing, testing the agronomic efficiency of pre-selected bacteria under greenhouse conditions, and evaluating the agronomic efficiency of pre-selected microorganisms in field conditions. The results of the study showed that different levels of nitrogen fertilization affect the composition of the diazotrophic community associated with various parts of the sorghum plant, reducing its richness, uniformity, and diversity. Inoculation with selected plant-growth promoting bacteria (Rhizobium sp. and Sphingomonas sp.) in combination with reduced levels of nitrogen fertilization significantly improved stem diameter, shoot and total dry mass, and nitrogen content of the shoot under greenhouse conditions. In field conditions, inoculation with a mixture of all tested bacteria (Rhizobium sp. and Sphingomonas sp.) showed the potential to increase forage sorghum productivity and reduce nitrogen fertilization by 25-50 %. These results indicate the potential of using these microorganisms as a biotechnological tool for sustainable agriculture. The study concluded that nitrogen fertilization impacts the diazotrophic community of sorghum plants and that the N-fixing and growth-promoting bacteria selected from the sorghum rhizosphere as seed inoculants have the potential to reduce the need for synthetic nitrogen fertilizers in sorghum production. Further research is needed to determine the optimal balance between inoculants and fertilization rates for an integrated fertilization model. Keywords: Sorghum. Biological Nitrogen Fixation. Rhizobium. Sphingomonas.