Like all legumes, soybeans can take advantage of atmospheric nitrogen through the process known as biological nitrogen fixation (BNF). FBN brings notable benefits to the soybean sector in Brazil by eliminating the need for nitrogen fertilizers in the crop, reducing production costs and, consequently, increasing competitiveness in the global market.
In this sense, seed inoculation with symbiotic bacteria is a necessary practice to ensure that an FBN occurs efficiently and provides this nutrient throughout the development of the soybean crop.
What is soy inoculation and why do it
Soybean inoculation is a process that consists of adding beneficial microorganisms to the cultivation in the seeds themselves, or in the sowing furrow, with bacteria of the genus Bradyrhizobium being the main microorganisms used in the formulation of inoculants. These bacteria establish a symbiotic relationship with the soybean root system, providing all the nitrogen that the plants require throughout the production cycle.
In general, inoculation helps the establishment of the Bradyrhizobium spp. population. in the soil, enabling the immediate formation of nodules and the establishment of the biological nitrogen fixation process, avoiding initial nutrient deficiency and throughout soybean development.
When to carry out seed inoculation
In soybean cultivation, it is advisable to inoculate the seeds annually with Bradyrhizobium spp., even if the soybean has already been cultivated with inoculation in previous years. This procedure, known as reinoculation or annual inoculation, is considered a simple, low-cost management practice that can result in an increase of approximately 8% in soybean grain production. The survival of these bacteria in the soil can be limited by environmental and nutritional factors, therefore, the practice of annual inoculation ensures a faster formation of nodules in the root system and a more effective start of the biological nitrogen fixation process.
In crops previously not cultivated with soybeans or where a long period has passed since the last sowing of this crop, seed inoculation takes on even greater importance. In these cases, the amount of bacteria capable of fixing nitrogen tends to be greatly reduced in the soil, therefore, cultivation without inoculation can result in a deficiency of this essential nutrient for soybean development.
Important precautions
Inoculating soybean seeds requires attention to some essential aspects. It is essential to carry out the process in the shade, ensuring that the inoculated seeds are protected against direct exposure to the sun and excessive heat before and during sowing. Furthermore, it is important to sow the crop immediately after inoculation, especially if the seeds have been treated with fungicides and micronutrients (HUNGRIA; CAMPO, 2021).
Another important factor is the careful use of fungicides and micronutrients in seed treatment, together with the inoculant. These products may be incompatible with the inoculant and impair its effect, reducing nodulation and FBN. Therefore, it is highly recommended to choose active ingredients that are less aggressive to Bradyrhizobium spp. Furthermore, the application of both fungicides and micronutrients to the seeds must be carried out first and, only after the product has completely dried, should inoculation be carried out.
Furthermore, it is essential to highlight the importance of a production environment that provides favorable temperature and humidity conditions, and with corrected soil acidity, to enhance the effectiveness of the inoculant and the biological nitrogen fixation process.
By Gabriela Martins and Sônia Rafaela da Costa Bueno, members of AGR Jr. Consultoria Agronômica, Junior Company of the Agronomy Course at UFSM Campus Frederico Westphalen, under the guidance of professor Gizelli Moiano de Paula.
References:
HUNGRIA, Mariangela; CAMPO, Rubens José; MENDES, I. de C. Biological nitrogen fixation in soybean crops. 2001. Available at: <https://www.infoteca.cnptia.embrapa.br/infoteca/handle/doc/459673>. Accessed on: August 28, 2023.
HUNGRIA, Mariangela; CAMPO, Rubens José; Inoculation care. 2021. Available at: <https://www.embrapa.br/agencia-de-informacao-tecnologica/cultivos/soja/producao/inoculacao-e-inoculante/cuidados-na-inoculacao>. Accessed on: August 26, 2023.
MARTIN, T. N. et al. Technical indications for soybean cultivation in Rio Grande do Sul and Santa Catarina, harvests 2022/2023 and 2023/2024. Santa Maria: Editora GR, 2022. 136 p. Available at: https://www.embrapa.br/busca-de-publicacoes/-/publicacao/1152019/indicacoes-tecnicas-para-a-cultura-da-soja-no-rio-grande-do-sul-e -in-santa-catarina-safras-20222023-e-20232024. Accessed on: August 26, 2023.
OLIVEIRA, A. B. et al. Soy: the producer asks, Embrapa answers. Brasília, DF: Embrapa, 2019. 274 p. Available at: https://www.embrapa.br/busca-de-publicacoes/-/publicacao/1118408/soja-o-produtor-pergunta-a-embrapa-responde. Accessed on: August 26, 2023.
