Inoculation reduces fertilizer costs in soybeans

The addition of nitrogen-fixing bacteria to soybean seeds results in savings on nitrogen fertilizers and also promotes yield gains in the crop. The practice becomes even more important with the reduction in rainfall during the sowing season, when the biological activity of the soil and the availability of nutrients decrease. Learn more about the technology known as inoculation and coinoculation in soybeans.

Embrapa researchers have identified bacteria that are beneficial for soybean cultivation, capable of making nitrogen available and promoting the growth of the plants' root system, providing better conditions for the absorption of water and nutrients. “Bacteria already exist in the soil. With inoculation we guarantee a greater density of these bacteria of interest with a population capable of bringing benefits to soybeans”, explains Embrapa Trigo researcher José Pereira da Silva Junior.

The bacteria of Bradyrhizobium They are used in the preparation of inoculants that perform biological nitrogen fixation. They capture nitrogen from the air and transform it into compounds that the plant can absorb. The concentration of this symbiosis can be seen in the roots by the presence of nodules. “Inoculation allows for earlier formation of nodulation, consequently, greater availability of nitrogen for plant development”, says Pereira. 

According to the researcher, the inoculant can contribute more than 300 kilos of nitrogen per hectare (kg of N/ha) to soybeans, at a cost of up to 95% less compared to nitrogen fertilizer. On average, urea costs up to 500 reais per hectare, while the price of inoculant varies from 8 to 15 reais per hectare. “The bacteria does the work of mineral fertilizer, replacing almost all of the urea. With inoculation, it is recommended to apply only 30 kg of N/ha”, he concludes. The average gain from annual inoculation of soybeans with bacteria Bradyrhizobium in traditional cultivation areas it is 8%.

Advances in knowledge of soil microorganisms have allowed the use of a second bacteria in soybeans: Brazilian Azospirillum acts on the plant's root development, reducing losses in situations of water stress. The sum of the two bacteria - Bradyrhizobium e Brazilian Azospirillum forms the process called coinoculation, which can result in an average increase of 16% in soybean yield. Care in the process

Unlike mineral fertilizer, the inoculant contains living organisms, which have an expiration date, little tolerance to the sun and may lose their effect when combined with some fungicides and insecticides.

According to Embrapa, inoculation should be the last process in seed treatment, as the efficiency of bacteria exposed to heat reduces in the first hours after contact. The guideline is to apply the inoculant, whether granular or liquid, directly to the seeds, at most, two days before sowing, preserving this mixture in the shade to prevent the bacteria from drying out. Another way is to apply the inoculant directly to the sowing furrow, but in this case there is the disadvantage of needing to multiply the dose by six, increasing the final cost. Furthermore, it is necessary to add water to the inoculant.

Embrapa Soja researcher Marco Antonio Nogueira warns of the risks of inoculating soybeans directly into the seeder box:  “In addition to the bacteria not fully adhering to the seed, the movement of the machine can sediment the inoculant, compromising the results.” 

Soil moisture at sowing is also essential for the success of inoculation. The emergence of seeds depends on humidity and the bacteria need the plant to send out roots to start acting.