Currently, Brazilian agriculture feeds more than one billion people in the world, producing approximately 237 million tons of grains. Half of this total is represented by soybean cultivation, leading the national market and generating revenues of R$ 140 billion with its production. Due to its importance in these sectors, soybeans drive consecutive agronomic research to increase its productive efficiency, highlighting studies focused on the area of biological nitrogen fixation.
The adequate nutritional supply of the plant is essential to guarantee the success of the crop. Nitrogen, which is required in greater quantities, is traditionally applied through granulated fertilizers in inorganic form that generate high costs from transportation to application.
Therefore, to minimize these fertilization costs, the alternative of using nitrogen-fixing bacteria emerged. These, despite already being present in the soil microbiota, are added through concentrated inoculants with the aim of meeting the plant's needs.
Therefore, in inoculation, the genera stand out Bradyrhizobium sp. It is azospirillum sp. which are the most widespread and researched bacteria by the scientific community. This practice is initially carried out in the treatment of seeds, in liquid or peaty form. However, there is still the option of applying the commercial product in liquid form to the sowing furrow, which increases the efficiency of the sowing operation and the viability of microorganisms.
In the traditional method, one of the biggest obstacles was the lack of suitable machines, leading to the emergence of seed mixers designed to operate on the property or in the processing unit, which made it possible to homogenize chemicals and microorganisms in the treatment of seeds. However, its efficiency is debatable, as it requires more time in the pre-sowing operation.
The use of traditional seed treatment, with inoculation carried out before sowing, generally causes damage to the bacterial population (as it is carried out together with insecticides, fungicides and micronutrients) caused mainly by increased toxicity and changes in the pH of the environment, which are harmful. to the number of effective cells per seed.
One can also highlight a natural reduction in the viability of microorganisms in the period between inoculation until the seed comes into contact with the soil, whether due to climatic or operational issues on the property. This reduction can be corrected by using inoculation or re-inoculation via spraying at the time of sowing.
Judging only the viability of the Bradyrhizobium sp., inoculation in the sowing furrow has a more efficient behavior in areas of consecutive cultivation. However, for plots that have not been previously cultivated, the use of bacteria to treat seeds in peat form is still the most recommended.
In this type of inoculation via sowing furrow, research indicates variations in the application rate and its operational consequences, highlighting that grain productivity is higher when a higher dose of inoculant is used (6x106 CFU/seed) and a higher application rate (50L/ there is). The lowest costs and the highest operational field capacity are obtained by the lowest application rate (10L/ha), however, the cost/benefit ratio is obtained with an application rate of 20L/ha and a higher dose of inoculant. Since the Bradyrhizobium sp. commercial has a low percentage cost in the crop cycle and higher volumes result in a greater need to refill the inoculant tank, consequently increasing the value of the sowing operation.
The inoculation equipment in the sowing furrow has dimensional characteristics to suit the operation, consisting of a syrup storage tank, electric/bearing pump for suction and pressurization of the hoses, pressure regulator control with manometer, line filter, distribution with hoses and spray tips. Such equipment is fixed to the seeder chassis, with each seeding unit receiving a spray tip positioned between the implement's depth limiting wheels.
Inoculation can also be carried out using seed treatment equipment, such as mixers, concrete mixers and semi-mechanized drums, responsible for mixing the inoculant with the seeds. The most recent equipment is electrically driven or via the tractor's power take-off, storage capacity between 90kg and 4.000kg and allows seeds to be inoculated in the field or in a warehouse.
Likewise, in the case of mechanized inoculation, via furrows or with a seed treatment machine, the study of times is essential for determining operational performance, also helping with administrative systems for planning and organizing work.
In conventional inoculation, for good efficiency, it is recommended, after homogenizing the seeds with the inoculant, to leave them in the shade to set the product, for around 20 minutes beyond the preparation time of the mixture, and only then take them to the seeder. and start the operation. In terms of time, it is less efficient when compared to furrow, with a lower operational performance.
Added to this, inoculation in sowing furrows presents lower operational costs, as long as it is carried out with lower application rates, as the increase in the volume of spray solution linearly increases the values of the sowing operation.
Besides the Bradyrhizobium sp., coinoculation with the azospirillum sp. makes it possible to obtain superior results in farming. The application of the two species together in the furrow generates average increases in the field of 16% when compared to inoculation with only the Bradyrhizobium sp. This increase in production is related to the functions of the azospirillum sp., which in addition to biological nitrogen fixation, helps in root growth and solubilization of phosphorus present in the soil.
The benefits of inoculation go beyond the limits of the crop, bringing environmental gains to fauna and flora, reducing the emission of gases related to the manufacture and use of nitrogen fertilizers and facilitating carbon sequestration, thus being included in the Agriculture Program of Low Carbon from the Ministry of Agriculture, Livestock and Supply (Mapa).
Considering the advantages of this technology, we seek to guide producers of large crops towards rational use: as it is a biological product. The more inputs added to the seed, the less viable the bacteria will be. Therefore, the union of regulatory bodies linked to Mapa with companies that manufacture agricultural pesticides is necessary to provide farmers with correct instructions for the combined use of products and increased profitability.
Gabriel Ganancini Zimmermann, IFC/Rio do Sul-SC; Lucca Branco Giacomet and Samir Paulo Jasper, UFPR/Curitiba-PR
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