The interest in biological active ingredients to help plants acquire nutrients has been increasing exponentially in Brazil. Microorganisms, especially bacteria such as nitrogen fixers (diazotrophs), phosphate solubilizers, disease and pest biocontrollers, are part of a set of assets kept in germplasm banks that can compose new products for different crops, such as sugarcane sugar.

These products called bioinputs are today involved in two important public policies: the National Bioinputs Program and the National Fertilizers Plan. Both converge to expand the use of biologicals in agriculture. Research aimed at reducing dependence on synthetic fertilizers dates back decades. A striking example is soybean cultivation, in which diazotrophic bacteria completely replace the use of nitrogen fertilizer, maintaining high grain yields. Among the three main macronutrients used in the country, nitrogen accounts for 29% of the total, followed by potassium (38%) and phosphorus (33%).

If soybeans were dependent on synthetic nitrogen, twice as much fertilizer would be needed to maintain the current yield of this crop, in which this element is not applied but rather an inoculant capable of meeting 100% of the nitrogen demand. Regardless of the host plant, diazotrophic bacteria have the enzyme complex called nitrogenase, crucial in reducing gaseous nitrogen (a stable molecule that makes up 78% of the atmosphere) into ammonia. However, while legumes, such as soybeans, form nodules for Biological Nitrogen Fixation, grasses, such as sugarcane, have a distinct pattern. Without nodules, the efficiency of the nitrogen-fixing “factory” is reduced.

For Biological Nitrogen Fixation to operate efficiently, it is essential to protect nitrogenase from oxygen, a limiting factor, which seems paradoxical, since the air we breathe contains both gaseous nitrogen and oxygen. The nodules present in legumes provide this protection, increasing the efficiency of nitrogenase.

In grasses, Biological Nitrogen Fixation is reduced by greater exposure to oxygen. Furthermore, the breaking of the gaseous nitrogen bond to form ammonia requires high energy expenditure, favoring the preferential use of nitrate and ammonium from the soil, if available. It is crucial to remind farmers that, although sugarcane can use much of the nitrogen provided by microorganisms, Biological Nitrogen Fixation does not completely satisfy the plant's needs, as in soybeans.

In 2019, Brazilian crops received the first product containing a strain of diazotrophic bacteria for sugarcane. The absence of root nodules required a long period of research to understand how bacteria could contribute to reducing N-fertilizer use. For farmers, the main target of this research, what are the direct benefits?

Since the 1950s, when the first diazotrophic bacteria was isolated from sugarcane roots by researcher Johanna Döbereiner at kilometer 47 in Seropédica in Rio de Janeiro, there have been significant advances in the understanding of the root microbiota and the use of this biological process to increase the efficiency of nitrogen use. Currently, technology allows the use of inoculants with selected populations of bacteria, aiming to improve nitrogen efficiency in several crops, including sugar cane.

Let's talk about the application of diazotrophic bacteria to sugarcane using a fertilizer enriched with 15N atoms (10% atoms) to track the nitrogen absorbed by the plants. Two experiments were carried out in Quatá, in São Paulo, planted in an oxisol, using an inoculant containing diazotrophic bacteria, and a dose of 40 kilograms per hectare of nitrogen was applied to the sugarcane plant. The cultivars RB966928 (early) and RB92579 (medium-late) were evaluated. The fertilizer was applied 3 months after planting, and leaf samples were collected and evaluated at 10 months for nitrogen use efficiency (EUF-%). As observed in different studies, the EUN was less than 50% in both cultivars, however, in the RB92579 cultivar, the EUN was higher in plants inoculated in both planting locations, showing the contribution of bacteria to better use of the fertilizer.

In fact, studies have revealed that less than 40% of fertilizer nitrogen is used by sugarcane. The remainder is supplied via mineralized soil organic matter. Part of the applied nitrogen is immobilized in the microbiota associated with soil organic matter, releasing it throughout the cycle. Strategies such as rotation with legumes in sugarcane field renewal and the use of slow-release nitrogen sources can increase the efficiency of nitrogen use in this crop.

Since sugarcane is a plant that stores a lot of carbon in its stems and exudes part of this carbon fixed by its roots, it is expected that the pool of associated microorganisms benefits from several related biological processes growth and nitrogen acquisition, including Biological Nitrogen Fixation. In this process, estimates made with national cultivars showed that up to 40 kilograms per hectare of nitrogen can come from a beneficial association with diazotrophic bacteria.

Another important contribution of diazotrophic bacteria in various crops is the production of growth regulators that are exuded by the bacteria. These stimulate root development which absorb more water and nutrients and can produce more substances such as acids organic compounds that improve the release of phosphorus from the soil.

On the national market, several products contain species of diazotrophic or non-diazotrophic bacteria, boosting plant growth, including sugar cane. These products contain microorganisms that are non-pathogenic to plants, humans or animals, with guaranteed purity and high bacterial concentrations. Generally available in liquid form or with water-miscible polymers, they can be applied by spraying in conjunction with other operations.

In Brazil, we have legislation that allowed the development of research, industry and the bioinput market, the vast majority of which are aimed at reducing the use of N-fertilizers. These products reduce production costs and greenhouse gas emissions. Improvements in the legal framework are welcome, but discussions on bills need to pay attention to the good results harvested today and avoid setbacks.

Combined with a sugarcane improvement program, with the constant selection of higher-yielding cultivars, Brazil will continue to provide the world with technological solutions that have made it the world's largest producer of cane sugar and green energy and is now launching another byproduct, biogas. A scenario of energy efficiency and income for rural producers.