Biological nitrogen fixation (BNF) is a process carried out by groups of microorganisms that have the functional enzyme nitrogenase, which can be used as a source of nitrogen (N) for plant nutrition. BNF is the main way of incorporating nitrogen into the biosphere and, after photosynthesis, it is the most important biological process for plants and is essential to life on Earth.
It is estimated that BNF has a global contribution to different ecosystems of approximately 258 million tons of nitrogen (N) per year, and its contribution to agriculture is estimated at 60 million tons. In Brazil, the most successful case of such contribution is soybean cropping, in which the use of inoculants, which dates from the 1960s, has ensured competitiveness for soybeans when compared to the production of other countries, reflecting directly on Brazil trade balance. If the supply of nitrogen to soybeans had to be carried out via nitrogen fertilization, it would be necessary, for an average production of 49 sacks/ha (average productivity of soybean in 2012/2013), a total of 588 kg urea/ha (considering an efficiency of only 60%), at an average cost (October 2013) of BRL 906 /ha. The inoculation cost per hectare is BRL 8.00. That is, with the inoculation process, we saved BRL 898 per hectare. If we consider the 27.7 million hectares used for soybean crops in Brazil, the savings from not using nitrogen fertilizers total BRL 24.9 billion per year, about US$ 10.3 billion.
In Brazil, the most important crops both in terms of the area they occupy and of high fertilizer consumption are those that can benefit from biological processes such as the BNF to some extent, namely: soybeans, sugarcane, maize, beans + cowpeas, rice, and wheat. Together, these crops occupy 61.3 million hectares (Mha) and consume 1,890 million tons (Mt) of nitrogen fertilizers. It is estimated that in 2030 the area cultivated with these crops exceeds 70 Mha and the nitrogen fertilizer consumption will be more than 2.5 Mt.
It is important to mention that studies on nitrogen balance in Brazilian agriculture, considering total exports from the harvested products and input of nitrogen via fertilizers and BNF, show that soil is still one of the most important N sources for crops, covering about 40% of the N exported, from which one can deduce the great environmental impact caused by loss of soil organic matter and emission of significant amounts of CO2 into the atmosphere. This phenomenon is especially critical for Family Farming, in which the N input is much lower – this sector of the economy is precisely the one that in which microbiological techniques (BNF, etc) are the most needed.
These high figures for nitrogen fertilizer consumption in agriculture are today a major concern, both because it is associated with significant greenhouse gas (GHG) emissions and due to the high costs related to the oil cost and to the aggravating fact that about 70% of nitrogen fertilizers used in the Brazil are imported. GHG emissions associated with nitrogen fertilizers are related to chemical synthesis, transportation, N conversion in the soil, and emissions of nitrous oxide, which is a potent GHG.
As is the case for the current average soybean productivity levels in Brazil, in which inoculation with diazotrophic bacteria can meet the crop's demand for nitrogen, other species, such as beans, cowpeas, sugarcane, maize, rice, and wheat can also benefited from this technology. It is expected that the intensification of research in the area by 2020 can provide inoculants and management practices that use BNF to partially or totally reduce the amounts of fertilizer applied to legumes, grasses, and other species of interest. This will result in greater participation of the biological process to decrease the use of N fertilizers, and will contribute to the insertion of agriculture within a context of green economy, with high productivity levels, low costs, and low environmental impact. Regarding this issue, it should be noted that, with the exception of soybean crops, inoculants have currently been applied in only 10% of cultivated areas.
Moreover, with regard to environmental benefits, BNF is a technology that can give important support for the efforts of rehabilitating degraded areas, especially where the sustainable use of the soil is not so common and there has been previous loss of soil organic matter and productivity. The establishment of a new environmental law in Brazil (law 12,651/2012) has stipulated the rehabilitation of a significant extension of permanent preservation and legal reserve areas, and native tree species with BNF potential have a prominent role in plantations with this purpose since they are considered main structural species ("framework species").
Brazil's commitment at the 15th Conference of the parties (COP15) contemplated a 5.5 Mha expansion in the use of BNF, which would lead to a reduction in emissions of 10 million annual tons of CO2 equivalent by 2020. It is understood that the goal is solely oriented by the direct decrease in the use of N fertilizers with the cultivation of N2-fixing species. However, new contributions can also be made within the context of the ABC Plan (low-carbon agriculture), including the use of BNF in the rehabilitation of degraded pastures, No-Till Farming Systems (NTFS) and Integrated Crop-Livestock-Forest Systems (ICLFS).
In the international scenario, the outlook is worrying, not only by the fact that 70% of nitrogen fertilizers are imported, but also by the emergence of large international competitors to these inputs, such as China and India. In addition to the direct contribution of BNF, micro-organisms can also provide higher efficiency in the use of N fertilizers, for instance, by promoting root growth.
The introduction of leguminous plants as green fertilizers in crop rotation, crop succession, or intercropping, besides increasing crop productivity, results in higher amounts of organic matter back to the soil, which provides higher carbon (C) sequestration, especially in conservationist systems – such as NTFS and ICLFS – where a decrease in soil revolving contributes to increasing the quantity of organic matter.
From a social standpoint, the population growth and food security scenarios indicate that, in 2030, the world population is expected to reach 8.3 billion inhabitants, causing a 40% increase in the global demand for food. To deal with this scenario, it is necessary to optimize the production of food , textile fibers, oilseeds, and meat based on the adoption of good agricultural practices, of which BNF stands out by providing nitrogen that can be absorbed by plants.
The social gain from BNF technology becomes even more evident in the context of family farming, which now represents 84.4% of Brazilian rural establishments and 24.3% of the total cultivated area, where the adoption of technology can improve income generation and quality of life of families of this agricultural segment. As examples, we can cite bean and cowpea crops, whose main producers are linked to family farming.
It is worth noting that BNF has always stood out as a biotechnological innovation, for instance, in terms of the advances related to the formulation of high-efficiency inoculants, and large demands are expected for the years to come, including the development of multiple inoculants, selection of new strains, research to improve basic knowledge and future technologies such as nanobiotechnology.
Finally, it is relevant to mention that BNF is in full harmony with other relevant national government programs, including Brasil Sem Miséria [Brazil Without Extreme Poverty], Arco Verde [Green Arc], Green Economy, and demands generated by Brazil's new forest code and other clean technologies demanded by society.
Relevant developments for the innovation market
- Availability of new cultivars/varieties (sugarcane, maize, beans, soybeans, wheat, rice, and forage grasses) that are responsive to BNF;
- Availability of new strains, inoculants, and inoculation methods to increase the efficiency of BNF in crops of agricultural interest;
- Development of machinery for the inoculation of diazotrophic bacteria in seeds (nanotechnology), in their furrows, or in leaves;
- Development of protocols for the use of inoculants and defensive substances;
- Advances in studies of structural and functional genomics associated with bioprospecting of genes which can contribute to an increase in the efficiency of plant/bacteria interaction in agriculture;
- Practical application of BNF in different management systems, especially NTFS, ICLS and ICLFS;
- Adoption of practices involving legumes associated with inoculation with diazotrophic bacteria and mycorrhizal fungi in programs for the recovery of degraded areas and to meet the Brazilian forest code;
- Seleção de estirpes de bactérias associadas a genótipos altamente eficientes em fixar nitrogênio em condições adversas de solo e clima;
- Selection of bacteria strains associated with highly-efficient genotypes that fix nitrogen under adverse soil and climate conditions.
- Technologies for the inoculation of multifunctional micro-organisms in legumes and grasses to obtain biofortified foods (i.e. foods enriched with proteins, P, Zn, Fe, etc.);
- Expansion of BNF in Brazil with actions by public-private partnerships, in order to promote social, economic, and environmental benefits, and improve farmers' access to this technology;
- Development of simplified inoculant production procedures for agricultural areas of limited access, especially for family farming.