Brazil Farmers Plant Legumes as Mini-fertilizer Factories

All living things need nitrogen to survive. Humans and animals are able to take in nitrogen from the air; most plants can only absorb nitrogen from the soil. Thus, the expensive commercial nitrogen fertilizers, if not used properly, can evaporate into the air as a greenhouse gas, which then contributes to climate change, or leach into the soil, polluting water supplies. Legumes offer a way to greatly decrease these side effects. The nodules on their roots act as mini-factories – and the factories’ output is nitrogen-rich fertile soil.

It all starts with planting a field of legumes. Through a biological process, the nodules on the roots are able to capture nitrogen from the air, which enables the plant to grow. When the legumes are harvested, not only does the yield provide food and income for the farmer, it leaves nitrogen-rich residue behind in the field. As that residue decomposes, the nitrogen in the nodules become incorporated into the soil as a natural fertilizer – a green manure – that will be there to nourish the next crop – meaning the farmer will be able to use less or even no chemical fertilizer for the next cropping season.

Although farmers have long recognized that planting certain crops would improve soil fertility, they didn’t understand why and they didn’t know the best way to take advantage of this natural phenomenon. Since the 1970s, the Joint FAO/IAEA Division has focused on improving the process of nitrogen fixation and thereby farmer’s success, working through national and regional field projects and coordinated research projects to identify the most suitable legumes for different regions and agro-ecosystems of the world, and then disseminating the technology through training, fellowships and workshops. Using nuclear tracing methods based on the nitrogen-15 isotope, they have also studied the impact of chemical fertilizers and, in turn, provided farmers with information on how to use them more efficiently and economically without fear of unduly harming the environment.

Through its work, the Joint Division has helped make nitrogen fixation an important part of soil management systems. It now supports an international network of scientists who share information and promote these natural, no-cost bio-fertilizers across the spectrum of agricultural systems.
 

In 2016–2017, Brazil’s total grain production reached 230 million tonnes on 58 million hectares. Of that, almost 1 million hectares were farmed as organic, and that number is expected to increase. It is estimated that less than 20 percent of the nitrogen used by plants in Brazilian agriculture comes from chemical fertilizer and the rest from nitrogen fixation, particularly from soybean fields. Considering that the natural nitrogen can remain in the field for up to two planting seasons, farmers can intercrop, growing non-legume crops in alternating seasons to take advantage of the nitrogen that has been left behind.

This translates into enormous savings. Each year, Brazil’s farmers are able to use 7.5 million tonnes of natural nitrogen that comes from nitrogen fixation. That equals a savings of USD 13 billion, because that’s what it would cost to buy the same amount of chemical nitrogen fertilizer. In addition, farmers who employ nitrogen fixation have healthier soils and can greatly decrease the expense of purchasing chemical fertilizer. And with that, the risk of emission of greenhouse gasses and the fear of water pollution is reduced. It is a win-win for the farmers and the planet.