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In the 1960s, the United States built its soybean industry by pouring chemical nitrogen fertilisers into the soil. Brazil took a different path. Instead of buying chemicals, an agronomist named Johanna Döbereiner looked at the roots of the plants.
She proved that soybeans could get all the nitrogen they needed directly from the air, using bacteria that live in their roots. Her work changed tropical agriculture and saves Brazil over $2 billion every year (Embrapa).
Why do soybeans need nitrogen?
Nitrogen is a fundamental building block of life. Plants need it to make amino acids, which join together to form proteins. Because soybeans are grown specifically for their high protein content, they need large amounts of nitrogen to thrive. Plant growth is heavily dependent on nutrient availability, a concept detailed in Justus von Liebig's law of the minimum.
Most of the atmosphere is nitrogen gas, but plants cannot use it in this form. The triple bond holding the two nitrogen atoms together is exceptionally strong and too difficult for the plant to break on its own. To absorb nitrogen, the plant needs it "fixed" into a usable form, such as ammonia or nitrate.
How did chemical fertilisers change farming?
To meet the demand for nitrogen in agriculture, factories produce chemical fertilisers by forcing nitrogen from the air to react with hydrogen under extreme heat and pressure. This process allows farmers to add artificial nitrogen directly to the soil, which has boosted crop yields worldwide for decades.
But this heavy reliance on chemical intervention has significant downsides:
Cost: Making chemical fertiliser requires massive amounts of fossil fuel energy, making it expensive to produce and transport to farms.
Pollution: When it rains, excess fertiliser washes away from the fields into rivers and lakes, polluting water systems and harming aquatic ecosystems.
How did Johanna Döbereiner change soybean farming?
Johanna Döbereiner was a dedicated researcher at Embrapa, the Brazilian Agricultural Research Corporation. Starting in 1964, her work influenced Brazil's soybean breeding programme, guiding it away from the chemical-heavy approach used in the US (Embrapa).
Döbereiner focused on biological nitrogen fixation. Legumes like soybeans have a natural ability to partner with *Rhizobium* bacteria in the soil. The bacteria enter the plant's roots through root hairs and form small, visible bumps called nodules. Inside these nodules, the bacteria fix nitrogen from the air and feed it to the plant. In return, the plant gives the bacteria sugars it has made through photosynthesis. It is a perfect symbiotic relationship.
Döbereiner's team identified the most efficient bacterial strains for Brazil's hot, acidic tropical soils. They developed practical ways to coat soybean seeds with these specific bacteria before planting. Because of her work, Brazilian farmers grow soybeans without adding any chemical nitrogen fertiliser. This natural process provides all the nitrogen the crop needs, saving Brazil over $2 billion annually (Embrapa).
Over her career, Döbereiner published more than 500 papers and discovered nine new species of nitrogen-fixing bacteria, just as other pioneers like Hans Christian Gram found new ways to classify microbes. She was nominated for the Nobel Prize in Chemistry and remains one of the most important scientists in Brazil's history (Embrapa).
How can you learn biological cycles?
Döbereiner's work is a great example of solving a large-scale global problem by understanding biology at the microscopic level. If you are studying biology, simply memorising isolated facts about bacteria is not enough. You need to understand how the concepts connect to each other.
If you struggle to picture how bacteria interact with plant roots or how the nitrogen cycle works in practice, the Fermi Simulation Lab has interactive simulations for the ideas that are easier to see than to read. When you need to review the specific steps of biological nitrogen fixation or the role of leguminous plants, you can look them up in the Fermi Concept Library, which covers every concept in physics, chemistry, biology, mathematics and computing.
