Nitrogen fixation

Johan KjeldahlJohan Kjeldahl

Nitrogen fixation

Nitrogen fixation is an essential natural process, in which microorganisms convert the otherwise less-reactive nitrogen into inorganic nitrogen compounds, which in turn first appear in the nutritional chain as organic nitrogen compounds like proteins in plants.

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Nitrogen fixing bacteria live in the root nodules of plantsNitrogen fixing bacteria live in the root nodules of plants

Since the beginning of the twentieth century, when available soil nitrogen, primarily nitrates, proved to be deficient for intensive crop production, so several commercial processes, including the best known Haber-Bosch method for ammonia synthesis, have been developed to produce nitrogen fertilizers.


The achievability of balanced soil chemistry was underscored by the 1956 development of the Kjeldahl method to analyze automatically the amount of existing nitrogen present in organic compounds.

Nitrogen cycle

  1. Nitrogen in atmosphere (N2)
  2. Nitrogen-fixing bacteria in root nodules of legumes
  3. Nitrogen-fixing soil bacteria
  4. Ammonium (NH4)
  5. Nitrifying bacteria
  6. Nitrites (NO2-)
  7. Nitrifying bacteria
  8. Nitrates (NO3-)
  9. Denitrifying bacteria
  10. Decomposers (aerobic and anaerobic bacteria and fungi)

Did you know?

The amount of crop yield mainly—but not exclusively—depends on the soil's nitrogen content.