Nitrogen Fixation
. Nitrogen Fixation, biological or industrial process by which molecular atmospheric nitrogen is converted into a chemical compound that is essential for plant growth and is also used in industrial chemical production. BIOLOGICAL FIXATION The most widely used and most productive of the soil microorganisms capable of nitrogen fixation are symbiotic bacteria of the genus Rhizobium, which colonize and form nodules on the roots of leguminous plants such as clover, alfalfa , and peas.. These bacteria obtain food from the legume , which in turn is supplied with abundant nitrogen compounds. Soils are sometimes inoculated with a particular species of Rhizobium to increase a legume crop, which is often planted to replenish the nitrogen depleted by other crops. Much smaller amounts of nitrogen are fixed in the soil by nonsymbiotic (free-living) bacteria such as the aerobes, which function in the presence of oxygen, and bacteria of the genera Klebsiella and Bacillus, which function without oxyge...