nitrogen fixation

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nitrogen fixation

1. the conversion of atmospheric nitrogen into nitrogen compounds by certain bacteria, such as Rhizobium in the root nodules of legumes
2. a process, such as the Haber process, in which atmospheric nitrogen is converted into a nitrogen compound, used esp for the manufacture of fertilizer

Nitrogen Fixation


the process of binding molecular atmospheric nitrogen (N2) and converting it to nitrogenous compounds. Nitrogen fixation is accomplished by nitrogen-fixing microorganisms, including Rhizobia and other microorganisms (bacteria, actinomycetes, yeasts, fungi, and blue-green algae) that inhabit the soil, freshwater bodies, seas, and oceans.

Nitrogen fixation is a very important biological process, playing a large role in the nitrogen cycle in nature and enriching the soil and ponds with bound nitrogen. The atmosphere covering 1 hectare (ha) of ground contains over 70,000 tons of free nitrogen, and it is only as a result of nitrogen fixation that a portion of this becomes available to higher plants. Free-living nitrogen-fixing bacteria bind several tens of kilograms of nitrogen per ha per year. Blue-green algae in rice fields bind up to 200 kg per ha per year. The overall increase in nitrogen (in above-ground organs and postharvest residues) with legume culture is 57.5–335 kg per ha per year. The quantity of nitrogen carried into the soil by legumes because of the activity of Rhizobia amounts to 100–250 kg per ha in a season. Naturally, this process has great significance for the improvement of soil and for increasing the yield of agricultural crops. It is for this purpose that legume seeds are mixed with Rhizobium preparations before sowing, legumes are used as predecessors to cereal grains in crop rotation, corn is sown with clover, vetch is sown with oats, and so forth.

Research on the mechanism of nitrogen fixation is very important. As far back as 1894, S. N. Vinogradskii suggested that ammonia was formed as a result of nitrogen fixation. This proposition has been confirmed by contemporary research methods, including the use of a heavy isotope of nitrogen (N15). A. N. Bakh assumed in 1934 that nitrogen fixation is a result of the conjugative effect of oxidation-reduction enzymes. It has been established that the reduction of molecular nitrogen (N2) to ammonia (NH3) occurs with the participation of an enzyme system containing iron, molybdenum, and magnesium and functioning as a carrier of electrons to the N2. Nitrogen-fixing enzyme systems catalyze the reduction of N2 in the presence of an energy source—adenosine triphosphate (ATP)—and a reducing agent—for example, molecular hydrogen (H2), or a hydrosulfite (Na2S2O4). Thus, nitrogen fixation does not require oxygen in the proper sense and is a reductive process.


Kretovich, V. L., and B. I. Liubimov. “Biokhimiia fiksatsii azota.” Priroda, 1964, no. 12. Pages 14–21.
Mishustin, E. N., and V. K. Shi’ nikova. Biologicheskaia fiksatsiia atmosfernogo azota. Moscow, 1968.


nitrogen fixation

[′nī·trə·jən ‚fik¦sā·shən]
(chemical engineering)
Conversion of atmospheric nitrogen into compounds such as ammonia, calcium cyanamide, or nitrogen oxides by chemical or electric-arc processes.
Assimilation of atmospheric nitrogen by heterotrophic bacteria. Also known as dinitrogen fixation.
References in periodicals archive ?
The isolate ST-B2 was capable of growth on the Burks medium agar, a typical nitrogen free medium generally used for classification of nitrogen fixing bacteria (Fig.
Banding pattern of that cultures started from 24 hrs and intensity of protein bands were gradually increased with the increasing time that means when increasing the growth period of culture their specific nitrogen fixing protein intensity increases.
Root nodules, a habitat of nitrogen fixing bacteria, of different plants such as Sesbania concolor (Tingin), Trifolium alexandrinum (Berseem), Iresine herbstii (Laljhari) and Dahlia sp.
Nitrogen fixing were the majorly consumed biofertilizers in the industry in 2012, accounting for over 78% of the global demand.
Nitrogen fixing activity was assayed by growing the culture in N-free medium (Biological [N.
Mycorrhizas and their significance in nodulating nitrogen fixing plants.
Current research is however focused on isolation and selection of wild strains of agriculturally important microorganisms, screening and evaluating the pH tolerance, nitrogen fixing ability and p-solubilizing ability.
Although they may be fast growing and nitrogen fixing, they're also toxic to livestock.
Analysis of regulation of Klebisiella pneumonia nitrogen fixing (nif) gene cluster with gene fusions.
Finally, we investigated the diversity of putative nitrogen fixing bacteria within the oral flora.
Some other areas discussed include the role of growth-promoting rhizobacteria and symbiotic nitrogen fixing bacteria in the improvement of plant health in metal contaminated soils, and pesticides affecting both microbial communities of soils and certain agronomic crops.