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.

REFERENCES

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.

V. L. KREMOVICH and V. I. LIUBIMOV

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.
(microbiology)
Assimilation of atmospheric nitrogen by heterotrophic bacteria. Also known as dinitrogen fixation.
References in periodicals archive ?
Although there is an availability of exotic species with high efficiency in nitrogen fixation for several legume species, selection of native strains provides perspectives to broad the exploration of new isolates adapted to dry environments, favoring low responsive cultivars to commercial isolates.
Excess amount of nitrogen in the solution may be utilized for cell metabolism of the bacteria rather than nitrogen fixation process.
Nitrogen fixation is energetically expensive, and plants pay for it by supplying sugars to the nodules.
Their analysis, which could discern human-derived nitrogen from natural nitrogen fixation, revealed that the oceanic nitrate concentration increased significantly over the last 30 years in surface waters of the North Pacific due largely to the enhanced deposition of nitrogen from the atmosphere.
3b), indicating that the ratio of nitrogen fixation rate to the rate of carbon incorporation into the cells remained constant in all conditions.
At Wileirog, the Jenkinses are aiming for 50-60% rye grass and 20-30% clover in their leys to achieve yield, pasture quality and nitrogen fixation.
Nitrogen fixation is where nitrogen (N2) in the atmosphere is converted into ammonia (NH3).
Among specific topics are oxygenic photosynthesis, molecular chaperons and stress tolerance, sensing and molecular responses to low temperature, regulatory mechanisms in response to osmotic stress, environmental factors regulating nitrogen fixation in heterocystous and non-heterocystous cyanobacteria, the role of spontaneous mutation in adaptations to anthropogenic and natural stress, and benthic Microcystin and climate change.
If he's right, organic farming won't save us because it relies on natural nitrogen fixation.
The resulting material can be used for the preparation of uranium starting materials, to turn nuclear waste into a valuable commodity, or for nitrogen fixation and fertilizer/crop production.