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 ?
2006) investigated the effect of root zone temperature on nodulation and nitrogen fixation of three ecotypes of Zanjan, Ardebil, and Shahrekord in Lathyrus and showed that all three ecotypes at 25[degrees]C had the highest nodulation and nitrogen fixation and the temperatures of 5 and 10[degrees]C decreased nitrogen fixation and nodulation in the studied ecotypes [17].
Peoples MB, Baldock JA (2001) Nitrogen dynamics of pastures: nitrogen fixation inputs, the impact of legumes on soil nitrogen fertility, and the contributions of fixed nitrogen to Australian farming systems.
It is known that under nitrogen fixation conditions the energetic demands are greater and therefore the net growth might be lower.
Uliassi DD, Ruess RW (2002) Limitations to symbiotic nitrogen fixation in primary succession on the Tanana River floodplain.
Changes in fat and moisture contents, and nitrogen fixation in laboratory maintained termites.
Second author Daniel Sigman, Princeton's Dusenbury Professor of Geological and Geophysical Sciences, said that the finding that nitrogen fixation is determined by precession-driven upwelling appears to indicate that the ocean's fixed nitrogen reservoir is resilient and that the ocean biosphere can recover from even the most dramatic ecological changes.
The most common method of industrial nitrogen fixation is the Harber-Bosch process, which requires extremely harsh conditions, 200 atm of pressure and 400 degrees C of temperature.
The carbohydrates formed in photosynthesis are translocated from leaves to nodules in the form of sucrose, whose oxidation leads to the production of the reducers NADH or NADPH and ATP, which are sources of electrons and energy for nitrogen fixation (TAIZ; ZEIGER, 2008).
7) Other anthropogenic sources of reactive nitrogen include industry, transportation, and electricity generation; natural inputs include lightning and bacterial nitrogen fixation.
They are among the few marine microbes that can convert nitrogen gas into organic nitrogen, a process called nitrogen fixation.
The handbook describes primary cover crop species and includes photos, seeding details, winter vigor descriptions, nitrogen fixation and scavenging, weed suppression and nematode resistance.
The world is now starting to understand how in a sustainable context, in a climate change context and in a carbon footprint context, nitrogen fixation from Rhizobium and legumes is something everyone wants to get into their agricultural systems.