Nitrogen cycle is a continuous series of natural processes by
which nitrogen passes successively from air to soil to organisms and back to
air or soil involving principally nitrogen fixation, nitrification, decay, and
denitrification.
The major processes in nitrogen fixation are
1. Nitrogen fixation:
Conversion of atmospheric nitrogen to ammonia (NH3) in soil
N2 + 8 H+ + 8 e−+ 16 ATP → 2 NH3 + H2 +16 ADP +16 Pi
2. Nitrification:
biological oxidation of ammonia (NH3) to nitrite (NO2-)
and then to nitrate (NO3-)
3. Nitrate assimilation: Soil nitrate (NO3-) used
by plants for synthesis of N containing biomolecules like proteins, nucleic
acids
4. Ammonification: Formation of ammonia (NH3) from
N containing biomolecules of dead organisms
5. Denitrification and Anammox. : Reversal of nitrification
where nitrate (NO3-) is converted to N2 and released to atmosphere
Refer this post for simple step wise explanation: 5 steps in N2 cycle with notes on Anammox
Nitrogen fixation
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Nitrification
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Nitrogen
fixation is the conversion of nitrogen (N2) to ammonia (NH3) or
compounds that can be readily utilized by plants for the synthesis of
nitrogen containing bio-molecules like amino acids, nucleic acids etc
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It
is a two step process that converts ammonia (NH3) to nitrate (NO3-)
|
Nitrogen
fixation is the first step in nitrogen cycle that fix atmospheric nitrogen to
soil as ammonia (NH3)
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Nitrification
is a major step in the nitrogen cycle in soil where soil ammonia (NH3)
is converted to soil nitrate (NO3-)
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Nitrogen
fixation occurs by a) biological Nitrogen Fixation, b) non-biological N2
fixation by lightning, volcanic eruptions etc and c) Industrial N2 fixation
called Haber-Bosch process. More than 70% of Nitrogen is fixed by biological
methods
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Nitrification
is the biological oxidation of ammonia (NH3) to nitrite (NO2-)
and then to nitrate (NO3-) by nitrifying bacteria
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The
microorganisms involved in Nitrogen fixation are called nitrogen fixers or
diazotrophs
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The
microorganisms involved in Nitrification are called nitrifying bacteria
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Nitrogen
fixers are either symbiotic or free living.
Nitrogen
fixers include some bacteria like Rhizobium
in symbiotic association with leguminous plants, blue green algae like Anabaena and lichens like Collema.
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Nitrification
is carried out by two groups of bacteria; nitrite bacteria like Nitrosomonas which converts ammonia
(NH3) to nitrite (NO2-) and nitrate bacteria like Nitrobacter that converts nitrite (NO2-)
to nitrate (NO3-)
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its really cleared my confusion
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