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5 Differences between Nitrogen fixation and Nitrification

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
5 Differences between Nitrogen fixation and Nitrification
Nitrogen fixation
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 

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)
Nitrification is a major step in the nitrogen cycle in soil where soil ammonia (NH3) is converted to soil nitrate (NO3-)
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
Nitrification is the biological oxidation of ammonia (NH3) to nitrite (NO2-) and then to nitrate (NO3-) by nitrifying bacteria
The microorganisms involved in Nitrogen fixation are called nitrogen fixers or diazotrophs
The microorganisms involved in Nitrification are called nitrifying bacteria
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.
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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