Microbiology of Soils
Nitrogen fixation by the microorganisms can be detected by adopting the approach of

demonstrating growth in a nitrogen free medium
measuring15N2 by mass spectrometer
All of these
cultivating the microorganisms in the presence of nitrogen labeled with isotropic nitrogen

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Microbiology of Soils
Denitrification is

changing of atmospheric nitrogen (N2) to nitrogen compounds
reduction of nitrate to organic nitrogen compounds
both (a) and (b)
reduction of nitrate (NO3-) to nitrogen gas

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Microbiology of Soils
Nitrogen fixation

fix the free nitrogen (N2) by which it should not be usable by plants
both (a) and (b)
changes the free nitrogen (N2) to a form usable by plants
especially changes nitrogen compounds, mostly amines such as NH2

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