Microbiology of Soils
Nitrogen fixation

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

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Microbiology of Soils
Nitrogen oxidation (nitrification)refers to the

sulfur is oxidized to the sulfate form through Thiobacillus bacteria
changing of atmospheric nitrogen (N2) to nitrogen compounds
conversion of ammonium ions into nitrates through the activities of certain bacteria.
None of these

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