nitrogen cycle
The cycle of chemical changes exchanging nitrogen
between the air and the soil. Nitrogen
fixation – industrial (producing fertilizers)
or by microorganisms – yields combined nitrogen as ammonia
or nitrates, which can be absorbed from
the soil by plants, which use them to make protein.
Animals ingest nitrogen by eating these plants. Excretion
products and animal and plant remains return nitrogen to the soil as complex
compounds which are converted by fungi and
bacteria to ammonium salts, which may then
be oxidized to nitrites and nitrates by other bacteria. These are either
reused by plants, or converted to nitrogen (by denitrifying bacteria) which
returns to the air, thus completing the cycle.
Related
category
• ECOLOGY
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