Nitrogen Cycle

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Nitrification

  • Nitrification is carried out by nitrifying bacteria in the soil. They convert ammonium ions into nitrite ions (NO2-), and then into nitrate ions (NO3-).
  • This is a oxidation reaction.

  • Oxygen is required for nitrification and so oil is kept aerated by farmers to increase productivity
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Nitrogen Fixation

The process by which nitrogen gas is converted into nitrogen containing compound.The most common forms of nitrogen fixation is carried out by either free-living bacteria found in the soil, or mutualistic bacteria, found on the nodules of plant roots.

  • Free living bacteria – Reduces gaseous nitrogen into ammonia, which they then use to manufacture amino acids. Nitrogen rich compounds are released when they die.

  • Mutualistic nitrogen-fixing bacteria – The bacteria on the nodules require carbohydrates from the plant and in turn they provide the plant with amino acids.
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Denitrification

When there is little oxygen present in soil, there are fewer aerobically respiring nitrogen fixing/nitrifying bacteria and more denitrifying anaerobically respiring bacteria. There denitrifying bacteria convert soil nitrates into gaseous nitrogen.

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Ammonification

  • Production of ammonia from organic ammonium containing compounds.
  • Saprobiotic bacteria feed on the materials (e.g. dead organisms and faeces releasing ammonia which then forms ammonium ions in the soil.
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