Nitrogen cycle

• Main processes

  • Ionisation
  • Fixation
  • Food chains
  • Nitrification
  • Denitrification
  • Leaching
  • Root absorption
  • Ammonification
• Ionisation - Processes such as lightning and meteor trails provide the energy for atmospheric nitrogen and oxygen to react and produce oxides of nitrogen
• Fixation - some micro-organisms can chemically reduce nitrogen to ammonia. they may be free-living bacteria in the soil, or they may live symbiotically in the root nodules of legumes
• Nitrification - involves the oxidation of ammonium ions to nitrites, then to nitrates by nitrifying bacteria in the soil
• Denitrification - The chemical reduction of nitrates in soil to nitrogen and nitrogen oxide gases, by denitrifying bacteria in the soil, reduces soil fertility. This normally occurs under anaerobic conditions.
• Leaching - The high solubility of nitrates means they are easily leached out of soils into water bodies where they act as nutrients for aquatic plants and algae
• Root absorption - Plants absorb nitrogen as soluble ions, mainly as nitrates but also as ammonium ions
• Ammonification - The amino groups in proteins are released as ammonium ions by the action of bacteria, fungi, and detritovores as they decompose dead organic matter
• Human impacts on the nitrogen cycle:

  • Haber process (industrial production of ammonia)
  • Agriculture
  • Pollution
• Sustainable management of the nitrogen cycle

  • Control of combustion processes
  • Control of NOx releases
  • Management of biological wastes
  • Eutrophication
  • Organic fertilisers
  • Management of soil processes