processes

• ionisation


  lightning and meteor trails provide energy for atmospheric nitrogen
• fixation


  some micro-organisms can chemically reduce nitrogen to ammonia

  -> may be bacteria living in the soil or in the root nodules of legumes
• food chains


  nitrogen passes between organisms as amino acids and proteins in food
• nitrification


  involves the oxidation of ammonium ions to nitrites then to nitrates by nitrifying bacteria in the soul
• denitrification


  chemical reduction of nitrates in soil to nitrogen reduces soil fertility

  -> by denitrifying bacteria

  -> occurs under anaerobic conditions