Nitrogen Cycle

• Nitrogen Fixation
  • N₂ is most stable form of Nitrogen
  • N₂ + 8H→ 2NH₃ +H₂
  • Most Nitrogen on earth is “fixed”
    • Combined with other elements NH₃ or NO₃^–

Dentrification

• Reduction of NO₃^– to gaseous nitrogen compounds
  • How N₂ and N₂O are formed
• Can be detrimental
• Aids in wastewater treatment
• Can also contribute to global warming
  • O₃ destruction- increases passage of UV radiation to the surface of Earth

Ammonification

• Ammonia released during decomposition of organic nitrogen compounds
  • Amino acids and nucleotides
• Reduction of NO₃^– to NH₃ (dissimilative reduction of nitrate to ammonia
• At neutral pH NH₃ exists as NH₄⁺
• NH₃ is volatile
  • Can be lost from alkaline soils by vaporization and there are major losses of NH₃ to the atmosphere in areas with dense animal populations

Nitrification and Anammox

• Nitrification major process in well drained oxic soils at neutral pH
  • Nitrification of prokaryotes
• Two step process
  • NH₃ to NO₂^–
  • NO₂^– to NO₃^–
• NO₃^– is readily assimilated by plants
  • Readily soluble
  • Nitrification is not beneficial for plant agriculture
• Ammonium is positively charged and strongly adsorbed to negatively charged soils
• Ammonia can be oxidized under anoxic conditions by Brocadia(Bacterium) by a process called anammox
• NH₃ is oxidized anaerobically with NO₂^–as the electron acceptor
  • N₂ is final product
  • Anammox is a major process in sewage and in anoxic marine basins and sediments, but significant in well-drained soils