Pathways for loss of Nitrogen :

a) Leaching and runoff

b) Denitrification

c) Ammonium volatalization

d) Ammonium fixation

a) Leaching and runoff :

• Nitrogen is available in two forms in soil solution : ammonical (NH₄⁺) and nitrate (NO₃^–) ions.
• The loss of nitrogen is more in nitrate form as compared to ammonical form.
• Negatively charged nitrate ions are not easily adsorbed by negatively charged soil colloids.
• Hence , nitrate ions free move laterally along with drainage water and are loosed by runoff.

b) Denitrification :

• It is the anaerobic process in soil system , where the nitrate ions (NO₃^–) are reduced to elemental nitrogen (N₂) in the presence of denitrifying bacteria and lost to the atmosphere in gaseous form.
• Denitrifying bacteria are Bacillus , Pseudomonas , Micro-coccus , etc.
• Nitrogen loss is due to denitrification , is most common in low land rice where fertilizer is flooded for no. of days.

                                  Fig : Nitrification and denitrification process

c) Ammonia volatilization :

• Loss of ammonium source of fertilizer in the form of ammonia gas in the atmoshphere.

                   Fig : Ammonia volatilization

d) Ammonia fixation :

• Ammonium ions absorbed with negatively charged soil collides and become fixed within the cavities of clay structure.
• These ions aren’t easily available for plants.