Nitrogen cycle and processes involved in this...

1. Nitrogen Cycle

2. Introduction
The sequence of biochemical changes
undergone by nitrogen wherein it is used
by a living organism, liberated upon the
death and decompositions of the
organisms and converted ultimately to
its original oxidation state.

3. Overview of the nitrogen cycle, showing major pools
(shaded areas) and transformations (lines) of N.

4. Processes Involved in N-Cycle
• Mineralization
• Immobilization
• Aminization
• Ammonification
• Nutrification
• Biological Nitrogen Fixation
• Denitrification
• Leaching

5. Mineralization
The conversion of nitrogen from its organic form to
inorganic form as a result of microbial activity

6. Immobilization
Conversion of nitrogen from its inorganic form to organic
form in microbial or plant tissues.

7. Aminization
It is the conversion of protein into amino acids and amides
by heterotrophic (use organic substances as energy source)
microbes.

8. Ammonification
It is the conversion of amino acids and other N-containing compounds
into NH4 form of nitrogen.
Fate of NH4 released during ammonification process
• Can be taken up by plants and microorganisms
• Can be adsorbed on exchange complex
• Can be fixed by 2:1 type clay minerals
• Some NH4 can be lost as NH3 through volatilization can be Nitrified

9. Nitrification
It is the biological oxidation of NH4 to NO2 and then to NO3 by
autotrophic (use inorganic substances as energy source) soil
bacteria under aerobic conditions.
This NO3 can undergo (Fate of nitrate)
• Up take by plants and microbes
• Denitrification under anaerobic conditions
• Leaching

10. Ammonia Volatilization
Mass transfer of N as ammonia gas from soil, plant, or liquid systems
to the atmosphere. This is particularly important when fertilizer
salts containing Ammonium salts (e.g. Urea) are applied on the
surface of an alkaline soil at high temperature.

11. Ammonium Fixation
It is the entrapment of NH4 in the interlayer spaces of some clay
minerals such as illite.

12. Biological Nitrogen Fixation
Next to photosynthesis, biological nitrogen fixation is probably the
most important biochemical reaction for life on earth. Through this
process, certain organisms (called diazotrophs) convert the inert
dinitrogen gas of the atmosphere (N2) to ammonia with the help of
an enzyme called nitrogenase. The ammonia changes to ammonium
and becomes available to plants. The process is carried out by
limited number of microorganisms, including several species of
bacteria, a number of actinomycetes, and cyanobacteria (blue
green algae). Nitrogen fixing microbes can exist as free living or in
association with other microbes or plants

13. Denitrification
This is the biological reduction of NO3 or NO2 to molecular N (N2) or
nitrous oxide (N2O) by microbial activity under ananerobic
conditions. The N2 or N2O thus produced are lost to the atmosphere.

14. Leaching
The removal of nitrogen especially NO3-N out of root zone in
solution by downward movement of water through the soil.

15. N-Balance Sheet
Gain and Losses of Soil Nitrogen
Gains Losses
1. Biological nitrogen fixation
2. Industrial fixation (chemical fertilizers)
3. Crop residues, manures etc.
4. Electrical discharge
1. Crop removal
2. Leaching
3. Volatilization
4. Denitrification
5. Immobilization (for the time being)