The document summarizes the nitrogen cycle. It discusses the main sources of nitrogen including the atmosphere, soil, fertilizers and volcanic activity. It then describes the key processes in the nitrogen cycle including nitrogen fixation, ammonification, nitrification, and denitrification. Nitrogen fixation occurs through symbiotic and non-symbiotic bacteria. Ammonification and nitrification are multi-step biological processes converting organic and ammonia forms of nitrogen into nitrites and nitrates. Denitrification returns nitrogen to the atmosphere through bacteria. The factors that impact these nitrogen transformations such as oxygen, temperature, pH and carbon levels are also outlined.

1. R. THULASI MEENAKSHI

3. Sources of Nitrogen
 Atmosphere- 78%
 Soil and rocks- non exchangable form
 Inorganic nitrogen ions- ammonia, nitrites and
nitrates
 Humus
 Fertilisers
 Volcanic activity

4. Nitrogen cycle
Immobilisation
Nitrogen
Fixation
Denitrification
Mineralisation
Ammonification
and Nitrification

5. NITROGEN FIXATION
 Two types of nitrogen fixation biologically
1. symbiotic relationship- with the root- nodules
eg. Rhizobium.
2. Asymbiotic fixation- free living bact.
eg. Azotobacter, beijernicka
 Environmental fixation
 Human activities

6. AMMONIFICATION
 Organic N  NH4
+
 Ammonifiers are involved- decomposers
 Protein  Amino acids  Proteases
Bacteria- Pseudomonas, Bacillus,
Clostridium, Serratia
Fungi- Alternaria, Mucor, Aspergillus
 Urea Urease – Bacillus, Proteus, Micrococcus,
Sarcina etc
 Amines Amino oxidases- Mycobacterium,
Pseudomonas, Protoaminobacter
 Amides Amidase - Chlorella
 Nucleic acid Ribonucleases, Deoxyribonucleases

7. NITRIFICATION
Ammonia is converted into nitrite and
then nitrite.
NH3 or NH4
+ --> NO2
- --> NO3
-
Two step process- 1. Ammonium oxidation
2. Nitrite oxidation

8. AMMONIUM OXIDATION
 NH3  NO2
 Immediate oxidation process
 Bacteria are chemolithotropic, gram –ve, motile,
rod, non spore forming
 Nitrosomonas, Nitrosococcus, Nitrosolobus etc.

9. NITRITE OXIDATION
 NO2 NO3
 Bact involved- Nitrobacter, Nitrospira etc
 Aerobic, g –ve, spherical, or spiral shaped
 Ph- 5.8-8.5
 Opt temp- 28*c

10. Factors affecting nitrification
 Acidity- slow activity
 Oxygen- obligate
 Moisture
 Temperature- 30* -35*c
 Waste- C:N ratio – faster in low C:N ratio
FATE OF NO3-
Assmilated by plants, leached, eutrophication,
infant methaemoglobinemia

11. DENITRIFICATION
 Last step
 Replenishing N2 to atmosphere
 The reaction involved is
2HNO3  2HNO2 NO  N2O  N2
 Enzyme involved nitrate reductase or nitratase.
E.coli, Pseudomonas aeruginosa, Micrococcus
denitrificans

12. Factors affecting denitrification
 Slow in low carbon than on land that is rich in
organic matter
 When soil is water logged, loss of nitrogen is
more when compared to well-drained soils which
is due to the immobilisation of inorganic nitrogen.
 Aeration affects the transformation in two ways-
1. Denitrification proceeds only when the oxygen
supply is insufficient to satisfy the demand.
2. Oxygen is necessary for the formation of nitrites
and nitrates which are essential for
denitrification.
 Sensitive in high hydrogen ion conc.
 Optimum temp – 25*c -60*c

13. THANK YOU