The nitrogen cycle involves the transformation of nitrogen between its various forms through biological and physical processes. Key steps include nitrogen fixation by bacteria and lightning, ammonification by microbes converting organic nitrogen to ammonia, nitrification of ammonia to nitrites then nitrates, denitrification by bacteria reducing nitrates to nitrogen gas, and assimilation of nitrates by plants. The major reservoir of nitrogen is the atmosphere, with nitrogen-fixing bacteria and cyanobacteria converting atmospheric nitrogen to ammonia or nitrates through symbiotic and non-symbiotic biological nitrogen fixation.

1. Submitted by
Thara .R

2. INTRODUCTION
Two basic types of biogeo chemical cycles.
Gaseous cycle
Sedimentary cycle
 Gaseous cycle – carbon cycle, nitrogen cycle and oxygen cycle.
 Nitrogen is converted between its various chemical forms through following
steps.
1. Nitrogen fixation
2.Ammonic fixation
3.Nitrification
4.De nitrification
5.Assimilation
 Content about 78%
 Essential constituent of plants and animals.
 Plants take up nitrogen either as nitrates or ammonia.
Due to thunderstorm and lightening the gaseous nitrogen is converted in to
nitric oxide.

3. PROCESSES OF NITROGEN CYCLE
 Nitrogen present in variety of forms
 Organic nitrogen, nitrous oxide (NO) or inorganic
nitrogen gas (N2)
 Processes of the nitrogen cycle transforms nitrogen
from one form to another

4. NITROGEN CYCLE
 The major reservoir of nitrogen – Atmosphere
 Various steps involved in this cycle
Nitrogen fixation
 Atmospheric free nitrogen _ Ammonia
Nitrogen fixation are of two type
 None biological fixation
 Biological fixation

5. NONE BIOLOGICAL FIXATION
 Physical process/ high energy fixation
 Two processes
 Natural process ie, photochemical fixation
 Man made process ie, industrial fixation

6. a) Photochemical Fixation/Natural
process
 Dissociation of nitrogen molecule and its combination
with oxygen and hydrogen of water provided by
lightening
 The high energy is required
 It is provided by cosmic radiation and meteorite trails

7. b) Industrial Fixation/ Man
Made Process
 Fertilizers in various industries
 Most chemical fertilizers are nitrates or ammonium
 For agriculture field to yield crop to increase soil
fertility

8. BIOLOGICAL FIXATION
 Carried out by certain bacteria cyanobacteria and few
fungi
 Nitrogen is fixed in the form of ammonia –
Ammonium salts or nitrates
 Nitrogen fixing organisms are called diazotrophs
This process is two type
 Symbiotic nitrogen fixation
 Non-symbiotic nitrogen fixation

9. SYMBIOTIC NITROGEN FIXATION
 Carried out by micro organisms
 Symbiotic nitrogen fixation
 Rhizobium that lives in the root nodules of
leguminous plants.

10. NON SYMBIOTIC NITROGEN FIXATION
 Carried out by micro-organisms.
 Living free in the soil.
Eg:- Bacteria : Basillus, Clostridium Pasteurianum
Aerobicforms: Azotobacter
Blue green algae(cyanobacteria):Nostoc,Anabaena

11. AMMONIFICATION
 Ammonification organic matter converted to
Ammonia
 Heterotrophic bacteria, actinomycetes and fungi
 Organic nitrogen – Inorganic form as ammonia.
 Energy releasing reaction.

12. NITRIFICATION
 Ammonia/ ammonium salts-nitrites and nitrates.
 This process – nitrification.
 NH3 cannot be utilized directly.

13. DE-NITRIFICATION
 Bacteria and fungi convert nitrates – nitrites, nitrous
oxide
 De-nitrification – conversion of nitrates to gaseous
nitrogen gas
 Occur in oxygen depleted water – logged soils.
 Common denitrifying bacteria- Pseudomonas,
Thiobacillus.
NO3 - NO2- NO2 NO N2
(Nitrate) (Nitrite) (Nitrous oxide) (Nitric oxide) (Nitrogen gas)

14. ASSIMILATION
 Principle source of nitrogen for plants – Nitrate ions
and water
 Nitrate assimilation – absorb nitrates for the synthesis
of proteins.

15. CONCLUSION
 Nitrogen is an important components.
 This conversion is a Cyclic process.
 The process of nitrogen cycle transforms nitrogen
from one form to another.