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.
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.
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.