Nitrogen cycle.ppt

Nitrogen cycle

1. Nitrogen Cycle
Dr. S. Sivasankara Narayani., M.Sc.,M.Phil.,Ph.D., MRSB (UK)

2. Intro
•Nitrogeniskeynutrientforplants.
•Theabundantnitrogenintheatmospherecannotbeuseddirectlybyplantsoranimals.
•Nitrogencycleisabiogeochemicalprocessthroughwhichnitrogenisconvertedintomany
forms,consecutivelypassingfromtheatmospheretothesoiltoorganismandbackintothe
atmosphere.
•Definition:“Nitrogencycleisabiogeochemicalprocesswhichtransfomstheinertnitrogen
presentintheatmospheretoamoreusableforrmforlivingorganism

3. Nitrogen Gas types
•Organic
•Itexistinlivingorganism.
•Theygetpassedthroughfood
chainbytheconsumptionofother
livingorganisms
•Inorganic
•Abundantinatmosphere
•Nitrogenismadeavailabletoplants
bysymbioticbacteriawhichconvert
theinertnitrogenintoausable
formsuchasnitritesandnitrates

4. Stages
•Nitrogen fixation
•Nitrification
•Assimilation
•Ammonification
•Denitrification

6. Nitrogen Fixation
•Initial step
•N
2 -------NH
3
•Inert form is deposited into soils from the atmosphere and surface waters, through
precipitation.
•Two nitrogen atoms get separated and combines with hydrogen to form ammonia (NH4+).

7. Cont…
•Entire process of nitrogen fixation is completely by symbiotic bacteria which
are known as Diazotrophs.
•Ex: Azotobacter , Rhizobium
•Nitrogenase enzyme –N + H = Ammonia

8. Types
•Atmospheric Fixation
•Lightning breaks nitrogen into nitrogen oxides –used by plants
•Industrial mode
•Direct combination of nitrogen and hydrogen to produce ammonia
•Converted into various fertilisers such as Urea.
•Biological
•Rhizobium and Blue green algae

9. Nitrification
•Ammonia is converted into nitrate
•Nitrites are formed by oxidation of ammonia by Nitrosomonas
•Nitrites are converted into nitrates by Nitrobacter
2NH
4
+
+ 3NO
2 2NO
2
-
+ 4H
+
+ 2H
2O
2NO
2
-
+ O
2 2NO
3
-

10. Assimilation
•Plants -ammonia, nitrite ions, nitrate ions or ammonium ions
•Used in the formation of plant and animal proteins
•Enters the food web

11. Ammonification
•Plant or animal die –released into soil
•decomposers –bacteria and fungi -convert organic matter back into
ammonium.
•Used for the biological process

12. Denitrification
•Conversion of nitrate into gaseous nitrogen.
•Occurs in the absence of oxygen
•Done by Denitrifying bacterial species –Clostridium and Pseudomonas
•Organism will process nitrate to gain oxygen and gives out free nitrogen gas as
byproduct.

13. Importance
•Synthesis Chlorophyll
•Decomposition
•Enriching the soil –with esseential nutrients required for cultivation.

14. 12-07-2023Dr.SS