Nitrogen Cycle

  • Nitrogen is most abundant element found in the earth’s atmosphere i.e. 78 percent.
  • Nitrogen cannot be absorbed directly by the plants and animals until it is converted into compounds they can use. This process is called the Nitrogen Cycle.
  • Plants take Nitrogen in the form of Nitrate.
  • Nitrogen is useful in opening and closing of Stomata.
  • Deficiency of Nitrogen in plants causes Chlorosis.

The Nitrogen Cycle basically involves these following four Processes (Nitrogen Cycle Steps): –

  1. Nitrogen Fixation
  2. Ammonification
  3. Nitrification
  4. De-nitrification

Nitrogen Fixation –

  • The nitrogen molecule (N2) is quite inert. To break it apart so that its atoms can combine with other atoms requires the input of substantial amounts of energy.
  • The reduction of atmospheric nitrogen (N2) to the ammonium ion (NH+4) is called nitrogen fixation.
  • Special bacteria convert the nitrogen gas (N2 ) to ammonia (NH3) which the plants can use.
  • Three processes are responsible for most of the nitrogen fixation in the biosphere –
  1. Atmospheric fixation- by lightning
  2. Industrial fixation
  3. Biological fixation by certain microbes – Alone or in a symbiotic relationship with some plants and animals.

Ammonification –

  • After all of the living organisms have used the nitrogen, decomposer bacteria convert the nitrogen-rich waste compounds into simpler ones.
  • It is the formation of Ammonia from Protein and Nucleic Acid.
  • Bacteria that helps – Clostridia, Actinomycetes.

Nitrification –

  • Nitrification is the process which converts the ammonia into nitrite ions which the plants can take in as nutrients.
  • In short Ammonia to Nitrite ions.
  • Nitrite to Nitrate (Plant absorbs this nitrate)

De-nitrification –

  • De-nitrification is the final step in which other bacteria convert the simple nitrogen compounds back into nitrogen gas (N2), which is then released back into the atmosphere to begin the cycle again.
  • In short, Nitrate (the Nitrate which is not absorbed by plants) to Free Nitrogen (N2).

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