N2 Cycle

Background: Nitrogen Cycle

  • Nitrogen, which makes up 78 percent of our atmosphere, is an essential nutrient for all life forms.
  • Nitrogen is an integral part of many molecules like proteins, nucleic acids DNA and RNA and some vitamins.
  • Atmospheric nitrogen is inert and cannot be used by life forms directly.
  • This atmospheric nitrogen has to be converted into nitrates and nitrites to facilitate its use by various organisms.
  • Leguminous plants have nitrogen fixing bacteria (Azatobacter, Anabeana, Nostoc) living in their root nodules help to fix atmospheric nitrogen into nitrates and nitrites.
  • Nitrogen is also fixed is during lightning due to high temperatures and pressures created convert nitrogen in the air into oxides of nitrogen.
  • Plants take up nitrates and nitrites and convert them into amino acids which are used to make proteins
  • Proteins and other complex compounds are then consumed by animals.
  • When the animal or the plant dies bacteria present in the soil convert various compounds of nitrogen back into nitrates and nitrites.
  • The decomposition of organic nitrogen of dead plants and animals into ammonia is called as ammonification.
  • Ammonia is first oxidized into nitrites by the Nitrosomonas bacteria, and then the nitrites are converted into nitrates by the Nitrobacter bacteria. This is called as nitrification.



Key results of the study

  • Nitrogen particles make up the largest fraction of PM2.5.
  • PM 2.5 is closely linked to cardiovascular and respiratory illness.


Major Sources of Nitrogen Pollution in India

  • Indian Nitrogen oxides emissions grew at 52% from 1991 to 2001 and 69% from 2001 to 2011.
  • Agriculture is the largest contributor to nitrogen oxides emissions.
  • Besides the non-agricultural emissions include sewage and fossil-fuel burning — for power, transport and industry.
  • Also India is globally the biggest source of ammonia emission.
  • Cattle account for 80% of the ammonia production


Nitrogen oxides (NOX nitric oxide and nitrogen dioxide) emissions

  • Burning of crop residue is the key contributor to winter smog in many parts of North India, contributing 240 million kg of nitrogen oxides.
  • Coal, diesel and other fuel combustion sources are other main sources of NOx emissions which is growing at the rate 6.5% every year.


 Nitrous oxide emissions (N2O)

  • Since 2002, N2O has replaced methane as the second largest Greenhouse Gas (GHG) from Indian agriculture, Carbon dioxide being the largest.
  • Agricultural soils contributed to over 70% of N2O emissions from India in 2010, followed by waste water (12%) and residential and commercial activities (6%).
  • Chemical fertilizers, mainly urea account for over 77% of all agricultural N2O emissions in India.
  • Most of the fertilizers are consumed for the production of cereals, especially rice and wheat.
  • Burning of crop residue contributes about 7 million kg of nitrous oxide (N2O) per year.
  • Nutrient recovery/recycling from waste water for agriculture could cut down N2O emissions from sewage and waste water by up to 40%.


Ammonia emissions

  • India is globally the biggest source of ammonia emission
  • Cattle account for 80% of the ammonia production.
  • The poultry industry with an annual growth rate of 6% is another source of ammonia emission due to excretion of reactive nitrogen compounds.