Write the steps and processes involed …

The various steps of nitrogen cycle are as follows :
(i) Nitrogen fixation: It is the conversion of atmospheric nitrogen into water-soluble compounds like nitrates and nitrites either by the free-living bacteria or Rhizobium that are found in the root nodules of legumes. Atmospheric nitrogen also gets converted into nitrates and nitrites naturally by lightning.
(ii) Ammonification: Death and decay of plant bodies release ammonia into the atmosphere. Animals also give out ammonia along with urea and uric acid as excretory products. These nitrogenous compounds are converted to ammonia by putrefying bacteria and the process is known as ammonification.
(iii) Nitrification: Ammonia is then onverted first into nitrites and then into nitrates by the nitrifying bacteria, the process being called as nitrification. Plants generally take up nitrates and nitrites and convert them into amino acids.
(iv) Denitrification: When the animal or the plant dies, denitrifving bacteria in the soil convert the various compounds of nitrogen back into nitrates and nitrites. The nitrates and nitrites are çonverted into elemental nitrogen by Pseudomonas. This process is called denitrification.