Answer:
The nitrification, denitrification, ammonification and nitrogen fixation are the different steps of the nitrogen cycle which converts the one form of nitrogen compound to another nitrogen compound.
1. Nitrification: the oxidation of the ammonia to the nitrites and later to nitrates through nitrifying bacteria like Nitrosomonas.
2. Denitrification: The reduction of the nitrites and nitrates to the atmospheric nitrogen by denitrifying organisms like decomposers, bacteria and others.
3. Ammonification: The process which converts the reduced organic nitrogen to the available ammonia ions.
4. Nitrogen fixation: The process by which the atmospheric nitrogen is fixed to the biosphere by the bacteria, lightning.