What is the difference between nitrification, denitrification, ammonification and nitrogen fixation?

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.