Why are bio-fertilisers preferred over chemical fertilisers?

Explanation

Biofertilizers are organisms that enrich the nutrient quality of the soil such as Azotobacter while chemical fertilizers degrade the soil fertility if excessively used and cause land pollution also.
Biofertilizers are preferred over chemical fertilizers because :
1. They do not pollute environment.
2. They are cheap and easy to produce, no energy is utilised in their production.