What are biofertilizers and how many types of biofertilizers are available?

Biofertilizer is defined as the capability of a microorganism to fix the atmospheric nitrogen by planting suitable crops in the soil. These microorganisms tend to mobilize nutritive elements from a non usable form to a usable form by a biological process. There are two types of biofertilizers:

Symbiotic N-fixation (Rhizobium)

Asymbiotic N-fixation (azotobacteria, azospirillum, blue green algae, azolla and mycorrhiza).