Answer-Main function of bio fertilizer is:

A biofertilizer is a substance which contains living micro-organisms which, when applied to seeds, plant surfaces, or soil, colonize the rhizosphere or the interior of the plant and promotes growth by increasing the supply or availability of primary nutrients to the host plant. Biofertilizers such as Rhizobium, Azotobacter, Azospirilium and blue green algae BGA have been in use a long time.