how are biofertilisers diffrent from fertilisers such as NPK that we buy in the market? justify the role of rhizobium as a biofertiliser

Hello Student,
In contrast to fertilizers that are harsh chemicals and add to the toxicity of the soil, biofertilizers comprise of microorganisms that when added to the soil promote growth of plants through natural processes like nitrogen fixation, solubilizing phosphorus and synthesizing growth promoting substances. Rhizobium is a group of microorganism that helps in nitrogen fixation thus increasing the content of nitrogen of soil and promoting plant growth.