Nitrogen is essential for both plants and animals for their growth and development. Nitrogen fixation is the process by which nitrogen in the atmosphere is converted into ammonia by bacteria like Rhizobium, Azotobacter, etc.
Rhizobium is a type of bacteria which helps in nitrogen fixation. They live on roots of leguminous plants like beans and peas and help in fixing nitrogen in the soil. They convert the nitrogen in the non-absorbable form into a usable form. Blue green algae are also helpful in fixing nitrogen from the atmosphere.