Why is Rhizobium categorized as a 'symbiotic bacterium'? How does it act as a biofertiliser ?

Explanation

Rhizobium is a .symbiotic bacteria. as it lives in mutually beneficial association in the nodules on the roots of leguminous plants. The bacteria fix atmospheric nitrogen into organic forms, which is used by the plant as nutrient and in turn bacteria get carbohydrate food and shelter. The leguminous, plants with nodulated roots are ploughed back into the field as green manure. They act as biofertilisers that enrich the nutrient quality of the soil. Beside inorganic nutrients, they also add organic matter to the soil, thereby also improving the texture of the soil.