What role do nodule bacteria play in nature? How is x used in agriculture?

Nodule bacteria live on the roots of legumes. They are perhaps the only creatures on our planet that can assimilate nitrogen from the air. Plants need nitrogen to form proteins. Bacteria provide legumes with them, and in return they receive organic matter. In agriculture, legumes are used in crop rotation – after them other crops can be planted – there will be a lot of nitrogen in the soil. Or they plant legumes along with cereals to feed the animals with protein-rich foods.