Nitrogen-fixing bacteria are microorganisms that convert atmospheric nitrogen into a form that plants can use. This process, known as nitrogen fixation, is essential for plant growth because most plants cannot utilize nitrogen gas directly from the air. These bacteria can be found in the soil or in symbiotic relationships with certain plants, such as legumes like soybeans and clover. There are two main types of nitrogen-fixing bacteria: free-living bacteria, which thrive in the soil, and symbiotic bacteria, which live in root nodules of specific plants. By enriching the soil with nitrogen, these bacteria play a crucial role in maintaining soil fertility and supporting agricultural productivity.