The process by which bacteria convert nitrogen in the atmosphere into usable forms is called nitrogen fixation. Certain bacteria, particularly those found in the soil and within the root nodules of some plants (like legumes), can utilize nitrogen gas (N2) from the atmosphere and convert it into ammonia (NH3) or related compounds. This process is essential for maintaining soil fertility, as nitrogen is a crucial nutrient for plant growth. Nitrogen-fixing bacteria form symbiotic relationships with plants, enhancing nutrient uptake and productivity.