Nitrogen, although abundant in the atmosphere, is not directly accessible to plants; it is primarily made available through the activity of nitrogen-fixing bacteria that either live freely in the soil or form symbiotic relationships with legumes. For this nitrogen to become accessible to a broader range of plants, a series of biological processes must occur, including the decomposition of the bacteria and their host plants. The form and availability of nitrogen in the soil can vary depending on factors like pH and microbial balance.