How do nitrogen-fixing cover crops add fertility to farm soil?

Nitrogen-fixing cover crops, typically members of the pea family (legumes), enhance soil fertility through a symbiotic relationship with nitrogen-fixing bacteria such as Rhizobium.12

These bacteria inhabit root nodules on the host plant, where they convert atmospheric nitrogen—which is otherwise unavailable to plants—into ammonia and other nitrogen compounds that the plant can utilize for growth.12

When these cover crops are plowed into the soil as green manure, the nitrogen compounds stored within the plant tissues are released into the soil as the organic matter decays, thereby increasing the fertility for subsequent crops. In addition to this biological nitrogen fixation, these crops improve the soil's physical condition, help prevent erosion, and reduce nutrient loss from leaching.2345