Fava beans...

Broad beans (fava beans) are nitrogen-fixing plants, which means they can take nitrogen from the air and convert it into a form that improves the soil. They do this through a natural partnership with bacteria in small nodules on their roots. This process enriches the soil and reduces the need for artificial fertilisers.

Because of this, broad beans are often used as green manure. They can be grown to improve soil structure and fertility, then cut down and dug into the soil before or during flowering. As the plants decompose, they release nitrogen and organic matter, making the soil richer and better prepared for future crops.