Beans

Beans are also nitrogen fixers, meaning that they can fix, or supply, nitrogen to the soil by a process called biological nitrogen fixation. This process is prevalent in other members of the Fabaceae family, which includes other Phaseolus species. Bean plants contain symbiotic rhizobia bacteria within nodules in their root systems. These nodules produce nitrogen compounds that help the plant grow. When the plant dies, the fixed nitrogen is released into the soil. For this reason, it is considered good practice to leave legume roots in the soil after harvest.