why is it a good agricultural practice to plant a field with alfalfa every few years?

Alfalfa (Medicago sativa) is a perennial leguminous crop that fixes nitrogen in the soil and is often cultivated as a cover crop. It is a good agricultural practice to plant a field with alfalfa every few years to replenish the lost nitrogen from the soil. Cereal crops exhaust high amounts of nitrogen from the soil. … Read more