Why do farmers plant leguminous crops in crop rotations/mixed cropping?

Explanation

1. The bacteria rhizobium forms root nodules in the leguminous crops only and lives in symbiotic association with the plant.
2. They help to convert atmospheric nitrogen to nitrate salts in the soil thereby adding to soil fertility.
3. Hence growing leguminous crops in crop rotations / mixed cropping helps to maintain fertility of the soil.