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

Step 1. Identify the organism responsible. Leguminous crops (such as pulses and beans) form a symbiotic partnership with the nitrogen-fixing bacterium Rhizobium, which lives inside specialised swellings on the plant's roots called root nodules.

Step 2. Explain what Rhizobium does there. Inside the root nodules, Rhizobium converts atmospheric nitrogen gas (N2, which most plants cannot use directly) into organic nitrogen compounds that the plant - and, once the plant residue decomposes, the surrounding soil - can use.

Step 3. Connect this to soil fertility. This nitrogen-fixing activity is one of the three processes (alongside ammonification and nitrification) that the chapter groups under bacterial contributions to soil fertility, and it directly increases the amount of usable nitrogen available in the soil. …

Trace the biological role of Rhizobium (nitrogen fixation in root nodules) th …

• Naming the wrong bacterium (e.g. Azotobacter, which fixes nitrogen but is free-living in soil, not root-nodule-symbiotic like Rhizobium). …