The soil's fertility can be increased by growing more

Growing leguminous plants raises soil fertility because their root nodules fix atmospheric nitrogen into the soil.

Food grains generally draw nutrients from the soil rather than enriching it.

Fibre crops such as cotton and jute are heavy feeders that can deplete fertility.

Since legumes uniquely add nitrogen, there is a clear best choice and none-of-these does not apply.

Rhizobium bacteria in the nodules convert nitrogen gas into usable compounds.

Crop rotation with pulses is a traditional way to restore soil nitrogen.