Why are leguminous crops grown along with cereals?

Most legumes have symbiotic nitrogen-fixing bacteria in structures called root nodules. For that reason, they play a key role in crop rotation.When a legume plant dies in the field, for example following the harvest, all of its remaining nitrogen is released back into the soil.

In the soil, the amino acids are converted to nitrate (NO3−), making the nitrogen available to other plants, thereby serving as fertilizer for future crops.