Any legume has the ability to fix nitrogen from the atmosphere.
The nitrogen is incorporated into the plant as protein, and legumes are inherently high in protein. Stem, leaf, and root residues left in the field from a legume crop are higher in nitrogen than grasses. The breakdown of legume plant residues commonly releases some of this nitrogen for use by the next and succeeding crops. Corn or small grains that require external sources of nitrogen can benefit from nitrogen released by a previous legume or cover crop.