Legumes are the second most important plant family used as forage. Some could argue that legumes may be more important fundamentally since the family is noted for having symbiotic associations with the Rhizobium bacteria which allow legumes to fix nitrogen. Legumes are therefore generally least dependent upon nitrogenous fertlizer. That makes them a great asset to primitive and sustainable agriculture. The self-sufficiency in nitrogen exhibited in legumes makes them rich sources of protein. For forage they have no equal, especially when partnered with grasses. When the term "grasslands" is used, legumes are assumed to play a part. The major legumes used as forage are: alfalfa, trefoils, clovers, and vetches.