Forage Legumes: Greater Quality, Fixed Nitrogen, or Both?.

Forage Legumes: Forage Quality, Fixed Nitrogen, or Both.

As a forage class, legumes have the highest forage quality which is primarily influenced by plant maturity. In a symbiotic association with Rhizobia bacteria, legumes are also capable of fixing nitrogen from the atmosphere.  The amount of fixed nitrogen by legumes is influenced by numerous factors such as legume species, Rhizobium strain, climatic conditions, soil type, plant nutrient availability, etc. and therefore is more variable and unpredictable than forage quality. Annual fixed N rates can range from near 0 to over 200 kg/ha. The high cost of nitrogen fertilizer has placed a higher value on N-fixation than in the past. Alfalfa is the principal forage legume in the northeast, north central, and western US. Alfalfa is a major hay crop for the dairy industry and beef cattle without the need for N fertilizer because of high yields and quality. Perennial clovers and other perennial forage legumes are mainly grown with cool-season perennial grasses in these areas for grazing because of their N contribution. In the southeastern US the principal livestock enterprises are small beef cattle operations utilizing warm-season perennial grasses which have the lowest forage quality of any forage class. Annual legumes are used extensively because perennial legumes persistence is poor because of the hot and usually dry summers.  Because the cool-season legume precedes the warm-season grass, it extends the grazing season, provides higher quality forage than warm-season grasses, supplies nitrogen to the pasture system, and provides spring weed control. Forage quality of legumes has the greatest impact where warm-season grasses are grown.