It is well known that legumes have unique value in forage/livestock operations, but recently there has been renewed interest among cattle producers about the advantages and disadvantages of adding legumes.
Nitrogen fixation. Most legumes form a mutually beneficial association with rhizobium bacteria that "fix" nitrogen (N) in nodules on the roots. This allows them to provide enough N for their own growth as well as some or all of the N needed for grasses growing in the same field. In various studies, the amount of N produced per acre by a good legume stand ranges 50 lb. to 150 lb. for annual clovers and vetches, 75 lb. to 200 lb. for white and red clover and 150 lb. to 200 lb. for alfalfa. This alone justifies the use of legumes in many forage/livestock situations. If the energy inputs required for producing N fertilizers result in even higher costs to farmers, it will become even more important.
Improved quality. A legume-grass mixture offers better forage quality than grass-only grazing. This can mean higher weaning weights, improved conception rates, fewer health problems and less need for supplements.
Increased forage yield. The total dry matter yield per acre from a legume-grass mixture is often higher than that of a grass-only field. This is especially true when a legume stand is compared to grass that receives little or no N fertilizer.
Extended grazing season. Stored feed is expensive, so extend the grazing period as long as possible. For example, perennial legumes such as white clover and, especially, red clover will compensate with summer growth when tall fescue and orchardgrass reduce forage quality and growth in hot weather.
Reduced risk. Growing a legume-grass mixture rather than grass alone helps reduce the risk of getting little or no grazing from a pasture in the event of disease or harsh weather conditions. Plus, the nutritional value of legumes lessens the likelihood of diet-related disorders such as grass tetany and fescue toxicity.
Disadvantages. Using legumes and legume-grass mixtures requires a higher level of management than grass alone. Legume seed must be inoculated and planted with more precision, and soil nutrient levels and pH must be monitored more closely. For mixtures, proper grazing or clipping management is necessary to avoid "shading out." Legumes are also more sensitive to herbicides than grasses.
Bloat can be a problem with some legumes but is unlikely unless they have dominated the pasture stand. If 50% or more of the ground cover is grass, bloat is normally not a problem, and various management practices can reduce its likelihood.
In the long run, livestock producers facing rising production costs can hardly afford to not use legumes when possible.
Don Ball is an Extension agronomist and professor at Auburn University.