Maintaining grass and legume pastures as well as hay fields are important management factors for feeding beef cattle. Many beef producers plant a mixture of grass and legumes during hayfield establishment – but over time legumes can die out and become a lower percentage of the forage stand.
Legumes generally contain lower fiber content with slightly higher energy and protein values than grasses. Consequently, cattle must consume more grass forage to attain the same quantities of energy and protein as compared to legume forages. Unfortunately, cattle cannot consume grass forages at the same rate as legumes due to fiber content differences.
Another benefit of maintaining legumes in a mixed forage stand comes from their ability to fix nitrogen. Rhizobia bacteria nodulate the roots of legumes and convert atmospheric nitrogen into ammonia nitrogen for fertilization of the legume plant. Nitrogen becomes available to the grasses as root and aerial portions of the legume plants die and decompose into the soil. In pasture situations, animals consuming the legume plants will release nitrogen in urine and manure to feed the grass plants.
Legumes should make up 40-60 percent of the forage stand. During hay production, the top portion of the plant is removed from the field along with the contained nitrogen. Hay fields should contain legume percentages closer to 60 percent to compensate for the lost nitrogen. Pasture systems allow for more recycling of nutrients as nitrogen is excreted back onto the fields in the form of manure and urine. Maintaining legume stand near 40 percent is the desired target for pasture.
Frost seeding legumes is a common and economical method of maintaining or increasing legume stand. Management of the forage stand during the summer and fall before frost seeding is important to ensure there is little forage mat to allow seeds to obtain soil contact. Late season grazing or cutting will prevent forage mat formation. This generally reduces the vigor of the existing plants allowing new seedlings to better compete next spring.