Legumes are commonly associated with cool-season forage systems, particularly through the use of clovers to improve spring grazing and reduce nitrogen fertilizer requirements. However, warm-season legumes can provide similar benefits during the summer months. As input costs remain elevated and forage quality becomes more variable through the summer, incorporating warm-season legumes offers an opportunity to improve both system efficiency and nutritional value.
The primary advantage of legumes lies in their ability to fix atmospheric nitrogen through a symbiotic relationship with rhizobia bacteria. This biological nitrogen fixation can supply a portion of the nitrogen required for plant growth, reducing dependence on synthetic fertilizers. During the summer, when warm-season grasses such as bermudagrass actively growing and highly responsive to nitrogen, the inclusion of legumes can contribute to both forage production and crude protein content.
Several warm-season legumes are adapted to Oklahoma and similar environments. Cowpeas are widely used due to their relatively strong establishment and grazing tolerance, along with their contribution to forage quality. Sunn hemp has gained interest for its rapid growth and high biomass production, although it tends to mature quickly and requires timely utilization to maintain quality. Forage-type soybeans are another option that can be incorporated into systems targeting higher nutritional demands.
Warm-season legumes are generally most effective when included in mixtures rather than grown as monocultures. When combined with grasses such as bermudagrass or summer annual species, they contribute to a more balanced forage system. Grasses provide yield and persistence, while legumes enhance protein concentration and supply nitrogen. When 30%-50% of the total forage production in a pasture is from legumes, it is predicted that the N fixation annually is the equivalent of 100-150 units of N. A grass-legume combination can improve overall forage utilization and animal performance, particularly in grazing systems where diet selection plays an important role.
Soil temperatures should be consistently warm, generally above 60 degrees, and adequate soil moisture is necessary to support germination and early growth. This typically makes ideal planting fall in May across much of Oklahoma. Proper inoculation is essential to ensure effective nitrogen fixation.
While warm-season legumes are not a complete substitute for nitrogen fertilizer, they represent a practical tool for reducing input costs and improving forage quality. Incorporating these species into summer forage systems can enhance overall productivity and provide greater flexibility in grazing management.
Sources: Oklahoma State University Extension, USDA-NRCS, University of Georgia Extension, and Hay & Forage Grower.
