Drought, prolonged summer heat and the high price of nitrogen fertilizer lead to the topic of this article. At the time of this writing, many Oklahoma producers are either waiting to plant cool season annuals for winter grazing, or waiting to see if a stand emerges from the seed dusted in a month ago. With rain in the forecast there is still high potential for excellent cool season pasture. The benefits and return on investment of incorporating cool season legumes merit consideration.
Benefits
The most significant benefit of adding legumes into a pasture mix is potentially supplying the successive cash crop with nitrogen (N) without adding it as fertilizer. Legumes have a mutually beneficial partnership with soil bacteria, Rhizobium. These bacteria infect legume root hairs forming small nodules near the point of root elongation. These bacteria pull nitrogen gas (N2) from the atmosphere and convert it into plant-available forms of nitrogen through a process known as nitrogen fixation. The relationship benefits both partners. The bacteria provide the plant with nitrogen and essential nutrients for growth, and the legume host supplies the bacteria with sugars and other compounds they need to survive and fix nitrogen. The amount of N to be expected will vary. For example, mixing Austrian Winter Peas into winter wheat pasture is an effective strategy for Oklahoma producers looking to slash synthetic nitrogen costs while boosting forage quality. A successful winter pea stand can fix 30 – 100 pounds of N per acre, which directly translates to saving on spring top dressing of urea. While incorporating a legume into your cool season grass mix doesn’t necessarily result in greater tonnage as compared to a cereal grain monoculture, it will increase crude protein and digestibility for stocker cattle.
Management Considerations
Soil testing is an important first step to take before planting. Legumes are more sensitive to low soil pH (less than 6.0) and require adequate levels of phosphorus and potassium. Also, inoculation of legume seed immediately prior to planting is critical. When legume seeds are properly inoculated and planted in favorable soil conditions, root nodules can begin forming within three to four weeks after emergence. As the plant grows, the number and size of these nodules provide a good indication of how much nitrogen fixation is occurring. If soil conditions are suitable for growth of the legume, they are typically suitable for bacterial infection and nitrogen fixation. Rhizobium populations can be reduced by extreme weather conditions like drought and flooding which will impact nitrogen fixation in the system. Planting depth and grazing management also are important with regard to getting the maximum benefit from legumes. While some legumes can increase the risk of bloat, the likelihood is generally low when legumes make up less than half of pasture ground cover. Poloxalene, a bloat preventative, must be consumed by cattle daily, both prior to turning cattle onto legumes and thereafter, to be effective. Further details on seeding rates and management considerations are available in the reference materials below.
Mark Johnson, OSU Extension beef cattle breeding specialist, speaks with Mason Henson, OSU animal and food sciences assistant professor, about how producers can utilize legumes as forage for cattle herds on SunUpTV from May 23, 2026. https://www.youtube.com/watch?v=8mhbyVyWqW8
References:
https://extension.okstate.edu/fact-sheets/forage-legumes-for-oklahoma
https://extension.okstate.edu/announcements/cropping-systems/cover-crop-garden-winter-legume-mix
