Now that it's January, the time for seeding legumes is fast approaching, with many species falling into a spring seeding window from March to April. Need a few reasons why incorporating legumes into a grass mixture can be beneficial? Here is a short list:
- reduction or elimination of nitrogen fertilizer,
- an improvement in forage distribution,
- improvement in animal performance through improved forage quality,
- dilution of forage anti-quality factors, and
- wildlife benefits. Not only are these great reasons, each one can be backed up by research data.
Now the catch: Species compatibility in a mixture is often not equal, which many times leads to the demise of a mixture's legume component. Ideally, we would like to see species in a mixture be of equal height at maturity, respond equally to grazing frequency and intensity, equal in environmental adaptability, equal in palatability and equal in nutrient uptake. In addition, many legume species are cool-season plants trying to compete in an environment favoring warm-season perennials.
Of the benefits listed, reducing nitrogen fertilizer generates the most producer interest as nitrogen fertilizer prices increase. How much legume do you need in a mixture to obtain this benefit? At least 30 percent of a mixture should be made up of legumes for elimination of nitrogen. Figure 1 gives you an idea of what such a mixture looks like. As you can see, it looks like a bunch of clover and it is. At this level and higher, nitrogen fixation can conservatively range from 20-80 pounds per acre depending upon species. If you then assign a value to nitrogen supplied equal to commercial fertilizer cost, it becomes a valuable contribution. So why don't we see more legumes in our pastures? Here are some reasons why I think we don't. Each of these can be overcome or minimized with proper management.
Annual precipitation from the eastern to western edge of the Noble Research Institute service area ranges from approximately 52 to 28 inches per year. When selecting a legume, pay attention to its minimum precipitation requirement. This is probably more critical for perennial legumes than annuals, since annuals can avoid dry summer periods by completing their life cycle prior to seasonal dry periods. But with annuals, meeting seasonal moisture needs is crucial. As you move east of I-35, your choices greatly increase.
Legumes cannot compete with grasses for phosphorus and potassium, and supplying these nutrients in adequate amounts according to soil test is essential for their production and persistence. Legumes are also more sensitive to soil pH than forage grasses and generally prefer pH levels of 6.0-7.0. Most of our soils range in pH between 5.0 and 6.0.
Palatability sounds like a strange problem to have in forage, but grazing animals will prefer legumes over grasses. Grazing management must then be such as to provide adequate rest periods for legumes, otherwise persistence will become an issue.
- Failure to properly inoculate
To capture nitrogen from the air, legume roots must be infected with a species-specific strain of Rhizobium bacteria. Once infected, Rhizobium bacteria are dependent upon the legume plant for survival. Therefore if you limit growth of the legume plant (fertility, grazing management, plant-to-plant competition and moisture) nitrogen fixation is limited and nitrogen benefit is lost.
- We don't put seed out
Credit for this one goes to Dr. Don Ball, Extension forage specialist at Auburn University, who at a clover symposium stated that in his mind, the number one reason we don't see more clovers in pastures is that we don't put the seed in the pasture.
- Fear of bloat
A lot of variables play into this including legume species, environmental conditions, pure stand or mixture, but good management can minimize the risk.
Legumes are an interesting and valuable plant to livestock grazing systems. To capture their potential contribution takes management and work. Research continues to develop varieties that can provide a greater contribution to our area. Two such releases are Durana white clover, selected for increased plant persistence, and Apache arrowleaf clover, selected for increased disease resistance. Table 1 provides a summary of several spring-seeded legume species that could be potential contributors to a forage-livestock grazing program.