Cool Season Forage Legume Requirements and Characteristics
by Dr. Don Ball, Extension Agronomist/Professor, Dept. of Agronomy and Soils, Auburn University, AL 36849

Interest in growing forage legumes as companion species to grasses is increasing. Reasons for this include that forage legumes can improve forage quality and animal performance; in many situations they can extend the growing season and/or increase total yield; and they offer the unique trait of fixing nitrogen, thus potentially lowering nitrogen fertilizer costs.

While forage legumes are highly desirable plants to have in pastures, they generally require a higher level of management and are more fickle than forage grasses. Therefore, it is important to plant them in situations in which they are well suited to be grown. Otherwise, the results are likely to be disappointing.

Most forage legumes commonly grown for forage purposes in Alabama are cool season species which should be planted in the autumn. This information sheet provides a review of some of the most important characteristics of these legume species. Table 1 provides a summary of the optimum soil attributes for, and key characteristics of, selected cool season legume. Table 2 indicates various grass species with which selected autumn-planted legumes are generally considered to be compatible.

Establishment of legumes in existing perennial grass sods generally requires suppressing the grass by tillage, trampling and heavy grazing by livestock, or use of grass herbicides. In the case of seeding legumes into warm season perennial grasses, failure to remove grass residue from the soil surface is a common cause of stand failure.

Planting at the proper time and using the proper seeding rate and depth for a given legume are critically important. Table 3 provides recommendations regarding these needs for a number of autumn planted forage legumes commonly grown in Alabama.

Once a stand of legumes has been established, management should favor the legume. Legumes generally require higher levels of phosphorus and potassium, as well as a higher soil pH than grasses. Excessive nitrogen fertilization of a grass/legume mixture will often result in loss of the legume stand due to grass competition.

Optimum grazing managment varies widely among forage species, but (except in the case of white clover) close, continuous grazing usually favors sod-forming grasses over legumes. It is important to remember that even with good management, legume stands will not last forever, so periodic replanting will be required.