By Don Ball
The cost of commercial nitrogen fertilizer has greatly increased recently, which has in turn greatly increased the cost of producing grass forage. As a result, many forage/livestock producers are actively seeking ways to reduce the amount of nitrogen fertilizer they purchase. One very sensible strategy is to grow forage legumes where possible, as they have the ability (in association with Rhizobium bacteria) to capture nitrogen from the air and fix it in nodules on their roots.
Consequently, it seems likely this autumn there will be some producers who will be planting legumes for the first time, and others who will be planting them for the first time in a long while. In addition to biological nitrogen fixation, legumes offer other benefits including excellent forage quality and the possibility of increasing forage yield and/or distribution of growth. When overseeded on the dormant sods of warm-season perennial grasses, like bahiagrass and bermudagrass, they also tend to suppress winter weeds. However, legumes require more precision and attention to detail than grasses, so a review of some unique aspects of growing them should be in order.
Herbicide residue - Legumes are sensitive to some herbicides, including some commonly-used pasture herbicides. Be sure to check the labels of any materials used within the past year in any area where the planting of legumes is being considered.
Soil Fertility - While legumes do not require nitrogen fertilizer, it is quite important to apply phosphorus and potassium according to soil test recommendations. It is best to plant legumes in an area in which little or no nitrogen fertilizer was applied during summer.
Soil pH - Various legumes have differing pH requirements, but most pasture legumes do best when the soil pH is in the range of 6.0 to 6.5. Alfalfa and berseem clover do best when the soil pH is 7.0 or higher.
Fit Species To The Site - No legume species is adapted to all soils and sites. Information pertaining to requirements of various legumes (as well as other forage information) is available on the website: www. alabamaforages.com.
Seed Inoculation - Much of the legume seed commercially available is coated seed containing the proper inoculants and holds it tightly to the seed. If pre-inoculated seed is not available, the proper type of inoculant should be purchased and applied to the seed just prior to planting.
Stubble Height - When legume seed is planted into warm-season perennial grass pastures, it is important to have a short stubble height (less than two inches).
Planting Depth - Small-seeded legumes, like ball clover and white clover, can be broadcast over the soil surface. Medium-sized legume seeds, like those of arrowleaf clover or crimson clover, should ideally be planted about one-fourth inch deep. Large-seeded legumes, like vetch or Austrian winter pea, should be planted about one inch deep.
Planting Date - Legume plantings on a prepared seedbed can be made as early as early-September in North Alabama or mid to late-September in South Alabama. Guidelines for overseeding warm-season perennial grass pastures are October 1-15 in North Alabama, October 15-30 in Central Alabama and November 1-15 in South Alabama.
Seeding Rate - Seeding rates vary for various legumes (see website mentioned earlier). Planting annual ryegrass and/or a small grain (rye, wheat, oats or triticale) with an annual legume will provide earlier grazing and reduces the likelihood of bloat.
Post-Planting Grazing - Over-seeded warm-season pastures can continue to be grazed until low temperatures are about 40o or less and summer pasture growth ceases. If clover is seeded into tall fescue, the field can be grazed until livestock begin biting the tops of the clover, but livestock should then be removed to give the clover a chance to become established. Grazing should be reinitiated if grass begins to shade the clover.
Don Ball is an Extension Forage Crop Agronomist with Auburn University.