Overseeding is the term commonly used to refer to the technique of planting winter annuals into the dormant sods of warm-season perennial grasses like bermudagrass, bahiagrass and dallisgrass. Benefits of overseeding include extension of the grazing season, production of high-quality forage, suppression of weeds in spring and, if a legume is used, addition of nitrogen to the forage system.
Crop Selection- Crop selection decisions can vary depending on producer objectives, date of planting, soil types, seed prices and other factors. Annual ryegrass is the most productive, versatile and widely-adapted winter annual and should be a component of most overseeded fields. Small grains make more autumn and winter growth than ryegrass, but may not make enough growth to justify their use. Annual legumes can furnish from 50 to well over 100 pounds of nitrogen per acre and provide high-quality forage in spring. Rye and, in Southern Alabama, oats are usually the best small grains to use on sandy soil; wheat is a good choice for heavy or moist areas and triticale performs best with good but not excessive moisture availability. Various legumes require different soils or sites. Lime and fertilizer should be applied according to recommendations provided by a soil test taken well ahead of planting.
Sod Height And Condition- A common reason for poor results is leaving too much stubble or too thick of a thatch on the soil surface. Ideally a one or two-inch stubble works best for small-seeded forage crops like clovers and ryegrass. Large-seeded species like small grain and vetch are more tolerant of slightly higher stubble heights. Light disking of a field is one way to compensate for high stubble on thick, tight sod. In particular, the success of overseeding an old, thick stand of bahiagrass is enhanced by disking. Otherwise, cutting hay or stocking heavily enough to graze the sod closely are the best approaches. Simply clipping a field may leave excessive plant residue on the soil surface.
Date Of Planting- The earlier winter annuals are planted, the earlier they can provide grazing. However, if they are planted too early, the summer grass may continue growing and compete with the young seedlings. Also, a hot, dry period may result in stress and even death of seedlings. Generally, winter annuals should be overseeded four to six weeks before a killing frost. Planting date guidelines for situations in which no disking will be done are October 1-15 for North Alabama, October 15-30 for Central Alabama and November 1-15 for South Alabama.
Seeding Rates- Auburn University seeding rate recommendations for small grain alone or ryegrass alone are 90 to 120 lb/ac and 25-30 lb/ac, respectively. In mixtures, the recommendation is 60-90 lb/ac and 15-20 lb/ac for these grasses, respectively. The recommended seeding rates per acre for various legumes vary depending on seed size. Examples are 5-8 lb/ac for arrowleaf, 2 for ball clover, 15-20 for crimson clover and 20-30 for hairy vetch. Seeding rates should be increased by about 25 percent if seed is broadcast rather than drilled. The ryegrass seeding rate should be 10-15 lb/ac when grown with a legume.
Planting Technique- Large-seeded species like small grain and vetch should be covered with about one-inch of soil, which means they either need to be planted with a drill or broadcast and covered by disking. Species having smaller seeds, like ryegrass and crimson clover, can either be drilled or broadcast, ideally about a quarter-inch deep. Extremely small-seeded species like ball clover or white clover are difficult to drill without planting the seed too deep, and thus should normally be broadcast. If significant disking has been done, a cultipacker or drag should be used in conjunction with broadcasting small-seeded forage crops.
Don Ball is an Extension Forage Crop Agronomist with Auburn University.