Legumes are used as a forage primarily to improve quality and alter the green season. There is only a minor benefit to nitrogen supply when the legume is totally grazed. For upper-level benefit from legume nitrogen, these legumes must produce massive top growth, which is then returned to the soil surface as decomposed organic matter or manure and urine.
Legumes can be grown separately or added to grass pastures, in which case the grass cannot be highly fertilized or managed for upper production because it will dominate and diminish the legume. Legumes require higher levels of phosphorus, potassium, and lime than grasses.
Legumes tend to encourage spot grazing in a grass-legume pasture. Horses will graze legumes, but they often strongly prefer good grass pasture. This tendency enhances the need for rotational grazing management, since in a grass-legume mixture, horses may eat grass and leave legumes to mature. In this case, the legume residue should be mowed to allow it to decompose and release nitrogen for grass production. Horses may leave excellent vetch and clover and graze grasses almost exclusively in a low-stocking-rate syndrome, which characterizes the grazing response.
Alfalfa. Alfalfa can be used for both hay and green grazing, but it must be grown on good soil to be very effective. Horses have a good tolerance to it in the grazing stages. Refer to figure 1 and the section on horse research on forage for more information.
Lespedeza. Annual and perennial lespedezas have limited adaptation in Oklahoma. They can be produced in northeastern Oklahoma, Arkansas, and other more humid areas and can be produced poorly in thin grass pastures throughout the eastern half of Oklahoma and into Arkansas, Kansas, and Missouri. They tolerate very little grass competition. The annual lespedezas are good quality and may be considerably beneficial in extensive rather than intensive pastures.
Sericea lespedeza is a perennial that can be produced in the eastern half of Oklahoma and the eastern United States. It is relatively unpalatable to horses and difficult to manage for grazing. It does not offer much as a good horse forage.
Clovers. Clovers have always been popular in combination with grasses for a horse pasture. They are usually higher in phosphorus, calcium, and protein, providing a more nutritious and balanced diet for the horse.
Arrowleaf and crimson clover are the two main winter annual clovers best adapted to southeastern Oklahoma. These clovers in combination will produce some fall forage and then become dormant from December to March. Then they will be available as spring pasture from late March to June. Arrowleaf alone will remain dormant until late March or early April and then begin rapid growth in late April, with production lasting until early June. Arrowleaf clover is not very palatable to horses, but it is useful.
Red, white, yellow hop, subterranean, sweet, and berseem clovers are adapted to various regions in the eastern half of Oklahoma. All can be used for horse pasture. Crimson clover is among the easiest to establish. Red clover and white clover may cause profuse slobbering, and the horses should be removed from the pasture if that happens. The pasture may be regrazed later.
In the southern and eastern sections of Oklahoma, winter annual clover and annual ryegrass can be grown successfully. These forages need good rainfall, and even though they are planted in the fall, they produce forage primarily in the spring. Ryegrass can be very productive in the fall when wet mild growing conditions prevail. Most cattle producers will use one or more of these legume forages in combination with rye or wheat.
Vetch. Hairy vetch grows well in Oklahoma and is the choice for annual legumes for the western half of Oklahoma. It can be sod-seeded into bermudagrass, mixed with winter pasture, or planted alone. Hairy vetch is one of the easiest legumes to establish. It will add about one to two months to early pasture during spring.