For the past 50 years, relatively inexpensive nitrogen fertilizer has been the primary determinant of forage productivity in the southeastern U.S. As was the case prior to this period, the recent dramatic increases in price of inorganic nitrogen could now be changing the status of pasture legumes from simply desirable to essential for economic levels of productivity. Temperate (cool season) legume species such as clovers (Trifolium species) and alfalfa (Medicago sativa) are useful forage plants and nitrogen sources in the region, but the long summer growing season also provides tremendous opportunity for effective use of warm-season legume species. The list of warm-season legumes useful as forage plants prior to the extended era of inexpensive nitrogen fertilizer [Sturkie, 1951] is very similar to current lists of available species [as illustrated by Ball et al., 2002]. As noted by Sturkie in 1951, the annual species on this list are excessively expensive due to direct cost and risk associated with annual establishment. The remaining species include only sericea lespedeza and kudzu as perennial warm-season legumes from the early list with rhizoma peanut (Arachis glabrata) added in recent years for specific uses in a portion of the region. The additional widely adapted, naturalized woody legume mimosa has been identified as a promising forage plant [Bransby, 1993]. All three of the widely adapted species, sericea lespedeza, kudzu, and mimosa, are introduced species which are on various lists of invasive species in the southeastern region. In consideration of the likely increasing forage demand for these species in the southeastern U.S., some reconciliation of their continuing recommendation for forage use with their identification as invasive species in the region appears warranted. Additional less widely adapted tropical species provide similar situations for specific ecosystems in peninsular Florida. Rather than an exhaustive review of each species, this overview of ecological aspects potentially affecting invasiveness and control of the perennial warm-season legumes useful as forage plants will emphasize recent advances.
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