yr Ϫ1 ; Wolf and Fiske, 1995; Brejda, 2000). The compromise between yield and quality does not apply to bio-Management practices for biomass production of bioenergy grasses mass production for bioenergy feedstock because the may differ from management for forage. Our objective was to determine the yield and stand responses of 'Alamo' switchgrass (Panicum goal generally is to maximize production of lignocelluvirgatum L.) to N and P fertilization as affected by row spacing. A lose (Sanderson et al., 1999a). Thus, management praccombination of five rates each of N and P were applied to plots during tices that maximize biomass production may differ from 1992 to 1998 at Stephenville, TX and 1993 to 1995 at Beeville, TX.that for herbage production. Annual yield of several Three row-spacing treatments were applied as subplots. Biomass proswitchgrass cultivars in Texas fertilized with 134 kg N duction was determined each year with a single harvest in late summer. ha Ϫ1 ranged from 8 to 20 Mg ha Ϫ1 , depending mainly Tiller density and tiller mass were measured during 1993 to 1996 at on seasonal rainfall variations (Sanderson et al., 1999b). Stephenville. Biomass production was not influenced by the additionAlamo switchgrass was the most adapted cultivar for of P. Biomass production response to N at Beeville was greater in the south-central USA. narrow rows than wide rows during the establishment year only. Bio-Phosphorus fertilizer recommendations for switchmass production responses to N were quadratic in 5 of 7 yr at Stephenville and linear at Beeville. A maximum yield of 22.5 Mg ha Ϫ1 occurred grass depend on soil pH, P supplying power of the soil, during 1995 at Stephenville at 168 kg N ha Ϫ1 . Lodging occurred atand soil test P (Brejda, 2000). In the central Great Plains, both locations but only at the 224 kg N ha Ϫ1 rate. Tiller density and P recommendations for switchgrass ranged from 0 to mass increased as row width increased. Tiller mass also increased 35 kg ha Ϫ1 , depending on soil test P (Brejda, 2000). In Oak Ridge Natl. Lab. managed by Martin Marietta Energy Systems.

Grazing lands in warm-temperate and subtropical North America have become less diverse. Pastures are typically grass monocultures, while rangelands are generally managed for the grass components. Overstocking, selective herbicides, fire exclusion and heavy rates of nitrogen fertilizer have contributed to near exclusion of native, warm-season legumes. The simplicity of managing grass monocultures, pasture production responses to nitrogen fertilizer and profitability of grass-only systems have limited interest in legume-based approaches. Changing economics and ecological concerns with ecosystem accumulation of industrial inputs contribute to an increasing interest in legumes. Unlike the development of temperate pasture legumes and recent research in the tropics, legumes tolerant of both freezing temperatures and hot weather have received less attention. Poor establishment, limited persistence and potential invasiveness limit currently available introduced species. Native, herbaceous, warm-season legume species occur throughout warm-temperate North America, but little attention has been directed to these plants as potential forage species. Some success with a few native legume species, primarily in the genus Desmanthus, suggests potential for expanded assessment of forage value of the many species available. Current assessments of native legumes, primarily for conservation purposes, provide an opportunity to expand evaluations of these species for pasture and rangeland potential while economics of livestock production and public interest in ecosystem health are supportive. Experiences with legumes of warm-temperate origin in North America, along with results with temperate and tropical pasture legumes globally, provide a starting point for future efforts at incorporating greater legume diversity in pastures and rangelands of subtropical and warm-temperate regions around the world.

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The beneficial effects of forages containing condensed tannins (CTs) on ruminants are well documented, but the chemical features of CT that yield benefits have not been defined. Some evaluations of limited numbers of highly purified compounds have resulted in positive correlations between CT molecular weight (M W ) and biological activity, while others have failed to show a correlation. The objectives of this study were to determine if M W of CT could predict biological activity relative to protein precipitability. M W of condensed tannin, proteinprecipitable phenolics (PPP), and the amount of protein bound (PB) were determined for nine species of warmseason perennial legumes. There was no correlation between PPP or PB and M W (R 2 0.11 and R 2 0.02, respectively). However, CT concentration did correlate with PPP and PB (R 2 0.81 and R 2 0.69, respectively). It was concluded that CT M W does not explain the variation in protein precipitation by CT from the forage legumes surveyed.