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.

BACKGROUND: Several factors affect condensed tannin (CT) levels in plants and accuracy of the butanol-HCl assay for total CT. Six native, perennial, herbaceous legumes from Texas were harvested at three stages of growth over a growing season; young vegetation, initial flowering, and late season. The samples were subjected to oven-drying and freeze-drying and analyzed for extractable (ECT), protein-bound (PBCT), and fiber-bound (FBCT) CT using a butanol-HCl procedure, comparing several types of purified CT as standards.

Optimizing feedstock production from switchgrass (Panicum virgatum L.) requires careful matching of genotype to environment, especially for southern U.S. regions. Nine genotypes from four combinations of ecotype and morphological type were harvested once yearly in autumn for 3 or 4 yr at five locations across Texas, Arkansas, and Louisiana that varied in latitude and precipitation. Genotypes were evaluated for dry matter yield (DMY), plant density, tiller density, lodging, and rust (caused by Puccinia spp.) infection. Genotype × environment (G×E) interactions were identified for most traits. Biomass yield of all genotypes tended to increase with latitude, but lowland morphological types may have been more sensitive than upland morphological types to differences in moisture availability. Yield (5.82 vs. 14.97 Mg ha−1, respectively) and persistence (final stand density, 3.99 vs. 5.96 plants m−2) were lower for upland than for lowland genotypes, particularly at higher rainfall and more southern sites. Lowland genotypes were often able to compensate for stand thinning by increasing individual plant size, but upland genotypes were not. Lodging and rust scores were higher for upland than for lowland genotypes. Yield (13.65 vs. 9.75 Mg ha−1) and final plant density (5.58 vs. 4.95 plants m−2) were higher for southern than northern ecotypes. The southern‐lowland combination exhibited the best yield and persistence over the study region, and genotypes within this group exhibited variability in yield among sites. Therefore, development of switchgrass cultivars for biomass production in the southern USA should focus on the southern‐lowland genotypes.

from early March, when grazing on dual-use wheat must be terminated to produce grain crop, until May when Introduced cool-season perennial grasses may become an imporgrazing on warm-season perennial grass pastures can be tant complementary winter forage to dual-use wheat (Triticum aestivum L.) in high-risk semiarid environments of the southern Great initiated (Reuter et al., 1999). Plains. Currently recommended, summer semidormant cultivars are Introduced cool-season perennial grasses are becomnot adapted to prolonged and severe summer drought and not producing an important source of high quality winter forage tive in the autumn grazing season. In an experiment planted at Vernon, to complement or replace wheat forage and perennial TX, on a Miles fine sandy loam (fine-loamy, mixed, thermic Udic warm-season grass pastures in the southern Great Plains Paleustalfs) in October 2000, we evaluated productivity and plant (Reuter and Horn, 2002). Perennial cool-season grasses survival of an obligatory summer-dormant 'Grasslands Flecha' and may potentially be a more reliable and economically summer semidormant 'Georgia 5', 'Jesup', and 'Kentucky 31' tall sound source of early-season forage than wheat, saving fescue (Festuca arundinacea Schreb.); a highly summer semidormant farmers about $100 per ha annually (Redmon, 1997). 'Grasslands Maru' hardinggrass (Phalaris aquatica L.); and summer They also contribute to environmental sustainability of semidormant 'Grasslands Matua' and 'Grasslands Tango' prairiegrass (Bromus wildenowii Kunth) under two defoliation intensities of 7.5 the agroecosystems by reducing water runoff and soil and 15 cm. Georgia 5, Jesup, and Grasslands Flecha were either erosion (Brady and Weil, 1996), conserving soil water infected with the novel Neotyphodium coenophialum Glenn, Bacon, during summer drought (Hanselka et al., 1994), improvand Hanlin endophyte strain AR542, with their endemic endophytes ing soil physical and chemical properties (Dormaar et (except for Grasslands Flecha), or noninfected (E-). Only Grasslands al., 1995), and providing habitat for wildlife (Duebbert Flecha and Grasslands Maru successfully survived summer droughts et al., 1981). during 2001-2004. Prairiegrass behaved as an annual but did not Severe and often prolonged summer droughts and reseed in 2003. Aboveground biomass was greater at 15-vs. 7.5-cm poorly understood management practices adversely afdefoliation height, except for 2004 growing season. In Grasslands fect persistence and productivity of introduced cool-Flecha, the novel endophyte increased tiller survival during summer season perennial grassland ecosystems at the margin of drought by 150% (2001) and 121% (2002) when compared with Eplants. Obligatory and highly summer semidormant cultivars of peren-