Current methods for measuring ethanol yields from lignocellulosic biomass are relatively slow and are not well geared for analyzing large numbers of samples generated by feedstock management and breeding research. The objective of this study was to determine if an in vitro ruminal fermentation assay used in forage quality research was predictive of results obtained using a conventional biomass-to-ethanol conversion assay. In the conventional assay, herbaceous biomass samples were converted to ethanol by Saccharomyces cerevisiae cultures in the presence of cellulase enzymes. Cultures were grown in sealed serum bottles and gas production monitored by measuring increasing head space pressure. Gas accumulation as calculated from the pressure measurements was highly correlated (r(2)>0.9) with ethanol production measured by gas chromatography at 24 h or 7 days. The same feedstocks were also analyzed by in vitro ruminal digestion, as also measured by gas accumulation. Good correlations (r(2) approximately 0.63-0.82) were observed between ethanol production during simultaneous saccharification and fermentation and gas accumulation in parallel in vitro ruminal fermentations. Because the in vitro ruminal fermentation assay can be performed without sterilization of the medium and does not require aseptic conditions, this assay may be useful for biomass feedstock agronomic and breeding research.

Sdtchgrass (Punicum virgatum L.) has potential as a forage and biomass crop, but difficult establishment has limited its use. Germination and emergence were studied for 6 eultivars of suitchgrass ('Alamo', 'Blac~~ell', 'Cave-in-Rock', 'Kanlow', 'Pathfinder', and 'Trailblazer'). Germination studies Tvere conducted to determine the effect of light on germination and coleoFfile length, and to determine the effect of seed size (40,50, 63, 700, and SO" air valve settings for a South Dakota seed blower) an germination. A greenhouse study was also conducted to examine the effect of seed size, planting depth, (5,10, and 20 mm), and soil type (sand and 2 silt loams) on emergence. Germination of unsized seed increased linearly as duration in the germination chamber increased from 7 to 21 days for all cultivars. Although presence of light did not affect germination, coleoptile length under continuous darkness averaged 4.1 cm and was greater than the 1.9 cm measured for those v.ith daily light exposure of 16 hours. Both germination and emergence increased nonlinearly as seed size increased. For both silt-loam soils, emergence was low acd not affected by planting depth. A nonlinear decline in emergence with increased planting depth uas detected in sand 7 days after pIant&, but not after 14 and 21 days. Results of the study indicate that seed size and soil texture had a greater effect on emergence than did planting depth dolm to a depth of 20 mm.

Increasing atmospheric [CO ] and temperature are expected to affect the productivity, species composition, biogeochemistry, and therefore the quantity and quality of forage available to herbivores in rangeland ecosystems. Both elevated CO (eCO ) and warming affect plant tissue chemistry through multiple direct and indirect pathways, such that the cumulative outcomes of these effects are difficult to predict. Here, we report on a 7-yr study examining effects of CO enrichment (to 600 ppm) and infrared warming (+1.5°C day/3°C night) under realistic field conditions on forage quality and quantity in a semiarid, mixedgrass prairie. For the three dominant forage grasses, warming effects on in vitro dry matter digestibility (IVDMD) and tissue [N] were detected only in certain years, varied from negative to positive, and were relatively minor. In contrast, eCO substantially reduced IVDMD (two most abundant grasses) and [N] (all three dominant grass species) in most years, except the two wettest years. Furthermore, eCO reduced IVDMD and [N] independent of warming effects. Reduced IVDMD with eCO was related both to reduced [N] and increased acid detergent fiber (ADF) content of grass tissues. For the six most abundant forage species (representing 96% of total forage production), combined warming and eCO increased forage production by 38% and reduced forage [N] by 13% relative to ambient climate. Although the absolute magnitude of the decline in IVDMD and [N] due to combined warming and eCO may seem small (e.g., from 63.3 to 61.1% IVDMD and 1.25 to 1.04% [N] for Pascopyrum smithii), such shifts could have substantial consequences for the rate at which ruminants gain weight during the primary growing season in the largest remaining rangeland ecosystem in North America. With forage production increases, declining forage quality could potentially be mitigated by adaptively increasing stocking rates, and through management such as prescribed burning, fertilization at low rates, and legume interseeding to enhance forage quality.

Growing complementary plant species is an alternative approach to enhancing pasture production. Our objective was to estimate combining ability for native, warm‐season grasses and legumes grown in binary mixtures in the field using a combining ability analysis of variance. Six monocultures and 15 binary mixtures of the following species were studied: big bluestem, Andropogon gerardii Vit.; Illinois bundleflower, Desmanthus illinoensis (Michx.) MacM.; roundhead lespedeza, Lespedeza capitata Michx.; slender lespedeza, L. virginica (L.) Britt.; switchgrass, Panicum virgatum L.; and indiangrass, Sorghastrum nutans (L.) Nash. General combining ability (GCA) effects were found for forage dry matter yields (DMY, P ≤ 0.05) of Illinois bundleflower (−1240 kg ha−1), roundhead lespedeza (−3460 kg ha−1), slender lespedeza (−3300 kg ha−1), and switchgrass (8370 kg ha−1). Specific combining ability (SCA) effects were found for DMY (P ≤ 0.1) of switchgrass‐legume mixtures (1360 kg ha−1) and indiangrass‐Illinois bundleflower mixtures (1230 kg ha−1). General combining ability and SCA effects were found for crude protein concentration (CPC) of all species and mixtures (P ≤ 0.1), respectively. General combining ability effects were found for in vitro dry matter digestibility (IVDMD) for switchgrass and the three legume species (P ≤ 0.05). The compatibility of these species could not be predicted solely by DMYs. Compatible mixtures, however, were identified with greater confidence when other variables, such as CPC, IVDMD, and visual observations, were taken into account. On the basis of total forage protein (DMY times CPC), the only compatible grass‐legume mixture was indiangrass‐Illinois bundleflower (SCA effect = 100 kg ha−1, P ≤ 0.05).