Improving the biomass yield of switchgrass (Panicum virgatum L.) will improve its utility as a dedicated energy crop by increasing both its net and total energy yield per hectare. In a previous space‐transplanted study, midparent heterosis for biomass yield was reported for population and specific F1 hybrids of the lowland‐tetraploid cultivar Kanlow and the upland‐tetraploid cultivar Summer. These two cultivars were proposed to be two different heterotic groups. The objective of this study was to determine the extent of heterosis for biomass yield in reciprocal Kanlow (K) and Summer (S) F1 population hybrids grown in simulated swards and to determine the effect of advance in generation on biomass yield. Parent populations and their F1, F2, and F3 population hybrids were grown in transplanted sward plots located near Mead, NE, for a three‐year period. Plant density in the simulated swards was equivalent to acceptable stands in seeded plots. Plots were not harvested the establishment year to enable them to become fully established. Biomass yields were determined for the following two years. There was significant high‐parent heterosis of 30 to 38% (P ≤ 0.01) for biomass yield for both the K × S F1 and S × K F1 hybrid populations. Heterosis for biomass yield declined with advance in generation. Heterosis for biomass yield in switchgrass may need the competitive conditions of swards to be fully expressed. Additional trials of specific hybrids established from seed are needed to further verify these conclusions. These results do provide ample justification for additional research to develop switchgrass population and specific hybrids.

The United States Department of Energy (DOE) has identifi ed switchgrass (Panicum virgatum L.) as a viable perennial herbaceous feedstock for cellulosic ethanol production. Although switchgrass bioenergy research was initiated by USDA-ARS, Lincoln, NE, USA in 1990, switchgrass research has been conducted at this location since the 1930s. Consequently, a signifi cant amount of genetic and agronomic research on switchgrass has been conducted for the Corn Belt and Central Great Plains of the USA that is directly applicable to its use as a biomass energy crop. Similar research must be conducted in other major agroecoregions to verify or modify switchgrass management practices (agronomics) for bioenergy production. The technology to utilize switchgrass for producing ethanol using a cellulosic platform or by pyrolysis to generate syngas is advancing rapidly. Regardless of platform, using switchgrass for ethanol production will require the development of improved bioenergy cultivars or hybrids and improved agronomics to optimize production and will introduce competing uses for the land base. Published in

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Switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerardii Vitman) are important warm‐season grasses in livestock production systems in the central and eastern USA. The objectives of this study were to quantify the morphological development of ‘Trailblazer’ switchgrass and ‘Pawnee’ big bluestem and to evaluate day of the year (DOY) and growing degree day (GDD) as predictors of switchgrass and big bluestem morphological stage. Pure stands of each species were sampled at weekly intervals in 1990 and 1991 at Mead, NE, and classified as to mean stage count (MSC) and mean stage weight (MSW). Prediction equations for MSC and MSW were developed based on DOY and GDD. The validation study was harvested at 2‐wk intervals in 1992 and 1993 at Mead, NE, and Manhattan, KS, and classified as to MSC and MSW. Switchgrass and big bluestem MSC and MSW were related linearly in all environments. Linear DOY calibration equations accounted for 96% of the variation in switchgrass MSC across four environments, which indicates that switchgrass development was related to photoperiod and that general management recommendations could be based on DOY in the central Great Plains. Quadratic GDD calibration equations accounted for 83% of the variation in big bluestem MSC across four environments, which indicates that big bluestem development is more difficult to predict and management recommendations in the central Great Plains should be based on morphological development (which is best predicted by GDD). The comprehensive growth staging system gave repeatable results for quantifying the morphological development of switchgrass and big bluestem. The morphological development of switchgrass and big bluestem can be reliably predicted for adapted cultivars in the central Great Plains during years with near‐normal precipitation using DOY and GDD because of the determinate growth habit of these grasses.

documented for switchgrass and big bluestem (Perry and Baltensperger, 1979;George and Hall, 1983; Griffin Predicting forage quality would help producers schedule hay har- and Jung, 1983; Mitchell et al., 1994a). However, most vesting to obtain desired hay quality. Our objective was to determine if growing degree day (GDD), day of the year (DOY), mean stage of the studies that have evaluated changes in forage count (MSC), and mean stage weight (MSW) could be used to predict quality have been comparisons of switchgrass and big in vitro digestible dry matter (IVDDM), crude protein (CP), and bluestem on specific DOYs or at generalized vegetative neutral-detergent fiber (NDF) of 'Trailblazer' switchgrass (Panicum or reproductive stages. No studies have been conducted virgatum.) and 'Pawnee' big bluestem (Andropogon gerardii Vitman) where changes in the forage quality of switchgrass and grown in Nebraska and Kansas. This field study was conducted from big bluestem have been documented with quantified 1990 to 1993 at Mead, NE on Typic Argiudoll soils and from 1992 to changes in morphological development. 1993 at Manhattan, KS on Aquic Argiudoll soils. Plants were sampled The morphological development of perennial grasses at 1-wk intervals in 1990 and 1991 and at 2-wk intervals in 1992 and is an important consideration when making forage man-1993. They were morphologically classified as MSC and MSW and agement decisions (Kalu and Fick, 1983; Moore and analyzed for IVDDM, CP, and NDF. Switchgrass IVDDM and CP were best predicted by GDD models, which accounted for 86 and Moser, 1995). Plant maturity is the primary factor affect-91% of the variation, respectively, whereas NDF was best predicted ing the morphological development and forage quality by MSC and MSW. Big bluestem IVDDM was best predicted by within a species (Kalu and Fick, 1983; Nelson and Moser, MSW and CP was best predicted by GDD, which both accounted for 1994). A system for quantifying the morphological de-90% of the variation. Mean stage weight accounted for 74% of the velopment of perennial grasses based on the MSC and variability in big bluestem NDF. The DOY model adequately pre-MSW was developed by Moore et al. (1991). This system dicted forage quality due primarily to the determinate growth habit was used to quantify the morphological development of these species. Morphological development accurately predicted of switchgrass and big bluestem in Nebraska and Kansas forage quality in many instances. Although no universal parameter (Mitchell et al., 1997) and differentiate the developadequately predicted concentrations of IVDDM, CP, and NDF, it mental stages in weeping lovegrass [Eragrostis curvula was possible to accurately predict quality with readily available environmental data and measures of plant maturity. R. Mitchell and D. Wester, Dep. of Range, Wildlife, and Fisheries Management, Texas Tech Univ., Lubbock, TX 79409; J. Fritz, Dep. ments in the central Great Plains. of Agron., Kansas State Univ., Manhattan, KS 66506; K. Moore,

or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Alternative conversion systems such as consolidated bioprocessing which combines the enzymatic production, hydrolysis, and fermentation process into one reactor, thus reducing capital costs and increasing biorefi nery effi ciency, are expected to be commercially available as well (Lynd et al., 2005). Cellulosic biomass conversion to biofuels via biochemical or thermochemical methods require more complex and ABSTRACT Information on temporal and spatial variation in switchgrass (Panicum virgatum L.) biomass composition as it aff ects ethanol yield (L Mg -1 ) at a biorefi nery and ethanol production (L ha -1 ) at the fi eld-scale has previously not been available. Switchgrass biomass samples were collected from a regional, on-farm trial and biomass composition was determined using newly developed near-infrared refl ectance spectroscopy (NIRS) prediction equations and theoretical ethanol yield (100% conversion effi ciency) was calculated. Total hexose (cell wall polysaccharides and soluble sugars) concentration ranged from 342 to 398 g kg -1 while pentose (arabinose and xylose) concentration ranged from 216 to 245 g kg -1 across fi elds. Th eoretical ethanol yield varied signifi cantly by year and fi eld, with 5 yr means ranging from 381 to 430 L Mg -1 . Total theoretical ethanol production ranged from 1749 to 3691 L ha -1 across fi elds. Variability (coeffi cient of variation) within established switchgrass fi elds ranged from 1 to 4% for theoretical ethanol yield (L Mg -1 ) and 14 to 38% for theoretical ethanol production (L ha -1 ). Most fi elds showed a lack of spatial consistency across harvest years for theoretical ethanol yield or total theoretical ethanol production. Switchgrass biomass composition from farmer fi elds can be expected to have signifi cant annual and fi eld-to-fi eld variation in a production region, and this variation will signifi cantly aff ect ethanol or other liquid fuel yields per ton or hectare. Cellulosic biorefi neries will need to consider this potential variation in biofuel yields when developing their business plans.

Introduced forages offer alternatives to traditional cropping sys-Tech University) suggested that nutritive value of old tems in the semiarid Texas High Plains, but effects of irrigation on nutritive value are not well known. Three old world bluestem (Bothri-world bluestems (OWB) was influenced by species, enochloa) species [B. bladhii (Retz) S.T. Blake 'WW-B. Dahl', B. vironmental conditions, management, and physiographic ischaemum (L.) Keng. var. ischaemum (Hack.) 'WW-Spar', and B. location. Morphological characteristics of forages influcaucasica (Trin.) C.E. Hubbard 'Caucasian'] were surface drip-irrience and can help in predicting nutritive value (Mitchell gated with zero (dryland) and low, medium, and high irrigation levels, et al., 2001). to determine nutritive value and morphological development in 2001Available moisture as precipitation and irrigation is to 2003 under a completely randomized block design, a split-plot directly related to growth and total productivity of these treatment arrangement, and three replicates. Water applied in the OWB species (Philipp, 2004). In the Texas High Plains, high treatment was 100% replacement of potential evapotranspiration water for irrigation is declining and additional land will minus precipitation. Medium and low treatments were 66 and 33% likely be converted from cropland to grassland. While of the high treatment. Dry matter digestibility (DMD) of all species was higher (P Ͻ 0.05) at low irrigation than at other levels (580, 560, Bothriochloa species have been widely adopted, little 550, and 570 g kg Ϫ1 for low, medium, high, and dryland, respectively;information is available regarding their nutritive value SE ϭ 4.0). Dahl was higher (P Ͻ 0.05) in crude protein (87 g kg Ϫ1 )and morphological responses to a variety of water rethan Spar (76 g kg Ϫ1 ) and Caucasian (75 g kg Ϫ1 ; SE ϭ 2.0) during the gimes when grown in the climatic conditions of Texas growing season. In all species, total nonstructural carbohydrates and High Plains. Thus, our objectives were to determine DMD declined while neutral detergent fiber and acid detergent fiber nutritive value and growth characteristics of B. caucasincreased with increasing irrigation. Before hay harvest, leaf blade: ica, B. ischaemum, and B. bladhii under the semiarid stem-plus-sheath ratio declined also, but after hay harvest, effects of environmental conditions of the southern High Plains irrigation were less consistent. Results suggested that irrigation likely of Texas as influenced by amount of irrigation water. affected nutritive value through effects on plant morphology and physiological age. Thus, irrigation strategies and species selection may aid in optimizing forage quality. MATERIALS AND METHODSThree old world bluestem species (B. caucasica, ischaemum, and bladhii) and four water treatments (dryland, low, medium, vation District No. 1, Lubbock, TX.

placed on clipping, using it only for calibration and validation within trials. Nondestructive standing crop estimators are important for efficientThe canopy analyzer (CA) (LI-COR, Lincoln, NE) monitoring of native and agronomic systems. This study evaluated is a fast, nondestructive instrument that indirectly estiplot and pasture estimates of standing crop using LAI-2000, visual mates leaf area index (LAI; Welles and Norman, 1991). obstruction, canopy height, and weighted plate measurements. Research was conducted in Lubbock County, Texas, in 1999 on areas Direct measurements of LAI using the LAI-3000 area dominated by Amarillo fine sandy loam (fine-loamy, mixed, thermic meter (LI-COR, Lincoln, NE) have shown a positive Aridic Paleustalfs). Five hundred plot estimation samples were collinear relationship between leaf area and SC (Engel et lected for each method along 25 transects, and each transect mean was al., 1987). Since the CA measures foliage area per unit used for the pasture estimation trials. Coefficients of determination of ground area, we hypothesized a positive relationship improved as we moved from plot (0.34, 0.85, 0.37, and 0.70) to pasture would exist between CA measurements and SC.(0.67, 0.87, 0.59, and 0.83) estimation for LAI-2000, visual obstruction,