Switchgrass (Panicum virgatum L.) is a C4 grass with high biomass yield potential and is now a model species for the Bioenergy Feedstock Development Program. Two distinct ecotypes (e.g., upland and lowland) and a range of plant morphotypes (e.g., leafy and stemmy) have been observed in switchgrass. The objective of this study was to determine the influence of ecotype and morphotype on biomass feedstock quality. Leaf and stem tissues of leafy and stemmy morphotypes from both lowland and upland ecotypes were analyzed for key feedstock traits. The leaf : stem ratio of leafy morphotype was more than 40% higher than the stemmy morphotype in both upland and lowland ecotypes. Therefore, the stemmy morphotype has significant advantages over leafy morphotype during harvesting, storage, transportation and finally the feedstock quality. Remarkable differences in feedstock quality and mineral composition were observed in switchgrass genotypes with distinct ecotypic origins and variable plant morphotypes. Lignin, hemicelluloses and cellulose concentrations were higher in stems than in the leaves, while ash content was notably high in leaves. A higher concentration of potassium was found in the stems compared to the leaves. In contrast, calcium was higher and magnesium was generally higher in the leaves compared to stems. The upland genotypes demonstrated considerably higher lignin (14.4%) compared with lowland genotypes (12.4%), while hemicellulose was higher in lowland compared with upland. The stemmy type demonstrated slightly higher lignin compared with leafy types (P < 0.1). Differences between the ecotypes and morphotypes for key quality traits demonstrated the potential for improving feedstock composition of switchgrass through selection in breeding programs.

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The effects of 4 Ν application levels, 0, 45, 90, and 135 kg N/ha, and 2 cultivars, 'Centennial' and 'Jewel', on total Ν and NO 3 -N concentration of leaf blades and NO 3 -N concentration of petioles were determined in 2 field experiments. The concentrations of NO 3 -N in petioles of 'Centennial' plants were much higher than those of 'Jewel' plants. Petiole NO 3 -N concentrations were more sensitive to differences in soil Ν application levels than blade total Ν concentrations. Petiole NO 3 -N concentrations were also affected by plant age at sampling. While petiole NO 3 -N concentration was a reliable indicator of current Ν status of the plants, total Ν concentration of blades appeared to be a more reliable predictor of yield. Critical concentrations of total Ν 529

Accurate predictions of forage quality of winter wheat (Triticum aestivum L.) during spring would allow targeting of harvests or grazings to desired levels of nutritive composition to meet specific animal requirements. The objectives of this study were to compare number of days since 15 February (DAYS) and growing degree days (GDD, base 4.4 °C) as predictors of Feekes and Zadoks growth stages, and to compare DAYS, GDD, Feekes, and Zadoks growth stages as predictors of forage yield and quality. The 2‐yr study on a Captina silt loam (fine, mixed, mesic, Typic Fragiudult) at the University of Arkansas Main Experiment Station, Fayetteville, AR, involved four cultivars of soft red winter wheat. Plots were harvested at six growth stages: beginning of pseudostem elongation, second node detectable, flag leaf collar just visible, boot swollen, inflorescence completely emerged, and soft dough. Feekes and Zadoks growth stage scales were regressed on DAYS and GDD. Forage yield, percentage lamina (ratio of leaf lamina to whole‐plant dry weight), and nutritive concentrations were regressed on Feekes, Zadoks, DAYS, and GDD. Lower root error mean squares were generally obtained with GDD than DAYS for predicting growth stages. Zadoks scale and DAYS were generally the best predictors of forage yield, whereas Feekes scale and DAYS were the best predictors of percentage lamina and crude protein. Zadoks and GDD were the best predictors of neutral detergent fiber and in vitro dry matter digestibility. The Zadoks scale and GDD would be useful parameters in wheat growth models designed to target harvests to desired levels of forage quality.

Lignocellulosic biomass is composed of complex structures of cellulose, hemicellulose, lignin, and other biochemical and structural components of cell wall. Because of its obligatory outcrossing nature, broad adaptation, and extensive genetic variation, both biomass production and cell wall composition traits could be improved for biofuel production. Among the cell wall components, lignin has been found to be a major inhibitor of the conversion process of cellulosic