Alfalfa (Medicago sativa L.) is a promising bioenergy and bioproduct feedstock because of its high yield, N-fixation capacity, potential for planting in rotation with corn (Zea mays L.), and valuable protein co-product (leaf meal). Our objective was to examine the effect of growth environment on biomass yield, cellulosic ethanol traits, and paper pulp fiber characteristics of alfalfa stems. Landscape position (summit and mild slope), season of harvest (four harvests per season), and multiple years (2005 and 2006) provided environmental variation. Alfalfa stem samples were analyzed for cell wall carbohydrate and lignin concentration. Stems were subjected to dilute acid pre-treatment, enzymatic saccharification, and pulping processes to measure relevant cellulosic ethanol and paper production traits. Landscape position was not a significant source of variation for yield or any biomass quality trait. Yields varied among harvests in 2005 (1,410-3,265 kg ha -1) and 2006 (1,610-3,795 kg ha -1). All cell wall, conversion test, and paper production traits exhibited year by harvest interactions with no clear pattern. Total carbohydrates and lignin ranged from 440 to 531 gkg -1 DM and from 113 to 161 gkg -1 DM, respectively. Release of cell wall sugars by the conversion test ranged widely (419 to 962 g kg -1 DM). Fiber traits were similarly variable with length and fine content ranging from 1.24 to 1.59mm and from 15.2% to 21.9%, respectively. Utilizing alfalfa biomass for cellulosic ethanol and paper pulp production will involve dealing with significant feedstock quality variation due to growth environment.
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Acknowledgments We appreciate the valuable training and technical assistance of Ted Jeo, Matt Bickell, Tom Hoverstad, and Paul Adam. Funding for this project was provided by the Initiative for Renewable Energy and the Environment of the University of Minnesota. Mention of a proprietary product does not constitute a recommendation or warranty of the product by the University of Minnesota or the USDA-ARS and does not imply its approval to the exclusion of other suitable products.
- Cellulosic ethanol
- Paper pulp fiber