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Title: Alfalfa leaf protein and stem cell wall polysaccharide yields under hay and biomass management systems

Author
item Lamb, Joann
item Jung, Hans Joachim
item SHEAFFER, CRAIG - UNIVERSITY OF MINNESOTA
item Samac, Deborah - Debby

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2007
Publication Date: 7/30/2007
Citation: Lamb, J.F., Jung, H.G., Sheaffer, C.C., Samac, D.A. 2007. Alfalfa leaf protein and stem cell wall polysaccharide yields under hay and biomass management systems. Crop Science. 47:1407-1415.

Interpretive Summary: Alfalfa has the potential to be a significant contributor to America's renewable energy future. In an alfalfa biomass energy production system, alfalfa forage would be separated into stems and leaves. The stems would be processed to produce liquid fuel (ethanol), and the leaves would be sold separately as a livestock feed. One of the advantages of alfalfa over other crops to produce biomass energy is this potential for a secondary income selling the leaves as an animal feed. Therefore, concentrations and yields of leaf protein and stem cell wall sugars (used to produce ethanol) are key plant traits in new alfalfa varieties developed for use in biofuel production systems. We proposed a modified management regime with a reduction in the numbers of plants seeded per field and delayed, less frequent cuttings be used for alfalfa biomass/biofuel production to maximize both leaf and stem yield. We compared a biomass management strategy to traditional hay production practices on alfalfas with different genetic backgrounds. Two hay-type alfalfas adapted to the Upper Midwest region of the U.S. and two biomass-type alfalfas of southern European origin were seeded 42 plants per square foot and harvested at the early bud maturity stage three to four times each year (hay management system) and at 18 plants per square foot and harvested twice per growing season at the green pod maturity stage (biomass management system) in several locations. The biomass-type alfalfas under the biomass management system had comparable leaf protein yields and 37% higher stem sugar yields and nearly double the potential ethanol production (99% increase) compared to the hay-type alfalfas under the hay management system. Clearly, using appropriate alfalfa varieties with modified production practices, opportunities exist for alfalfa to be a significant contributor to America's renewable energy future.

Technical Abstract: Alfalfa (Medicago sativa L.) has been proposed as a biofuel feedstock in which the stems would be processed to produce ethanol and the leaves sold separately as a livestock feed. We propose a modified management regime with reduced population density and delayed, less frequent harvests be implemented for biomass/biofuel production. Our objectives were to evaluate the effects management strategy has on leaf crude protein (CP), stem carbohydrate concentrations, and yields of alfalfa germplasms differing in genetic background. Two hay-type and two biomass-type alfalfas were established at 450 plants m**-2 and harvested at early bud (hay management system) and at 180 plants m**-2 and harvested at green pod (biomass management system) in three environments. Cell wall material under the biomass management system was more lignified and contained more xylose, similar glucose, and less of the other polysaccharide components compared to plant material under the hay management system. Stem lignin composition and leaf CP yields were similar for all four germplasms, but stem glucose, mannose, and xylose DM concentrations and yields were greater in the biomass-type alfalfas than the hay-type alfalfas. The biomass-type alfalfas under the biomass management had lower leaf CP, higher stem cell wall polysaccharide, and higher stem lignin concentrations, comparable leaf CP yield, and 37% higher stem cell wall polysaccharide yields compared to the hay-type alfalfas under the hay management treatment. The impact of altered stem cell wall composition and increased stem DM yield of a biomass-type alfalfa under the biomass system compared to a hay-type alfalfa under the hay system increased the theoretical potential ethanol yield by 99%.