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ARS Home » Midwest Area » St. Paul, Minnesota » Plant Science Research » Research » Publications at this Location » Publication #129369
Title: PLANT DENSITY AND MATURITY EFFECTS ON LEAF AND STEM YIELD IN ALFALFA

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

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/4/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary: Biomass fuels are being explored to replace or supplement nuclear and fossil fuels. Alfalfa is being investigated as a source of biomass for a biofuel production system where the stems are processed to produce biofuels and the leaves are sold as a source of animal feed. This biomass system provides a new use for the stem portion of alfalfa hay and has an advantage eover other crops by providing a secondary income from selling the leaves a a high value livestock feed. The key to success in an alfalfa biomass system will be to develop management systems and cultivars that will maximize both leaf and stem yield. Normally, alfalfa is harvested at an early age to increase the nutrient value of the hay for livestock. As alfalfa matures the stem portion of the hay increases while leaves are lost. We investigated the effects of plant age and plant population number on leaf and stem yield to make economic and management decisions about a biomass production system using alfalfas that differed in feed value, stem size, and winter hardiness. Delaying forage harvest until the alfalfa plants were starting to produce pods and decreasing the plant population to 40 percent of what is customarily used by growers allowed all of the alfalfas we tested to produce the greatest leaf and stem yield. Delaying harvest allowed for only two cuts per season and produced maximum stem yield. Opening the plant stand by decreasing the population number decreased plant to plant competition and incidence of disease and permitted more leaves to last until harvest at this more mature plant age. This research is important to farmers and agriculturally based alternative energy interests because it shows alfalfa management can be modified to meet biomass energy needs by delaying harvest and decreasing stand density.

Technical Abstract: A system has been proposed using alfalfa (Medicago sativa L) as a biofuel feedstock in which the stems would be processed to produce energy and the leaves used as a livestock feed. A biomass energy production system adds value to the stem component and has an advantage over other crops by a secondary income from selling the leaves as a high value livestock feed supplement. The key to success in an alfalfa biomass energy production system will be to develop management systems and germplasms that would maximize both leaf and stem yield. Our objectives were to evaluate the effects and interactions of environment, plant density, and harvest maturity on leaf and stem yield of alfalfa germplasms differing in fall dormancy, leaf to stem ratio, and forage quality. Five alfalfa germplasms established at four plant densities (450, 180, 50, and 16 plants m-2) were harvested at early bud and green pod maturity stages and evaluated in three eenvironments for leaf, stem, and total forage yield. The plant density x harvest maturity interaction had the greatest impact on all yield components. Forage, leaf, and stem yield per unit area tended to increase as plant density increased from 16 to 450 plants m-2 at the early bud stage. In contrast, forage, leaf, and stem yield at the green pod maturity stage increased as plant density increased from 16 to 180 plants per m-2, but at 450 plants per m-2 forage yield dropped off dramatically. The greatest leaf, stem, and forage yield occurred at the green pod maturity stage at the 180 plants m-2 treatment. Delaying harvest until the green pod maturity stage and lowering plant population density to 180 plant m-2 maximized both leaf and stem yield for all alfalfa germplasms.