Maturity and plant density effects on stem and leaf traits for alfalfa biomass production .

JoAnn F. S. Lamb, Craig C. Sheaffer, Deborah A. Samac, and Neal P. Martin.
USDA-ARS, Plant Science Research Unit, and University of Minnesota, St. Paul, MN

Alfalfa was chosen as the dedicated biomass feed stock resource for a 75 MW power station at Granite Falls, MN (De Long, et al., 1995). In this biomass production system alfalfa hay will be fractionated into stem material for conversion to electricity and leaf meal to be sold as a high quality livestock protein supplement. To meet the economic demands of this new biomass production system the yield of both leaf and stem fractions will need to be maximized. A study was established to assess environmental and harvest management effects on biomass production in alfalfa. Five unrelated germplasms, two Flemish sources, (Barnes et al. 1977) and three moderately dormant North American sources were established at two locations at four plant population densities (450, 180, 50, and 16 plants m-2). All germplasm by plant density combinations were harvested at two stages of plant maturity, early bud (3 harvests per season) and late flower/early pod (2 harvests per season). Stem and leaf yield, percent crude protein (%CP) and percent neutral detergent fiber (%NDF) are being compared among germplasms under the different plant density and maturity treatment combinations. Desirable stem traits for conversion to electricity include high yield, high % NDF and low % CP. Preliminary data from one year and location showed the greatest seasonal leaf and stem yield for all germplasms was found at the 180 plants m-2 density at the late flower/early pod maturity under a 2 harvest management. No differences in stem % CP was found among the alfalfa germplasms. Stems harvested at the late flower/early pod maturity had lower % CP and greater % NDF than those harvested at early bud and the 450 plants m-2 density had significantly greater stem % CP and lower % NDF compared the rest of the plant density treatments. Leaf % CP was greater under early bud management treatment, but season total harvested leaf crude protein was the same when harvested at either the early bud (3 cuts) or the late flower/ early pod (2 cuts) maturity stages. The three moderately dormant North American germplasms sources had greater leaf yield than the Flemish types, but the Flemish types had fewer lodged plants. Preliminary results demonstrated that decreased plant population densities and harvesting forage at later maturities may enhance the profitability of an alfalfa biomass production sytem.

References

Barnes, D.K., E.T. Bingham, R.P.M. Murphy, O.J. Hunt, D.F. Beard, W.H. Skrdla, and L.R. Teuber. 1977. Alfalfa germplasm in the United States: Genetic vulnerability, use, improvement, and maintenance. Vol. 1571. Technical Bulletin ed. USDA ARS, Washington, DC.

De Long, M.M., E.A. Oelke, M. Onischak, M.R. Schmid, and B.C. Wiant. 1995. Sustainable biomass energy production and rural economic development using alfalfa as feedstock. In Proc. Second Biomass Conf. Americas. p.1582-1592. National Renewable Energy Laboratory, Dept. of Energy, Publication NREL/CP- 200-8098.