Biomass Yield and Biofuel Quality of Switchgrass Harvested in Fall or Spring

Seasonal time of switchgrass (Panicum virgatum L.) harvest affects yield and biofuel quality and balancing these two components may vary depending on conversion system. A field study compared fall and spring harvest measuring biomass yield, element concentration, carbohydrate characterization, and total synthetic gas production as indicators of biofuel quality for direct combustion, ethanol production, and gasification systems for generation of energy. Switchgrass yields decreased almost 40% (from about 7–4.4 Mg ha) in winters with above average snowfall when harvest was delayed over winter until spring. The moisture concentration also decreased (from about 350– 70 g kg) only reaching low enough levels for safe storage by spring. About 10% of the yield reduction during winter resulted from decreases in tiller mass; however, almost 90% of the yield reduction was due to an increase in biomass left behind by the baler. Mineral element concentrations generally decreased with the delay in harvest until spring. Energy yield from gasification did not decrease on a unit biomass basis, whereas ethanol production was variable depending on the assessment method. When expressed on a unit area basis, energy yield decreased. Biofuel conversion systems may determine harvest timing. For direct combustion, the reduced mineral concentrations in spring-harvested biomass are desirable. For ethanol fermentation and gasification systems, however, lignocellulose yield may be more important. On conservations lands, the wildlife cover provided by switchgrass over the winter may increase the desirability of spring harvest along with the higher biofuel quality. ANUMBER OF PLANT SPECIES have been considered as dedicated energy crops (Lewandowski et al., 2003b; Walsh et al., 2003; Angelini et al., 2005), representing both annual and perennial herbaceous crops and shortrotation trees. Perennial grasses have several advantages over annual crops such as lower establishment costs, reduced soil erosion, increased water quality, and enhanced wildlife habitat (McLaughlin et al., 2002; Roth et al., 2005). Switchgrass has been evaluated as a biofuel crop in the Midwest (Vogel et al., 2002; Casler and Boe, 2003), the Southern (Sanderson et al., 1999; Muir et al., 2001; Cassida et al., 2005) and Northern Great Plains of the USA (Berdahl et al., 2005; Lee and Boe, 2005), southeastern Canada (Madakadze et al., 1999), and Europe (Elbersen et al., 2001). The latitude-of-origin has a large impact on switchgrass yield potential and ability to survive in extreme environments (Casler et al., 2004); lowland ecotypes from the southern latitudes have higher yield potential than upland ecotypes from the north, but are not as cold tolerant. Seasonal time of harvest affects switchgrass yield (Madakadze et al., 1999; Sanderson et al., 1999; Vogel et al., 2002; Casler and Boe, 2003). In the south-central USA, a single harvest in mid-September maximized biomass yields (Sanderson et al., 1999), in the Midwest maximum yield was found in mid-August (Vogel et al., 2002). However, Casler and Boe (2003) found that a mid-August harvest in north-central USA reduced stand density over time and recommended harvesting later in the season when regrowth would be minimized or not occur. Conversion systems have different requirements for biofuel feedstock quality; the composition of the biomass affects its quality as a biofuel. Several biomass conversion technologies have been under investigation to generate energy from biomass: ethanol production from biorefineries, direct combustion, and thermochemical conversion by gasification/pyrolysis (Boateng et al., 2006). The water concentration of biomass affects its safety in storage, the cost of transportation, and its combustion efficiency (Lewandowski and Kicherer, 1997). In direct combustion systems, the mineral concentration can cause corrosion, slagging, and fouling of boilers and increased emissions (Lewandowski and Kicherer, 1997). The composition of C compounds in the biomass can also affect conversion and yield of ethanol from biomass (Weimer et al., 2005; Dien et al., 2006). The energy density affects the energy production from gasification (Boateng et al., 2006), as it does in other energy-production systems. Seasonal time of harvest not only affects switchgrass yield, but also biofuel quality. The ash concentration of switchgrass decreases as it matures during the growing season (Sanderson andWolf, 1995), leading to increased biofuel quality and potentially lower N requirements with a fall vs. summer harvest (Vogel et al., 2002). When harvest is further delayed until spring, the mineral concentration of reed canarygrass (Phalaris arundinacea L.) (Burvall, 1997) and Miscanthus sp. (Lewandowski et al., 2003a) have decreased further, although yields decreased. Our objective was to examine how the seasonal time of harvest, comparing fall and spring harvest, affected switchgrass biomass yield and biofuel quality for energy production from fermentation, gasification, or direct combustion systems. P.R. Adler and M.A. Sanderson, USDA-ARS Pasture Systems and Watershed Management Research Unit, Building 3702, Curtin Road, University Park, PA 16802; A.A. Boateng, USDA-ARS, Eastern Regional Research Center, Wyndmoor, PA 19038; P.J. Weimer, USDAARS, U.S. Dairy Forage Research Center, Madison, WI 53706; H.-J.G. Jung, USDA-ARS, Plant Science Research Unit, 411 Borlaug Hall, 1991 Upper Buford Circle, St. Paul, MN 55108. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USDA. Received 22 Dec. 2005. *Corresponding author ([email protected]). Published in Agron. J. 98:1518–1525 (2006).