Submitted to: Agronomy Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/29/2006
Publication Date: 10/3/2006
Citation: Adler, P.R., Sanderson, M.A., Boateng, A.A., Weimer, P.J., Jung, H.G. 2006. Biomass yield and biofuel quality of switchgrass harvested in fall or spring. Agronomy Journal. 98:1518-1525. Interpretive Summary: The season when biomass crops are harvested can affect the yield and quality of the crop for use as biofuel. Switchgrass was harvested in the fall and spring on farm and conservation lands in Pennsylvania over a 4-year period and the quality of biofuel determined. The highest biofuel quality was obtained when switchgrass harvest was delayed over winter until spring; minerals were lower and biomass drier. However, biomass yield generally decreased from 3 tons in the fall to 2 tons per acre in the spring. Producers will need to consider the yield, biofuel quality, and system that will be used to convert the biomass to energy when deciding when to harvest their crop.
Technical Abstract: Harvest management of switchgrass (Panicum virgatum L.) grown for biofuel must consider not only biomass yield, but also the fuel quality of the biomass. A field study was conducted over a range of landscape scales to determine the effect of fall and spring harvest on biomass yield and biofuel quality. Biomass yield, element concentration, carbohydrate characterization, and total synthetic gas production were measured as indicators of biofuel quality for direct combustion, ethanol production, and gasification systems for generation of energy. In a winter with low snowfall, delaying harvest from fall to spring did not affect yield. However, in winters with above average snowfall, biomass loses were more than 40% and yields ranged from 4.4 to 7 Mg ha-1 in the spring and fall, respectively. About 10% of the yield reduction during winter resulted from decreases in tiller mass with reductions in leaves and the panicles; however, almost 90% of the yield reduction was due to an increase in biomass not picked up by the baler. Mineral element concentration generally decreased with the delay in harvest until spring, thereby enhancing biomass quality for direct combustion. Switchgrass moisture concentration was not low enough in the fall for safe storage (350 g kg-1), but was in the spring (70 g kg-1). Although the biomass yield decreased over the winter, energy yield from gasification did not decrease on a unit biomass basis, whereas ethanol production per unit of biomass was predicted to increase or decrease depending on the assessment method. Although there was a reduction in switchgrass yield when harvest was delayed until the spring, the biofuel quality of spring-harvested biomass was greater than fall biomass. Biofuel conversion systems may determine harvest timing. For direct combustion, the reduced mineral concentrations in spring-harvested biomass are desirable. For ethanol fermentation 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.