Switchgrass, a perennial warm-season grass and potential energy crop, is usually harvested during the time
between full maturity in the fall to the following spring. During this wide harvest window, the changes in
fuel properties that could occur are important for making appropriate decisions with respect to the optimum
harvest time for maximum fuel quality. A field plot study was carried out to investigate the quantitative fuel
properties (proximate, ultimate and mineral analyses) of switchgrass over a harvest period from crop maturity
in July through November. Harvest moisture decreased from July to November and moisture was uniformly
distributed in the switchgrass plant at all times in the harvest period. There were significant differences
in ash, volatiles, fixed carbon and nitrogen among months of harvest. Nitrogen, ash and fixed carbon contents
decreased while oxygen and volatiles increased through the harvest period. Also, there were significant differences
in oxides of silicon, calcium, potassium, phosphorus and sulfur among harvest times. The concentration
of oxides of potassium and sulfur decreased at the end of the harvesting period. Fouling and slagging
indices decreased as harvest was delayed but remained low throughout harvest. However, the decreases are
small and might not dramatically impact fouling and slagging. Overall, the results appear to favor a later
harvest for switchgrass used for direct combustion. This study will benefit feedstock producers as well as
biomass feedstock facility operators by providing a better understanding of how the properties of switchgrass
vary over a typical harvest period and their potential effect on boiler equipment.