COMPOSITIONAL CHANGES DURING STORAGE OF LARGE ROUND SWITCHGRASS BALES

'Alamo' switchgrass (Panicum virgatum L.) was harvested in two differe nt years and stored as large round bales, unprotected outside, for 26 weeks. Fresh and scored switchgrass samples were analyzed for their st ructural and non-structural constituents. These summative analyses of the switchgrass showed differences in the composition of materials har vested at different rimes and indicated that the compositions changed during storage. On a dry weight, whole biomass basis, significant diff erences were observed in the extractives (+3%), ash (+1%), hemicellulo ses (-1.4%), and cellulose (-4%) components of the switchgrass harvest ed in October 1991 relative to August 1992. The bales from the switchg rass harvested in October 1991 were exposed to high rainfall (65 cm) d uring storage and experienced much greater weathering than bales from the second harvest. The largest change in composition occurred in the ethanol-extractable component. The switchgrass showed a significant lo ss of extractives in both the weathered outer layer (11%) and the unwe athered inner fraction (8%) of the bales prepared from the first harve st. Switchgrass harvested in August 1992 underwent much smaller compos itional changes compared to the October 1991 harvest. The extractives in switchgrass and other grasses may contain substantial amounts of fe rmentable carbohydrates. If so, their loss during storage could have a significant impact on the conversion of switchgrass into ethanol. Thi s is an example of the feedstock assessment research being conducted t o determine the influence of harvest and storage conditions on the the rmochemical and biochemical conversion of various biomass feedstocks i nto fuels and chemicals. The results of this research are expected to provide a guide to agricultural practices that optimize production of feedstocks for conversion into fuels. (C) 1996 Elsevier Science Ltd.