Potential economic return from fiber residues produced as by-products of juice expression from sweet sorghum

Abstract

The potential market for by-products is a critical question in the system analysis of sweet sorghun as a feedstock for ethanol. Possible sweet sorghun by-products (rind-leaf hay, pith-presscake silage, combination (pith presscake plus rind-leaf) silage, and whole-stalk silage) were analyzed and evaluated for their potential economic return when used for cattle feed, fiber conversion to ethanol, and paper production. Ensiling the rind-leaf had an economic advantage over drying it as hay, because most of the preparation for ensiling was done as part of the jiice removal process, whereas hay harvesting represented additional expense. Projected returns ranged from US$318 ha −1 for combination silage fed locally to cattle, to $129 ha −1 for pith presscake silage and rind-leaf hay delivered to a fiber conversion plant. Chopped whole-stalk sorghum, ensiled as a conventional forage crop (no juice expression), can be delivered to a fiber conversion plant at a cost (no profit) of $79 dry Mg −1, as compared with approximately $44 dry Mg −1 for baled switchgrass. It does not appear that a high-moisture crop like sweet sorghum can compete as a fiber crop. Further study is needed to determine if sweet sorghum can compete asa combinaton sugar and fiber crop.