Biomass Magazine, June 2014, by Chris Hanson.
http://biomassmagazine.com/articles/10458/north-dakotas-subterranean-fuel-feedstock

"When the advanced biofuel industry thinks feedstocks, ideas may drift toward dried corn stover on a freshly harvested field, or swathes of switchgrass or miscanthus swaying in the breeze. In the Red River Valley and Drift Prairie regions of North Dakota, however, the next advanced biofuel might be found below the ground in the form of sugar beets. But why sugar beets?" Includes a table that shows U.S 10-Year Sugar Beet Production, by state.