Dryland Performance of Sweet Sorghum and Grain Crops for Biofuel.

Sweet sorghum [Sorghum bicolor (L.) Moench.] is a potential biofuel crop for the Midwest. Sweet sorghum (SS) was compared to corn [Zea mays (L.)] and grain sorghum at seven rainfed site-yr across southern Nebraska for estimated potential ethanol yield, energy use efficiency, and greenhouse gas (GHG) emissions. Sowing rate, N rate, and variety effects were evaluated. Seasonal rainfall ranged from approximately 340 to 660 mm and soils at all site-yr were deep with medium texture. Sweet sorghum sugar yield was affected by sowing rate and increased by N application (19%) at one site-yr only. Estimated ethanol yield with an early compared with a late maturity cultivar was 33% more. Estimated potential ethanol yield and net energy yield were 39% and 10% less, respectively, with SS than with the grain crops but mean net energy yield of the earlier maturing SS cultivar was comparable with the grain crops. Sweet sorghum was 50-60% more efficient than grain crops for the ratio of energy produced per total energy invested and had much less GHG emission per liter of ethanol produced. The grain crops compared with SS were more efficient for liquid transportation fuel produced per liter invested because of higher yields and less consumption; much was needed for harvest, crushing, and transport of SS. Very efficient use of the ethanol co-products was assumed for the grain crops while the bagasse of SS was returned to the field. Sweet sorghum is competitive with grain crops for some criteria with at least one cultivar but not for total or net liquid transportation fuel produced per hectare.