Nitrogen Fertilization for Ethanol Production with Sweet Sorghum and Corn.

Most of the ethanol in the United States is manufactured from corn which typically requires 130 to 225 kg N ha^-1 to produce optimum grain yields. Rising natural gas prices have resulted in increased nitrogen fertilizer costs to farmers.  Research was begun at Portageville, Missouri to determine the effects of N fertilization on corn and sweet sorghum used to produce ethanol. A field experiment was conducted on a Tiptonville silt loam soil with sprinkler irrigation. Seven N rate treatments per crop were used with four replications on each crop. Ammonium nitrate was broadcast applied. Corn plots were harvested with a plot combine and sweet sorghum plots were harvested with a sickle mower. In 2007, the highest ethanol amounts were produced with 67 kg N ha^-1 on sweet sorghum and 179 kg N ha^-1 on corn. The optimum corn yield was 12857 kg ha^-1.  Sweet sorghum stalks with 67 kg N ha^-1 produced 45.7 Mg ha^-1 fresh biomass and contained 329 g solids kg^-1.  Water soluble sugars were measured on a fresh weight basis. Sweet sorghum stalks contained 121 g sucrose kg^-1, 17 g glucose kg^-1, and 14 g fructose kg^-1. On a dry weight basis, bagasse contained 436 g cellulose kg^-1, 228 g hemicellulose kg^-1, and 325 g lignin kg^-1. Fermentation from raw sugars and sugars from cellulose in sweet sorghum was done in a laboratory. Assuming 90% recovery from sugars and 85% recovery from cellulose, 4250 liter ha^-1 was produced from sugars and 1342 liter ha^-1 from cellulose.