Forage and Energy Sorghum Responses to Nitrogen Fertilization in Central and Southern Illinois

Recently introduced forage and energy sorghums (Sorghum bicolor L. Moench) have potential as cellulosic biofuel feedstocks in the Midwest. The objectives of this study were to evaluate the effect of N fertilization on biomass yield and to determine the relationship between biomass yield and plant height, leaf development, and leaf area index (LAI) on two forage and two energy sorghum hybrids in four central and southern Illinois (IL) environments. Sorghum hybrids were evaluated in Urbana in 2009 under four N rates and in Urbana, Dixon Springs, and Perry in 2010 under five N rates. Forage sorghums harvested twice (summer and fall) annually produced less biomass than the energy sorghums harvested once in the fall both in 2009 and 2010. Averaged across all environments in 2010, maximum biomass yields were 30.1 Mg DM ha(-1) for the energy sorghums and 19.2 Mg DM ha(-1) for the forage sorghums at the 224 kg N ha(-1) application rate. Biomass yields, LAI, and plant-height responses to N applications were observed up to 150 kg N ha(-1) in 2009 and up to 224 kg N ha(-1) in 2010. Leaf development was linearly related to growing-degree days and the average number of fully expanded leaves on the energy sorghum reached 28 in Perry-10 with the longest growing season. Photoperiod-sensitive energy and forage sorghums have potential in central and southern IL as bioenergy feedstocks because these grasses continue vegetative growth until late September, and therefore, produce large amounts of biomass.