Nitrogen Rate and Variety Impact Diseases and Yield of Sorghum for Biofuel

Sorghum [Sorghum bicolor (L.) Moench] is a potential bioenergy feedstock, for which the disease threat is unknown. Impact of N rate on aboveground dry matter (ADM), total fermentable sugar concentration (degrees Bx), total fermentable sugar yield (TFSY), and diseases on sweet, forage, and silage/grain sorghum varieties was evaluated in 2009, 2010, and 2011 on rainfed sites in southwest Alabama. A factorial design arranged in a split plot with four replications of 22, 44, 88, and 132 kg ha(-1) N as the main plot and variety as subplots was used. Dale and M81-E sweet sorghum were grown in all years, SS405 forage and NK300 silage/grain sorghum replaced Sugar Drip sweet and SS1515 silage/grain sorghum in 2010 and 2011, respectively. No significant N rate or N rate x variety interaction for any variable was noted. Variety impacted plant population, ADM, TFSY, and Bx. Mean ADM and TFSY peaked at 32.0 Mg ha(-1) for M81-E and 3.78 Mg ha(-1) for Dale. Despite a lower ADM than M81-E, Dale had higher Bx and TFSY. Sugar Drip, SS1515, and NK300 had low biomass and sugar yields. Anthracnose, rough leaf spot, and zonate leaf spot severity differed by variety. Severe anthracnose occurred on SS405 and less so on M81E, while the remaining varieties suffered limited rough leaf spot and/or zonate leaf spot damage. As potential bioenergy feedstocks for the Southeast, Dale and M-81E had comparable ADM along with higher TFSY and Bx with restricted disease, while anthracnose poses a significant roadblock to forage sorghum feedstock utilization.