Producing Sorghum Biomass Under Different Irrigation Tillage Systems for Cellulosic Bioenergy Production in Southeastern U.S.

Seeking alternative and renewable sources of energy is necessary. Sorghum (Sorghum bicolor L.) might be a reasonable alternative as an energy crop in Southeastern US, because it is drought and nematode resistant. The types of sorghum evaluated were: grain sorghum - NK300 (GS), high biomass forage sorghum - SS 506 (FS), and photoperiod sensitive forage sorghum - 1990 (PS). These 3 different varieties and a forage corn (Zea mays L.) - Pioneer 31G65 were grown in 2008 and 2009 under irrigated and non-irrigated treatments, and under two different tillage systems: conventional and conservation tillage.  Additionally, a rye cover crop (Secale cereale L.) and sunn hemp (Crotalaria juncea L.) was integrated as a treatment to maximize the amount of biomass produced and provide ground cover during winter months. Results showed that all sorghum varieties had higher dry aboveground dry matter production (ADM) than corn. ADM production was higher in 2008 than 2009 for all varieties due to high incidence of Anthracnose (Colletotrichum graminicola) and Southern corn leaf blight (Bipolaris maydis) diseases at field in 2009. Lodging was observed in PS and FS plots due to high plant populations (> 370,000 plants ha^-1). Irrigation affected ADM positively in both years, but conservation system improved ADM production only in 2009. Stomatal Conductance reading indicated that high ADM yields in irrigated and conservation tillage were related to good soil water content which might increase plant metabolism and growth. Holocellulose, lignin and ash content variation among varieties were lower, and they were considered minor. PS was considered the best tested variety in order to produce ADM which produced 26.04 and 30.13 Mg ha^-1 at 18 and 24 weeks after planting. Thus, low plant population and crop rotation were recommended to maximize cellulosic biomass for bioenergy production.