Radiation Use Efficiency of Late Planted Sweet Sorghum.

As the United States phases in second generation ligno-cellulosic mandates, the need for biomass for ethanol production will increase.  This, in turn, will influence land usage and require that biomass production be re-evaluated to maximize production per unit area and efficiently use available resources.  Sweet sorghum(Sorghum bicolor) has received significant attention in recent years as both a first and second generation biofuel.  However, few studies have evaluated the productivity of sweet sorghum and its efficiency of converting available light into biomass.  This study evaluated the radiation use efficiency of four sweet sorghum cultivars at two planting dates corresponding to planting after normal and late winter wheat harvests for the region.  Aboveground productivity was assessed by sampling stem and leaf biomass, leaf area, and sugar content of whole-stem juice extract.  At each biomass sampling, canopy light interception was determined by measuring photosynthetically active radiation above the canopy and beneath the canopy near solar noon.  Differences in radiation use efficiency, biomass productivity, and sugar content corresponded with planting date, cultivar, and maturity date, suggesting that of matching cultivars with specific planting dates is critical to achieving high sugar yields in a wheat-sweet sorghum double cropping system.