SOLAR-ENERGY RECOVERY BY ELEPHANTGRASS, ENERGYCANE, AND ELEPHANTMILLET CANOPIES

Elephantgrass (Pennisetum purpureum Schum.) and energycane (Saccharum spp.) have been identified as biomass plants for renewable energy. A field study was conducted at Gainesville, FL, in 1989 and 1990 to identify plant attributes that allowed these C4 bunchgrasses to accumulate high annual dry matter (DM) yields and to compute the efficiency by which solar energy is collected and stored in plant biomass. Entries were PI 300086 (PI3) and N51 elephantgrasses, L79-1002 (L79) energycane, and S41 elephantmillet [Pennisetum glaucum (L.) R. Br. x P. purpureum Schum.]. Plots were mowed to 10-cm height on 28 March to begin the season. For PI3, light interception by the top green portion of the canopy was greater than 90% from 49 to 217 d after mowing. For L79, interception increased from 83% on 49 d after mowing to 90% on 91 d and remained above 90% to 245 d after mowing. Two-year means for radiation-use efficiency (RUE), computed for near-linear DM accumulation phase, were 1.25 g DM MJ-1 of total solar radiation (TSR) for PI3, 1.26 for N51, 1.24 for L79, and 1.11 for S41. Mean energy concentrations of mature growth ranged from 17.1 to 18.2 kJ g-1 DM. Two-year average percentages of TSR converted to chemical DM energy, were 2.3 for P13, 2.3 for N51, 2.2 for L79, and 1.9 for S41. These bunchgrasses produced greater annual DM yields than other C4 plants because tillers grew vegetatively for 30 to 35 wk. During this period, a green canopy top was maintained and light interception and RUE continued at levels generally expected for actively growing C4 grasses.