NAPIERGRASS GENOTYPES AND PLANT-PARTS FOR BIOMASS ENERGY

Twenty Pennisetum genotypes were evaluated at Gainesville, FL, USA, in 1987 for biomass as an alternative energy source via bioconversion to methane. The genetic lines included napiergrass and interspecific hybrids (triploid and hexaploid) between pearl millet and napiergrass. Studies included determinations for ultimate methane yield [l g-1 volatile solids (VS)], methane production rate (day-1), biomass yield, in vitro organic matter digestibility (IVOMD), crude protein (CP), neutral detergent fiber (NDF), plant height and leaf/stem ratio. Biomass yields ranged from 8.3 to 24.8 Mg ha-1 yr-1 among the genotypes. At the time of harvest, leaves of six genotypes were separated from stem material to calculate leaf percentage. This trait varied from 27.4% leaves in cv. Kinggrass (PI 300086) to 57.1 % in cv. Mott, a dwarf. Internode length also varied widely among the lines and ranged from 2.5 to 15.5 cm. Highest ultimate methane yields of leaves (0.31 0.331 g-1 VS) were recorded for three triploids (41S, 44S, 23AX) and were higher (P < 0.10) than the yield (0.278 l g-1) obtained from leaves of the tall tetraploid (PI 300086). For the estimated ultimate methane yield, overall means for leaves and stems were 0.31 and 0.29 l g-1 VS, respectively. The tall tetraploid (Kinggrass) was lower in IVOMD and CP, but significantly higher in NDF than the other genotypes tested. Positive correlations were obtained between CP, IVOMD, and ultimate methane yields indicating that it is possible to predict methane production. In an additional experiment, performed in 1990, the tall tetraploid (Kinggrass) again was low in IVOMD and CP, whereas cv. Mott and line 551 were high in concentrations of IVOMD and CP and low in NDF. This supportive evidence indicates that breeding for improved quality components is a possibility in this genus.