Search

Elephantgrass (Pennisetum purpureum Schum.) and energycane (Saccharum spp. interspecific hybrid) are perennial C4 grasses with potential for use as bioenergy feedstocks. Their biomass production has been quantified, but differences in plant morphology and the relationship of morphology with biomass harvested and plant persistence are not well understood. The objective was to quantify monthly changes in morphological characteristics of elephantgrass (cv. Merkeron and breeding line UF1) and energycane (cv. L 79-1002) and relate these changes to biomass accumulation and plant responses to defoliation. All were evaluated monthly during full-season growth or when defoliated once in mid-season. Merkeron and UF1 elephantgrass generally showed similar morphological characteristics. Relative to energycane, elephantgrass had fewer tillers early in the growing season, less seasonal variation in tiller number, greater tiller mass and maximum leaf area index (LAI), and earlier spring development of LAI. Energycane showed slower leaf area development in spring, lower maximum LAI, and shorter period of increasing tiller mass and canopy height during the growing season relative to UF1. Elephantgrass had greater incidence of lodging than energycane when exposed to high wind, likely due to greater elephantgrass tiller mass. Morphological characteristics of tall-growing bioenergy grasses help to explain differences among them in biomass production and plant persistence responses to defoliation.

Harvest management practices affect productivity and persistence of grasses grown for bioenergy, but data are limited that describe their effects on the tall-growing grasses adapted to the USA Gulf Coast region. The objective was to determine harvest frequency and timing effects on biomass yield, nutrient removal, and persistence of three perennial bioenergy grasses in the southeastern USA. The experiment was conducted from 2010 through 2012. Harvest management treatments were two harvests per year (2X; July and November), one harvest per year in early November (fall), and one harvest per year after first freeze (winter). Elephantgrass (Pennisetum purpureum Schum.) cv. Merkeron and breeding line UF1 and energycane (Saccharum spp.) cv. L 79-1002 were compared. Three-year average biomass harvested was greatest for UF1 followed by Merkeron and L 79-1002 (27.8, 24.6, and 21.1 Mg ha−1year−1, respectively). Biomass harvested was not affected by harvest management in 2010 and 2011, but in 2012, the 2X treatment yielded 47 % less than winter. Biomass dry matter (DM) concentration for single harvest treatments was greater than 2X (34 vs. 25 %), but the 2X treatment removed two times more N and P in harvested biomass than fall or winter. For these grasses, fall and winter single harvest treatments were superior to 2X due to greater third year biomass yield, less nutrient removal, and harvested biomass had a greater DM concentration that may be advantageous for postharvest transport and processing.

A recent alternative strategy to reduce environmental problems associated with P transport from agricultural soils is the use of bioenergy crops to remediate excess soil P. In addition to the positive impacts associated with P mitigation, harvested biomass used as a renewable energy source can also offset the cost associated with plant-based P remediation strategies. The objective of this study was to identify potential crop species that can be used for remediation of soil P and as a cellulosic feedstock for production of renewable energy in South Florida. Fifteen crop entries were investigated for their potential to remove P from a P-enriched soil. Dry matter (DM) yield varied among crop species with greatest yield observed for elephantgrass (Pennisetum purpureum Schum.) and sugarcane (Saccharum spp.) (43 and 39 Mg ha−1 year−1, respectively). Similarly, greater P removal rates were observed for elephantgrass (up to 126 kg P ha−1 year−1 in 2008) followed by sugarcane (62 kg P ha−1 year−1 in 2008). Although there was no effect (P = 0.45) of crop species on P reduction in the soil, soil P concentrations decreased linearly during the 3-year study. Because of its relatively greater DM yield and P removal rates, elephantgrass was shown to be a good candidate for remediation of excess soil P in South Florida Spodosols.