Jane M.F. Johnson; Garold L. Gresham
Switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerdardii Vitman) are potential perennial bioenergy feedstocks. Feedstock storage limitations, labor constraints for harvest, and environmental benefits provided by perennials are rationales for developing localized perennial feedstock as an alternative or in conjunction with annual feedstocks (i.e., crop residues). Little information is available on yield, mineral, and thermochemical properties of native species as related to harvest time. The study’s objectives were to compare the feedstock quantity and quality between grasses harvested in the fall or the following spring. It was hypothesized that biomass yield may decline, but translocation and/or leaching of minerals from the feedstock would improve feedstock quality. Feedstock yield did not differ by crop, harvest time, or their interactions. Both grasses averaged 6.0 Mg ha-1 (fall) and 5.4 Mg ha-1 (spring) with similar high heating value (17.7 MJ kg-1). The K/(Ca + Mg) ratio, used as a quality indicator declined to below a 0.5 threshold, but energy yield (Megajoule per kilogram) decreased 13% by delaying harvest until spring. Only once during the four study-years were conditions ideal for early spring harvest, in contrast during another spring, very muddy conditions resulted in excessive soil contamination. Early spring harvest may be hampered by late snow, lodging, and muddy conditions that may delay or prevent harvest, and result in soil contamination of the feedstock. However, reducing slagging/fouling potential and the mass of mineral nutrients removed from the field without a dramatic loss in biomass or caloric content are reasons to delay harvest until spring.
Smith, Melinda D.
Over the project period, we have addressed the following objectives: 1) assess the effects of altered precipitation patterns (i.e., increased variability in growing season precipitation) on genetic diversity of the dominant C4 grass species, Andropogon gerardii, and 2) experimentally assess the impacts of extreme climatic events (heat wave, drought) on responses of the dominant C4 grasses, A. gerardii and Sorghastrum nutans, and the consequences of these response for community and ecosystem structure and function. Below is a summary of how we have addressed these objectives. Objective 1 After ten years of altered precipitation, we found the number of genotypes of A. gerardii was significantly reduced compared to the ambient precipitation treatments (Avolio et al., 2013a). Although genotype number was reduced, the remaining genotypes were less related to one another indicating that the altered precipitation treatment was selecting for increasingly dissimilar genomes (based on mean pairwise Dice distance among individuals). For the four key genotypes that displayed differential abundances depending on the precipitation treatment (G1, G4, and G11 in the altered plots and G2 in the ambient plots), we identified phenotypic differences in the field that could account for ecological sorting (Avolio & Smith, 2013a). The three altered rainfall genotypes also have very different phenotypic traits in the greenhouse in response to different soil moisture availabilities (Avolio and Smith, 2013c). Two of the genotypes that increased in abundance in the altered precipitation plots had greater allocation to root biomass (G4 and G11), while G1 allocated more biomass aboveground. These phenotypic differences among genotypes suggests that changes in genotypic structure between the altered and the ambient treatments has likely occurred via niche differentiation, driven by changes in soil moisture dynamics (reduced mean, increased variability and changes in the depth distribution of soil moisture) under a more variable precipitation regime, rather than reduced population numbers (A. gerardii tiller densities did not differ between altered and ambient treatments; p = 0.505) or a priori differences in genotype richness (Avolio et al.2013a). This ecological sorting of genotypes, which accounts for 40% of all sampled individuals in the altered plots, is an important legacy of the press chronic climate changes in the RaMPs experiment. Objective 2 In May 2010, we established the Climate Extremes Experiment at the Konza Prairie Biological Station. For the experiment, a gradient of temperatures, ranging from ambient to extreme, were imposed in 2010 and 2011 as a mid-season heat wave under well-watered or severe drought conditions. This study allowed us for the first time to examine species-specific thresholds of responses to climate extremes and assess how these phenotypic responses may impact selection of particular genotypes, with the ultimate goal of linking alterations in individual performance and genetic diversity to ecosystem structure and functioning. We found that tallgrass prairie was resistant to heat waves, but it was not resistant to extreme drought, which reduced aboveground net primary productivity (ANPP) below the lowest level measured in this grassland in almost thirty years (Hoover et al. in press(a)). This extreme reduction in ecosystem function was a consequence of reduced productivity of both C4 grasses and C3 forbs. This reduction in biomass of the C4 grasses (Andropogon gerardii and Sorghastrum nutans) was, in part, due to significant reductions in photosynthesis, leaf water potential and productivity with drought in the dominant grasses species, with S. nutans was more sensitive than A. gerardii to drought (Hoover et al. in press(b)). However, the dominant forb was negatively impacted by the drought more than the dominant grasses, and this led to a reordering of species abundances within the plant community. Although this change in community composition persisted post-drought, ANPP recovered completely the year after drought
Aschenbach, Todd, A; Foster, Bryan, L.; Imm, Donald, W.
AbstractAbstract The significant loss of the longleaf pine-wiregrass ecosystem in the southeastern United States has serious implications for biodiversity and ecosystem functioning. In response to this loss, we have initiated a long-term and landscape-scale restoration experiment at the 80,125 ha (310 mi2) Department of Energy Savannah River Site (SRS) located near Aiken, South Carolina. Aristida beyrichiana (wiregrass), an important and dominant grass (i.e., a “matrix” species) of the longleaf pine savanna understory, and 31 other herbaceous “non-matrix” species were planted at six locations throughout SRS in 2002 and 2003. Of the 36,056 transplanted seedlings, 75% were still alive in June 2004, while mean 1–2 year survival across all planted species was 48%. Lespedeza hirta (hairy lespedeza) exhibited the greatest overall survival per 3 ×3 m cell at 95%, whereas Schizachyrium spp. (little bluestem) exhibited the greatest mean cover among individual species at 5.9%. Wiregrass survival and cover were significantly reduced when planted with non-matrix species. Aggregate cover of all planted species in restored cells averaged 25.9% in 2006. High rates of survival and growth of the planted species resulted in greater species richness (SR), diversity, and vegetative cover in restored cells. Results suggest that the loss of the longleaf pine-wiregrass ecosystem may be ameliorated through restoration efforts and illustrate the positive impact of restoration plantings on biodiversity and vegetative cover.
Sara Bergan, Executive Director; Brendan Jordan, Program Manager; Subcontractors as listed on the report.
The following report contributes to our knowledge of how to economically produce wildlife-friendly grass mixtures for future fuel feedstocks in the northern plains. It investigates northern-adapted cultivars; management and harvest regimes that are good for yields, soils and wildlife; comparative analysis of monocultures and simple mixtures of native grasses; economic implications of growing grasses for fuel feedstocks in specific locations in the northern plains; and conversion options for turning the grasses into useful chemicals and fuels. The core results of this study suggest the following; Native grasses, even simple grass mixtures, can be produced profitably in the northern plains as far west as the 100th meridian with yields ranging from 2 to 6 tons per acre; Northern adapted cultivars may yield less in good years, but have much greater long-term sustainable yield potential than higher-yielding southern varieties; Grasses require very little inputs and stop economically responding to N applications above 56kg/hectare; Harvesting after a killing frost may reduce the yield available in that given year but will increase overall yields averaged throughout multiple years; Harvesting after a killing frost or even in early spring reduces the level of ash and undesirable molecules like K which cause adverse reactions in pyrolysis processing. Grasses can be managed for biomass harvest and maintain or improve overall soil-health and carbon sequestration benefits of idled grassland; The carbon sequestration activity of the grasses seems to follow the above ground health of the biomass. In other words plots where the above ground biomass is regularly removed can continue to sequester carbon at the rate of 2 tons/acre/year if the stand health is strong and yielding significant amounts of biomass; Managing grasses for feedstock quality in a biomass system requires some of the same management strategies as managing for wildlife benefit. We believe that biomass development can be done in such a way that also maximizes or improves upon conservation and other environmental goals (in some cases even when compared to idled land); Switchgrass and big bluestem work well together in simple mixture plots where big bluestem fills in around the switchgrass which alone grows in bunches and leaves patches of bare soil open and susceptible to erosion; Longer-term studies in the northern plains may also find that every other year harvest schemes produce as much biomass averaged over the years as annual harvests; Grasses can be grown for between $23 and $54/ton in the northern plains at production rates between 3 and 5 tons/acre; Land costs, yields, and harvest frequency are the largest determining factors in the farm scale economics. Without any land rent offset or incentive for production, and with annual harvesting, grass production is likely to be around $35/ton in the northern plains (farm gate); Average transportation costs range from $3 to $10/ton delivered to the plant gate. Average distance from the plant is the biggest factor - $3/ton at 10 miles, $10/ton at 50 miles; There is a substantial penalty paid on a per unit of energy produced basis when one converts grasses to bio-oil, but the bio-oil can then compete in higher priced fuel markets whereas grasses alone compete directly with relatively cheap coal; Bio oil or modified bio-oil (without the HA or other chemical fraction) is a suitable fuel for boiler and combustion turbines that would otherwise use residual fuel oil or number 2 diesel; Ensyn has already commercialized the use of HA in smokey flavorants for the food industry but that market is rather small. HA, however, is also found to be a suitable replacement for the much larger US market for ethanolamines and ethalyne oxides that are used as dispersants; Unless crude oil prices rise, the highest and best use of grass based bio-oil is primarily as a direct fuel. As prices rise, HA, phenol and other chemical fractions may become more attractive; Although we were able to create available glucose from the AHG fraction in the bio-oil it proved recalcitrant to fermentation by yeast. Although fermentation results were much more positive with wood based bio-oil sugars, ethanol does not appear to be a likely product from grass based bio-oil; and A package of policy recommendations has been developed with roughly 75 key stakeholders from throughout the region that would support the transition to greater development of advanced biofuels and products in the region, as well as a strong role for native grass agriculture to support those industries.