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Managed forests in southern U.S. are a potential source of lignocellulosic biomass for biofuel production. Changes in management practices to optimize biomass production may impact the quality of waters draining to nutrient-sensitive waters in coastal plain regions. We investigated shallow groundwater quality effects of intercropping switchgrass ( Panicum virgatum L.) with managed loblolly pine ( Pinus taeda L.) to produce bioenergy feedstock and quality sawtimber in a poorly drained soil of eastern North Carolina, U.S.A. Treatments included PINE (traditional pine production), PSWITCH (pine-switchgrass intercropped), SWITCH (switchgrass monoculture) and REF (mature loblolly pine stand). Each treatment was replicated three times on 0.8 ha plots drained by parallel-open ditches, 1.0–1.2 m deep and 100 m apart. Water samples were collected monthly or more frequently after fertilizer application. Water samples were analyzed for organic nitrogen (ON), ammonium N (NH 4 + - N), and nitrite+nitrate N (NO 3 − + NO 2 − - N), ortohophosphate phosphorus (OP), and total organic carbon (TOC). Overall, PSWITCH did not significantly affect shallow groundwater quality relative to PINE and SWITCH. ON, NO 3 − + NO 2 − - N, and TOC concentrations in PSWITCH, PINE and SWITCH were substantially elevated during the two years after tree harvest and site establishment. The elevated nutrient concentrations at the beginning of the study were likely caused by a combination of rapid organic matter decomposition of the abundant supply of post-harvest residues, warming of exposed soil surfaces and reduction of plant nutrient uptake that can occur after harvesting, and pre-plant fertilization. Nutrient concentrations returned to background levels observed in REF during the third year after harvest. [ABSTRACT FROM AUTHOR]

Switchgrass is a promising bioenergy feedstock, but industrial-scale production may lead to negative environmental effects. This study considers one such potential consequence: the life cycle monetized damages to human health from air pollution. We estimate increases in mortality from long-term exposure to fine particulate matter (PM 2.5 ), which is emitted directly (“primary PM 2.5 ”) and forms in the atmosphere (“secondary PM 2.5 ”) from precursors of nitrogen oxides (NO x ), sulfur oxides (SO x ), ammonia (NH 3 ), and volatile organic compounds (VOCs). Changes in atmospheric concentrations of PM 2.5 (primary + secondary) from on-site production and supporting supply chain activities are considered at 2694 locations (counties in the Central and Eastern US), for two biomass yields (9 and 20 Mg ha −1 ), three nitrogen fertilizer rates (50, 100, and 150 kg ha −1 ), and two nitrogen fertilizer types (urea and urea ammonium nitrate). Results indicate that on-site processes dominate life-cycle emissions of NH 3 , NO x , primary PM 2.5 , and VOCs, whereas SO x is primarily emitted in upstream supply chain processes. Total air quality impacts of switchgrass production, which are dominated by NH 3 emissions from fertilizer application, range widely depending on location, from 2 to 553 $ Mg −1 (mean: 45) of dry switchgrass at a biomass yield of 20 Mg ha −1 and fertilizer application of 100 kg ha −1 N applied as urea. Switching to urea ammonium nitrate solution lowers damages to 2 to 329 $ Mg −1 (mean: 28). This work points to human health damage from air pollution as a potentially large social cost from switchgrass production and suggests means of mitigating that impact via strategic geographical deployment and management. Furthermore, by distinguishing the origin of atmospheric emissions, this paper advances the current emerging literature on ecosystem services and disservices from agricultural and bioenergy systems. [ABSTRACT FROM AUTHOR]

Environmental concerns and energy security have led to growing interest to second-generation biofuel production from non-edible feedstock such as switchgrass. In this article, sustainable and ecological indicators are introduced to evaluate the candidate locations efficiency for switchgrass cultivation. To optimize the candidate locations, a novel data envelopment analysis (DEA) cross-efficiency model is proposed which attempts to maximize output worst-cases of all candidate locations. Moreover, in order to consider both mean and standard deviation of candidate locations cross-efficiencies, a new ranking measure is presented. The performance of proposed model is investigated in comparison with several models through a real case study in Iran. The efficiency values of Iran provinces are calculated by several DEA cross-efficiency models. The numerical results show that proposed model manages to evaluate the candidate locations efficiency more moderate than other models. Besides, the standard deviation of cross-efficiencies for this model are lower than that of other models. The obtained findings from introduced DEA model reveal that based on the defined ranking measures, Khouzesan and Fars provinces are non-dominate locations for switchgrass cultivation. [ABSTRACT FROM AUTHOR]

Ongoing severe drought and increased demand for freshwater by municipal and industrial sectors have reduced the freshwater availability for agriculture in the far west Texas region. The region has enormous potential for developing alternative water sources for a bioenergy crop that requires less water and can grow on saline soils. In addition to improving farm income, this can help in producing 137 billion liters of bio-based transportation fuels goal set by the U.S. Congress by the year 2022. This study evaluated switchgrass ( Panicum virgatum L.) performance under treated urban wastewater irrigation on salt affected soils amended with gypsum and polymer using soil columns prepared from a salt affected land over six years under greenhouse conditions that mimicked the climatic conditions of the study region. Results indicated that switchgrass produced appreciable biomass even under highly saline and sodic conditions. Qualities of biomass under treated urban wastewater were comparable to that produced under freshwater irrigation. Expectedly, soil salinity increased with time at a greater rate under wastewater irrigation than freshwater. Soil SAR values were below threshold when adequate Ca was available to counter sodicity. In addition irrigation with treated wastewater improved nitrogen and potassium status in the root zone. This can reduce of cost of fertilization and increase farm profitability. [ABSTRACT FROM AUTHOR]

This study assesses the supply of switchgrass and miscanthus, in Ontario, Canada, under different biomass prices and supply chain structures, using an integrated economic, biophysical and GIS model, to assess bioenergy policy. In a local, domestic supply chain, 4 million tonnes of baled biomass production per year becomes attractive for transport to the Nanticoke Generation Station at $69/t. For a larger scale export supply chain to Rotterdam in the form of biomass pellets aggregated on the farm, 20 million tonnes of production becomes attractive at approximately $198/t. For an export supply chain with aggregation at the major ports of Ontario, 20 million tonnes of baled biomass product is attractive for shipping to ports, with pellets subsequently transported to Rotterdam, at around $137/t. Higher bale transportation costs mean that agricultural lands closer to ports, but with lower yields, are preferred compared to the on-farm aggregation scenario. Given government incentives to ease the transition between annual and perennial crops and an actual realized demand from the Nanticoke Generation Station for biomass, this supply chain scenario is plausible. However, export scenarios are not attractive due to infrastructure constraints from current pellet processing capacity, and volatile international energy and commodity markets. [ABSTRACT FROM AUTHOR]

Switchgrass ( Panicum virgatum L.) intercropped with Loblolly pine ( Pinus taeda L.) has been proposed as a potential biomass feedstock for biofuel production in the southeastern United States. This study investigated effects of treatments (intercropping vs . grass only) on biomass increment processes and morphological properties of switchgrass at two experimental plots (Lenoir1) located in the coastal plain of North Carolina. We also evaluated effects of trimming lower tree branches of pine trees on switchgrass growth at another watershed-scale site (Carteret7) in the same region. Results showed that biomass yield of intercropped switchgrass was reduced by adjacent trees and negatively affected by relative position of grass to trees at the 6th year after planting at Lenoir1. Relative grass-to-tree position was also found to be a significant (p < 0.001) factor affecting grass growth at Carteret7 site with tree age of 5 years old, which is irrespective to the trimming practice. Trimming lower tree branches did not significantly (p = 0.57) improve biomass yield of switchgrass at Carteret7. We also observed intercropped switchgrass typically had higher specific leaf area and grew taller compared to grass-only plots. Stem-to-leaf ratios of switchgrass were significantly (p = 0.02) affected by trees at Lenoir1, but not by trimming lower branches in Carteret7 and relative position of grass to trees at both study sites. Findings from this study are important for evaluating the viability of producing biofuel feedstocks using this proposed intercropping system in the southeastern United States. [ABSTRACT FROM AUTHOR]

Currently we lack knowledge on how the soil microbial community responds to the transition from traditional grain production to cellulosic feedstock production systems with residue removal for biofuel production. Implementation of second-generation biofuel production systems could create a challenge in meeting the goal of providing cellulose biomass if the processes impact soil's function as part of ecosystem services. Our goal was to assess the transition period as we move from a grain harvest system with residue return into biomass production systems with both residue and grain removal. The existing traditional systems were continuous corn (CC) and corn–soybean rotations (corn–soybean–corn (R1) or soybean–corn–soybean (R2)). The biomass production systems include a previously established mixed tall grass prairie dominated by big bluestem ( Andropogon gerardii ; PR) where the above ground biomass is now harvested when it had been previously burned, corn–soybean rotations transitioned to residue recovery based on: Miscanthus × giganteus (MS), dual-purpose sorghum ( Sorghum bicolor ; SG), upland switchgrass ( Panicum virgatum ; c.v. Shawnee ; SW) and a tilled continuous corn changed to continuous no-till corn ( Zea mays ; CR) with the residue removed. Over a three-year transition period, biological indicators of soil health included microbial biomass and community structure profile using phospholipid fatty acid (PLFA) biochemical markers, and an assessment of the saprotrophic fungal diversity using denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction amplified ITS rRNA genetic marker. Over the course of the transition, bacterial biomass dominated soils in the annual systems of CC, R1, R2, CR and SG, and the perennial system of MS. While fungal biomass dominated soils under PR. Fungal PLFA signatures and ITS-DGGE profiles demonstrated similarity between PR and the transitioned SW system, and to a lesser extent SG. In contrast, MS did not statistically alter the microbial biomass, community structure or fungal diversity away from patterns observed in the corn–soybean system. Our findings support microbial community stability and resilience as we found no negative impacts in any of the biomass recovery systems (PR, MS, SG, SW and CR) relative to the traditional systems (CC, R1 and R2), as indicated by measures of soil health. We did find that the selection of the plant types used in the biomass system could have a significant impact on the structure of both bacterial and fungal communities. With respect to soil health indicators including the fungal community, our findings suggest the dual-purpose SG system provides an encouraging alternative to continuous maize when considering plant biomass production. The selection of this dedicated perennial biomass system offers an avenue to enhance indicators of soil health and associated ecosystem services while supporting the bioenergy economy. [ABSTRACT FROM AUTHOR]

The objective of this paper is to design two types of subsidies for biofuel feedstock production and water quality improvement and to analyze how each subsidy affects biomass supply and the abatement of nutrient runoff associated with the conversion of cropland to biomass production. Per-hectare (per-ha) subsidy was designed as a system that pays producers for each ha of cropland converted to switchgrass production and per-megagram (per-Mg) subsidy was a system that pays producers for each Mg of switchgrass produced. This study focuses on Oostanaula Creek watershed in East Tennessee. The analysis used a dynamic programming model coupled with a Soil and Water Assessment Tool (SWAT) simulation model to predict profit-maximizing fertilizer application rates, crop yields, and nitrogen (N) runoff for a biofuel feedstock (switchgrass) and a conventional crop (corn) across 28 different landscapes in the watershed. A Monte Carlo analysis was conducted to simulate the impact of stochastic N fertilizer and corn prices and yields on subsidies over a ten-year planning horizon. A per-ha subsidy system is more cost effective and feasible than a per-Mg system because the former has significantly lower subsidy than the latter for each kilogram (kg) of N reduction and for each Mg of switchgrass harvested. Converting all of the cropland from corn to switchgrass over ten years results in 124,084 dry Mg of switchgrass and 23% reduction in nitrogen runoff for the per-ha system and 122,347 dry Mg of switchgrass and 3% reduction for the per-Mg subsidy system. [ABSTRACT FROM AUTHOR]

Improper management of cattle manure and poultry litter from confined animal farming are usually source of water pollution. However, appropriate application of these products on switchgrass ( Panicum virgatum L.) field can enhance biomass yield and promote nutrient recycling. We evaluated the effects of harvest frequency and nutrient sources on yield and quality of switchgrass for biofuel feedstock. The experiment was carried out at Perkins and Lake Carl Blackwell, Oklahoma, from 2009 to 2011 using split plot design with four replications. The main plot treatments were two harvest frequencies single (June), and twice (June and November). The subplot treatments were nutrient sources: 1) cattle manure (CM), 2) poultry litter (PL), 3) urea (nitrogen at 150 kg ha −1 ), 4) combined chemical fertilizer (nitrogen-P 2 O 5 –K 2 O) with nitrogen at 150 kg ha −1 , P 2 O 5 at 40 kg ha −1 , and K 2 O at 20 kg ha −1 , 5) inter-seeded Crimson clover ( Trifolium incarnatum L.), and 6) control. Mean biomass yield was higher (12.4 Mg ha −1 ) in 2010 than other years possibly due to optimum moisture and temperature in 2010. At Perkins in 2010, application of CM and PL increased biomass yield significantly by 30 and 23% compared with combined chemical fertilizer (12.9 Mg ha −1 ). The effect of nutrient sources on cellulose, hemicellulose and lignin content was not significant at both locations. Cumulative biomass from twice harvest was similar to single harvest except in 2011 due to dry weather after the first cut. The cellulose and lignin content were significantly higher for single harvest compared with twice harvest at both locations. [ABSTRACT FROM AUTHOR]

The goal of the study was to evaluate and compare the physical properties of control, pretreated and densified corn stover, switchgrass, and prairie cord grass samples. Ammonia Fiber Expansion (AFEX) pretreated switchgrass, corn stover, and prairie cord grass samples were densified by using the comPAKco device developed by Federal Machine Company of Fargo, ND. The densified biomass were referred as “PAKs” in this study. All feedstocks were ground into three different grind size of 2, 4 and 8 mm prior to AFEX pretreatment and the impact of grinding on pellet properties was studied. The results showed that the physical properties of AFEX-PAKed material were not influenced by the initial grind size of the feedstocks. The bulk density of the AFEX-PAKed biomass increased by 1.2–6 fold as compared to untreated and AFEX-pretreated materials. The durability of the AFEX-PAKed materials were between 78.25 and 95.2%, indicating that the AFEX-PAKed biomass can be transported easily. To understand the effect of storage on the physical properties of these materials, samples were stored in the ambient condition (20 ± 2 °C and 70 ± 5% relative humidity) for six months. After storage, thermal properties of the biomass did not change but glass transition temperature decreased. The water absorption index and water solubility index of AFEX-treated and AFEX-PAKed biomass showed mixed trends after storage. Moisture content decreased and durability increased upon storage. [ABSTRACT FROM AUTHOR]

To reduce the recalcitrance of lignocellulosic biomass for subsequent biological processing, we pretreated energy crop feedstocks with mild steam treatment (ST; 130 and 150 °C for 60 min) and wet disk milling (WDM). We tested two phylogenetically different, but typical energy crop feedstocks: Populus trichocarpa and switchgrass ( Panicum virgatum ). WDM after ST facilitated the fibrillation of both types of biomass, resulting in an increase of specific surface area, improved enzymatic saccharification yield, and decrease in cellulose crystallinity. After steam treatment at 150 °C followed by 17 cycles of WDM, enzymatic hydrolysis resulted in almost complete glucan to glucose conversion in both feedstocks. [ABSTRACT FROM AUTHOR]

The objective of this study was to estimate the storage dry matter (DM) losses for switchgrass bales that were preprocessed using an industrial baler technology prior to storage with three particles sizes of feedstock and two types of bale wraps. Mixed models were used to test difference in DM losses across the particle sizes, wrap materials, and storage days. Response functions were also estimated to determine DM losses for each particle size and wrap material at storage over time. DM losses were found to be different across particle size, wrap material, and storage period. Specifically, the DM losses were lower when the particle size of switchgrass baled decreased from full length to less than two centimeters. The results show switchgrass bales stored at the smallest particle size had lower DM losses than bales stored at the full length of feedstock. Also, applying additional film wrap that completely covers the net wrapped bale reduced DM losses relative to bales wrapped only in net. Furthermore, storage DM losses of preprocessed switchgrass bales increased linearly with days in storage. Our findings suggest that applying both net and film wrap to switchgrass bales composed by a particle size less than two centimeters can reduce DM losses during storage. Economic analysis indicates the price of switchgrass was also important in the choice of storage method for switchgrass. The results provide valuable insight into improving feedstock logistics and the feasibility of the advanced biofuels industry. [ABSTRACT FROM AUTHOR]

Switchgrass is being evaluated as a potential feedstock source for cellulosic biofuels and is being cultivated in several regions of the United States. The recent availability of switchgrass land cover maps derived from the National Agricultural Statistics Service cropland data layer for the conterminous United States provides an opportunity to assess the environmental conditions of switchgrass over large areas and across different geographic locations. The main goal of this study is to develop a data-driven multiple regression switchgrass productivity model and identify the optimal climate and environment conditions for the highly productive switchgrass in the Great Plains (GP). Environmental and climate variables used in the study include elevation, soil organic carbon, available water capacity, climate, and seasonal weather. Satellite-derived growing season averaged Normalized Difference Vegetation Index (GSN) was used as a proxy for switchgrass productivity. Multiple regression analyses indicate that there are strong correlations between site environmental variables and switchgrass productivity ( r = 0.95). Sufficient precipitation and suitable temperature during the growing season (i.e., not too hot or too cold) are favorable for switchgrass growth. Elevation and soil characteristics (e.g., soil available water capacity) are also an important factor impacting switchgrass productivity. An anticipated switchgrass biomass productivity map for the entire GP based on site environmental and climate conditions and switchgrass productivity model was generated. Highly productive switchgrass areas are mainly located in the eastern part of the GP. Results from this study can help land managers and biofuel plant investors better understand the general environmental and climate conditions influencing switchgrass growth and make optimal land use decisions regarding switchgrass development in the GP. [ABSTRACT FROM AUTHOR]

High cost of technology is seen as the primary barrier to full commercialization of cellulosic biofuels. There is broad expectation that once conversion technology breakthroughs occur, policy support is only needed to accelerate cost reductions through “learning by doing” effects. In this study, we show that droughts pose a significant economic risk to biofuel producers and consumers regardless of the rate at which technology costs fall. We model a future switchgrass derived cellulosic biorefinery industry in Kansas based on spatially resolute historic (1996–2005) weather data, representing a rainfall regime that could reflect drought events predicted to occur throughout the U.S. Midwest by climatologists (Karl et al. (2009) U.S. Global Change Research Program USA). We find that droughts reduced modeled biorefinery capacity factors, on average, by 47%, raising biofuel production costs by 35% between a modeled dry and wet year. Interestingly, we find that two logical strategies to plan for drought; (1) building large biorefineries to source feedstock from a larger area and, (2) Storing switchgrass in good production years for use in drought years; are not very effective in reducing drought risks. Our findings should be of particular concern to low carbon fuel policies like California's Low Carbon Fuel Standard and the U.S. Second Renewable Fuel Standards (RFS2) whose costs of compliance may be much higher than expected. [ABSTRACT FROM AUTHOR]

Biofuel production from second-generation feedstock has become critical due to environmental concerns and the need for sustainable energy supply. This paper provides a unique optimization approach of quantifying and formulating the economic and environmental benefits of switchgrass production at the farm level. In particular, we propose a multi-objective mixed-integer programming model, which maximizes the revenue from harvested switchgrass biomass and the economic value obtained from the positive environmental impacts of switchgrass yield during a ten-year planning horizon. Environmental impacts include soil erosion prevention, sustainability of bird populations, carbon sequestration, and carbon emissions, while economic impacts are analyzed under various budget, yield, and sustainability scenarios. The proposed model is then applied to a case study in the state of Kansas. Results show that given the current market prices, switchgrass cultivation on grassland and cropland is highly profitable. The model results also suggest that if utilized by the government, conservation reserve program (CRP) incentives could make marginal land more favorable over cropland. We perform sensitivity analysis to address the uncertainty in budget, yield, and utilization of cropland, and present insights into the economic and environmental impacts of switchgrass production. This model can also be extended to biomass production from any other types of energy crops to identify the most efficient production planning strategies under various management scenarios. [ABSTRACT FROM AUTHOR]

Highlights: [•] Switchgrass yields were generally not affected by the type of nitrogen fertilizer used. [•] Optimum N rates were variable for different locations, requiring site-specific recommendations. [•] Biomass yields and moisture content were reduced with progressively later harvest timing. [•] Quality of biomass as a bioenergy feedstock was optimized with a winter or spring harvest timing. [Copyright &y& Elsevier]

Abstract: Intercropping biofuel feedstocks in managed forests of the southeastern United States is a potentially sustainable source of renewable energy. Ecological effects of energy crops in forests are poorly understood, and it is unknown whether the ecological role of native rodents is influenced by alternative food resources. Therefore, we used a stable isotope analysis to compare diet and trophic responses of white-footed mice (Peromyscus leucopus) in 1) plots where switchgrass (Panicum virgatum), a C4 plant, was intercropped with loblolly pine (Pinus taeda), a C3 plant, 2) plots of loblolly pine, and 3) plots of monocropped switchgrass. We collected fur from live-trapped rodents and potential dietary sources in 2010. We predicted δ13C and δ15N values of mice in switchgrass plots would reflect a C4-based, granivorous, diet if there was an effect of intercropping on the functional role of mice. Del13C values of mouse fur in monocropped switchgrass, but not intercropped switchgrass plots, shifted more toward a C4 signal. However, δ15N values indicated that mice remained functionally omnivorous across treatments. Our results were supported by isotope values from invertebrates across guilds. Diet and trophic position of white-footed mice was not influenced by intercropping switchgrass in pine plantations indicating they maintained their functional role in this biofuels management regime. Future research should focus on individual and population responses of rodents to altered vegetation structure where biofuels feedstocks are grown and indirect effects on inter- and intra-species interactions. [Copyright &y& Elsevier]

Abstract: In this paper, we present a superstructure optimization approach for the integration of the simultaneous production of liquid fuels and hydrogen from switchgrass and shale gas. The process is based on Fischer-Tropsch technology in which the shale gas is reformed with steam, while the switchgrass is gasified and reformed (with steam or partial oxidation). The raw gas is cleaned up and its composition may be adjusted (using either water gas shift reaction or pressure swift adsorption). Next, the sour gases are removed before the liquid fuels are produced using an FT reactor. The heavy liquids are upgraded using hydrocracking to increase the yield towards FT-diesel. A sensitivity study on the raw material prices reveals that production costs for the biomass-shale gas facility are below $1/gal as long as biomass price is below $100/t and the price of the shale gas is not higher than $11.5/MMBTU. Furthermore, hydrogen is produced as long as the demand for liquid fuels can be met and there is enough shale gas available. [Copyright &y& Elsevier]

Abstract: Nitrogen-fixing bacteria (NFB) and other plant growth promoting rhizobacteria (PGPR) have been used to increase growth and yield of corn and sugarcane, two graminaceous crops utilized as bioenergy feedstocks. Switchgrass (SG, Panicum virgatum L.), a native perennial grass of North America, is also a desirable bioenergy crop because it can be grown on marginal lands and thus does not necessarily displace food production. Yet no investigations have been conducted on the use of NFB and/or PGPR as inoculants to increase SG growth and productivity. Studies reporting high biomass yields from SG with minimal to no fertilizer nitrogen (N) input prompted us to hypothesize that SG is obtaining part of its N from an alternative source, perhaps through biological nitrogen fixation from root/rhizome associated PGPR. We isolated bacteria from SG rhizomes that had not received fertilizer N input for over ten years and which increased plant growth in the absence of the fertilizer N under growth chamber conditions. The bacteria were identified as a strain of Paenibacillus polymyxa, a N2-fixing bacterium, and several other PGPR capable of solubilizing phosphate and/or producing auxins. Our objective was to test this PGPR inoculum under field conditions with low-N inputs. Here, we present the findings regarding SG productivity in the establishment year. Switchgrass seeds inoculated with the PGPR culture had greater tiller density, and taller tillers resulting in 40% higher yield than uninoculated plants. PGPR have the potential to be effectively utilized as inoculants to enhance SG yields in a low-N input production system. [Copyright &y& Elsevier]

Abstract: The U.S. Energy Independence and Security Act of 2007 mandates the use, if produced, of 6.06 × 1010 L of advanced biofuels by 2022. The objective of this study is to determine the ethanol price necessary for a biorefinery to breakeven when using switchgrass as the single feedstock to produce ethanol. A holistic model that encompasses acquisition of land use services, feedstock production, harvest, harvest machine investment, feedstock logistics (storage, transportation), biorefinery location and size, and biorefinery investment is constructed and used to determine breakeven ethanol price. The model was solved for each of three biomass to ethanol conversion rates (250, 334, and 417 L of ethanol Mg−1 of biomass) and each of three biorefinery investment cost estimates ($2, $4, and $6 × 108 for a biorefinery with annual capacity of 379 × 106 L). Breakeven ethanol prices ranged from $0.44 L−1 with a conversion rate of 417 L of ethanol Mg−1 and an investment cost of $2 × 108, to $0.72 L−1 with a conversion rate of 250 L Mg−1 and an investment cost of $6 × 108. Improving the efficiency of conversion from 250 to 334 L Mg−1 decreases the estimated breakeven cost by $0. 07 L−1. Improved conversion efficiency results in a reduction of the total quantity of feedstock required and in the cost to deliver feedstock. Most of the cost reduction follows from reductions in land required (rent), and biomass harvest, storage, and transportation costs. [Copyright &y& Elsevier]

Abstract: The production of cellulosic feedstocks for renewable fuels will increase over the coming decades. However, it is uncertain which feedstocks will be best suited for bioenergy production. A key factor dictating feedstock selection for a given region is water use efficiency (WUE), the trade-off between evapotranspiration (ET) and carbon uptake or productivity. Using an ecosystem model, two of the top candidate cellulosic feedstocks, Miscanthus × giganteus (miscanthus) and Panicum virgatum (switchgrass) were compared to Zea mays L. (maize), the existing dominant bioenergy feedstock, with 0 and 25% residue removal for the Midwest US. We determined productivity in three ways: harvested yield (HY), net ecosystem productivity (NEP) and net biome productivity (NBP). Evapotranspiration was compared against each of the three productivity metrics, respectively, to yield Harvest Water Use Efficiency (HWUE), Ecosystem Water Use Efficiency (EWUE) and Biome Water Use Efficiency (BWUE). Simulations indicated that, over the study domain, miscanthus had a significantly higher HWUE compared to switchgrass and maize, while maize and switchgrass were similar. When EWUE was compared miscanthus was higher than both maize and switchgrass, which were similar for most of the region. Biome WUE was similar for both of the perennials and higher compared to maize for most of the study domain with the exception of the driest regions where maize showed the highest BWUE. Removing 25% of maize residue slightly increased HWUE and greatly decreased BWUE throughout the domain, however only HWUE changes were statistically significant. These results indicate that the feedstock with the highest WUE varied based on the productivity metric, but BWUE for maize was consistently lower than the perennials. [Copyright &y& Elsevier]

Abstract: Switchgrass (Panicum virgatum L.) is being evaluated as a bioenergy crop for the northern Great Plains. Field measurements of CO2, CH4, and N2O flux are needed to estimate the net greenhouse gas (GHG) balance of this biofeedstock. The study objective was to determine effects of recommended Nitrogen (N) fertilization (67 kg ha−1 of N applied) and unfertilized switchgrass on growing season soil-atmosphere CO2, CH4, and N2O flux using static chamber methodology. Mean hourly CO2 flux was greatest during periods of active switchgrass growth and was similar between N fertilizer treatments (P = 0.09). Mean hourly N2O flux was consistently greater under N fertilization than without N throughout the growing season. Overall, N fertilization of switchgrass affected cumulative growing-season N2O flux (27.6 kg ha−1 ± 4.0 kg ha−1 vs. 86.3 kg ha−1 ± 14.3 kg ha−1 as CO2 equivalents (CO2eq) for 0 kg ha−1 and 67 kg ha−1 of N applied, respectively; P < 0.01), but not cumulative CO2 or CH4 flux (P = 0.08 and 0.51, respectively). Aboveground biomass production was greater with N application (6.8 Mg ha−1 ± 0.5 Mg ha−1 dry matter) than without N (3.2 Mg ha−1 ± 0.5 Mg ha−1) (P < 0.05). Net greenhouse gas intensity (GHGI; kg GHG flux kg− 1 harvest yield as CO2eq) for switchgrass production was similar between N treatments (0.71 vs. 0.44 for 0 kg ha−1 and 67 kg ha−1 of N applied, respectively; P = 0.18). [Copyright &y& Elsevier]

Abstract: We examined the impacts of increased biofuel feedstock production on regional water resource and water quality. We focused on the Upper Mississippi river basin, from which a majority of U.S. biofuel is produced at present. The production of biofuel from both conventional feedstock and cellulosic feedstock will potentially increase in the near future, and a significant portion of the cellulosic feedstock is expected to come from this region. In this work, we developed future scenarios of biofuel feedstock production in 2015 to assess the potential water quality and quantity changes associated with an increase in biofuel production through corn yield increase, harvesting a fraction of corn stover, and converting land to perennial grass (switchgrass). The estimates are accomplished by a watershed model SWAT. Results project a slight increase in phosphorus loading and decrease in nitrogen loading when corn yield is increased without cellulosic feedstock production. Harvesting a fraction of corn stover with improved management and efficient nitrogen use could lead to a decrease in nitrogen loading (up to 10%) and phosphorus loading (2%) when soil properties remain constant. Changes in sediment loadings are relatively minor. Growing switchgrass reduces soil erosion considerably and positively impacts nitrogen and phosphorus loadings at the projected yield and fertilizer input while switching from pasture to switchgrass would increase the water loss associated with ET (1% of total precipitation), decrease base flow (2%), and decrease the surface runoff flow to the basin. Major factors – including land use changes, feedstock types, fertilizer inputs, crop yield, and soil properties – were analyzed for their direct and composite impacts. [Copyright &y& Elsevier]

Abstract: Feedstock quality of switchgrass for biofuel production depends on many factors such as morphological types, geographic origins, maturity, environmental and cultivation parameters, and storage. We report variability in compositions and enzymatic digestion efficiencies for three cultivars of switchgrass (Alamo, Dacotah and Shawnee), grown and harvested at different locations and seasons. Saccharification yields of switchgrass processed by different pretreatment technologies (AFEX, dilute sulfuric acid, liquid hot water, lime, and soaking in aqueous ammonia) are compared in regards to switchgrass genotypes and harvest seasons. Despite its higher cellulose content per dry mass, Dacotah switchgrass harvested after wintering consistently gave a lower saccharification yield than the other two varieties harvested in the fall. The recalcitrance of upland cultivars and over-wintered switchgrass may require more severe pretreatment conditions. We discuss the key features of different pretreatment technologies and differences in switchgrass cultivars and harvest seasons on hydrolysis performance for the applied pretreatment methods. [Copyright &y& Elsevier]

Abstract: Silicon (Si) concentrations in biofuel feedstock crops have a critical role in combustion processes. The purpose of this study was to quantify Si concentrations in plant biomass samples and to evaluate the contributing factors for Si concentrations. We determined total Si concentrations in Miscanthus × giganteus (M. × giganteus) collected from various research trial plots in the eastern U.S. and in Miscanthus spp. and Panicum virgatum, ‘Cave-in-Rock’ (switchgrass) from an additional eight trial plots established across Illinois. Whole aboveground plant biomass at each site were air-dried and ground. Total Si concentrations in plant samples were determined by dry-ashing plant tissue in a muffle furnace, followed by alkaline fusion and then colorimetric analysis. Average Si concentrations in statewide M. × giganteus plant samples ranged from 0.72% to 1.6% and samples from within Illinois ranged from 0.55% to 2.4%. The overall median value of concentrations in M. × giganteus samples among all sites was 1.08%. The median value in switchgrass samples (1.5%) was 1.4 times higher than that for M. × giganteus. Among six other Miscanthus spp. samples from the Urbana trial plot in Illinois, Si concentrations were about 1/3 that of M. × giganteus. Variation in Si concentrations tended to be associated with temperature and precipitation of the location where the biofuel crops are being grown. We did not find any relationship between soil type and plant Si concentrations. Long-term evaluations of soil mineral concentrations and additional environmental factors are required to better understand the contributing factors for Si concentrations. [Copyright &y& Elsevier]

Abstract: An efficient and sustainable biomass feedstock production system is critical for the success of the biomass based energy sector. An integrated systems analysis framework to coordinate various feedstock production related activities is, therefore, highly desirable. This article presents research conducted towards the creation of such a framework. A breadth level mixed integer linear programming model, named BioFeed, is proposed that simulates different feedstock production operations such as harvesting, packing, storage, handling and transportation, with the objective of determining the optimal system level configuration on a regional basis. The decision variables include the design/planning as well as management level decisions. The model was applied to a case study of switchgrass production as an energy crop in southern Illinois. The results illustrated that the total cost varied between 45 and 49 $ Mg−1 depending on the collection area and the sustainable biorefinery capacity was about 1.4 Gg d−1. The transportation fleet consisted of 66 trucks and the average utilization of the fleet was 86%. On-farm covered storage of biomass was highly beneficial for the system. Lack of on-farm open storage and centralized storage reduced the system profit by 17% and 5%, respectively. Increase in the fraction of larger farms within the system reduced the cost and increased the biorefinery capacity, suggesting that co-operative farming is beneficial. The optimization of the harvesting schedule led to 30% increase in the total profit. Sensitivity analysis showed that the reduction in truck idling time as well as increase in baling throughput and output density significantly increased the profit. [Copyright &y& Elsevier]

Abstract: The energy requirement for biomass comminution and the resulting particle physical properties are important factors to study logistic components, select equipment, and assess the overall efficiency of feedstock supply–conversion chain. In this study, mechanical size reduction of Miscanthus (Miscanthus giganteus), switchgrass (Panicum virgatum), willow (Salix babylonica), and energy cane (Saccharum spp.) was carried out using a commercial-scale hammer mill, a bench-scale Retsch SM2000 knife mill and a Retsch SK100 hammer mill. The results showed that the specific energy consumption of biomass comminution and the aperture sizes of the milling screens were related in power-law forms. Biomass moisture significantly influenced comminution energy consumption, especially for finer size reduction. Given a specific milling screen, the Retsch SK100 hammer mill was found more energy efficient than the SM2000 knife mill. This was mainly attributed to the higher motor speed and axial feeding mechanism of the hammer mill. The particle sizes after comminution were found inversely proportional to the bulk densities of all four energy crops used in experiments. In addition, the comminution ratio, being the ratio of the final mean particle size and the original mean particle size, was proportional to energy consumption for all four energy crops. The bulk densities for 4-mm and smaller Miscanthus and switchgrass particles were higher than those of the original bale. Particle size and surface area estimates using commonly used ANSI/ASAE Standards S424.1 and 319.4 were highly sensitive to particle size distributions and shapes. Further studies on standardization of particle size and surface area estimates are needed. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the potential of biobutanol was evaluated as an alternative to bioethanol which is currently the predominant liquid biofuel in the US. Life-cycle assessments (LCAs) suggest that the net energy generated during corn-to-biobutanol conversion is 6.53MJ/L, which is greater than that of the corn-derived bioethanol (0.40MJ/L). Additionally, replacing corn with lignocellulosic materials in bioethanol production can further increase the net energy to 15.90MJ/L. Therefore, it was interesting to study the possibility of using domestically produced switchgrass, hybrid poplar, corn stover, and wheat straw as feedstocks to produce liquid biofuels in the US. By sustainable harvest based on current yields, these materials can be converted to 8.27 billion gallons of biobutanol replacing 7.55 billion gallons of gasoline annually. To further expand the scale, significant crop yield increases and appropriate land use changes are considered two major requirements. [ABSTRACT FROM AUTHOR]

Abstract: Switchgrass (Panicum virgatum L.), a native of eastern and central North America, is a leading candidate as a dedicated biofuel feedstock in the US due to its broad adaptability, rapid growth rate, and ability to grow in low production soils. To begin to characterize the important agronomic and ecological traits related to environmental tolerance of switchgrass, we evaluated fitness under stressful growing conditions. We assessed the germination, establishment, performance, and reproductive potential of four common accessions, both upland and lowland ecotypes, at various levels of soil moisture availability (moisture deficit to flooded) in the greenhouse. Seeds emerged and established (55–90% survival) under all soil moisture conditions (−0.3MPa to flooded). Transplants of lowland ecotypes performed as well in flooded conditions as in field capacity controls, though flooding reduced performance of upland ecotypes. Drought treatments (−4.0 and −11.0MPa) reduced tiller length and number, leaf area, and biomass production by up to 80%. However, once established, all plants survived at −4.0MPa and had the same proportion of tillers in flower as at field capacity. The ability of switchgrass to germinate, establish, and flower in low moisture and flooded conditions, particularly lowland ecotypes, may increase the range of environments suitable for biofuel cultivation, and can serve as a baseline for further ecological studies and genetic improvement. [Copyright &y& Elsevier]

Abstract: A 10-year US Department of Energy-sponsored research program designed to evaluate and develop switchgrass (Panicum virgatum), a native perennial warm-season grass, as a dedicated energy crop is reviewed. The programmatic objectives were to identify the best varieties and management practices to optimize productivity, while developing an understanding of the basis for long-term improvement of switchgrass through breeding and sustainable production in conventional agroecosystems. This research has reduced the projected production cost of switchgrass by about 25% ($8–9Mg−1) through yield increases of about 50% achieved through selection of the best regionally adapted varieties; through optimizing cutting frequency and timing; and by reducing the level (by about 40%) and timing of nitrogen fertilization. Breeding research has made further gains in productivity of switchgrass that exceed the historical rate of yield improvement of corn. Studies of soil carbon storage under switchgrass indicate significant carbon sequestration will occur in soils that will improve soil productivity and nutrient cycling and can substantially augment greenhouse gas reductions associated with substituting renewable energy for fossil energy. Collaborative research with industry has included fuel production and handling in power production, herbicide testing and licensing, release of new cultivars, and genetic modifications for chemical coproduct enhancement. Economically based life cycle analyses based on this research suggest that switchgrass produced for energy will compete favorably both as an agricultural crop and as fuel for industry. [Copyright &y& Elsevier]

[Display omitted] • Nationwide facility database to meet target cost, quality and quantity for biofuels. • In 2022, 42.8 M dt of corn stover and switchgrass could be accessible nationwide. • An $8/dt reduction in delivery cost could reduce total accessible biomass by 67%. • KS, NE, SD and TX were identified as potential states with a strong biofuel economy. • CO, AL, GA, MN, MS and SC could greatly benefit from a nationwide depot network. The sustainability of the biofuel industry depends on the development of a mature conversion technology on a national level that can take advantage of the economies of scale: the nth-plant. Defining the future location and supply logistics of conversion plants is imperative to ultimately transform the nation's renewable biomass resources into cost-competitive, high-performance feedstock for production of biofuels and bioproducts. Since the US has put restrictions on production levels of conventional biofuels from edible resources, the nation needs to plan for the widespread accessibility and development of the cellulosic biofuel scenario. Conventional feedstock supply systems will be unable to handle cellulosic biomass nationwide, making it essential to expand the industry with an advanced feedstock supply system incorporating a distributed network of preprocessing depots and conversion plants, or biorefineries. Current studies are mostly limited to designing supply systems for specific regions of the country. We developed a national database with potential locations for depots and biorefineries to meet the nation's target demand of cellulosic biofuel. Blended feedstock with switchgrass and corn stover (harvested by either a two- or three-pass method) are considered in a Mixed Integer Linear Programming model to deliver on-spec biomass that considers both, a desired quantity and quality at the biorefinery. The model solves for a network of varying size depots that supply to biorefineries of 725,000 dry tons/year. A total delivered feedstock cost that is less than $79.07/dry tons (2016$) is evaluated for years 2022, 2030, and 2040. In 2022, 124 depots and 59 biorefineries could be supplied with 42.8 million dt of corn stover and switchgrass. In 2030 and 2040, the total accessible biomass could increase to 215% and 393% respectively when compared to 2022. However, an $8/dry tons reduction in targeted delivery cost could reduce total accessible biomass by 67%. Kansas, Nebraska, South Dakota and Texas were identified as potential states with a strong biofuel economy given that they had six or more biorefineries located in all scenarios. In some scenarios, Colorado, Alabama, Georgia, Minnesota, Mississippi and South Carolina would greatly benefit from a depot network as these could only deliver to a biorefinery in a nearby state. To elaborate the impact of a nationwide consideration, the findings were compared with existing literature for different US regions. We also present results for biorefinery capacities that are double, triple and quadruple in size. [ABSTRACT FROM AUTHOR]