Switchgrass Field Research Articles

Comparison of carbon budget, evapotranspiration, and albedo effect between the biofuel crops switchgrass and corn

Interest in biofuels produced from perennial crops like switchgrass (Panicum virgatum L.) has increased over the past decades. It has been suggested that perennial biofuel crops have additional climate benefits compared to annual crops, such as carbon sequestration and albedo increase, but these effects have not been quantified in field studies. We compared carbon dioxide and water exchange results from eddy covariance measurements and surface albedo over a switchgrass and a corn field in Southwestern Ontario, Canada, for the year 2014. Results for the carbon budget showed more carbon uptake for switchgrass compared to corn (annual net ecosystem exchange NEE of −336±40 vs +64±41gCm−2). Switchgrass was a small sink of carbon with a net ecosystem carbon balance (NECB) of −66±59gCm−2 but corn was a source for a scenario where corn grain only is harvested (NECB 393±44gCm−2) and a 1.5 times larger source if both corn grain and stover are harvested (NECB 699±47gCm−2). Switchgrass had, however, a lower yield 568±93gm−2 than either corn scenario (751±40gm−2 for grain only and 1439±52gm−2 for grain plus stover). Results from the albedo measurements showed a negative radiative forcing on an annual basis for the switchgrass field compared to corn. Differences in albedo were especially pronounced during spring and fall when radiative forcing values of −10.2 and −5.5Wm−2 were observed, respectively. Qualitative analysis of the carbon budget, evapotranspiration, and albedo results from this study suggests that biofuel produced from switchgrass can have more climate benefits than biofuel produced from continuous corn cropping systems.

Evapotranspiration and Ecosystem Water Use Efficiency of Switchgrass and High Biomass Sorghum

Water and energy flux densities of co‐located cellulosic feedstocks, switchgrass (Panicum virgatum L.) and high biomass sorghum (Sorghum bicolor L. Moench), were measured using the eddy covariance technique during the 2012 and 2013 growing seasons to quantify and compare evapotranspiration (ET) and ecosystem water use efficiency (EWUE). Peak growing season ET from the switchgrass field was approximately 6 mm d−1 in both years; whereas, the sorghum ET reached 6.7 in 2012 and 4.8 mm d−1 in 2013. While both species showed similar water use patterns during the active growing period, seasonal cumulative ET was higher in switchgrass due to a longer growing season. Monthly ET integrals were strongly correlated with monthly integrals of gross primary production (GPP) and net ecosystem production (NEP) for both species, suggesting a strong linkage between C gain and water loss over the season. Different methods of EWUE estimations yielded different EWUE values. The ratio of seasonal sums of GPP to ET yielded EWUE of 9.41 to 11.32 and 8.98 to 9.17 g CO2 mm−1 ET in switchgrass and sorghum, respectively. The ratio of seasonal sums of NEP to ET was 2.75 to 2.81 and 2.06 to 2.18 g CO2 mm−1 ET in switchgrass and sorghum, respectively. Slightly larger EWUE in switchgrass than sorghum shows that the switchgrass was more efficient than the sorghum on using water to gain C. Results suggest that larger seasonal C uptake by switchgrass was enough to offset its higher water use due to the longer growing season. Eddy covariance technique can be used to assess bioenergy crops ecosystem water use efficiency. Swithcgrass has higher ET than sorghum due to longer growing season. Greater seasonal carbon uptake by switchgrass than sorghum was enough to offset higher water use.

Diurnal and seasonal variations of soil respiration rate under different row-spacing in a Panicum virgatum L. field on semi-arid Loess Plateau of China

Soil respiration (SR) in crop field is affected by environmental factors, agronomic practices and crop types. To clarify how planting density affects the SR dynamics in switchgrass (Panicum virgatum L.) field on the semi-arid Loess Plateau, this research investigated diurnal and seasonal changes of soil respiration rate (RS) under three different row-spacing treatments (20, 40 and 60 cm) in the fourth growing year of switchgrass. Results showed that RS presented a pronounced seasonality under all row-spacing treatments. The highest daily average RS values appeared in August, while the lowest (P<0.05) were in September for each row-spacing. Diurnal variations of RS exhibited single-peak curves in each month. Daily average RS increased significantly as row-spacing enlarged during May and August but there was no significant difference among row-spacing treatments in September. Soil water storage in the depth of 0–100 cm had no significant difference (P>0.05) among the row-spacing treatments, and similar results were found for soil temperature in 0–15 cm soil depth. Soil respiration temperature sensitivity (Q10) values were 1.0–3.7 during the growing months, which were strongly correlated with air temperature in May and June and the soil temperature at 15 cm depth in August. Higher aboveground biomass production and lower RS in most growth months indicated that 20 cm row-spacing treatment was beneficial for increasing the carbon fixation in switchgrass field. Results also implied that it is necessary to take into account the influence of phenology and root growth of switchgrass on soil respiration for accurately evaluating the carbon cycle in the region.

Converting Abandoned Hayfield to Switchgrass Increases Small Mammal Relative Abundance

Switchgrass (Panicum virgatum L.) has been identified as a versatile and broadly useful bioenergy feedstock, with potential for use in coal-fired power plants as well as ethanol production. However, in order for switchgrass use to markedly influence energy production, conversion to this grass species must occur at a large scale. Little is known about the potential ecological consequences of widescale conversion of land to switchgrass. This study was conducted to identify potential effects of switchgrass planting on small mammal populations. An abandoned perennial cool season grass hayfield in central Kentucky was subdivided into two fields; one field was planted with switchgrass and the control field was maintained as an unmanaged hayfield. Small mammal relative abundance was quantified using a tracking method through the third year following switchgrass planting. Small mammal relative abundance was greater in the switchgrass field than in the control field. Vegetative community analysis showed the control field was dominated by tall fescue, suggesting that thickness of stand and/or fescue toxicity may have been a factor in reduced small mammal abundance. These data suggest that conversion of abandoned old fields to switchgrass will not have a negative effect on small mammal populations. Further research should target potential mechanisms for this variation in small mammal relative abundance, as well as other species in the community which may be affected by conversion to switchgrass.

Evaluating the impacts of landscape positions and nitrogen fertilizer rates on dissolved organic carbon on switchgrass land seeded on marginally yielding cropland

Dissolved organic carbon (DOC) through leaching into the soils is another mechanism of net C loss. It plays an important role in impacting the environment and impacted by soil and crop management practices. However, little is known about the impacts of landscape positions and nitrogen (N) fertilizer rates on DOC leaching in switchgrass (Panicum virgatum L.). This experimental design included three N fertilizer rates [0 (low); 56 (medium); 112 (high) kg N ha−1] and three landscape positions (shoulder, backslope and footslope). Daily average DOC contents at backslope were significantly lower than that at shoulder and footslope. The DOC contents from the plots that received medium N rate were also significantly lower than the plots that received low N rates. The interactions of landscape and N rates on DOC contents were different in every year from 2009 to 2014, however, no significant consistent trend of DOC contents was observed over time. Annual average DOC contents from the plots managed with low N rate were higher than those with high N rate. These contents at the footslope were higher than that at the shoulder position. Data show that there is a moderate positive relationship between the total average DOC contents and the total average switchgrass biomass yields. Overall, the DOC contents from leachate in the switchgrass land were significantly influenced by landscape positions and N rates. The N fertilization reduced DOC leaching contents in switchgrass field. The switchgrass could retain soil and environment sustainability to some extent. These findings will assist in understanding the mechanism of changes in DOC contents with various parameters in the natural environment and crop management systems. However, use of long-term data might help to better assess the effects of above factors on DOC leaching contents and loss in the switchgrass field in the future.

Effects of Nitrogen Fertilizer on Switchgrass Productivity and Soil Trace Gas Production

Atmospheric greenhouse gas (GHG) concentrations continue to increase and one of the major culprits is the continued elevation and use of fossil fuels for energy. Using bioenergy, a renewable and sustainable source of natural energy, could help to reduce the effect that fossil fuels are having on the planet by slowing the rate of input of atmospheric GHG’s. Perennial crops such as switch grass can be grown and used as a bioenergy crop. In some cases, nitrogen fertilizers are used to increase the growth of bioenergy crops with potential negative environmental consequences. For example, nitrogen fertilizer can impact soil chemical processes and lead to an increase in the production of greenhouse gases, mainly N2O and CH4. Production of these gases would negate some of the benefits achieved by substituting bioenergy crops for fossil fuels. When I examined the amount of gas flux being produced by switchgrass fields, with 0 lbs/acre, 50 lbs/acre and 150lbs/acre fertilizer treatments we observed, as predicted, an increase in N2O production with more fertilization. In some cases the increase in N2O production in the 150lbs/acre treatment was as extreme as being over 200% larger compared with no fertilization. I also observed some very interesting results with methane production, which has been showing production of methane, along with after around 30 minutes of gas collection in a chamber. Based on the results of my research, I have created a cost benefit analysis of using nitrogen fertilizer on switchgrass crops.

Land Use Change Effects on Soil Quality in Prince Edward County, ON

Soils play a key role in Earth System function. When original vegetation cover is converted to cultivated land, soils often become degraded and lose their productivity potential. We examined the effects of land-use change on a clay/clay loam soil on a farm in Ameliasburg on the northern part of Prince Edward County. Three cover types were examined: perennial sod (for lawns), perennial switchgrass (potential bioengery crop) and undisturbed forest. For each soil type, cores to a depth of 40cm were collected along three random 30m transects (at 8, 16 and 24m), then divided into 10cm increments and combined along one transect according to depth. Soil quality was assessed by analyzing various soil physical and chemical properties. Bulk density was almost two-fold higher (1.5 vs. 0.82 g/cm3) in both grass systems compared to the forest, but only in the 0-10cm layer, likely due to surface compaction associated with land management. Soil pH was slightly lower in the forest compared to the switchgrass field. The sod and switchgrass fields showed losses of ~33% and ~53% organic matter, respectively in contrast to the forested area. The largest differences for organic matter and total carbon were in the top 20cm. Soil C: N ratios were highest for the forested site and lowest for the sod field. Although perennial grass systems often enhance soil quality compared to extensively tilled sites, it appears that long-term (10y) sod production has led to a decline in some, but not all, soil quality measures, particularly soil organic matter and carbon content.

Evapotranspiration, water use efficiency, and energy partitioning of a mature switchgrass stand

With the current interest in cellulosic biofuel feedstocks, switchgrass (Panicum virgatum L.) research has increased in North America over the past decades. However, implications of large-scale switchgrass production on local and regional water budgets are largely unknown. We conducted eddy covariance measurements over a large (60ha) commercial switchgrass field in Southern Ontario, Canada, to determine evapotranspiration and energy fluxes during the sixth (2012) and seventh (2013) year since establishment of switchgrass. Annual total evapotranspiration was slightly smaller in the wet year of 2013 compared to the dry year of 2012 (562±12 and 598±9mm, respectively; error estimate based on gap filling error). Canopy conductance was larger in the wet year (11.2±1.5mms−1 in 2013; average±standard error) than in the dry year (7.7±0.9mms−1 in 2012), which suggests that switchgrass regulated stomatal opening to reduce water loss. Although this regulation reduced atmospheric CO2 fixation, it did not result in yield reduction. Water use efficiency of harvested dry matter was larger in 2012 compared to 2013 (1.82±0.12 and 1.40±0.11gDM(kgH2O)−1, respectively; error estimates based on Gaussian error propagation). Water use efficiency based on gross ecosystem production (EWUE) in 2013 was 14.0±0.6gCO2(kgH2O)−1, compared to 13.3±0.3gCO2(kgH2O)−1 in 2012 (error estimates based on Gaussian error propagation). Daily, monthly, and seasonal EWUE showed a trend to lower values in the dry year of 2012 compared to 2013. These results indicate that the switchgrass crop was able to reduce the water cost of aboveground biomass in the dry year by relocating carbon from belowground structures, but it fixed more atmospheric carbon per unit water evapotranspired in the wet year. Our findings show that mature switchgrass has the potential to withstand the impact of moderate drought or dry conditions. However, the impact of repeated drought and prolonged dry conditions on switchgrass and implications for regional water budgets are not clear yet.

Vulnerability of crops and native grasses to summer drying in the U.S. Southern Great Plains

The Southern Great Plains are characterized by a fine-scale mixture of different land-cover types, predominantly winter-wheat and grazed pasture, with relatively small areas of other crops, native prairie, and switchgrass. Recent droughts and predictions of increased drought in the Southern Great Plains, especially during the summer months, raise concern for these ecosystems. We measured ecosystem carbon and water fluxes with eddy-covariance systems over cultivated cropland for 10 years, and over lightly grazed prairie and new switchgrass fields for 2 years each. Growing-season precipitation showed the strongest control over net carbon uptake for all ecosystems, but with a variable effect: grasses (prairie and switchgrass) needed at least 350mm of precipitation during the growing season to become net carbon sinks, while crops needed only 100mm. In summer, high temperatures enhanced evaporation and led to higher likelihood of dry soil conditions. Therefore, summer-growing native prairie species and switchgrass experienced more seasonal droughts than spring-growing crops. For wheat, the net reduction in carbon uptake resulted mostly from a decrease in gross primary production rather than an increase in respiration. Flux measurements suggested that management practices for crops were effective in suppressing evapotranspiration and decomposition (by harvesting and removing secondary growth), and in increasing carbon uptake (by fertilizing and conserving summer soil water). In light of future projections for wetter springs and drier and warmer summers in the Southern Great Plains, our study indicates an increased vulnerability in native ecosystems and summer crops over time.

Nutrient sources and harvesting frequency on quality biomass production of switchgrass (Panicum virgatum L.) for biofuel

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-P2O5–K2O) with nitrogen at 150 kg ha−1, P2O5 at 40 kg ha−1, and K2O 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.

Carbon dioxide exchange dynamics over a mature switchgrass stand

AbstractSwitchgrass (Panicum virgatum L.) has gained importance as feedstock for bioenergy over the last decades due to its high productivity for up to 20 years, low input requirements, and potential for carbon sequestration. However, data on the dynamics of CO2 exchange of mature switchgrass stands (&gt;5 years) are limited. The objective of this study was to determine net ecosystem exchange (NEE), ecosystem respiration (Re), and gross primary production (GPP) for a commercially managed switchgrass field in its sixth (2012) and seventh (2013) year in southern Ontario, Canada, using the eddy covariance method. Average NEE flux over two growing seasons (emergence to harvest) was −10.4 μmol m−2 s−1 and reached a maximum uptake of −42.4 μmol m−2 s−1. Total annual NEE was −380 ± 25 and −430 ± 30 g C m−2 in 2012 and 2013, respectively. GPP reached −1354 ± 23 g C m−2 in 2012 and −1430 ± 50g C m−2 in 2013. Annual Re in 2012 was 974 ± 20 g C m−2 and 1000 ± 35 g C m−2 in 2013. GPP during the dry year of 2012 was significantly lower than that during the normal year of 2013, but yield was significantly higher in 2012 with 1090 g m−2, compared to 790 g m−2 in 2013. If considering the carbon removed at harvest, the net ecosystem carbon balance came to 106 ± 45 g C m−2 in 2012, indicating a source of carbon, and to −59 ± 45 g C m−2 in 2013, indicating a sink of carbon. Our results confirm that switchgrass can switch between being a sink and a source of carbon on an annual basis. More studies are needed which investigate this interannual variability of the carbon budget of mature switchgrass stands.

Net ecosystem carbon dioxide exchange of dedicated bioenergy feedstocks: Switchgrass and high biomass sorghum

As switchgrass (Panicum virgatum L.) and high biomass sorghum (Sorghum bicolor L. Moench) acreages are expanding for cellulosic biofuels, it is critical to improve understanding of carbon dynamics of these two potential bioenergy crops. Eddy flux measurements from co-located switchgrass and high biomass sorghum fields during the 2012 and 2013 growing seasons were analyzed to quantify and compare net ecosystem CO2 exchange (NEE) between two species. Monthly ensemble averaged NEE reached seasonal peak values of −36.9±1.78 and −35.9±2.32μmolm−2s−1 in switchgrass and sorghum, respectively. Similar magnitudes of NEE (−10 to −11gCm−2d−1), gross primary production (GPP, 19–20gCm−2d−1) and ecosystem respiration (ER, 10–12gCm−2d−1) were observed in both ecosystems. Similarly, carbon fluxes of both ecosystems had similar response to air temperature and vapor pressure deficit (VPD). Carbon fluxes exhibited an optimum temperature of slightly over 30°C and decreased markedly beyond 35°C. The NEE decreased markedly at higher VPD (>3kPa) because of the stomatal closure control of photosynthesis. The switchgrass field was a larger carbon sink, with a cumulative seasonal carbon uptake of −406±24 to −490±59gCm−2 compared to −261±48 to −330±45gCm−2 by the sorghum field. The switchgrass stand was a net carbon sink for four to five months (April/May–August), while sorghum appeared to be a net carbon sink for only three months (June–August). Our results imply that the difference in carbon sink strength between the two species was driven mainly by the length of the growing season.

Simulated biomass, environmental impacts and best management practices for long-term switchgrass systems in a semi-arid region

Long-term information on switchgrass (Panicum virgatum L.) as a biomass energy crop grown on marginally saline soil and the associated impacts on soil carbon (C) and nitrogen (N) dynamics, greenhouse gas (GHG) emissions, and best management practices (BMPs) are limited. In this study, we employed the DAYCENT model, based on a 4-year switchgrass field experiment, to evaluate the long-term biomass yield potential and environmental impacts, and further to develop BMPs for switchgrass in a semi-arid region.The model showed that long-term (14-year) annual mean biomass yields were 9.6 and 5.2 Mg ha−1 for irrigated and rainfed switchgrass systems, respectively. The simulated biomass yields correlated well with field-measured biomass with r2 values of 0.99 and 0.89 for irrigated and rainfed systems, respectively. Soil organic carbon (SOC) and soil total nitrogen (STN) accumulated rapidly after switchgrass establishment, with mean accrual rates of 0.99–1.13 Mg C ha−1 yr−1 and 0.04–0.08 Mg N ha−1 yr−1, respectively. Based on the outputs of numerous long-term model simulations with variable irrigation water supplies and N rates, the irrigation regime and N rate with the highest yield to input ratio were chosen as BMPs. The DAYCENT model predicted-BMP was irrigating every 14 days at 70% potential evapotranspiration combined with an N rate of 67 kg ha−1 yr−1. Switchgrass established and produced biomass reasonably well in this semi-arid region; however, appropriate irrigation and N fertilization were needed for optimal biomass yield. Switchgrass had a great potential to sequester C into soils with low N2O emissions while supplying significant quantities of biomass for biofuel synthesis.

Is Switchgrass an Emerging Allergy Risk?

Panicum virgatum (switchgrass) is currently receiving a lot of attention as an emerging biofuel crop because of its propensity for high yields and resistance to pests and diseases. Depending on a variety of factors, switchgrass could potentially cover large acreages of “low quality” cropland. Although switchgrass is not considered highly allergenic, increased production could lead to increased exposure resulting increased sensitivity. Determining pollen levels at various distances from the crop could help prepare allergists to consult patients on potential risks. Two Burkard volumetric pollen traps were placed near a switchgrass field in Ames, IA from July to September of 2013. Samplers were placed 2 m and 500 m from the edge of field. The switchgrass field was surrounded by corn and soybean crops and warm-season grassy weeds were minimal in the area. Standard methods were used in the preparation and analysis of slides. Grass pollen levels were very different at the two different sampling sites. The 2 m sampler recorded 6 “very high” days and peak daily mean concentration occurred on August 21st with a mean concentration of 713 pollen grains/m3. The 500 m sampler experienced no “high” or “very high” days and only experienced one day where pollen concentration was “moderate”. The 500 m sampler peaked on August 30th with a mean concentration of 23 pollen grains/m3. While pollen levels adjacent to the switchgrass field may pose a threat to sensitive individuals, exposure can be drastically reduced by separating the patient from the field by a relatively short distance.

Fine and Coarse Scale Sampling of Spatial Variability within a Switchgrass Field in Oklahoma

Aim: The objective of this study was to describe the spa tial patterns of selected soil properties and biomass yield at fine and coarse scale in a switchgrass field to determine the appropriate sampling approach to enable the calculation of means with minimum variance. Methodology: Spatial variability of biomas s yield and soil properties at fine (2.5 m sampling interval) and coarse (10 m sampling interval) scales were assessed through semivariogram analysis. The site located in Chickasha, Oklahoma, consisted of two soil types a Dale silt loam (fine - silty, mixed, superactive, thermic Pachic Haplustolls) and McLain silty clay loam (fine, mixed, superactive, thermic Pachic Argiustolls). Eighty soil samples were collected along two 100 m transects at 2.5 and 10 m intervals established across each soil type in both 20 12 and 2013. Results: The semivariograms revealed coarse scale organic carbon (OC) to be strongly correlated with range values from 56 – 78 m for both soils. Normalized difference vegetative index (NDVI) was

Switchgrass Field Performance on Two Soils as Affected by Bacterization of Seedlings with Burkholderia phytofirmans Strain PsJN

Switchgrass (Panicum virgatum L.) is a perennial warm season grass capable of growth on marginal lands without major inputs of water and fertilizers. However, full utilization of its agronomic potential as a bioenergy crop requires improvement of its stand establishment, disease resistance, and prevention of the biomass yield variation from year to year. Our program focuses on the utilization of beneficial bacterial endophytes to enhance switchgrass performance under a low-input production system on marginal lands. We demonstrated earlier that inoculation of switchgrass cv. Alamo with a growth promoting endophyte, Burkholderia phytofirmans strain PsJN (PsJN), can significantly enhance seedling vigor and plant growth under both in vitro and greenhouse conditions. In this study, we tested the effects of PsJN bacterization of switchgrass seedlings on stand establishment, plant growth, and biomass yield in three field experiments conducted over 2 years on highly fertile prime land, and on a former tobacco farm with low fertility soil. PsJN bacterization improved growth and development of switchgrass seedlings, significantly stimulated plant root and shoot growth, and tiller number on the low fertility soil (p < 0.001), and enhanced biomass accumulation on both poor (p < 0.001) and rich (p < 0.05) soils, with more effective stimulation of plant growth in low fertility soil than in high fertility soil. The study indicates the potential for the use of PsJN and/or other beneficial bacterial endophytes in the development of low-input switchgrass feedstock production systems.

Energy Potential and Greenhouse Gas Emissions from Bioenergy Cropping Systems on Marginally Productive Cropland

Low-carbon biofuel sources are being developed and evaluated in the United States and Europe to partially offset petroleum transport fuels. Current and potential biofuel production systems were evaluated from a long-term continuous no-tillage corn (Zea mays L.) and switchgrass (Panicum virgatum L.) field trial under differing harvest strategies and nitrogen (N) fertilizer intensities to determine overall environmental sustainability. Corn and switchgrass grown for bioenergy resulted in near-term net greenhouse gas (GHG) reductions of −29 to −396 grams of CO2 equivalent emissions per megajoule of ethanol per year as a result of direct soil carbon sequestration and from the adoption of integrated biofuel conversion pathways. Management practices in switchgrass and corn resulted in large variation in petroleum offset potential. Switchgrass, using best management practices produced 3919±117 liters of ethanol per hectare and had 74±2.2 gigajoules of petroleum offsets per hectare which was similar to intensified corn systems (grain and 50% residue harvest under optimal N rates). Co-locating and integrating cellulosic biorefineries with existing dry mill corn grain ethanol facilities improved net energy yields (GJ ha−1) of corn grain ethanol by >70%. A multi-feedstock, landscape approach coupled with an integrated biorefinery would be a viable option to meet growing renewable transportation fuel demands while improving the energy efficiency of first generation biofuels.

Confounding Effects of Soil Moisture on the Relationship Between Ecosystem Respiration and Soil Temperature in Switchgrass

Understanding the response of ecosystem respiration (ER) to major environmental drivers is critical for estimating carbon sequestration and large-scale modeling research. Temperature effect on ER is modified by other environmental factors, mainly soil moisture, and such information is lacking for switchgrass (Panicum virgatum L.) ecosystems. The objective of this study was to examine seasonal variation in ER and its relationship with soil temperature (Ts) and moisture in a switchgrass field. ER from the nighttime net ecosystem CO2 exchange measurements by eddy covariance system during the 2011 and 2012 growing seasons was analyzed. Nighttime ER ranged from about 2 (early growing season) to as high as 13 μmol m−2 s−1 (peak growing period) and showed a clear seasonality, with low rates during warm (>30 °C) and dry periods ( 0.20 m3 m−3), indicating that soil moisture 0.35 m3 m−3) as well. Consequently, both dry and wet conditions lowered temperature sensitivity of respiration (Q10). Stronger ER–Ts relationships were observed at higher soil moisture levels. These results demonstrate that soil moisture greatly influences the dynamics of ER and its relationship with Ts in drought prone switchgrass ecosystems.

Liquid AFEX Pretreatment and Enzymatic Hydrolysis of Switchgrass from Different Harvest and Storage Conditions

Abstract. Switchgrass harvest and storage conditions increasingly affected a representative biochemical process and theoretical ethanol yield. The approach used a novel liquid ammonia fiber explosion (LAFEX) pretreatment technique implemented through engineered introduction of ammonia in liquid phase to biomass with controlled pressures, temperatures, and a mechanical liquid pump. The LAFEX pretreatment involved pressurizing an AFEX reactor with nitrogen prior to adding ammonia, and then nitrogen pressure was increased as the reactor temperature was increased to 100°C after the addition of ammonia. LAFEX pretreatment improved Alamo switchgrass xylan digestibility up to 63.3% compared to AFEX pretreatment that had published levels of xylan digestibility up to 38.3%, all using Accellerase enzyme for enzymatic hydrolysis. This improvement occurred at less water loading (0.8 vs. 2.0 g H 2 O per g dry switchgrass), less ammonia loading (1.0 vs. 1.6 and 2.0 g NH 3 per g dry switchgrass), lower temperature (100°C vs. 160°C and 150°C), and increased pretreatment time (120 vs. 30 and 25 min) for LAFEX vs. AFEX pretreatments, respectively. Additional potential for LAFEX pretreatment was noted based on published studies documenting enzymes that outperform the enzyme selected for this study. A wide range of switchgrass field harvest conditions, including one-cut versus two-cut strategies and harvest times ranging from June to January, indicated relatively small differences in fresh switchgrass cellulose and hemicellullose levels (64% to 68%) determined with wet chemistry, and associated trends in lignin increases (21.9% to 25.7%) and ash decreases (5.3% to 2.2%) across samples obtained at harvest time, not including storage effects. Baseline theoretical ethanol yield for freshly harvested samples ranged from 462 to 485 L per dry Mg. Field storage conditions included covered and uncovered bales and piles of field-chopped switchgrass and ensiled field-chopped switchgrass. Field storage conditions affected cellulose and hemicellulose levels, as determined by wet chemistry, for theoretical ethanol yield (243 to 477 L per dry Mg) to a greater degree than variation due to field harvest conditions. Implementation of enzymatic hydrolysis for 72 h with Accellerase 1000 introduced to LAFEX-pretreated samples represented a biorefinery process for theoretical ethanol yield based on fresh harvest conditions (232 to 270 L per dry Mg) and revealed an exaggerated effect of storage conditions on theoretical ethanol yield (79 to 283 L per dry Mg). Essentially, switchgrass that got wet and stayed wet, compared to switchgrass that stayed dry or was allowed a drying cycle if exposed to precipitation during storage, reduced available cellulose and hemicelluloses (to ~50%) and further reduced the available sugars from enzymatic hydrolysis (to ~30%). It should be noted that no amount of improved pretreatment or enzymatic hydrolysis can overcome or recover the degraded sugars that occurred at the bale bottom under wet conditions. Overall results demonstrated the supply logistics challenge to deliver biomass feedstock with predictable, uniform conditions year-round to allow consistent biochemical conversion at commercial scale. Harvesting and storage conditions could also affect biochemical processes associated with ethanol fermentation that were not investigated.

Transmission of Switchgrass mosaic virus by Graminella aureovittata

Switchgrass mosaic virus (SwMV) was identified in switchgrass (Panicum virgatum) and was proposed as a new marafivirus based on its genome sequence and comparison with its closest relative, Maize rayado fino virus (MRFV), a type member of the genus Marafivirus. MRFV only infects maize (Zea mays) and its wild relatives, and is naturally transmitted by a corn leafhopper, Dalbulus maidis. Proving that SwMV is transmitted by a different species of leafhopper than D. maidis would provide additional evidence that SwMV is a new species of the genus Marafivirus. In 2010, three leafhopper species were identified in switchgrass fields near Champaign, Illinois – Graminella aureovittata, Graminella mohri and Flexamia atlantica. Switchgrass mosaic virus was detected by two independent RT–PCR assays in 100% of G. mohri and F. atlantica, and 95% of G. aureovittata. Twenty specimens of each species were evaluated. Of the three leafhoppers, only G. aureovittata transmitted the virus to ‘Cave in Rock’ switchgrass plants in a growth chamber. Transmission efficiency was 80% and only one of the eight SwMV-infected plants displayed mosaic/yellow streak symptoms. Switchgrass mosaic virus was detected in 78% and 83% of the switchgrass plants in the two fields from which the leafhoppers were collected. The detection of a leafhopper vector of SwMV will facilitate the transmission of the virus and the study of its impact on switchgrass biomass yield.