Biomass Yield and Quality of Reed Canarygrass under Five Harvest Management Systems for Bioenergy Production

Reed canarygrass, Phalaris arundinacea L., produces high biomass yields in cool climates and wetlands. The number and timing of harvests during a growing season directly affect biomass yield and biofuel quality. In order to determine optimum harvest management, seven cultivars of reed canarygrass were planted in field experiments at Ames, IA; McNay, IA; and Arlington, WI in the upper Midwestern USA and harvested once in autumn or in winter, twice in spring + autumn or spring + winter, or three times during the season as hay. Biomass yield varied considerably among harvest treatments, locations, and years, ranging up to 12.6 Mg ha^?1. Dry matter percentage ranged from 37% for spring-harvested biomass to 84% for overwintered biomass. The three harvest hay and two harvest spring + autumn managements produced the highest biomass yield compared to other systems, but the advantage, if any, of hay management was small and probably does not justify the cost of additional fieldwork. More mature biomass, such as that found in the single harvest systems, had higher fiber concentrations. Overwintered biomass had superior biofuel quality, being low in P, K, S, and Cl and high in cell wall concentration. However, winter harvest systems had lower yield than autumn harvest and in some years, no harvest was possible due to lodging from snow compaction. The main limitation of a two harvest system is the high moisture content of the late spring/early summer biomass.     

Biomass and seed yields of big bluestem, switchgrass, and intermediate wheatgrass in response to manure and harvest timing at two topographic positions

A principle attribute of perennial grasses for biomass energy is the potential for high yields on marginal lands. Objectives of this study were to compare biomass and seed production of intermediate wheatgrass ( Thinopyrum intermedium [Host] Barkworth and D.R. Dewey), big bluestem ( Andropogon gerardii Vitman), and switchgrass ( Panicum virgatum L.) as affected by harvest timing and manure application on two topographic positions (footslope and backslope). Footslope is the hillslope position that forms the inclined surface at the base of a slope and backslope forms the steepest, middle position of the hillslope. Grasses were harvested for biomass at anthesis (summer), after a killing frost (autumn), or the following spring after overwintering in the field. Seed was harvested at maturity during 2003 and 2004. Two rates of beef cattle ( Bos taurus L.) manure (target rates of 0 and 150 kg total-N ha⁻¹) were surface applied annually. Maximum annual biomass yield ranged from 4.4 to 5.2, 2.7 to 4.2, and 3.7 to 5.6 Mg ha⁻¹ for intermediate wheatgrass, big bluestem, and switchgrass, respectively. Biomass yields were not different between fall and spring harvest treatments. Biomass yields of big bluestem and switchgrass at the backslope position were 86% and 96% of biomass yields at the footslope position with normal precipitation, respectively. Manure application increased biomass yield approximately 30% during the second year on both topographic positions. The highest seed yield was obtained from intermediate wheatgrass, followed by switchgrass and big bluestem. Utilizing these management practices in our environment, it appears that switchgrass and big bluestem could be allowed to overwinter in the field without suffering appreciable loss of biomass.     

Switchgrass for forage and bioenergy: harvest and nitrogen rate effects on biomass yields and nutrient composition

Switchgrass (Panicum virgatum L.) may have value as forage and a bioenergy feedstock. Our objective was to evaluate how harvest system and N fertilizer rates affected biomass yield and nutrient composition of young stands of switchgrass (cv. Alamo) in the southern Great Plains, USA. Nitrogen fertilization increased biomass yields from 10.4, 10.8, and 12.2 Mg ha^?1 at 0 kg N?ha^?1 to 13.7, 14.6, and 21.0 Mg ha^?1 at 225 kg N?ha^?1 when harvested after seed set (October), after frost (December), and twice per year after boot stage (July) and frost, respectively. Nutrient concentrations and removal were generally twice as great when biomass was harvested twice versus once per year. Precipitation strongly affected biomass yields across the two years of these experiments. When late-summer precipitation is available to support regrowth in this environment, harvesting switchgrass twice per year will result in greater biomass yields. Harvesting twice per year, however, will increase fertilization requirements and reduce feedstock biomass quality. Switchgrass harvested during mid-summer after boot stage was of poor forage quality. To have value as a dual-purpose forage and bioenergy feedstock, switchgrass would need to be utilized during spring to early summer while in a vegetative stage.     

Switchgrass Biomass and Nitrogen Yield with Over-Seeded Cool-season Forages in the Southern Great Plains

In dry climates with long, hot summers and freezing winters, such as that of the southern Great Plains of North America, switchgrass (Panicum virgatum L.) has proven potential as a cellulosic bioenergy feedstock. This trial looked at dry matter (DM) and N yield dynamics of switchgrass overseeded with cool-season legumes and rye (Secale cereale L.), compared to switchgrass fertilized with 0, 56 and 112 kg N ha^-1 yr^-1 at an infertile and a fertile location. Optimal N fertilizer rate on switchgrass was 56 kg N ha^-1 at the infertile location. Legume yield was greater in the first season after planting, compared to subsequent years where annual legumes were allowed to reseed and alfalfa (Medicago sativa L.) was allowed to grow. This suggests that the reseeding model for annual legumes will not work in switchgrass swards grown for biomass unless soil seed banks are built up for more than one year, and that overseeding with alfalfa may have to be repeated in subsequent years to build up plant populations. Overseeding rye and legumes generally did not suppress or enhance switchgrass biomass production compared to unfertilized switchgrass. However, cumulative spring and fall biomass yields were generally greater due to winter and spring legume production, which could be beneficial for grazing or soil conservation systems, but not necessarily for once-yearly late autumn harvest biofuel production systems.     

Agricultural Management of Switchgrass for Fuel Quality and Thermal Energy Yield on Highly Erodible Land in the Driftless Area of Southwest Wisconsin

Converting row crop production to a perennial grass crop on highly erodible land has numerous benefits. Switchgrass, grown as a biofuel crop, can provide soil conservation benefits as a perennial crop and also provide economic value to the grower. However, little information exists regarding switchgrass management and production on these lands. The objectives of this study were to determine the effect of two management practices, nitrogen (N) fertilizer rate (0, 56, 112, 168, and 224 kg ha^?1) and harvest timing (mid-fall, late-fall, and spring), on: (1) dry matter (DM) yield, (2) switchgrass quality components (moisture, ash, and chloride (Cl^?) concentrations), and (3) combustion energy content and yield. The study was conducted in 2009 and 2010 on highly erodible lands in the Driftless Area of southwest Wisconsin. Results showed a positive response of switchgrass DM to N fertilizer, with no yield gain above 112 kg ha^?1 of N, although application of N increased Cl^? concentrations. Harvest timing also affected switchgrass yield, with decreases in yield observed with progressively later harvest timings; this yield decrease was slightly greater compared with previous studies. Progressively later harvest timings led to a decrease in moisture, ash concentration, and Cl^? concentration in both years. Energy content of switchgrass was not significantly affected by management. Energy yields, similar to DM yields, were maximized with 112 kg ha^?1 of N with a mid-fall harvest. The similarities between this study and other research indicate there is a universal response of switchgrass to N in the northern USA and yields determined in this study indicate that highly erodible lands in the Driftless Area can be used to produce switchgrass at regionally expected yields.     

Do Yield and Quality of Big Bluestem and Switchgrass Feedstock Decline over Winter?

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.     

Impact of Harvest Time and Cultivar on Conversion of Switchgrass to Bio-oils Via Fast Pyrolysis

The study of the effects of harvest time on switchgrass (Panicum virgatum L.) biomass and bioenergy production reported herein encompasses a large study evaluating the harvest of six switchgrass cultivars grown at three northern US locations over 3 years, harvested at upland peak crop (anthesis), post-frost, and post-winter. Delaying harvest of switchgrass until after frost and until after winter has resulted in decreased yields of switchgrass and reduced amounts of minerals in the biomass. This report examines how changes in biomass composition as a result of varying harvest time and other factors affect the distribution of products formed via fast pyrolysis. A subset (50) of the population (n = 864) was analyzed for fast pyrolysis and catalytic pyrolysis (zeolite catalyst) product yields using a pyrolysis-GC/MS system. The subset was used to build calibrations that were successful in predicting the pyrolysis product yield using near-infrared reflectance spectroscopy (NIRS), and partial least squares predictive models were applied to the entire sample set. The pyrolysis product yield was significantly affected by the field trial location, year of harvest, cultivar, and harvest time. Delaying harvest time of the switchgrass crop led to greater production of deoxygenated aromatics improving the efficiency of the catalytic fast pyrolysis and bio-oil quality. The changes in the pyrolysis product yield were related to biomass compositional changes, and key relationships between cell wall polymers, potassium concentration in the biomass, and pyrolysis products were identified. The findings show that the loss of minerals in the biomass as harvest time is delayed combined with the greater proportion in cellulose and lignin in the biomass has significant positive influences on conversion through fast pyrolysis.     

Effect of Potassium and Nitrogen Fertilizer on Switchgrass Productivity and Nutrient Removal Rates under Two Harvest Systems on a Low Potassium Soil

Biomass demand for energy will lead to utilization of marginal, low fertility soil. Application of fertilizer to such soil may increase switchgrass (Panicum virgatum L.) biomass production. In this three-way factorial field experiment, biomass yield response to potassium (K) fertilizer (0 and 68 kg?K?ha^?1) on nitrogen (N)-sufficient and N-deficient switchgrass (0 and 135 kg?N?ha^?1) was evaluated under two harvest systems. Harvest system included harvesting once per year after frost (December) and twice per year in summer (July) at boot stage and subsequent regrowth after frost. Under the one-cut system, there was no response to N or K only (13.4 Mg?ha^?1) compared to no fertilizer (12.4 Mg?ha^?1). Switchgrass receiving both N and K (14.6 Mg?ha^?1) produced 18 % greater dry matter (DM) yield compared to no fertilizer check. Under the two-cut harvest system, N only (16.0 Mg?ha^?1) or K only (14.1 Mg?ha^?1) fertilizer produced similar DM to no fertilizer (15.1 Mg?ha^?1). Switchgrass receiving both N and K in the two-cut system (19.2 Mg?ha^?1) produced the greatest (P?<?0.05) DM yield, which was 32 % greater than switchgrass receiving both N and K in the one-cut system. Nutrient removal (biomass?×?nutrient concentration) was greatest in plots receiving both N and K, and the two-cut system had greater nutrient removal than the one-cut system. Based on these results, harvesting only once during winter months reduces nutrient removal in harvested biomass and requires less inorganic fertilizer for sustained yields from year to year compared to two-cut system.     

Biomass Yield and Composition of Switchgrass Bales on Marginal Land as Influenced by Harvest Management Scheme

Switchgrass (Panicum virgatum L.) is well suited to marginal croplands, but is difficult to manage sustainably both for maximum yield and optimal biomass composition. Quality can be improved by overwintering switchgrass in the field, but more information is needed on amount and consistency of yield recovery in spring. Two cultivars of switchgrass were sown on separate fields in Freeville, NY, and mowed and baled in late fall (FALL), mowed in fall and baled in spring (WINTER), or mowed and baled in spring (SPRING), using conventional field harvesting equipment. Samples were collected for analysis of plant morphological components and for determining the influence of harvest stubble height on yield and composition. Recovery of FALL biomass yields the following spring ranged from 52 to 82% and was related to both total winter snowfall and to the spring date when soil was dry enough to allow equipment traffic. Approximately 1% of dry matter yield was left in the field for each centimeter of stubble height following mowing. Bale moisture content was very low in spring, averaging 7.3%, but was much more variable and higher in the fall, averaging 22% for “Cave-in-Rock”. Inflorescence and leaf blade were the primary morphological components lost in standing switchgrass over winter. The SPRING treatment can be mowed and baled on the same day without other field operations and has higher quality than WINTER, with no consistent yield advantage for either spring baling treatment. The large and variable yield loss due to overwintering switchgrass in the field makes the practice questionable.     

Energy Potential of Biomass from Conservation Grasslands in Minnesota,USA

Perennial biomass from grasslands managed for conservation of soil and biodiversity can be harvested for bioenergy. Until now, the quantity and quality of harvestable biomass from conservation grasslands in Minnesota, USA, was not known, and the factors that affect bioenergy potential from these systems have not been identified. We measured biomass yield, theoretical ethanol conversion efficiency, and plant tissue nitrogen (N) as metrics of bioenergy potential from mixed-species conservation grasslands harvested with commercial-scale equipment. With three years of data, we used mixed-effects models to determine factors that influence bioenergy potential. Sixty conservation grassland plots, each about 8 ha in size, were distributed among three locations in Minnesota. Harvest treatments were applied annually in autumn as a completely randomized block design. Biomass yield ranged from 0.5 to 5.7 Mg ha⁻¹. May precipitation increased biomass yield while precipitation in all other growing season months showed no affect. Averaged across all locations and years, theoretical ethanol conversion efficiency was 450 l Mg⁻¹ and the concentration of plant N was 7.1 g kg⁻¹, both similar to dedicated herbaceous bioenergy crops such as switchgrass. Biomass yield did not decline in the second or third year of harvest. Across years, biomass yields fluctuated 23% around the average. Surprisingly, forb cover was a better predictor of biomass yield than warm-season grass with a positive correlation with biomass yield in the south and a negative correlation at other locations. Variation in land ethanol yield was almost exclusively due to variation in biomass yield rather than biomass quality; therefore, efforts to increase biomass yield might be more economical than altering biomass composition when managing conservation grasslands for ethanol production. Our measurements of bioenergy potential, and the factors that control it, can serve as parameters for assessing the economic viability of harvesting conservation grasslands for bioenergy.     

Nutrient Uptake by ‘Alamo’ Switchgrass Used as an Energy Crop

Field studies were conducted in 2000 and 2001 to examine yields and nutrient removal by Alamo switchgrass (Panicum virgatum L.) grown at eight locations within five states in the upper southeastern USA. Plots, which had been established for >5 years as part of a larger study, were cut either once (late fall) or twice (midsummer and late fall). Plots cut once received 50 kg N per hectare per year, while twice-cut plots received 100 kg N per hectare per year. Nutrient concentrations of and nutrient removal by harvested biomass were determined. Partitioning of nutrients into leaf and stem fractions was determined at the time of the midsummer harvest in 2000. Biomass production during 2000 and 2001 averaged 15.9 Mg/ha per year across all sites and was as high as 21.7 Mg/ha per year at one site. Two cuttings plus the additional 50 kg N per hectare did not generally increase seasonal yields; and, in one quite productive location, that management caused a yield reduction. Nitrogen removal with two cuts was much higher than with a single cut due largely to the higher N content in the midsummer harvest. Over the 2 years, twice as much N was removed with the two annual cuts as with one cut. Nitrogen removal exceeded the amounts of N applied in both managements, suggesting N was being supplied via mineralization or other processes. Phosphorus removal also increased significantly with the two-cut management. Seasonal K and Ca removals were more similar between the two managements. Nitrogen and P concentrations generally declined basipetally in tillers, with older leaves and internodes having lower concentrations of both nutrients. Potassium was more uniformly distributed than N throughout the tiller components (leaf and stem). Calcium was higher in older leaf blades. Levels of soil P, K, and Ca at most locations appeared not to be limiting biomass production and were adequate for long-term productivity.     

Productivity, 15N dynamics and water use efficiency in low‐ and high‐input switchgrass systems

Sustainable and environmentally benign switchgrass production systems need to be developed for switchgrass to become a large‐scale dedicated energy crop. An experiment was conducted in California from 2009 to 2011 to determine the sustainability of low‐ and high‐input irrigated switchgrass systems as a function of yield, irrigation requirement, crop N removal, N translocation from aboveground (AG) to belowground (BG) biomass during senescence, and fertilizer ¹⁵N recovery (FNR) in the AG and BG biomass (0–300 cm), and soil (0–300 cm). The low‐input system consisted of a single‐harvest (mid‐fall) irrigated until flowering (early summer), while the high‐input system consisted of a two‐harvest system (early summer and mid‐fall) irrigated throughout the growing season. Three N fertilization rates (0, 100, and 200 kg N ha^?1 yr^?1) were applied as subtreatments in a single application in the spring of each year. A single pulse of ¹⁵N enriched fertilizer was applied in the first year of the study to micro‐plots within the 100 kg N ha^?1 subplots. Average yields across years under optimal N rates (100 and 200 kg ha^?1 yr^?1 for low‐ and high‐input systems, respectively) were 20.7 and 24.8 Mg ha^?1. However, the low input (372 ha mm) required 47% less irrigation than the high‐input system (705 ha mm) and achieved higher irrigation use efficiency. In addition, the low‐input system had 46% lower crop N removal, 53% higher N stored in BG biomass, and a positive N balance, presumably due to 49% of ¹⁵N translocation from AG to BG biomass during senescence. Furthermore, at the end of 3 years, the low‐input system had lower fertilizer ¹⁵N removed by harvest (26%) and higher FNR remaining in the system in BG biomass plus soil (31%) than the high‐input system (45% and 21%, respectively). Based on these findings, low‐input systems are more sustainable than high‐input systems in irrigated Mediterranean climates.     

Nitrogen and harvest date affect developmental morphology and biomass yield of warm‐season grasses

Information on the growth and development of warm‐season grasses in response to management is required to use them successfully as a biomass crop. Our objectives were to determine optimum harvest periods and effect of N fertilization rates on the biomass production of four warm‐season grasses, and to investigate if traits of canopy structure can explain observed yields with varying harvest dates and N rates. A field study was conducted at Sorenson Research Farm near Ames, IA, during 2006 and 2007. The experimental design was split‐split plot arranged in a randomized complete block with four replications. Big bluestem (Andropogon gerardii Vitman), eastern gamagrass (Tripsacum dactyloides L.), indiangrass (Sorghastrum nutrans L. Nash), and switchgrass (Panicum virgatum L.) were main plots. Three N application rates (0, 65, and 140 kg ha^?1) were subplots, and 10 harvest dates were sub‐sub plots. Biomass of warm‐season grasses increased with advanced maturity, but differently among species. The maximum yield of eastern gamagrass occurred at the highest MSC (1.6 and 2.2) when the largest seed ripening tillers were present. Big bluestem, switchgrass, and indiangrass obtained the maximum yields at MSC 3.5, 3.9, and 2.9, respectively when the largest reproductive tillers were present. In terms of a biomass supply strategy, eastern gamagrass may be used during early summer, while big bluestem and switchgrass may be best used between mid‐ and late‐ summer, and indiangrass in early fall. Nitrogen fertilization increased yield by increasing tiller development. Optimum biomass yields were obtained later in the season when they were fertilized with 140 kg ha^?1.     

Field Note: Comparative Efficacy of A Woody Evapotranspiration Landfill Cover Following the Removal of Aboveground Biomass

Woody vegetation cultivated for moisture management on evapotranspiration (ET) landfill covers could potentially serve a secondary function as a biomass crop. However, research is required to evaluate the extent to which trees could be harvested from ET covers without significantly impacting their moisture management function. This study investigated the drainage through a six-year-old, primarily poplar/cottonwood ET test cover for a period of one year following the harvest of all woody biomass exceeding a height of 30 cm above ground surface. Results were compared to previously reported drainage observed during the years leading up to the coppice event. In the first year following coppice, the ET cover was found to be 93% effective at redirecting moisture during the spring/summer season, and 95% effective during the subsequent fall/winter season. This was slightly lower than the 95% and 100% efficacy observed in the spring/summer and fall/winter seasons, respectively, during the final measured year prior to coppice. However, the post-coppice efficacy was higher than the efficacy observed during the first three years following establishment of the cover. While additional longer-term studies are recommended, this project demonstrated that woody ET covers could potentially produce harvestable biomass while still effectively managing aerial moisture.     

Crop Management Impacts Biofuel Quality: Influence of Switchgrass Harvest Time on Yield, Nitrogen and Ash of Fast Pyrolysis Products

Although upgrading bio-oil from fast pyrolysis of biomass is an attractive pathway for biofuel production, nitrogen (N) and mineral matter carried over from the feedstock to the bio-oil represents a serious contaminant in the process. Reducing the N and ash content of biomass feedstocks would improve process reliability and reduce production costs of pyrolytic biofuels. This study investigated: (1) How does switchgrass harvest date influence the yield, N concentration ([N]), and ash concentration of biomass and fast pyrolysis products? and (2) Is there a predictive relationship between [N] of switchgrass biomass and [N] of fast pyrolysis products? Switchgrass from five harvest dates and varying [N] from central Iowa were pyrolyzed using a free-fall reactor. Harvestable biomass peaked in August (8.6 Mg ha^?1), dropping significantly by November (6.7 Mg ha^?1, P?=?0.0027). Production of bio-oil per unit area mirrored that of harvested biomass at each harvest date; however, bio-oil yield per unit dry biomass increased from 46.6 % to 56.7 % during the season (P?=?0.0018). Allowing switchgrass to senesce lowered biomass [N] dramatically, by as much as 68 % from June to November (P?<?0.0001). Concurrently, bio-oil [N] declined from 0.51 % in June to 0.17 % by November (P?<?0.0001). Significant reductions in ash concentration were also observed in biomass and char. Finally, we show for the first time that the [N] of switchgrass biomass is a strong predictor of the [N] of bio-oil, char, and non-condensable gas with R ² values of 0.89, 0.94, and 0.88, respectively.     

青贮对柳枝稷制取燃料乙醇转化过程的影响

青贮是一种传统的生物质原料保存方法,广泛应用于纤维素乙醇炼制领域尚需要考察其对原料品质和下游乙醇转化过程的影响。文中以秋季(初、中和末)收割的柳枝稷为原料,通过青贮、高温水热(LHW)预处理、纤维素酶水解和同步糖化与发酵(SSF)实验对上述问题予以回答。结果显示,秋季初收割的柳枝稷以不同湿度青贮后pH均小于4.0,干重损失小于2%,各主要成分与青贮前相比无明显变化;LHW预处理中青贮样品半纤维素水解率普遍高于未贮存样品,但青贮同样使原料获得了更高的发酵抑制物产生水平;青贮柳枝稷葡萄糖、木糖和半乳糖产量(预处理+酶水解)高于未贮存柳枝稷;经过168 h的SSF,青贮样品乙醇浓度为12.1 g/L,未贮存的秋季初、秋季中和秋季末柳枝稷为底物的浓度分别为10.3 g/L、9.7 g/L和10.6 g/L。综上,青贮有助于提高柳枝稷LHW预处理效率、酶水解率和乙醇产量。     

Biomass production potential of grasslands in the oak savanna region of Minnesota, USA

Biomass harvested from grasslands formerly used for forage production or set aside for conservation has been identified as a potential source of bioenergy feedstocks. Our objective was to characterize yield and chemical composition of biomass harvested from existing grasslands in the oak savanna region of Minnesota and to determine whether aggregated soil properties and grassland type influence biomass yield and feedstock properties. The influence of soil type and dominant functional plant groups on biomass yield, theoretical ethanol yield, and mineral, ash, and lignocellulosic concentration was measured on biomass harvested from 32 grassland sites. Soils with high productivity ratings, as measured by the Minnesota Crop Productivity Index, produced 36 % more biomass than lower quality soils. Grasslands dominated by warm-season species produced 18 % more biomass than those dominated by cool-season species, when measured after senescence during the late-fall harvest time. Biomass harvested from sites dominated by cool-season grasses had higher N, Mg and Cl concentrations than those dominated by warm-season grasses, suggesting that such grasslands could have lower efficiency in thermochemical conversion processes and that repeated harvesting from such grasslands could remove nutrients from the systems. In addition, glucose and xylose concentrations were slightly higher in biomass from sites dominated by warm-season grasses, which resulted in an estimated additional 12 L?Mg^?1 of ethanol over those dominated by cool-season grasses. Combined with the greater yields, warm-season grasslands could produce an additional 376 L?ha^?1 year^?1.     

Seasonal Changes in Shoot and Root Nitrogen Distribution in Switchgrass (Panicum virgatum)

Switchgrass is a promising bioenergy source that is perennial, productive, native to a broad geographic region, and can grow on marginal, nitrogen (N)-poor soils. Understanding N dynamics in switchgrass is critical to predicting productivity, conserving N, and optimizing the timing of harvest. We examined seasonal changes in N distribution in above- and belowground tissues in switchgrass to quantify N retranslocation rates. Above- and belowground biomass from three sites (two in PA and one in NE) were collected and analyzed for biomass growth and N concentrations at 30-day intervals from June through October. Total living plant mass ranged from 10.3?±?2.4 standard error (SE) to 14.9?±?2.5 SE Mg ha^?1. Belowground mass comprised 52–57 % of total mass. Blades had the highest N concentration during summer, ranging from 6 to 22 g kg^?1 N. Aboveground N concentrations decreased from September until autumn senescence, whereas belowground N concentration increased from August until senescence. Across the sites, total N retranslocated from aboveground to belowground components between September and October averaged 16.5?±?7.1 (SE)?kg ha^?1 N representing 26.7 % of the average maximum N content of aboveground biomass. Based on N fertilizer costs, delayed harvest would conserve some N and provide financial savings on fertilizer ($9 ha^?1) if harvest occurs after senescence but before overwinter biomass loss. However, biomass losses of even 10 % will negate potential economic savings accrued from N retention. To maximize environmental and economic savings from N retranslocation and to simultaneously minimize harvest losses, it would be optimal to harvest switchgrass as soon as possible after complete senescence.     

Switchgrass Response to Nitrogen Fertilizer Across Diverse Environments in the USA: a Regional Feedstock Partnership Report

The Regional Feedstock Partnership is a collaborative effort between the Sun Grant Initiative (through Land Grant Universities), the US Department of Energy, and the US Department of Agriculture. One segment of this partnership is the field-scale evaluation of switchgrass (Panicum virgatum L.) in diverse sites across the USA. Switchgrass was planted (11.2 kg PLS ha^?1) in replicated plots in New York, Oklahoma, South Dakota, and Virginia in 2008 and in Iowa in 2009. Adapted switchgrass cultivars were selected for each location and baseline soil samples collected before planting. Nitrogen fertilizer (0, 56, and 112 kg N ha^?1) was applied each spring beginning the year after planting, and switchgrass was harvested once annually after senescence. Establishment, management, and harvest operations were completed using field-scale equipment. Switchgrass production ranged from 2 to 11.5 Mg ha^?1 across locations and years. Yields were lowest the first year after establishment. Switchgrass responded positively to N in 6 of 19 location/year combinations and there was one location/year combination (NY in Year 2) where a significant negative response was noted. Initial soil N levels were lowest in SD and VA (significant N response) and highest at the other three locations (no N response). Although N rate affected some measures of biomass quality (N and hemicellulose), location and year had greater overall effects on all quality parameters evaluated. These results demonstrate the importance of local field-scale research and of proper N management in order to reduce unnecessary expense and potential environmental impacts of switchgrass grown for bioenergy.     

Accumulation and partitioning of biomass,nutrients, and trace elements in switchgrass for phytoremediation of municipal biosolids

In situ phytoremediation of municipal biosolids is a promising alternative to the land spreading and landfilling of biosolids from end-of-life municipal lagoons. Accumulation and partitioning of dry matter, nitrogen (N), phosphorus (P), and trace elements were determined in aboveground biomass (AGB) and belowground biomass (BGB) of switchgrass (Panicum virgatum L.) to determine the harvest stage that maximizes phytoextraction of contaminants from municipal biosolids. Seedlings were transplanted into 15-L plastic pails containing 3.9 kg (dry wt.) biosolids. Biomass yield components and contaminant concentrations were assessed every 14 days for up to 161 days. Logistic model fits to biomass yield data indicated no significant differences in asymptotic yield between AGB and BGB. Switchgrass partitioned significantly more N and P to AGB than to BGB. Maximum uptake occurred 86 days after transplanting (DAT) for N and 102 DAT for P. Harvesting at peak aboveground element accumulation removed 5% of N, 1.6% of P, 0.2% of Zn, 0.05% of Cd, and 0.1% of Cr initially present in the biosolids. These results will contribute toward identification of the harvest stage that will optimize contaminant uptake and enhance in situ phytoremediation of biosolids using switchgrass.