Switchgrass ( Panicum virgatum L.), a perennial warm-season grass indigenous to the eastern USA, has potential as a biofuels feedstock. The objective of this study was to investigate the performance of upland and lowland switchgrass cultivars under different environments and management treatments. Four cultivars of switchgrass were evaluated from 2000 to 2001 under two management regimes in plots established in 1992 at eight locations in the upper southeastern USA. Two management treatments included 1) a single annual harvest (in late October to early November) and a single application of 50 kg N/ha/yr and 2) two annual harvests (in midsummer and November) and a split application of 100 kg N/ha/yr. Biomass yields averaged 15 Mg/ha/yr and ranged from 10 to 22 Mg/ha/yr across cultivars, managements, locations, and years. There was no yield advantage in taking two harvests of the lowland cultivars (Alamo and Kanlow). When harvested twice, upland cultivars (Cave-in-Rock and Shelter) provided yields equivalent to the lowland ecotypes. Tiller density was 36% lower in stands cutting only once per year, but the stands appeared vigorous after nine years of such management. Lowland cultivars and a one-cutting management (after the tops have senesced) using low rates of applied N (50 kg/ha) are recommended.

Sustainable intensification of agricultural systems has been suggested - in addition to reducing waste and changing consumption habits - as a way to increase food, feed, fuel, and fiber security in the twenty-first century. Here we describe three primary strategies of agricultural intensification - conventional intensification, temporal intensification, and spatial intensification - and how they can be used to manage and integrate food and second-generation crop portfolios. While each strategy has individual merits, combining them to meet case-specific targets may achieve optimum results. Multiple experiments and examples from the USA and the EU illustrate the potential of combining these approaches for agroecological intensification that can provide ecosystem services while maintaining or increasing economic output, thus striking a balance between land sparing' and land sharing'. Management strategies will vary by the types of markets available, e.g., food, fuel and/or ecosystem services, and the scale of markets supplied, e.g., small heat and power vs. large cellulosic ethanol. Future research should holistically and methodologically evaluate the trade-offs between different management strategies. (c) 2013 Society of Chemical Industry and John Wiley & Sons, Ltd

Sustainable development of a bioenergy industry will require low-cost, high-yielding biomass feedstock of desirable quality. Switchgrass (Panicum virgatum L.) is one of the primary feedstock candidates in North America, but the potential to grow this biomass crop using fertility from biosolids has not been fully explored. The objective of this study was to examine the effects of harvest frequency and biosolids application on switchgrass in Virginia, USA. Cave-in-Rock' switchgrass from well-established plots was cut once (November) or twice (July and November) per year between 2010 and 2012. Class A biosolids were applied once at rates of 0, 153, 306, and 459kg Nha(-1) in May 2010. Biomass yield, neutral and acid detergent fiber, cellulose, hemicellulose, lignin, and ash were determined. Theoretical ethanol potential (TEP, l ethanolMg(-1) biomass) and yield (TEY, l ethanolha(-1)) were calculated based on cellulose and hemicellulose concentrations. Cutting twice per season produced greater biomass yields than one cutting (11.7 vs. 9.8 Mgha(-1)) in 2011, but no differences were observed in other years. Cutting once produced feedstock with greater TEP (478 vs. 438lMg(-1)), but no differences in TEY between cutting frequencies. Biosolids applied at 153, 306, and 459kg Nha(-1) increased biomass yields by 25%, 37%, and 46%, and TEY by 25%, 34%, and 42%, respectively. Biosolids had inconsistent effects on feedstock quality and TEP. A single, end-of-season harvest likely will be preferred based on apparent advantages in feedstock quality. Biosolids can serve as an effective alternative to N fertilizer in switchgrass-to-energy systems.

A concise and up‐to‐date review has been undertaken to summarize consistent or diverging agronomic points of view on dedicated energy crops for advanced biofuels in the USA and the EU ‐27. The main purpose of this review is to discuss those crops where many agronomic constraints have been resolved, bringing them closer to large‐scale production and commercialization. Where possible, examples of crop management practices that would enhance sustainability and energy yields are provided. The most promising crops and agronomic strategies for their production in the EU ‐27 and the USA are discussed. We also provide discussion of what the theoretically ideal characteristics of advanced biofuel crops might be. On both continents, understanding of management practices for switchgrass ( Panicum virgatum L.) and miscanthus ( Miscanthus x giganteus ) as energy crops appears to be at an advanced stage. Two other widely considered energy crop candidates – sorghum ( Sorghum bicolor (L.) Moench) and reed canary grass ( Phalaris arundinacea L.) – have production and management guidelines that were developed for forage uses, but can be easily applied to biomass feedstock production. Giant reed ( Arundo donax L.) has been developed as a bioenergy crop mainly in Europe. In the USA , giant reed is considered a noxious weed in many states, and its planting is prohibited. Establishing crop management practices that will be successful at a large scale and for the long term will help attract growers and investors to produce advanced biofuels, i.e. second‐generation biofuels, which can help reduce our dependence on fossil energy sources. © 2013 Society of Chemical Industry and John Wiley & Sons, Ltd

This chapter discusses the prehistoric origins of switchgrass, its mid-twentieth century adoption as a crop, and late-twentieth century efforts to develop it into an energy crop. The species probably first appeared about 2 million years ago (MYA) and has continued to evolve since, producing two distinct ecotypes and widely varying ploidy levels. We build the case that all existing switchgrass lineages must be descended from plants that survived the most recent glaciation of North America and then, in just 11,000 years, re-colonized the eastern two-thirds of the continent. Moving to historic times, we discuss how switchgrass was first considered as a crop to be grown in monoculture only in the 1940s. Based on scientific reports indexed in a well-known database, interest in switchgrass grew very slowly from the 1940s until it began being considered by the US department of energy (DOE) as a potential energy crop in the 1980s. The history of how switchgrass became DOE's 'model' herbaceous energy crop species is recounted here. Also chronicled are the early research efforts on switchgrass-for-energy in the US, Canada, and Europe and the explosive growth in the last decade of publications discussing switchgrass as an energy crop. If switchgrass—still very much a 'wild' species, especially compared to several domesticated grasses—truly attains global status as a species of choice for bioenergy technologies, it will have been a very remarkable evolution.

Several factors are generating interest in growing switchgrass for energy. To understand farmers' perspectives on possible switchgrass cultivation, Cooperative Extension conducted a survey in south-central and southwestern Virginia. The survey found that 66% of respondents had heard of using switchgrass for bioenergy, yet only 43% indicated they would be interested in cultivating switchgrass even if the enterprise were profitable. Reluctance to consider growing a potentially profitable crop is likely due to an underdeveloped market and lack of familiarity with switchgrass culture. The results indicate an important role for Extension in conveying technical information to producers as biofuel markets develop. Identifying Farmers' Interest in Growing Switchgrass for Bioenergy in Southern Virginia 10/26/09 08:07:49

Crop simulation models (CSMs) can evaluate the effects of management and environmental scenarios on crop growth and yields. Two corn (Zea mays L.) crop growth simulation models, Hybrid-Maize, and CERES-Maize, were calibrated and validated under mid-Atlantic United States conditions to provide better understanding of corn response to variable environmental conditions and developing management that decreases temporal yield variation. Calibration data were from small-plot population by maturity studies conducted across five site years. Model validation was performed on data from large, replicated trials from across Virginia. Both CSMs under-predicted corn grain yield. CERES-Maize grain yield prediction error was consistent across the range of plant density, whereas accuracy of Hybrid-Maize varied with density. Validation results of the calibrated CSMs showed reasonable accuracy in simulating planting date and environment on a range of corn hybrids. Because each model has unique strengths and assessment modules, the CSM can be matched to the indilidual use.

ABSTRACT Corn (Zea mays L.) production recommendations should be periodically evaluated to ensure that production practices remain in step with genetic improvements. Since most of the recent increases in corn grain yield are due to planting at higher densities and not to increased per-plant yield, this study was undertaken to measure the effects of plant density and hybrid on corn forage and grain yield and on nutrient uptake. Plant density (4.9, 6.2, 7.4, and 8.6 seeds m−2) and hybrid relative maturity (RM) [early (108 day RM); medium (114 day RM); and late (118 day RM)] combinations were evaluated over five site-years under irrigated and non-irrigated conditions. The interaction of hybrid with plant density was never significant for grain, stem, or leaf biomass. The latest RM hybrid out-yielded the medium and early hybrids by 550 and 1864 kg ha−1, respectively. Grain yield was highest at 8.6 plants m−2. Total stem yield was also greatest at the highest plant density but by only 340 kg ha−1 more than at 7.4 seeds m−2. Based on grain yield response over sites, the estimated optimum density was 7.6 seeds m−2, which is 0.7 seeds m−2 higher than the current recommendation at this average yield level (11.5 Mg ha−1). Grain nitrogen (N), phosphorus (P), and potassium (K) uptakes were highest for the medium RM hybrid. Nutrient uptake levels varied by planting density, with the lowest levels observed at the lowest and highest plant densities. At 4.9 seeds m−2, the reduced uptake is explained by lower biomass yields. At the 8.6 seeds m−2 rate, N and K levels may have been lower due to dilution.

Multiple biomass-for-energy feedstock resources have been proposed and many or all of these may ultimately be needed. This paper focuses on perennial lignocellulosic feedstocks. In the United States, Perlack and colleagues estimated that by 2050 1.3 billion Mg of biomass could be sustainably harvested annually. However, over half of the herbaceous biomass in their estimate was derived from crop residues, a source that presents numerous concerns. Availability of land resources and the economic prospects for diverting land from food to energy production is further clouded by unknown variables such as the impact of increased human populations and higher living standards. Much effort is currently being given to corn and other starch or grain crops that can be readily converted to ethanol. Although these crops have served to jumpstart the fuel ethanol industry, they have much less potential to meet the growing demand, much greater potential for negative environmental impacts, and their use feeds the "food versus fuel" debate. The 2007 Energy Bill mandated annual production of 136 billion L of fuel (ethanol, etc.) from renewable feedstocks by 2022, a goal that will greatly impact U.S. agriculture. From 2009, all increases in renewable fuel production are to come from nonstarch sources, yet production of "cellulosic ethanol" is currently limited by the conversion technologies. In addition to conversion constraints, all bioenergy technologies will require equipment systems that can cost effectively collect, store, and deliver bulky distributed biomass to the bioenergy plant. These systems will emulate commercial systems that move herbaceous crops (e.g., cotton and sugarcane) to processing plants; however they must be fine tuned to address the requirements of the crop and the constraints of the land base. Important interactions occur between each component of the supply chain—agronomy, logistics, and processing—that are best not studied in isolation. Significant social issues also stand to influence landowner decisions regarding market entry and these will affect the function and profitability of a bioenergy plant. The business plan must provide a "win-win" for both the feedstock supplier and the plant owner. Other large questions about the development of bioenergy resources reside outside the system, e.g., bioenergy systems may be more cost competitive if the policy allows them to benefit from the potential ecosystem services they provide such as sequestering carbon.

Using results from field trials of switchgrass (Panicum virgatum L.) in the United States, the EPIC (Environmental Policy Integrated Climate) process-level agroecosystem model was calibrated, validated, and applied to simulate potential productivity of switchgrass for use as a biofuel feedstock. The model was calibrated with a regional study of 10-yr switchgrass field trials and subsequently tested against a separate compiled dataset of field trials from across the eastern half of the country. An application of the model in a national database using 8-digit watersheds as the primary modeling unit produces 30-yr average switchgrass yield estimates that can be aggregated to 18 major watersheds. The model projects average annual switchgrass productivity of greater than 7 Mg ha-1 in the Upper Mississippi, Lower Mississippi, and Ohio watersheds. The major factors limiting simulated production vary by region; low precipitation is the primary limiting factor across the western half of the country, while moderately acidic soils limit yields on lands east of the Mississippi River. Average projected switchgrass production on all crop land in the continental US is 5.6 Mg ha-1. At this level of productivity, 28.6 million hectares of crop land would be required to produce the 16 billion gallons of cellulosic ethanol called for by 2022 in the 2007 Energy Independence and Security Act. The model described here can be applied as a tool to inform the land-use and environmental consequences of switchgrass production.

Switchgrass is being widely considered as a feedstock for biofuel production. Much remains to be learned about ideal feedstock characteristics, but switchgrass offers many advantages already and can perhaps be manipulated to offer more. When planning to grow switchgrass, select a cultivar that is well adapted to the location - generally a lowland cultivar for the southern United States and an upland cultivar at higher latitudes. Plant non-dormant seed after soils are well warmed, preferably with no-till methods and always with good weed control. Except for weeds, few pests appear to be widespread; but disease and insect pests could become more important as acreages increase. Fertilization requirements are relatively low, with 50 kg N/ha/year being a good "generic" recommendation where a single harvest is taken after plants have senesced; more will be needed if biomass is harvested while still green. Switchgrass should be harvested no more than twice per year and may generally be expected to produce 12 to >or=20 mg/ha/year across its usual range of distribution. A single harvest may provide for maximum sustainable yields - especially if the harvest is taken after tops die back at the end of the season. Several harvesting technologies are available, but the preferred technology may depend on logistics and economics associated with the local processing point, or biorefinery.

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.

Abstract World energy demand is straining energy supplies and spurring the search for alternative energy sources - especially transportation fuels. Ethanol produced from cellulosic feedstock has been called a 'second-generation' biofuel. (Ethanol made from maize and sugarcane represents a 'first-generation' biofuel.) When choosing a cellulosic species for fuel production, one must consider the type of fuel desired, the economics of producing the crop on a large scale, the system's energy balance and environmental effects. With suitable conversion technologies, cellulosic materials from maize, eastern gamagrass, giant reed (fibre cane), Miscanthus , reed canarygrass, sorghums, sugarcane and switchgrass might be used to produce biofuels in the USA and other non-arid, sub-tropical or temperate locations. Each of these species has characteristics that make it more or less suitable in particular situations. Because of generally reduced input requirements, perennial species might be favoured. Biofuel production systems can mitigate greenhouse gas (GHG) emissions by offsetting fossil fuel use and by sequestering carbon into the soil. The amount of GHG reduction depends on crop yields, conversion efficiencies, and net energy and carbon balances associated with each feedstock source.

Biomass Availability This was addressed through both oral presentations and posters. An update was given on the Billion-Ton Resource Assessment report by Bob Perlack. The original report was published in 2005 and estimated the current and potential availability of biomass feedstocks. The potential was projected as approximately 1.3 billion tons and was what might be reasonably available around midcentury when large-scale biorefineries are likely to exist. The report emphasized primary sources of forestand agriculture-derived biomass such as logging residues, fuel treatment thinnings, crop residues, and perennially grown grasses and woody crops. These primary sources have the greatest potential to supply large sustainable quantities of biomass. Since publication of the Billion-Ton Resource Assessment, follow-up efforts have focused on updating the results, disaggregating the resource potential to counties and fine spatial scales, examining how the resource potential is affected by environmental sustainability, and answering questions involving what feedstocks will be used, when will they be used, what will be the costs, and what will be the economic impacts. Answers to these latter questions are focused on nearer-term time periods coincident with implementation of the Energy Independence and Security Act. Michael Blaylock highlighted corn stover as a potential biomass feedstock for cellulosic ethanol. Currently grown on more than 93 million acres in the USA and annually yielding 300 million tons of biomass that could produce up to about 25 billion gallons of cellulosic ethanol, its planting, cultivation, and harvesting costs can be shared with a popular cash Appl Biochem Biotechnol (2009) 154:268–270 DOI 10.1007/s12010-009-8612-1