David J. Parrish

The Biology and Agronomy of Switchgrass for Biofuels

Switchgrass (Panicum virgatum L.)—a perennial, warm-season (C4) species—evolved across North America into multiple, divergent populations. The resulting natural variation within the species presents considerable morphological diversity and a wide range of adaptation. The species was adopted as a crop—initially as a forage—only in the last 50 yr. Its potential uses have recently been expanded to include biofuels. Management of switchgrass for biofuels is informed by an understanding of the plants biology. Successful establishment requires attention to seed dormancy and weed control as well as proper depth and date of planting. The plants growth rate is closely tied to temperature, but timing of reproductive development is linked to photoperiod. Accordingly, the period of vegetative growth can be extended by planting lower-latitude cultivars at higher latitudes. This strategy may provide a yield advantage, but cold tolerance can become limiting. Switchgrass is thrifty in its use of applied N; it appears able to obtain N from sources that other crops cannot tap. The N removed in harvested biomass is often greater than the amount of N applied. In areas with sufficient rainfall, sustainable yields of ∼15 Mg ha−1 yr−1 may be achievable by applying ∼50 kg N ha−1 yr−1. Harvesting biomass once per season—after plants have senesced and translocated N into perennial tissues—appears to allow plants to maintain an internal N reserve. Two harvests yr−1 may increase yields in some cultivars, but a single annual harvest maximizes yields in many cases. If two harvests are taken, more N must be applied to compensate for the N removed in the midseason harvest. Taking more than two harvests yr−1 often adversely affects long-term productivity and persistence. Switchgrass has potential as a renewable fuel source, but such use will likely require large infrastructural changes; and, even at maximum output, such systems could not provide the energy currently being derived from fossil fuels.

Potential soil carbon sequestration and CO2 offset by dedicated energy crops in the USA.

Energy crops are fast-growing species whose biomass yields are dedicated to the production of more immediately usable energy forms, such as liquid fuels or electricity. Biomass-based energy sources can offset, or displace, some amount of fossil-fuel use. Energy derived from biomass provides 2 to 3% of the energy used in the U.S.A.; but, with the exception of corn-(Zea mays L.)-to-ethanol, very little energy is currently derived from dedicated energy crops. In addition to the fossil-fuel offset, energy cropping might also mitigate an accentuated greenhouse gas effect by causing a net sequestration of atmospheric C into soil organic C (SOC). Energy plantations of short-rotation woody crops (SRWC) or herbaceous crops (HC) can potentially be managed to favor SOC sequestration. This review is focused primarily on the potential to mitigate atmospheric CO2 emissions by fostering SOC sequestration in energy cropping systems deployed across the landscape in the United States. We know that land use affects the dynamics of the SOC pool, but data about spatial and temporal variability in the SOC pool under SRWC and HC are scanty due to lack of well-designed, long-term studies. The conventional methods of studying SOC fluxes involve paired-plot designs and chronosequences, but isotopic techniques may also be feasible in understanding temporal changes in SOC. The rate of accumulation of SOC depends on land-use history, soil type, vegetation type, harvesting cycle, and other management practices. The SOC pool tends to be enhanced more under deep-rooted grasses, N-fixers, and deciduous species. Carbon sequestration into recalcitrant forms in the SOC pool can be enhanced with some management practices (e.g., conservation tillage, fertilization, irrigation); but those practices can carry a fossil-C cost. Reported rates of SOC sequestration range from 0 to 1.6 Mg C ha−1 yr−1 under SRWC and 0 to 3 Mg C ha−1 yr−1 under HC. Production of 5 EJ of electricity from energy crops—a perhaps reasonable scenario for the U.S.A.—would require about 60 Mha. That amount of land is potentially available for conversion to energy plantations in the U.S.A. The land so managed could mitigate C emissions (through fossil C not emitted and SOC sequestered) by about 5.4 Mg C ha−1 yr−1. On 60 Mha, that would represent 324 Tg C yr−1—a 20% reduction from current fossil-fuel CO2 emissions. Advances in productivity of fast-growing SRWC and HC species suggest that deployment of energy cropping systems could be an effective strategy to reduce climate-altering effects of anthropogenic CO2 emissions and to meet global policy commitments.

The Evolution of Switchgrass as an Energy Crop

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.

Plant Density and Hybrid Impacts on Corn Grain and Forage Yield and Nutrient Uptake

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.

Production of fermentables and biomass by six temperature fuelcrops

Abstract Several potential fuelcrops have been studied individually, but relatively little work has been done to compare the various temperate species in side-by-side trials. In this study, we have examined the production of readily fermentable carbohydrates and biomass by six fuelcrop candidates: grain sorghum (Sorghum bicolor), Jerusalem artichoke (Helianthus tuberosus), maize (Zea mays), sugarbeet (Beta vulgaris), sweet potato (Ipomoea batatas) and sweet sorghum (Sorghum bicolor). A randomized complete block design with four replicates was employed at each of three locations that were somewhat diverse in soil type, elevation, growing season length, and 1980 rainfall distribution. Fermentables in the harvestable dry matter were determined colorimetrically following dilute acid plus enzymatic hydrolysis. Overall, sugarbeet was the most prolific producer of fermentables (7.4 Mg/ha); Jerusalem artichoke (5.8 Mg/ha), maize (4.8 Mg/ha) and sweet sorghum stems (5.8 Mg/ha) were statistically equivalent, while sweet potato (4.0 Mg/ha) and grain sorghum (3.8 Mg/ha) were less productive than the other candidates. The crops performed somewhat differently at each location, but the most striking site-specific differences were seen at the site with the coarset textured soil and driest season. At that location, maize produced the least fermentables (0.6 Mg/ha). Biomass production generally reflected either the amount of time each species was actively growing or limitations to growth associated with drought. We make no general recommendations concerning a preferred temperature fuelcrop. Based on our studies, however, maize may not always be the fuelcrop of choice; others, especially sugarbeet and sweet sorghum (when harvested for grain also), may be superior to maize in productivity of fermentable substrates.

Effects of harvest frequency and biosolids application on switchgrass yield, feedstock quality, and theoretical ethanol yield.

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 459 kg N ha−1 in May 2010. Biomass yield, neutral and acid detergent fiber, cellulose, hemicellulose, lignin, and ash were determined. Theoretical ethanol potential (TEP, l ethanol Mg−1 biomass) and yield (TEY, l ethanol ha−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 Mg ha−1) in 2011, but no differences were observed in other years. Cutting once produced feedstock with greater TEP (478 vs. 438 l Mg−1), but no differences in TEY between cutting frequencies. Biosolids applied at 153, 306, and 459 kg N ha−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.

Switchgrass cultivar/ecotype selection and management for biofuels in the upper southeast USA.

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.

Reducing Corn Yield Variability and Enhancing Yield Through the Use of Corn-Specific Growth Models

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 individual use.

New Biofuels Industry: Biomass Availability and Supply Chain

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