[Advances in Agronomy] Volume 117 || Agronomic and Ecological Implications of Biofuels

C H A P T E R O N E

The Oand Se

AdvanceISSN 0DOI: h

Agronomic and Ecological

Implications of Biofuels

Catherine Bonin and Rattan Lal

Contents
1. Introduction 2 2. Ecosystem Functions and Services 6 3. Land Use Change 8
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3.1. Greenhouse gas emissions from land conversion
9 3.2. Using land enrolled in the Conservation Reserve Program 10 3.3. Biofuels and restoration of degraded lands 12
4. Soil Erosion and Water Quality
13 4.1. Use of agricultural residues 16
5. Nitrogen Cycling
17 5.1. Nitrogen and litter/residue management 19 5.2. Nitrogen uptake and biomass removal 20 5.3. Gaseous emissions and volatilization 21
6. Human Impacts on Biodiversity
22 6.1. Biodiversity in agroecosystems 22 6.2. Diverse perennial grasslands 23 6.3. Effects on wildlife 24 6.4. Diversity at the landscape level 25 6.5. Pests and biocontrol 26
7. Biofuels and the Soil Carbon Budget
28 7.1. Land/soil preparation 28 7.2. Soil carbon budget 29
8. Invasive Potential of Bioenergy Crop Species
30 8.1. Invasive species as feedstock 32
9. Food versus Fuel
32 10. Conclusions 34 11. Future Challenges 36 Acknowledgments 37 References 37
State University, School of Environment and Natural Resources, Carbon Managementstration Center, Columbus, OH, USA

Agronomy, Volume 117 � 2012 Elsevier Inc.-2113, All rights reserved.://dx.doi.org/10.1016/B978-0-12-394278-4.00001-5

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http://dx.doi.org/10.1016/B978-0-12-394278-4.00001-5

2 Catherine Bonin and Rattan Lal

AbstractBiofuels can be alternative energy sources which simultaneously reduce depen-dence on fossil fuels and mitigate climate change by reducing greenhouse gas(GHG) emissions. In the US, over 50 billion liters of ethanol produced in 2010 ismandated to increase to 136 billion liters by 2022. Globally, approximately33.3 million ha (Mha) of land under production of biofuels in 2008 may increaseto as much as 82 Mha by 2020. Whereas data on the energy efficiency and GHGbalances for biofuels are available, information on agronomic and ecologicalconsequences of large-scale production of bioenergy crops is sparse. Thus,this paper describes the potential effects that bioenergy production mayhave on ecosystems. Conversion of land to biofuel crops may have significantimpacts on ecosystem services such soil and water quality, GHG emissions,wildlife habitat, net primary productivity, and biological control, and plantdiversity at both the landscape and the regional levels. Production of exoticspecies for feedstock may increase the risk of escape from agriculture and inva-sion into natural ecosystems. Several feedstocks, while suitable on the basis ofenergy and GHG assessments, may have negative ecosystem impacts (i.e.,increased N export in the Gulf of Mexico). Bioenergy feedstock may competewith food crops for land, water, and nutrient resources, resulting in higher pri-ces for food as well as potential increases in malnutrition and food insecurity.Biofuels can be a sustainable and renewable source of energy, but assessmentsmust include ecological impacts, economic costs, and energetic efficiencies.

1. Introduction

Biofuels are widely considered as renewable and sustainable alterna-tives to fossil fuels. They are touted as an energy production system thatcan have both a positive energy balance while offsetting greenhouse gas(GHG) emissions through carbon (C) sequestration. The US set an auspi-cious goal of supplying the equivalent of 30% of the nation's petroleum usefrom biomass, requiring 900 MMg (1 Mg¼ 106 g¼ 1 metric ton) to 1billion Mg of feedstock, and predict that the generation of this extrabiomass will be based on increases in crop yields and changes in land use(Perlack et al., 2005; Somerville, 2006). In terms of bioethanol production,corn (Zea mays L.) grain is presently the most common source in the US,with over 50 billion liters produced by 189 plants in 2010 (Fig. 1;Renewable Fuels Association, 2011).

However, corn grain will likely be only a temporary feedstock optiondue to land limitations: even if all corn produced in the US were usedfor ethanol production, it would only supply 12% of US gasoline needs(Hill et al., 2006). In addition, the Energy Independence and SecurityAct of 2007 (EISA), which mandates that 136.3 billion liters ofrenewable fuels be produced annually by 2022, has capped contributions

Ethanol Plants

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1975 1980 1985 1990 1995 2000 2005 2010

Ethanol Produced

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Figure 1 United States ethanol production and ethanol plants. Data modified from theRenewable Fuels Association (2011).

Agronomic and Ecological Implications of Biofuels 3

from corn grain at 56.8 billion liters (Sissine, 2007). Therefore, a variety ofother bioenergy feedstocks are also being promoted for the development ofsecond generation biofuels such as perennial grasses, woody species, andagricultural residues (Table 1).

In the decade ending in 2010, bioenergy feedstocks have undergoneintense scrutiny and evaluation to determine the net energy yields andGHG balances through the use of life cycle assessment (LCA). Even thoughthe primary goal of biofuels is to provide energy with a low C footprint,LCAs show that not all biofuels are created equally in terms of energyand GHG fluxes (Adler et al., 2007; Davis et al., 2009). These assessmentssuggest that the varying results in energy and GHG balances may be causedby differences in species attributes, crop production practices, land usechanges, and conversion technologies (Fargione et al., 2008; Huang et al.,2009).

Corn grain is a feedstock within the first generation of biofuels, which arefuels derived from plant sugars, starches and oils (Soetaert and Vandamme,2009). Other first generation feedstocks include sugarcane (Saccharumofficinarum L.), oil palm (Elaeis guineensis Jacq.), and soybean (Glycine max(L.) Merr.). Primary feedstock options vary by country: the US uses corngrain, Brazil relies on sugarcane, the European Union uses wheat (Triticumaestivum L.) and sugar beet (Beta vulgaris L.), while both China and Canadause wheat and corn grain (Balat and Balat, 2009). Examination of ninefirst generation feedstocks based on ecological, energy, and GHG emissionparameters suggest that tropical species such as sugarcane and oil palm maybe a better option than temperate species such as corn and wheat in terms

Table 1 Biofuel feedstock production and ecological summary

Bioenergy speciesYield(Mg haL1)

Time toestablish(years)

Stand persis-tence (years)

Fertilizerneed

Stresstolerance

Ecologicalconcerns

Switchgrass(Panicum virgatum)

15 3 >20 low drought andflood

invasive potential inwestern US

Native grass mix 3.6 (degraded) 3 >20 low drought6.0 (fertile)

Miscanthus(Miscanthus �giganteus)

29.6 3 >20? low

Reed canarygrass(Phalarisarundinacea)

9.0 1e2 >10? medium drought andflood

invasive

Giant reed(Arundo donax)

37.7 2e3 >10? medium saline soils invasive

Corn (grain)(Zea mays)

9.3 1 e high may lower water quality

Corn (stover) 5.1 1 e high may lower soil qualityWoody species(Salix andPopulus spp.)

11.7 3þ >20 low/medium

flood

Sugarcane(Saccharumofficinarum)

82 1e2 5 high risk of soil erosion and Nleaching

Oil palm (Elaeisguineensis)

18.7a 3 25 medium/high

plantations may causedeforestation

Jatropha ( Jatrophacurcas)

5.0 2e3 50 medium drought plantations may causedeforestation

a Oil palm yield in fresh fruit bunch weight (FFB); crude oil conversion ratio of 0.18 kg oil per 1 kg FFB (Papong et al., 2010).Sources: Achten et al. (2007); Achten et al. (2008); Angelini et al. (2009); Djomo et al. (2011); Fillion et al, (2009); Hartemink (2008); Heaton et al. (2008);Hoskinson et al. (2007); Lewandowski et al. (2003); Linderson et al. (2007); Openshaw (2000); Papong et al. (2010); Parrish and Fike (2005); Tilman et al.(2006); USDA-NASS (2011); Whan et al. (1976).

4Catherine

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Lal


of sustainability (de Vries et al., 2010). Corn, while relatively high-yieldingand with a high ethanol productivity, also requires large amounts in inputs(i.e., fertilizers) which reduce its net energy ratio (NER, energyoutputs:energy inputs) to about 1.7 (Liska et al., 2009). Most temperateannual biofuel feedstock (i.e., cereal grains, sugar beet) have NERs thatrange between 1 and 4 (Venturi and Venturi, 2003). In contrast,sugarcane, which can yield over 80 Mg ha�1, has an NER of 9.2(Hartemink, 2008). Although sugarcane's energy production indicates it tobe a desirable biofuel feedstock, as with other first generation choices, itsuse as a fuel source directly affects food availability and brings it intocompetition with other food crops for land and other resources (Pimenteland Patzek, 2008).

Second generation feedstocks are suggested as a solution to the problemscaused by first generation options and as a way to reduce competition withfood crops for limited resources. Second generation, or lignocellulosic feed-stocks, include perennial grasses, trees, and agricultural and forestry residuesor wastes. Because the entire plant can be used instead of just the grains,sugars, or fats, energy yields per hectare can be much larger. In addition,grass and tree feedstocks may be grown on marginal lands with fewerinputs, which can reduce GHG emissions and energy requirements(Debolt et al., 2009). Switchgrass (Panicum virgatum L.) may have anNER as large as 13.1 and can reduce GHG emissions by 95% whencompared to gasoline, while miscanthus (Miscanthus x giganteus) canproduce 2.6 times more ethanol per hectare than corn grain can and hasa potential NER of 12e66 (Heaton et al., 2008; Schmer et al., 2008;Venturi and Venturi, 2003). Tree species such as willows (Salix spp.) andpoplars (Populus spp.) can produce 11.5 Mg ha�1 or more of biomasseach year and may have NERs of over 20 when burned for electricity(Djomo et al., 2011). Residues and waste products, as byproducts ofagricultural and anthropogenic activities, would not require anyadditional lands or resources for production. The NER for corn stover ofapproximately 2.2 is lower than that of some other second-generationfeedstocks; however, it is important to note that the corn grain may beused for other purposes (Luo et al., 2009). Nonetheless, excessive residueremoval may reduce agronomic yield and degrade soil quality byaccelerating soil erosion and depleting soil C levels (Blanco-Canqui et al.,2006; Lindstrom, 1986). Thus, residue removal rates must be balancedwith agronomic and environmental requirements. Other second-generation feedstocks include jatropha ( Jatropha curcas L.), which isa drought resistant tree that produces non-edible oils from its seeds thatcould reclaim eroded or degraded land (Openshaw, 2000). It can behigh-yielding under the appropriate environmental conditions, but morework needs to be done to determine the potential of this plant(Trabucco et al., 2010). A third generation of biofuels, microalgae and


cyanobacteria, are being developed for the production of biodiesel (Sayre,2010). Microalgae are very productive and would be land efficient,although the input costs for water and energy could be high, reducingthe NER to close to or less than one (Batan et al., 2010; Clarens et al.,2011).

While much research has focused on the energy and GHG aspects ofbiofuels, other questions on the sustainability of biofuel production in termsof ecosystem functioning and services are less commonly addressed. Theremay be significant repercussions to many ecosystem properties and servicesif there is a large-scale land-use change to bioenergy crop feedstock produc-tion. However, the ecological and agronomic implications of large-scalebioenergy cropping systems are not fully understood. Both feedstockspecies and management practices will likely affect ecosystem propertiesdifferently. Future growing demands will increase costs and reduce theavailability of vital resources such as arable land, water, nutrients, and pesti-cide inputs. If bioenergy systems are to be sustainable alternatives to fossilfuels, there must be an equilibrium between energy yields and the impactson soil quality, wildlife habitat, nutrient cycling, and water cycling (Clarenset al., 2010; Lardon et al., 2009).

Although all three generations of biofuels have advantages and disad-vantages in terms of energy balances, GHG emissions, net primary produc-tivity (NPP), and environmental quality, this paper focuses primarily on firstand second-generation feedstocks. The principal objective of this paper is todiscuss the potential consequences that biofuels have on agricultural andecological processes and services, and identify gaps in scientific knowledgethat must be addressed in order to understand the full ecological implica-tions of biofuels. Readers are referred to other reviews that discuss specificissues related to energy and GHG balances for biofuels (Adler et al., 2007;Davis et al., 2009; Hill et al., 2006).

2. Ecosystem Functions and Services

Ecosystem functions and services are related, but different.Ecosystem functions are described as the processes within an ecosystem,while ecosystem services are the benefits that humans receive fromecosystem functions (Costanza et al., 1997). A single ecosystem functionmay provide more than one service: for example, the function “soilretention” may both maintain farmland and also prevent soil erosion(de Groot et al., 2002). Examples of ecosystem services include waterand climate regulation, soil formation, nutrient cycling, and foodproduction (Table 2). These ecosystem services have a global value ofan estimated $33 trillion yr�1 (Costanza et al., 1997), but many of these

Table 2 Ecosystem services and related processes, modified from the MillenniumEcosystem Assessment (2005) and de Groot et al. (2002).

Type Service Process

Supporting Soil formation Rock weathering; accumulation oforganic matter

Primary production Transfer of solar energy into plant andanimal biomass

Nutrient cycling Storage and recycling of nutrientsWater cycling Regulation of runoff and water

dischargesRegulating Climate Interactions of biotic and abiotic

elements as well as land coverAir quality Regulation of pollutantsFlood Regulation of runoff and water

dischargesDisease Regulation of disease populations

through biotic interactionsWaste treatment Removal of wastes by organismsPest control Regulation of pests by predators and

biotic interactionsPollination Movement of floral gametes by biota

Provisioning Food Transfer of solar energy into plant andanimal biomass

Clean water Filtering and storage of fresh waterRaw materials:wood, fiber, etc.

Transfer of solar energy into plant andanimal biomass

Fuel Transfer of solar energy into plant andanimal biomass

Genetic resources Genetic variability of wild resourcesBiochemicals,pharmaceuticals

Variation and uses for medicinal plants

Ornamentals Variation in flora for aesthetic usesCultural Recreational,

ecotourismVariation in landscape for humanrelaxation

Spiritual Variation in landscape for spiritual andreligious needs

Educational Variation in landscape for educationalpurposes


ecosystem services are at risk. Fifteen of the 24 ecosystem servicesevaluated by the Millennium Ecosystem Assessment (2005) are beingdegraded or are in decline. Human modification of lands throughfarming and urbanization may affect food production, water and air


quality, climate control, and the availability of natural resources (Foleyet al., 2005; Hooper et al., 2005; Tilman et al., 2001). In addition,decreasing biodiversity may further impact ecosystem service declines(Loreau et al., 2001).

3. Land Use Change

Humans have been altering the appearance of the landscape for thou-sands of years and bioenergy cropping systems are likely to accelerate thechange (Meyer and Turner, 1992; Vitousek et al., 1997). As human popu-lations have increased, so has alteration of the landscape (Fig. 2). In 1700,only 5% of land was under urban settlements, with nearly 95% of landexisting in natural or semi-natural states, but by 2000 over one-half ofglobal land was dominated by humans, to form a new biome, the“anthrome,” one dominated by anthropogenic activities (Ellis et al.,2010). Between 1850 and 1990, the global agricultural land areaquadrupled to 1360 Mha, with land use change (LUC) for agricultural

Natural Vegetation 1700 1850 1990Forest/ShrublandGrasslandDesertAgriculture

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b)

0

2000

4000

6000

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10000

1700 1750 1800 1850 1900 1950 2000 2050 2100

Year

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latio

n (m

illio

ns)

Figure 2 a) Changes in land cover proportion from natural vegetation through 1990.Total land area is estimated at 134.1 million km2, and b) increase in world population(in millions) from 1700 through 2011, and predictions (dashed line) through 2100. Datafrom Goldewijk (2005), Goldewijk (2001), and the United Nations, Department ofEconomic and Social Affairs, Population Division (2011).


activities releasing approximately 105 Pg C (petagram¼ 1015 g¼ 1 GT) byvegetation and soil C losses (Houghton, 1999).

The amount of land in the US planted to corn will remain at record-high levels of 37 Mha due to high demand for ethanol and corn exportsand approximately 35e40% of the US corn crop will be used for ethanolproduction (USDA, 2010). Increases in ethanol production may come fromeither increases in feedstock yields or increases in land under feedstockproduction. An estimated 30% of the predicted increase in future cornproduction may be due to higher yields, which would be a preferredmethod of ethanol production increases, as it would not cause increasedcompetition for land resources (Keeney and Hertel, 2009). However,yield gains can only increase production to a certain point, and oncereached, future increases in feedstock production may result in LUC. In2008, 33.3 Mha were under biofuel production worldwide, but by 2020the land area is expected to increase to as much as 82 Mha (Fargioneet al., 2010). In the US, cropland, pasture, and idle land area is expectedto decrease, while area for perennial crops will increase by as much as20.2 Mha (Perlack et al., 2005). Conversion of a large area of land tofeedstock production will have repercussions on GHG emissions as wellas a variety of ecosystem processes such as C and N cycling, waterquality, and wildlife habitat.

3.1. Greenhouse gas emissions from land conversion

The impact that biofuels have on GHG emissions has been widelyaddressed by several papers (Adler et al., 2007; Hoefnagels et al., 2010; Whi-taker et al., 2010) and is briefly outlined here in terms of how LUC affectsemissions. Production of bioenergy feedstocks may affect LUC directly orindirectly. Direct LUC emissions stem from the conversion of land to feed-stock plantations. Indirect emissions occur as a result of additional landconversion that occurs from the land uses or ecosystems displaced by thebioenergy plantation (Melillo et al., 2009; Searchinger et al., 2008).Increased bioethanol demand in the US will affect the allocation of USland area under other crops and ecosystems, but will also indirectly causechanges in land uses around the globe (Keeney and Hertel, 2009). DirectLUC impacts on GHG emissions and their corresponding C debt maybe calculated by estimating loss of soil C stock due to land conversion(Fargione et al., 2008), but calculating indirect effects is morechallenging. Indirect LUC is a large source of uncertainty when assessingthe impacts of bioenergy crops, and due to this uncertainty, currentpredictions may be underestimating indirect emissions by as much as140% (Plevin et al., 2010).

Direct LUC can have significant impacts on GHG emissions, as landconversion results in a large initial release of GHG (i.e., a “C debt”) that


may take decades or centuries to recover (Fargione et al., 2008). Withouttaking LUC into account, some corn and cellulosic ethanol productionsystems show predicted 20% and 70% reductions in GHG compared togasoline, but after factoring in LUC, these two ethanol systems mayactually release 93% and 50% more GHGs (Searchinger et al., 2008), butthese calculations have been debated (Mathews and Tan, 2009).Although biofuel feedstock may sequester C and reduce emissions, theinitial costs of land conversion may make these systems more costly in Cterms for a significant period of time, particularly when converting landsnot currently under annual crop production. Set-aside lands, such asthose enrolled in the Conservation Reserve Program (CRP), maysequester more C than would their conversion to corn for ethanol for aslong as four decades, while conversion to cellulosic biofuels may nothave this effect (Piñeiro et al., 2009). As such, perennial feedstocksgrown on marginal or abandoned land may be preferred over theconversion of natural ecosystems because they may incur a lower C debt(Fargione et al., 2008).

3.2. Using land enrolled in the Conservation Reserve Program

As a response to increased demands for biofuels, increases in feedstockproduction may come from a variety of sources, including yield gainsand increases in land area under production. Some of this area will includemarginal and CRP lands. While models predict that much of the land usedfor perennial grass feedstocks will come from cropland, up to 31% maycome from previous CRP land (McLaughlin et al., 2002). Land underCRP is typically less productive, more erodible, and has steeper slopesthan cropland (Secchi et al., 2009). The primary objective of the CRP isto protect lands from soil and water erosion mainly through grasslandconversion, but wildlife have also benefited from this program (Bestet al., 1997; Reynolds et al., 2001). As corn prices rise due in part tobiofuel demands, producers will likely begin to crop on marginal land,increasing water erosion, N and P losses due to sediment loss, anddecreasing soil C stocks (Secchi et al., 2009). Conversion of CRP land tobioenergy feedstock production may also create a large C debt if annualcrops are cultivated and displace the perennial species currentlyestablished on the CRP land: approximately 11 Mg C ha�1 may bereleased in the first year through the conversion of CRP land to annualcrop production for biofuels, when accounting for increased GHGemissions and depletions of the soil organic carbon (SOC) stocks, whichwould take decades to repay (Gelfand et al., 2011).

Whereas corn production, particularly as a continuous corn crop, hasdeleterious impacts when grown on previous CRP lands, perennial grassfeedstocks have been suggested for growth on CRP and marginal lands.


Native grasses are one of the most common choices for vegetation in CRPlands, with 2.7 Mha of CRP land under native grass plantings in 2009(CRP, 2009). These long-lived species have deep roots that can stabilizesoil and reduce water runoff, potentially furthering the goals of theCRP. Several species of native grasses, in particular switchgrass, areproposed as CRP species as well as biofuel feedstock. Native, warm-season grasses such as switchgrass can be suitable for both CRP andbiofuel production because they are high-yielding under low fertilizerinputs, drought tolerant, can improve soil stability, and also grow undera wide range of conditions (Lewandowski et al., 2003). It would be idealif these lands could simultaneously be managed for biomass productionand also achieve the CRP objectives (Tilman et al., 2006).

The Food, Conservation, and Energy Act of 2008 permits haying andbiomass harvesting on CRP lands, provided that land is managed to protectthe soil and wildlife objectives of the program (U.S. Congress, 2008). Therehave been conflicting results as to whether bioenergy cropland can providethe same services as CRP and natural grasslands, depending on thefeedstock and land use management (Fargione et al., 2009). For example,monocultures may have lower wildlife habitat quality than diversemixtures (McCoy et al., 2001). Standing biomass remaining in the fieldafter harvest may be beneficial for control of soil erosion andwater runoff, and also provide habitat for wildlife. To meet both CRPand bioenergy needs, switchgrass biomass yields may be maximized withlow N fertilizer inputs and harvest after a killing frost (Mulkeyet al., 2006). Furthermore, perennial grass feedstock production onCRP land may mitigate GHG emissions by capturing a minimum of2.3 MgCO2e ha

�1 yr�1 (Gelfand et al., 2011). However, if grasses arefertilized, increased N2O emissions may cause a net release of GHG, eventhough SOC stocks increase (Robertson et al., 2011b).

Harvest management is important for both maintaining high yields andachieving CRP goals. Increased harvest frequency from one cut per year totwo or three cuts may lower yields of perennial grasses (Cuomo et al.,1996). Even repeated annual single-cut harvests on CRP lands withoutadditional fertilizers or organic amendments may lower total yields overtime as a result of nutrient loss through plant biomass removal withoutreplacement (Mulkey et al., 2006; Venuto and Daniel, 2010). Caseswhere there have been long-term high yields on marginal lands with lowinputs, such as the diversity experiment by Tilman et al. (2006), may besuspect in a bioenergy cropping system because of management choices,as Tilman et al.'s plots were burned rather than the biomass removed.Stand persistence and productivity may impact wildlife habitat quality aswell. While CRP and marginal lands have the potential to providebioenergy without interfering with food crop production, they must becarefully monitored to ensure plant vigor and persistence.


3.3. Biofuels and restoration of degraded lands

The CRP enrolls marginal cropland, but lands may be degraded for otherreasons. Degraded or marginal lands have low productivity and environ-mental quality due to a history of intensive use and disturbances such asfarming, mining, or erosion. These lands are generally infertile and havelow SOC stocks. Bioenergy feedstock such as perennial grasses and treeshave been proposed for use on marginal lands as a method to improvesoil quality, enhance SOC stocks, and improve soil fertility (Blanco-Canqui, 2010). Perennial species are already used in riparian buffers tocapture agricultural runoff. Bioenergy feedstock present opportunities toaddress both ecological and energy problems. “Extremophile energycrops,” species capable of high productivity under stresses such as salinity,drought, or extreme temperatures, have also been suggested for use onmarginal lands, as they are typically efficient in their use of nutrients andwater (Bressan et al., 2011).

Several biofuel feedstock options are tolerant of acid soils and varioustoxic compounds, and may aid in phytoremediation of contaminated soils(Blanco-Canqui, 2010; Peterson et al., 1998; Rockwood et al., 2004).Short-rotation woody crops (SRWC) may be able to take up nutrientsfrom wastewater, simultaneously reducing fertilizer needs and improvingwater quality (Adegbidi et al., 2001). Poplars grown as a vegetative filterstrip with landfill leachate take up 159 kg of leachate kg�1 abovegroundpoplar biomass, can treat 338 kg N ha�1 yr�1, and may yield nearly12 Mg ha�1 woody biomass (Licht and Isebrands, 2005). Based on anLCA comparing bioremediation with willows against a traditionalexcavation-and-fill method for a landfill, remediation using plants mayhave fewer negative environmental impacts (Suer and Andersson-Sköld,2011). Giant reed (Arundo donax L.) can tolerate arsenic and heavy metalsand could be used in phytoremediation of contaminated soils (Mirzaet al., 2010; Papazoglou et al., 2005).

Highly productive perennial species tolerant of poor soil conditions mayalso aid in revegetating degraded mine soils. Surface mine soils typicallycontain high amounts of rock fragments, low nutrient concentrations,and low SOC concentrations (Akala and Lal, 2000; Bendfeldt et al.,2001; Haering et al., 2004). In addition, these soils may also be compactedand acidic, all of which can make the establishment of persistent vegetativecover challenging (Haering et al., 2004). However, these degraded soilsmust be reclaimed and revegetated in order to limit soil erosion andrestore soil conditions, a process required by the Surface Mining Controland Reclamation Act (SMCRA) of 1977. Switchgrass and reedcanarygrass (Phalaris arundinacea L.) can be dominant species on surfacemine soils in Virginia, producing 16.5 Mg ha�1 and 5.0 Mg ha�1,respectively (Evanylo et al., 2005). Likewise, hybrid poplar has also been


recommended to reforest reclaimed mine soils as a result of high survivaland growth rates (Casselman et al., 2006). If biofuels can be grown oncontaminated or degraded land, they may be able to produce biomass forenergy without competing with food crops for land and maysimultaneously improve the condition of degraded or contaminated sites.

While growing perennial feedstock on degraded lands may be beneficialfor soil and water quality, the ecological consequences of using degradedlands to produce bioenergy is uncertain. Bioenergy production from aban-doned agricultural lands could provide as much as 8% of global energyneeds (Campbell et al., 2008), and including bioenergy production fromother marginal lands would further increase this value. However, yieldsare generally lower on marginal lands, requiring higher selling prices forproducers to break even (Mooney et al., 2009). As with CRP land,feedstock production on other marginal lands may require greater inputsto produce sufficient yields and may result in greater erosion andnutrient runoff (Dominguez-Faus et al., 2009). Harvesting degraded landsfor bioenergy could also have serious implications for conservation issues.While degraded lands may have lower diversity than natural systems, inmany situations they are more diverse than plantations and agriculturallands (Plieninger and Gaertner, 2011). Plant and animal species diversitymay be reduced if degraded lands are used for bioenergy crops instead ofrestored for nature conservation.

4. Soil Erosion and Water Quality

Land use choices and water quality are closely linked. Large-scale landuse changes from annual to perennial crops will affect sediment losses,nutrient runoff, and water yields (Schilling et al., 2008). Soil erosion andnutrient runoff into bodies of water may have serious effects on soilquality and plant productivity, as well as on ecosystem and humanhealth. The impacts that bioenergy cropping systems have on soil erosionand water quality could be either positive or negative, depending on thespecies and management practices. Fertilized annual cropping systems areexpected to have more negative effects on soil and water than low-inputperennial systems. Increased corn production for ethanol may increasenutrient runoff due to greater use of fertilizers, particularly in large corn-growing regions such as the Mississippi River Basin. An estimated 80%of the increased production of corn will occur in the Mississippi RiverBasin, and could increase N and P loads by 37% and 25%, respectively(Simpson et al., 2008). With a scenario of 136 billion liters of corn-grainethanol by 2022, dissolved inorganic N export into the Gulf of Mexico


would increase by 34%, dramatically increasing the risk of hypoxia andcontributing to the “Dead Zone” in the Gulf of Mexico (Donner andKucharik, 2008).

Perennial species provide an opportunity to reduce the negative soil andwater impacts that annual bioenergy crops present. Riparian buffer stripsestablished with grasses or trees reduce nutrient runoff, sediment loss, filterpesticides lost from crop fields, stabilize stream banks, and reduce bankerosion (Lyons et al., 2000; Udawatta et al., 2002). Perennial grasses suchas switchgrass have lower N requirements, are more efficient at using N,may reduce runoff, and also improve soil quality (Parrish and Fike,2005). Compared to a corn-soybean rotation system, switchgrassplantings can reduce N and P runoff by 50e90%, while delaying harvestuntil winter could prevent additional nutrient runoff (Simpson et al.,2008). Long term switchgrass stands fertilized at 68 kg N ha�1 may haveN losses through surface and ground water of under 2 kg ha�1, which isapproximately 3% of the N applied (Sarkar et al., 2011). Fertilizerapplication rates may affect the size of reduction of NO3eN in surfacerunoff, with greater reductions as application amount decreases: when224 kg N ha�1 is applied, there is a 16% reduction in NO3eN runoffcompared to the baseline cropping system, but with no fertilization, thisreduction increases to 65% (Nelson et al., 2006). Large-scale changes inland use to bioenergy plantations of either corn or perennial crops wouldsignificantly affect whether N or P losses would increase or decrease.Compared to a scenario where land is used for large-scale cornproduction, large-scale switchgrass bioenergy plantings would result ina 57% decrease in NO3eN losses and nearly a 98% decrease in P losses(Schilling et al., 2008). Woody species grown for bioenergy also have thepotential to significantly reduce N and P losses from runoff (Thorntonet al., 1998).

Along with reducing surface runoff nutrient losses, biofuels may reducenitrate leaching. Nitrates reduce subsurface water quality and when presentin drinking water may be harmful to human health, particularly young chil-dren (Townsend et al., 2003). Under miscanthus, nitrate losses decreasedafter the establishment year and, when fertilized with 60 kg N ha�1 orless, did not exceed the nitrate limit of 10 mgN l�1 set by the EPA(Christian and Riche, 1998; EPA, 2011). In contrast, the 10 mgN l�1

limit is often exceeded in a cornesoybean cropping system, especially asfertilizer application rates increase (Jaynes et al., 2001). In one four-yearstudy, nitrate losses under switchgrass and miscanthus were only 4e8% ofthose losses under cornesoybean rotations (McIsaac et al., 2010), whilenitrate loss reductions of up to 98% have been found when comparingCRP land to continuous corn systems (Randall et al., 1997). The firstyear of plantation establishment generally has the highest nitrate losses,and by the second or third year, losses drop sharply as stands establish


(Christian and Riche, 1998; McIsaac et al., 2010). Perennial grasses mayhave reduced nitrate losses for several reasons, including requiring lowerN applications, having a longer growing season and having a larger rootsystem, both of which should increase N uptake. Diverse perennialstands, with a potential for higher root biomass and more efficientresource use, may also reduce nitrate leaching (Scherer-Lorenzen et al.,2003).

Sediment loss from agricultural land and entry into surface waters isa major problem. Sediments can increase water turbidity, reducing plantphotosynthetic activity and productivity, and can also negatively affectfish and other aquatic invertebrates: even low levels of turbidity maydecrease primary productivity by as much as 13% (Ryan, 1991). Insugarcane production systems, residue is frequently burned on the fieldsto facilitate harvest and transport, a practice that releases GHG into theatmosphere and leaves bare ground at risk of soil erosion rates of17e505 Mg ha�1 yr�1 (Hartemink, 2008). Development of newharvesting equipment so that burning is not required can retain this soiland allow the soil to store an additional 1500 kg C ha�1 yr�1 (Galdoset al., 2010). Sediment loads are predicted to increase with theexpansion of annual row crops and be reduced for perennial grasses, butall feedstock plantations may generate sediment losses if grown onmarginal or steep lands (Love and Nejadhashemi, 2011). Althoughsediment and runoff from switchgrass may initially be higher during theestablishment year (Thornton et al., 1998), switchgrass may reducesediment yield by more than 99%, edge-of-field erosion by 98%, andsurface runoff by 55%, when compared to cropping systems (Nelsonet al., 2006). In contrast, SRWC may reduce sediment losses by asmuch as 85%, even in the first year of establishment (Thornton et al.,1998).

The conversion of large areas of land to bioenergy plantations mayimpact landscape hydrology. Changes in water yield would alter theamount of potential nutrient runoff, as increases in water yields may alsoincrease N and P runoff losses. Shifts to large-scale production of cornfor ethanol under a large area conversion from CRP grassland to cornwould reduce evapotranspiration, increasing water flow by as much as8%, particularly during spring and late fall (Schilling et al., 2008). Incontrast, perennial species have higher amounts of evapotranspirationstemming from a longer growing period and higher biomass productionthat would reduce the water yield. Under a large area conversion toswitchgrass, water yields could decrease by as much as 28%, whencompared to current cropping conditions (Schilling et al., 2008). Soilsunder CRP land have lower plant available water (PAW) within the top1.5e2 m, when compared to row crops due to greater water use by theperennial species (Randall et al., 1997).


Although conversion from annual to perennial crops may alterhydrology, each perennial feedstock species may behave differently. Thedifferences in root distribution and water capture can affect changes insoil water: soil under miscanthus, with most roots in the top 0.35 m, tendsto have higher summer soil moisture at lower depths than soil underswitchgrass or giant reed (Monti and Zatta, 2009). Just as with perennialgrasses, SRWC plantations would use more water than annual crops,lowering soil moisture and potentially reducing water yield and the sizeof floods if planted on a large scale (Perry et al., 2001). Compared to soilunder switchgrass, soil under miscanthus has lower soil moisture laterduring the growing season and in combination with greaterevapotranspiration, may potentially reduce surface flows by 32% ifplanted over a large area (McIsaac et al., 2010). Modeling simulationssuggest that miscanthus may be planted at under 10% of US crop areawithout impacts on hydrology; however, given that energy efficiency ismaximized by concentrating biofuel plantations, miscanthus landcoverage would likely exceed 25% or even 50% in areas surroundingrefineries or energy plants (VanLoocke et al., 2010). Reductions in wateryield may provide benefits such as reduced flooding, but may also haveadverse effects, such as later recharges of soil moisture and extendedperiods of low water flow.

4.1. Use of agricultural residues

Agricultural residues have many uses; i.e., as an input of organic matter(OM) to soils, as feed for animals, feedstock for bioenergy, and as raw mate-rials for industry. Using corn stover for cellulosic ethanol may reduce SOCstocks, soil quality, crop yields, and soil faunal activities due to the loss ofOM and surface residues (Blanco-Canqui and Lal, 2007; Karlen et al.,1994; Karlen et al., 2009; Lal, 2009). The data in Figs. 3 and 4 show therelationship between agricultural residues and SOC stocks or soil erosion,respectively: as residue is removed, SOC generally decreases and soilerosion increases. In addition, decreases in crop residues may also reducecrop yields: for each 1 Mg ha�1 of residue that is removed, grain yielddeclines by 0.10 Mg ha�1 while future residue production decreases by0.30 Mg ha�1 (Wilhelm et al., 1986). Agricultural residues are importantas a method for controlling nutrient runoff and soil erosion. Removal of50% of crop residues can double rates of soil erosion, while higher ratesof removal can greatly increase N and P sediment losses (Blanco-Canquiet al., 2009). Although complete removal of residues is detrimental to soiland water quality, it is possible that lower levels of residue removal,estimated at 25% or less, may be acceptable for maintaining soil andwater quality (Blanco-Canqui and Lal, 2007; Blanco-Canqui et al., 2009).The benefits of additional ethanol yield from agricultural byproducts must

r² = 0.4596

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2.0

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7.0

8.0

0 50 100 150 200

Rel

ativ

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Figure 4 Relative amount of soil erosion compared to residue remaining on fields.Soil erosion is relative based on erosion amounts when 100% of residue is left on thefields. Data from Blanco-Canqui et al. (2009), Lindstrom (1986), and Powers et al.(2011).

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Figure 3 Relative amount of soil organic C (SOC) compared to residue remaining onfields. The SOC is relative based on SOC amounts when 100% of residue is left on thefields. Data from Blanco-Canqui et al. (2006), Blanco-Canqui and Lal (2007), andMaskina et al. (1993).


be carefully weighed against the costs of increasing fertilizer inputs andpotential loss in soil quality.

5. Nitrogen Cycling

As discussed above, N losses through runoff and nitrate leaching aretypically lower under perennial species with established root systems anda longer period of standing vegetative cover. However, nutrient cycling


also includes the internal translocation of nutrients across seasons and theplant litter dynamics. Internal cycling, plant material decomposition, andmineralization by microorganisms provide readily accessible sources of Nfor plants, while some N turns into stable humus compounds that providea slow release of N (Clark, 1977). The schematic in Fig. 5 outlines thegeneral movement of N in traditional cropping systems and a perennialbiofuel system. While N cycling in traditional systems such as corn andwheat is more understood, knowledge of the movement of N througha perennial bioenergy system is incomplete and requires more work.Understanding the total system balance for N and other nutrients isimportant to optimize fertilizer applications to ensure adequate plantnutrient supply and to minimize nutrient loss. Ideally, biofuel specieswould be productive under low nutrient inputs and would furtherreduce their nutrient needs through three factors: nutrient-poor harvestedtissue, internal movement of nutrients to roots, and litter decomposition(Tom, 1994).

Figure 5 Movement of nitrogen within a) traditional cropping and b) perennial bio-fuel systems. Percentages represent the amount of N added to the system that isremoved by each component. Note: for part b, percentages do not add up to 100 due tovalues taken from multiple sources, uncertainty in calculations, and uncalculated Ntranslocation and storage in roots. Data from Adler et al. (2007); Bransby et al. (1998);Liebig et al. (2006); Marshall et al. (1999); McLaughlin et al. (2002), and Smil (1999).


5.1. Nitrogen and litter/residue management

Leaves, agricultural residues, and other sources of plant litter are an impor-tant part of nutrient cycling. In a mixed-grass prairie, litter may comprise upto 60% of the aboveground biomass and contain approximately 50% and60% of aboveground C and N stocks (Schuman et al., 1999). Litterdecomposition rates can be affected by its quality, as well as litter N andlignin concentrations (Fog, 1988; Melillo et al., 1982). Litter rich in Nand low in lignin content tend to decompose more quickly and maymake N available for plant uptake more rapidly (Melillo et al., 1982).Leaf litter impacts nutrient cycling through incorporation into the soil,through microorganism activities, and by leaching of surface litter (Clark,1977). As willow stands establish, N release from leaf litter may reachover 100 kg N ha�1, while internal recycling may be over 50 kg N ha�1,which will significantly reduce N fertilizer needs (Tom, 1994).Nitrogen cycling within an ecosystem may also be measured by using15N-enriched fertilizers and tracking it within plant parts and soil. In a


shortgrass prairie, 65% of applied 15N was in plant material in the first yearand 55% remained in plant tissue by the fifth year due to the cyclingprocesses inherent in the ecosystem (Clark, 1977).

Crop residues may also impact soil N as well as N uptake by plants as Nin residues mineralizes and becomes available for plant use (Maskina et al.,1993). Applying 16 Mg corn residue ha�1 yr�1 can increase soil organic N(SON) by as much as 37% over an 11-year period when compared to anapplication rate of 2 Mg ha�1 yr�1 (Larson et al., 1972). As residuesdecompose N is released, which may be immobilized by microorganisms,taken up by plants, or lost through nitrate leaching and N2O formation(Aulakh et al., 1991; Maskina et al., 1993). If residues are removed,additional increases in fertilizers may be required to compensate for thenutrients removed in stover biomass (Karlen et al., 2011). Therefore, theloss of leaf litter and surface residues for use as biofuel feedstock may havesignificant impacts on nutrient return to the system and nutrient cycling.

5.2. Nitrogen uptake and biomass removal

In addition to losses through runoff, leaching, and volatilization, nutrientsare also removed from the system through biomass harvest. As such, peren-nial plants and warm-season species that are efficient in their nutrient use orcan translocate nutrients to belowground storage organs will require lessfertilizer. The data in Table 3 show estimates of some of the losses in

Table 3 Nitrogen losses in biofuel cropping systems

Crop

N content inharvestedbiomass(kgMgL1)

Total Nharvesteda

(kg haL1)Nitrate leaching(kg haL1)

N runoff(kg haL1)

Switchgrass 8e10 135 1.4 0.5Miscanthus 5 150 3 ?Reedcanarygrass

6e8 63 20c ?

Corn grainb 13e14 135 55 1.6Stover 4e6 6.3d

Willow 4 48 18.5 1-2a Based on biomass yields from Table 1 and biomass N content (kgMg�1) (Thornton et al., 1998).b Leaching and runoff for no-till corn system.c Measured leaching under a high N application rate of 140 kg N ha�1.d Assumes stover removal of 25%.Sources: Beale and Long (1997); Bransby et al. (1998); Christian et al. (2006); Lemus et al. (2008);Maskina et al. (1993); McIsaac et al. (2010); McLaughlin et al. (2002); Mortensen et al. (1998); Partalaet al. (2001); Randall et al. (1997); Thornton et al. (1998); Tom (1994); Wrobel et al. (2009).


differentbiofuel systems, and indicate that theNcontent inperennial bioenergycrops is only a fraction of what is in corn grain. Nitrogen concentrations inharvested willow stems may be as low as 4 kgNMg�1 (Tom, 1994).In miscanthus, N in aboveground tissues at harvest is similarly low, at5 kgNMg�1 (Beale and Long, 1997). Nitrogen concentrations in reedcanarygrass and switchgrass may be slightly higher, at 6e8 kgNMg�1 and8e10 kgNMg�1, respectively (Bransby et al., 1998; Christian et al., 2006;Lemus et al., 2008; Partala et al., 2001). In contrast, corn grain contains13e14 kgNMg�1 and stover 4e6 kgNMg�1 (Maskina et al., 1993). Theability for plants to take up and use fertilizers also varies among species:fertilized switchgrass may have an N recovery of nearly 66%, while cornrecovery is estimated at approximately 50% (Bransby et al., 1998).

Although perennial species generally have lower concentrations of N inharvested biomass, some N still remains in the tissue. Some of this remain-ing N may also be recovered through nutrient recovery during the bioen-ergy process. As much as 78% and 23% of total N fertilizer input may berecovered as NH3 from switchgrass and corn stover bioenergy systems,respectively, which could potentially be applied back to the croppingsystem (Anex et al., 2007).

5.3. Gaseous emissions and volatilization

Gaseous soil N emissions are another source of system N loss and can bea significant source of GHGs. Emission of nitrous oxide (N2O) can bedue to direct factors such as the rate and type of fertilizer use, organicamendments, crop species, and crop residue management, or indirect sour-ces such as leaching and runoff, and atmospheric deposition of Ncompounds (Mosier et al., 1998). Estimates of N2O emissions caused byN applications vary and may be as high as 8% of N applied, althoughmost estimate emissions at 5% or less (Crutzen et al., 2008; IPCC, 2006;Mosier et al., 1996). Direct N2O emissions are lower for switchgrass andpoplar bioenergy cropping systems and higher for reed canarygrassfeedstock and conventional cropping rotations (Adler et al., 2007).Perennial species generally have lower N2O emissions than annualspecies as a result of lower N inputs, greater N use efficiency, higher soilwater content through shading, and reduced cultivation activities (Kavdiret al., 2008). In addition, emissions from unfertilized switchgrass areexpected to be less than those from CRP grassland, as plant material onthe unharvested CRP lands decomposes and is denitrified (Chamberlainet al., 2011).

In many cases, complete nutrient balances are lacking for biofuel crop-ping systems. Theoretically, perennial feedstock should have more efficientnutrient cycling, require fewer inputs, and retain nutrients within thesystem. Even though perennials may require fewer inputs, harvesting


biomass removes some nutrients from the system which must be replaced ifyields are to be maintained over the long term. However, it is unclearexactly how fertilization affects yields of many feedstock, nor is it knownhow much remains in plant tissue, in the soil, or is lost through runoff,leaching or volatilization. As such, more information is needed on thenutrient balances of biofuel crops.

6. Human Impacts on Biodiversity

Humans have impacted ecosystems over millennia. The entire planethas been affected by human activities that have resulted in land transforma-tions, changes in biota and genetics, and alteration of biogeochemical cycles(Haberl et al., 2007; Leu et al., 2008; Vitousek et al., 1997). In the pastseveral decades, the impact that biodiversity may have on ecosystem func-tioning has been a subject of intense debate for scientists (Cardinale et al.,2006; Huston et al., 2000; Loreau et al., 2001), as well as how ecosystemfunctioning may change due to human-caused species extinctions andintroductions (Balvanera et al., 2006; Hooper et al., 2005; Naeem et al.,2009). Plant biodiversity has been associated with many other ecosystemproperties such as system stability and invasibility (Tilman, 1999), butdiversity at multiple trophic levels may also impact ecosystem functioning(Naeem et al., 1994). Plant biodiversity in agricultural settings can affecta plethora of ecosystem services, including enhancing nutrient cycling,reducing pest occurrences, enhancing habitat for pollinators, andreducing weed competition (Altieri et al., 1983). Some biofuel systemspresent an opportunity to improve diversity in agricultural settings,reduce the land area allocated to traditional monoculture crops, andpotentially alter ecosystem properties and services.

6.1. Biodiversity in agroecosystems

The initial research on biofuel crops focused on fertilized monocultures(e.g., corn, sugarcane, soybeans, switchgrass plantations). Monoculturesare typically easier to establish and maintain, and harvest may be simpleras well, since all plants within the field mature at approximately the sametime. However, the high cost for fertilizers, pesticides, and water inputsto achieve high yields may be a disadvantage in monoculture croppingsystems (Williams et al., 2009). As resources become more limited,producers are increasingly attempting to simultaneously achieve multipleobjectives such as energy production, C sequestration, wildlife habitatenhancement, soil and water protection, and forage production.


Incorporating diversity into bioenergy systems is a potential answer tothis problem. Plant diversity is often associated with higher biomass yieldsand greater nutrient use efficiency (van Ruijven and Berendse, 2005),but in several cases no correlation between diversity and NPP has beenobserved (Huston et al., 2000). Diversity is already implemented inpasture settings, where incorporating legumes and grasses improves foragequality (Bullock et al., 2001; Sleugh et al., 2000), and species-richpastures can produce yields up to 60% greater than species-poor pastures(Bullock et al., 2001). The impact that plant diversity may have onbioenergy production and yields is less clear, however, and in low-inputsystems, careful selection of a few well-adapted species can produceyields similar to those of diverse mixtures (DeHaan et al., 2010).

6.2. Diverse perennial grasslands

Low-input high-diversity (LIHD) perennial grasslands have been consideredby some as a system that can potentially be high-yielding while requiringlower amounts of water, fertilizer, and pesticides (Tilman et al., 2006).Weed management may also be reduced in diverse grasslands, which maysuppress weedy species (Picasso et al., 2008). Diverse grasslands haveadditional ecological benefits, such as increased stability, resilience, andmore rapid recoveries from environmental perturbation (Hector et al.,2010; Tilman and Downing, 1994). Nutrient cycling is also affected byplant diversity and community composition. In plots with legumes, nitrateleaching is negatively associated with diversity and legume abundance(Scherer-Lorenzen et al., 2003). Diverse grasslands also store up to 600%more soil N and 500% more soil C than monocultures due in part toincreased root biomass (Fornara and Tilman, 2008). However, the increasesin soil C cannot be attributed entirely to root biomass, but also to plantdiversity (Steinbeiss et al., 2008). Total (root and soil) C sequestration inLIHD plantings may reach 4.4 Mg C ha�1 yr�1 in the first decade anddecrease to 3.3 Mg C ha�1 yr�1 after that, compared to monocultures thatmay store only 0.1 Mg C ha�1 yr�1 in the first decade and essentially nonein later years (Tilman et al., 2006), although in some cases moderatelyfertilized switchgrass monocultures can store more C than native prairiemixtures (Zeri et al., 2011).

Biomass production is just one step in the bioenergy system pathway.Plant material must then be converted into energy as efficiently as possible,and the effects of diversity on ethanol yields are debatable. Perennial diver-sity is often associated with increased biomass and ethanol yields (Tilmanet al., 2006), but negative relationships have also been observed (Adleret al., 2009). Energy production from biomass may vary due to thechemical compositions of species within mixtures as well as potentialallelopathy due to neighboring species (Adler et al., 2009; Carroll and


Somerville, 2009). Where there is a negative diversity-ethanol relationship,increasing diversity reduces ethanol yields due to two factors: lower plantbiomass yields, and lower cellulose and hemicellulose contents associatedwith higher species richness, such that the greatest ethanol yields comesfrom grasslands dominated by warm-season prairie grasses (Adler et al.,2009). Diverse plantings with few inputs may not maximize ethanolyields, as switchgrass monocultures with moderate N fertilization(74 kg N ha�1) can produce 93% more energy than LIHD grasslands(Schmer et al., 2008). The relationship between diversity and energyyields is a field of study that requires further research.

6.3. Effects on wildlife

Feedstock diversity at both small and large scales is important for wildlifeuse and biocontrol. Conversion of natural ecosystems to biofuel plantationsmay cause declines in floral and faunal diversity, with large losses ofspecialist species and species of concern (Danielsen et al., 2009; Fletcheret al., 2011). Large-scale plantations may actually generate biotic communi-ties that are distinct from other natural and agricultural habitats; forexample, natural and SRWC plantations do not support the same birdcommunity (Christian et al., 1998). Compared to perennial grasslands,corn biofuel fields typically contain lower levels of insect species richnessand abundances, as well as avian diversity, yet management of perennialgrasses for biofuels may lower wildlife habitat value (Gardiner et al.,2010; Robertson et al., 2011a). The conversion of cropland toswitchgrass plantations may increase habitat of some grassland bird speciesof concern (Murray et al., 2003). Bird diversity is generally higher inwarm-season grassland hayfields than in cool-season hayfields becausewarm-season fields are left undisturbed during the nesting season anda 15e20 cm stubble remains on the field during the winter to providecover (Giuliano and Daves, 2002). Perennial bioenergy grasslands couldprovide similar benefits to wildlife, since biomass is typically harvestedonce or twice a year and is cut to a 15e20 cm height. Increased plantdiversity may increase wildlife use, since diverse perennial bioenergysystems create a more heterogeneous habitat and have less soildisturbance than annual monocultures (Gardiner et al., 2010).

Heterogeneity is relatively low on commercial plantations, which mayreduce habitat quality (Christian et al., 1994). Managing switchgrass areas tomaintain vegetation structural heterogeneity by leaving some fieldsunharvested would further improve wildlife habitat quality (Murray et al.,2003). At the landscape level, bioenergy plantations could affect wildlifemovement and population processes if feedstock plantations serve aspopulation sinks that attract animals but are not areas that produce highreproduction rates (Christian et al., 1994). When managing diverse


grasslands for biofuel, trade-offs between wildlife habitat quality andpotential decreases in ethanol yield may also have to be considered(Adler et al., 2009).

Although wildlife use of native, warm-season grasses and corn arewidely studied, the effects of other perennial grasses and trees have alsobeen researched. Based on animal diversity, SRWC plantations can provideas good a habitat as croplands, but are poorer than natural woodlands, withspecies present commonly being habitat generalists rather than obligateforest species (Christian et al., 1998). Both miscanthus and reedcanarygrass provide habitat and cover from predators for small mammals(Semere and Slater, 2007). However, the tall and dense growth of reedcanarygrass monocultures create a poor breeding habitat for skylarks inEurope (Vepsäläinen, 2010). More bird species were found within young(2e3 year old) and more open miscanthus plantings than dense reedcanarygrass fields, although reed canarygrass field edges may supporta larger number of bird species (Semere and Slater, 2007). Althoughwildlife use of miscanthus in the US is not well documented, its value tograssland birds is suspect due to plant architecture that is different frommost plants in the US (Fargione, 2010). As the acreage dedicated tolignocellulosic feedstock increases, more research is needed to determinethe wildlife impacts of large-scale plantings of herbaceous and woodybioenergy crops.

6.4. Diversity at the landscape level

Wildlife use may be affected by feedstocks at both the field level, asdescribed above, and at the landscape level. A high concentration of nativeperennial grasslands for bioenergy around refineries may be advantageous tonesting and obligate grassland bird species (Robertson et al., 2011a).Conversely, this clustering of biofuel plantations in one area will alsoreduce landscape heterogeneity and may reduce biotic diversity (Wienset al., 2011). Establishment of SRWC on a large scale is predicted todecrease the overall biodiversity, with the largest declines in reptiles,butterflies, and birds, although vascular plant diversity is predicted toslightly benefit (Louette et al., 2010). Landscape level changes in diversitymay also impact pollination activities, as large, dense, plantations ofoilseed rape (Brassica napus L.) may increase competition for pollinatorsbetween crop plants and natural plants, reducing pollinator visits and seedset within nearby natural grasslands (Holzschuh et al., 2011).

Habitat heterogeneity at several scales is an important factor in main-taining species diversity (Hutchings et al., 2000). Wildlife may benefitfrom leaving some fields unharvested, which would increase landscapeheterogeneity and provide habitat for more species (Roth et al., 2005). Intree plantations, maintaining stands of varying ages through a region


would increase structural variability and improve wildlife diversity(Hanowski et al., 1997). Maintaining a mosaic landscape that containsboth open and forested areas may enhance avian diversity in willowplantations (Berg, 2002). The diversity and wildlife potential ofbioenergy systems may not be maximized if they are managed intensivelyas monocultures. However, if managed properly, with heterogeneity atmultiple levels (i.e., field, farm, and landscape) in mind, bioenergy-cropping systems may enhance wildlife diversity.

6.5. Pests and biocontrol

Changes in plant diversity have additional impacts on biocontrol, wherenatural enemies keep pest populations in check. Biocontrol is an importantecosystem service that is valued at $417 billion per year globally and hasa value of $24 ha�1 of cropland (Costanza et al., 1997). However, theintensification and simplification of agricultural landscapes has increasedthe odds of a severe spread of pests or disease. The loss of speciesdiversity and genetic diversity in agricultural settings has increased plantsusceptibility and the rate of pathogen and pest spread (Gonzalez-Hernandez et al., 2009). Crop monocultures have a higher risk of severepathogen attacks and pest infestations that could reduce yields or elserequire substantial pesticide inputs (Landis and Werling, 2010; Mitchellet al., 2002). Increasing plant diversity reduces the chance thata pathogen will encounter a susceptible host and reduces the chance ofa pest outbreak decimating an entire system.

Bioenergy systems are no exception. If grown in monocultures, a severedisease or insect attack can significantly reduce productivity and yields(Hartman et al., 2011). In contrast, diverse bioenergy plantations of nativeperennial species, already suggested as a potential method of increasingproductivity, may also be beneficial for reducing the severity andfrequency of pests. Compared to corn, biocontrol may be greater ingrasslands with moderate diversity and floral species richness, whichincrease natural enemy populations and the predation of pest eggs(Werling et al., 2011). Similarly, a genetically diverse plantation may alsoprovide some biocontrol by requiring pests to search farther for susceptiblehosts, slowing their spread across an area (Peacock et al., 1999). Therefore,managing for species and genetic diversity may become an important wayto keep pesticide inputs low, minimize pesticide impacts to theenvironment, and maintain profits.

Interactions between agronomic pests and feedstock species must also beassessed at the landscape level. Biofuel feedstock can be a host for both bene-ficial insects and agricultural pests, as well being reservoirs for insect-vectoredplant viruses (Landis and Werling, 2010). Landscape composition is an


important aspect of biocontrol services, with increasing biocontrol asperennial habitat increases (Werling et al., 2011). As more land is plantedto corn, biocontrol by predators of crop pests may decrease due to the lossof landscape diversity (Landis et al., 2008). The conversion of marginal andnon-crop lands to biofuel production may also reduce the population ofnatural enemies to pests, increasing pest populations (Tscharntke et al.,2005). Conversely, agricultural landscapes with higher diversity (i.e.,cropland interspersed with grassland and forestland) may increase theabundance of some native beetles that prey on crop pests (Gardiner et al.,2009). Biocontrol may therefore be maximized by including perennialgrass and woody species plantations in an agricultural landscape.

While perennial species such as switchgrass have few insect pests, it ispossible that pests have yet to be identified or that management of biofuelmonocultures may increase the prevalence of pest damage (Parrish andFike, 2005; Prasifka et al., 2009). Recently, several fungal diseases havebeen identified on switchgrass, suggesting that it may be a host for otherdiseases and that pathogens may need to be managed to sustain biomass(Layton and Bergstrom, 2011; Vu et al., 2011). Fall armyworm (Spodopterafrugiperda ( J.E. Smith) (Lepidoptera: Noctuidae)), a pest to corn, can surviveon switchgrass and miscanthus under ideal greenhouse conditions, butsurvival is poor to none in the field, suggesting that biofuel suitability forthis pest may be low (Nabity et al., 2011). Similarly, two species ofaphids have been reported on miscanthus stands in four US states,suggesting that damage from aphids and transmitted diseases is possibleand warrants more evaluation (Bradshaw et al., 2010). Cultivar selectionmay also increase pest susceptibility if selections that increase agronomicvalue (productivity, nutritive value) come at the expense of hostresistance. In switchgrass, highly selected cultivars exhibit greatersusceptibility to aphid-transmitted viruses and a greater preference byaphids, which may be linked to increased productivity (Schrotenboeret al., 2011).

The introduction of exotic species may have unexpected consequencesto current ecological and agronomic situations. For example, it is possiblethat miscanthus could either slow the buildup of a Bt resistant westerncorn rootworm (Diabrotica virgifera virgifera LeConte; WCR) populationor alternatively could be a reservoir for WCR population increases thatmay threaten corn production (Spencer and Raghu, 2009). Exoticfeedstocks are not the only potential pest source: native switchgrass standsmay also be reservoirs for insect-transmitted viruses, such as barley yellowdwarf viruses (BYDVs), that infect cereal grain crops and can reduceyields by 15e25% (Lister and Ranieri, 1995; Schrotenboer et al., 2011).The interactions between pests and large-scale bioenergy plantations isnot well understood and need be more thoroughly examined.


7. Biofuels and the Soil Carbon Budget

One of the primary goals of biofuel feedstock is to serve as C-neutralor even C-negative sources of energy, mainly through C sequestration. TheSOC stocks either increase or decrease, depending on land use changes,feedstock choices, and management practices (Conant et al., 2001; Guoand Gifford, 2002; Tolbert et al., 2002). The SOC is an important compo-nent of soil and environmental quality. It influences both soil physical prop-erties (e.g., soil color, structure, stability, and water-holding capacity) aswell as soil chemical properties (e.g., cation exchange capacity, pH buff-ering, and mineral decomposition) (Brady and Weil, 2008). Thus,changes in SOC stock may impact agriculture and the environment byaltering plant productivity and soil and water quality.

7.1. Land/soil preparation

Land for biofuel crops may be allocated from several sources, includingpreviously cropped land or by conversion from natural ecosystems. As dis-cussed in Section 3.1, LUC can result in significant losses in SOC stock anda large C debt. Land conversion may result in losses of 50e70% of theinitial C stock through mineralization, soil erosion, and dissolved organiccarbon (DOC) leaching (Lal, 2001). The SOC sequestration levels areestimated to be much greater in perennial species but may also be site-specific (Blanco-Canqui et al., 2005). Even if natural areas are neitherburned nor tilled in preparation for biofuel establishment, soil propertiesmay still be affected: conversion from native perennial grasslands tonever-tilled annual crops and using best management practices (BMPs)suggest that labile C fractions are reduced and soil biota are affectedwithin three years of land conversion (DuPont et al., 2010).

Besides land clearing, site preparation for biofuel crop establishmentmay include tillage, site preparation, fertilization, and herbicide applica-tions, all of which are sources of GHG emissions (Adler et al., 2007) andare described in Table 4. Conventional tillage (CT), which thoroughlyturns over the soil to leave less than 15% residue cover, can lead tooxidation of OM and exacerbate erosion by wind and water. In contrast,conservation tillage practices such as reduced till or no-till (NT) leavemore agricultural residue on the surface and may reduce SOC losses byerosion and mineralization (Lal, 1998). Conversion from CT to NT maysequester up to an additional 0.57 Mg C ha�1 until the system reachesa new equilibrium in about 20 years (West and Post, 2002). In additionto SOC sequestration, GHG emissions from farm machinery are reducedwhen comparing CT and NT systems: NT corn reduces CO2 emissions

Table 4 Emissions from select farming operations, in terms of C equivalents (CE).

Process Type kg CE haL1

Site preparation Conventional till (moldboard plow,discing, field cultivation, rotary hoeing)

35.3

Reduced till (no moldboard plow) 20.1No-till 5.8

Seeding Drill 3.2No-till drill 3.8

Fertilizer Spraying 0.9Spreading 7.6

Herbicide Spraying 1.4Harvest Corn combine 10.0

Forage harvester 13.6

Data modified from Lal (2004a).


by about 20%, while NT for switchgrass establishment can reduce CO2emissions by nearly 50% (Adler et al., 2007). A consequence of reducedmachinery use in NT systems is increased herbicide and pesticide inputs,but in combination with enhanced SOC sequestration and loweredmachinery costs (Lal, 2004c), NT systems have the potential for short-term sequestration of as much as 200 kg C ha�1 in annual crops, whilereducing agricultural inputs by 31 kg C ha�1 indefinitely through changesin agricultural practices (West and Marland, 2002).

7.2. Soil carbon budget

The soil C stock, containing approximately 2500 Pg C globally to 1-mdepth (Lal, 2004b), is closely connected to the biotic and atmospheric Cstocks primarily through photosynthesis and respiration (Fig. 6), but alsothrough the anthropogenic impacts of deforestation and agricultural andurban activities (Kirschbaum, 2000; Lal, 2004b). There are twocomponents to the soil C stock: organic and inorganic. The SOC stockis estimated at 1500 Pg within the top 1-m soil and 2344 Pg, to a 3-mdepth ( Jobbágy and Jackson, 2000). Almost 4.5 times larger than thebiotic C pool, the soil C stock presents an opportunity to sequesteratmospheric CO2 through biofuel feedstock production (Lal, 2004b).However, determining the net balance of C during biofuel productionrequires an accurate accounting of changes in the soil C stock. Althoughthere is a large potential of sequestering a significant amount of C underbiofuel feedstock, this potential is also associated with a large amount ofuncertainty that may make precise calculations of C balances highlychallenging (Ney and Schnoor, 2002).

Atmosphere800 Pg C

Plants620 Pg C

Soil2500 Pg C

Photosynthesis;

C fixati

on into biomass

120 Pg C yr

60 Pg C yr

Plant re

spiratio

n;

Autotrophic

60 P

g C y

r

Soil

resp

iratio

n;

Het

erot

roph

icdnuorgwole

Bssa

moi bry

Cg

P06

-1

-1

-1

-1

Figure 6 Carbon flows through the atmosphere, plants, and soil that impact Csequestration in soils, modified from Lal et al.(2011).


Feedstock production and management choices affect the SOC budget(Conant et al., 2001; Lemus and Lal, 2005). Compared to CT corn, theSOC stock under NT corn may be nearly 25% larger, while on averageSOC stocks under corn are only two-thirds of that under woodlands, sug-gesting that there is potential to store more SOC under NT (Mishra et al.,2010). While converting CT to NT corn may improve SOC stocks, cornhas a limited SOC sequestration capacity because it is an annual with a lowroot:shoot ratio. Perennial species such as switchgrass and willow, withdeep and extensive root systems, may have root:shoot ratios of up to0.5e0.7, and have the potential to store greater amount of SOC (Zanet al., 2001). Compared to cultivated croplands, soils under switchgrasscan store an additional 15.3 Mg SOC ha�1 when measured to 120 cmdepth (Liebig et al., 2005). Choices that increase root biomass, rootingdepth, and total plant biomass tend to increase the SOC stock and loweratmospheric GHG emissions.

8. Invasive Potential of Bioenergy Crop Species

There is a set desirable characteristics for a potential bioenergy crop:a perennial nature, high NPP, high nutrient and water use efficiency, real-location of nutrients to belowground in fall, competitiveness against weeds,few pests and diseases, and sterility (Raghu et al., 2006). However, many of


these traits are also advantageous to invasive species, and as a result, severalpotential bioenergy crops are already naturalized in portions of the US orhave a closely related species that is a known invasive species (Barneyand Ditomaso, 2008).

Human activities may greatly impact the invasive potential of any intro-duced bioenergy species. Anthropogenic activities such as agriculture, trans-port, and environmental modifications have rapidly increased the rate ofnon-native species introductions, either by accident or purposefully(Pimentel et al., 2000). Of the 5800 species of plants intentionallyintroduced to the US, 128 species have become pests (Pimentel et al.,1989). One example is kudzu (Pueraria montana (Lour.) Merr. var. lobata(Willd.) Maesen & S. Almeida), originally introduced for soil erosioncontrol, is now established on 3 Mha in the southern US and isincreasing at a rate of 50,000 ha yr�1, and has reached southern Ohio(Forseth and Innis, 2004). Johnsongrass (Sorghum halepense (L.) Pers.),originally planted as a forage species, is now one of the top ten worstweeds in the world (Holm, 1969). The weedy potential of exoticbioenergy species must be analyzed in order to limit the risk ofintroducing invasive or noxious species.

Protocols designed to determine the invasive potential of a species, suchas the Weed Risk Assessment (WRA) first developed in Australia, can indi-cate whether or not a species possess a set of life history, dispersal, andhabitat characteristics along with a previous record of impacts in otherregions that may make it invasive, but even these are not completely accu-rate in their predictions (Cousens, 2008). The WRA has been used toascertain the invasive potential of three biofuel crops, switchgrass,miscanthus, and giant reed, with both switchgrass and giant reedidentified as potentially highly invasive in parts of the US (Barney andDitomaso, 2008). Tools such as the WRA and others should be usedwhen assessing the potential ecological consequences of any introducedspecies.

In accordance with the results of the WRA, both giant reed and reedcanarygrass are currently listed as invasive species in the US but are stillbeing considered as bioenergy feedstocks (USDA-NRCS, 2011). Napiergrass (Pennisetum purpureum Schumach.), a warm-season grass fromAfrica, is a highly productive species that can yield up to 88 Mg ha�1

and also has biofuel potential (Somerville et al., 2010). However, theFlorida Exotic Pest Plant Council lists Napier grass as an exotic invaderthat has naturalized and has populations expanding in native Floridahabitats (Florida Exotic Pest Plant Council, 2011). Climate change mayfurther increase the invasive potential of a species as temperatures warm,precipitation patterns shift, and the concentration of atmospheric CO2increases. As temperatures increase, the suitable environment forswitchgrass is expected to expand northward, although the western US


still remains largely unfavorable due to water limitations (Barney andDiTomaso, 2010). Other species, which are currently not invasive, mayincrease in aggressiveness under the future climate conditions. Thus, it isessential to examine exotic feedstock responses to potential climatechanges to prevent a possible invader from establishing.

In addition to climate change, breeding efforts could potentially impactthe invasibility of biofuel species. Cultivars of reed canarygrass, used as a foragespecies, have been bred for increases in productivity and forage use, but theeffects that this may have on its invasive potential are unclear ( Jakubowskiet al., 2011). However, cultivars and invader populations produce similaryields in wetland environments, suggesting that breeding is not the causefor reed canarygrass invasion ( Jakubowski et al., 2011). Conversely, ifbreeding efforts can result in species being less fecund while still remainingproductive, such as the sterile triploid Miscanthus x giganteus, the invasivepotential could drop significantly ( Jakob et al., 2009).

8.1. Invasive species as feedstock

As discussed in Section 8, a few potential biofuel species are alreadyinvading native US habitats. Reed canarygrass, an invader frequentlyfound in wetlands of the northern US and southern Canada, canwithstand a wide range of soil moisture regimes and is one of the mosthigh-yielding cool-season grasses, especially under drought conditions(Galatowitsch et al., 1999). Similarly, giant reed, also an invader inwetlands, has a broad tolerance for a range of environmental conditions,and is highly productive (Quinn and Holt, 2008). When these speciesinvade an ecosystem, they typically become the dominant species, and asa result, diversity-related ecosystem services may suffer. Eradicatinginvasive species is a costly endeavor with no guarantee of success.However, it may be possible to harvest the biomass in areas where thesespecies have already invaded as a method of ecosystem restoration,simultaneously providing low-cost feedstock and mitigatingeutrophication through nutrient removal ( Jakubowski et al., 2010). Inthis manner, an invaded ecosystem may slowly become less dominatedby an invasive biofuel species while providing income from harvestingand conversion to biofuels.

9. Food versus Fuel

One of the increasingly important challenges for humans is to deter-mine how to allocate limited resources such as land, water, and nutrients.Biofuel feedstocks, although providing energy and reducing GHG


emissions, do so at the cost of diverting these limited resources from foodproduction (Pimentel et al., 2009). As a result, food crops and biofuel cropsmay compete for the use of arable lands and resources, so biofuelproduction could potentially jeopardize food security which is already athigh risk. As the demand for food crops increase due to both populationgrowth and biofuel production, food prices are also expected to increase.The cost of food has been on the rise since the early 2000s, with a sharpincrease in 2008 and a lesser increase in 2010 (FAO, 2011). Between2007 and 2008, the global price index for food increased by 45%, withbiofuel production accounting for anywhere between 3 and 30% of theprice increase, although there is disagreement about the impact thatbiofuels played in recent price increases (Ajanovic, 2011; Mueller et al.,2011). While rising food prices affect all consumers, the poor, who spendgreater than 70% of their household budget on food, are more at risk(FAO, 2011). As a result of rising food prices, the poor may faceincreasing malnutrition and reductions in caloric intake.

In 2008, about 13% of the global population was undernourished, butthis number increased to 33% in the least-developed countries (FAO,2011). Currently, global cropland area per capita is just under 0.22 ha,while a minimum of 0.5 ha per capita is necessary for a diverse andnutritious diet (Pimentel et al., 2008). In addition, the global populationis expected to rise to more than 10 billion by 2100 (Fig. 2b), generatingmore pressure to increase food supplies or risk increasing food insecurity.Continued biofuel expansion into croplands and competition for primearable land with food crops may continue to reduce per capita croplandand may also result in the cultivation of marginal or abandonedagricultural lands. Yields on poorer soils will be lower, or else requiregreater resource inputs, both of which could drive the price of food upfurther.

Grain products and other crops used both for food and biofuel will notbe the only types of food impacted through large-scale biofuel produc-tion. Corn grain in the US is used for human consumption, as a feed grainfor livestock, for industrial purposes, and is also exported to other coun-tries. In 2008, one quarter of corn grain was used for biofuel production,but with corn-based ethanol production predicted to consume as much as35e40% of the US corn crop by the end of this decade, reductions toother corn grain uses will likely occur (Mueller et al., 2011; USDA,2010). The livestock industry, which relies heavily on corn as a feed grain,may reduce meat production or increase prices, as will other food indus-tries that depend on corn (e.g., dairies and bakeries). For every $1 per25 kg ($1 bu�1) increase in corn prices, the average food price is predictedto increase by 0.8%, with a 2.9% increase in the cost of meat and a 1.7%increase in dairy products (Hayes et al., 2009). Increases in corn prices dueto biofuel demands in the US will also affect global trade and the price of


corn worldwide. Biofuel production using feedstock that are also staplefoods is not a long-term solution in the search for renewable energyfrom biomass.

Lignocellulosic feedstocks may reduce some of the competition betweenbiofuels and food, depending on management choices. Tilman et al. (2009)recommend establishing perennial species on abandoned cropland, carefuluse of agricultural and wood residues, double cropping of biofuel speciesand food crops, and the use of municipal wastes. However, perennialgrasses and trees growing on marginal croplands, grasslands, or grazinglandsmay displace grazing livestock, further altering the supply of livestock andraising the cost of meat. Grasslands would have to be managed carefully tomaintain other ecosystem services such as livestock production and wildlifehabitat, which would reduce the total amount of area for perennialfeedstock plantations. Perennial feedstocks on marginal lands could supplya portion, but not all, of energy needs.

Residues are already a vital part of nutrient cycling and act to protect soilquality. Removal of over 25% of residues can negatively impact crop yieldsand cause soil erosion, as mentioned in Section 4.1. Double cropping may bea challenge with current leading feedstock species, as most are perennial andcould not work in a double cropping system, while others are food /feedstock crops (i.e., corn) that could once again bring into question thefood versus fuel debate. The use of municipal wastes does hold potential.Of the more than 220 million Mg of municipal waste produced in the USin 2009, almost 12% was burned with energy recovery (EPA, 2010). Itmay be possible to collect municipal organic waste and process it intobiofuels, which would simultaneously reduce deposits in landfills and notrequire arable land for energy production. Some agricultural and treebyproducts (i.e., rice husks, coconut shells, food packing biomass, sawdust)may have specific niches as biofuel feedstocks and not compete for thefinite resources. Approximately 80 million Mg of rice husks are producedannually worldwide, most of which are deposited in fields or landfills orused as fuel for cooking, but if converted to energy, could provide1.2� 109 GJ each year (Natarajan et al., 1998; Tsai et al., 2004). Similarly,many other organic byproducts may also be able to be converted into energy.

10. Conclusions

Bioenergy systems are increasingly called to be multi-functional andprovide energy along with other ecosystem services. Life-cycle assessmentsfocusing on energy efficiency and GHG emissions are an important part ofevaluating bioenergy systems, but assessments must not stop at these twofactors. In order for any bioenergy feedstock to be a viable long-term


energy alternative, it must take into account ecological needs such as soilquality, soil C sequestration, nutrient and water cycling, wildlife habitatand protection of natural areas (Fig. 7). Because corn and othertraditional crop monocultures systems often have serious negativeconsequences on soil, water, and habitat quality, there is a need to findfeedstocks with lower ecological burdens. In comparison with non-nativespecies and intensively managed crop monocultures, low-input perennialnative species are recommended as feedstock that may reduce negativeecosystem effects.

All biofuel feedstock systems have specific advantages and challenges.Perennial feedstock may be a better alternative over monocultures, ifmanaged to minimize ecological impacts. Perennial grasses and trees havea variety of ecological benefits over corn bioenergy systems, including

Land usechanges

Biofueldemand

Assessment &Re-evaluation

C sequestration;soil structure

Erosion

Hydrology;water yield,runoff

Nitrate indrinking water

Hypoxia incoastal systems

Fertilizerrequirements

Invasionpotential

Wildlifehabitat

Biocontrol

Climate change

Soil quality

Water quality

Productivity

Nutrientcycling

Biodiversity

GHG emissions

I

M

P

A

C

T

A

C

T

I

O

N

P

L

A

N

Policy Interventions

Figure 7 Ecological impacts of increased biofuel demand. Depending on feedstockand management choices, impacts could be positive, neutral, or negative. Impacts maybe assessed to drive policy changes, which feed back to the demand for biofuels.


lower losses of soil and nutrients, the potential to improve soil quality,while also providing wildlife habitat and increasing biodiversity. However,these same perennial systems may also reduce water yields, lower biodiver-sity, reduce biological control, and become invasive into natural habitats. Interms of ecosystem services, low-input high-diversity (LIHD) perennialgrasslands may provide the greatest advantages to soil, water, and wildlifehabitat, but in terms of bioenergy yields, this system may not be as produc-tive as intensively managed monocultures. Alternatively, highly productivebut exotic perennials such as miscanthus and giant reed would require lessland to produce the equivalent amount of energy, but would require moreinputs (water and fertilizer), have unknown impacts to wildlife, and in thecase of giant reed, are known invaders of natural habitats. Landscape consid-erations are also important, as ecosystem services such as wildlife habitat andbiological control are enhanced under a mosaic landscape, but this must bebalanced against concentrating feedstock in one area to improve transpor-tation and energy efficiencies.

11. Future Challenges

A major challenge to bioenergy is balancing trade-offs among energy,ecology, and economics. While a positive balance between feedstockecology and energy impacts is vital for a sustainable bioenergy system, othersocial consequences must also be considered. Large-scale bioenergy planta-tions may also significantly alter landscape aesthetics as well as the socio-economic implications for the community (Domac et al., 2005; Skärbäckand Becht, 2005). Economic benefits and concerns of bioenergy also influ-ence feedstock-cropping systems, as may the potential impacts bioenergyplantations could have on recreation and aesthetic properties. Concernsabout global food security may also drive biofuel feedstock choices in thefuture.

Future work needs to be done to identify, cultivate, and breed for feed-stock species that can be very productive under low inputs while stillproviding ecosystems services, and that do not compete with food crops.Developing and implementing new management practices that couldmaintain or increase yields while reducing environmental impacts couldfurther increase the role of biofuel species in energy production. There isalso a lack of information on the impacts of large-scale implementationof biofuel crops as most studies have only examined species under experi-mental conditions, and the size of research biofuel areas must be scaled upto generate realistic estimations and predictions. Bioenergy decisionsrequire careful evaluation and potential compromise so that short-termenergy gains do not come at the cost of long-term ecosystem damages.


New technology and optimization of practices for currently developingfeedstock may also lower energy costs or increase energy yields. Forexample, biofuel from microalgae, while hampered by high energy inputs,may improve their NERs by capturing flue gases from power plants, using“gray” water (water polluted through human activities), or by burial ofalgae as biochar (Clarens et al., 2010; Clarens et al., 2011; Gerbens-Leeneset al., 2009; Sayre, 2010). In doing so, wastewater could be treated andCO2 emissions from power plants reduced while providing needed nutri-ents and CO2 to microalgae. With careful and ingenious use of resourcesas well as new biofuel technology and improved feedstock, it may bepossible to generate renewable energy in a sustainable manner.

ACKNOWLEDGMENTS

The research is funded through a grant from US-DOE, Office of Science, Biological andEnvironmental Research.

REFERENCES

Achten, W. M., Mathijs, E., Verchot, L., Singh, V. P., Aerts, R., and Muys, B. (2007).Jatropha biodiesel fueling sustainability? Biofuels, Bioprod. Biorefin. 1, 283e291.

Achten, W. M. J., Verchot, L., Franken, Y. J., Mathijs, E., Singh, V. P., Aerts, R., andMuys, B. (2008). Jatropha bio-diesel production and use. Biomass Bioenergy 32,1063e1084.

Adegbidi, H. G., Volk, T. A., White, E. H., Abrahamson, L. P., Briggs, R. D., andBickelhaupt, D. H. (2001). Biomass and nutrient removal by willow clones in experi-mental bioenergy plantations in New York State. Biomass Bioenergy 20, 399e411.

Adler, P. R., Del Grosso, S. J., and Parton, W. J. (2007). Life-cycle assessment of net green-house-gas flux for bioenergy cropping systems. Ecol. Appl. 17, 675e691.

Adler, P. R., Sanderson, M. A., Weimer, P. J., and Vogel, K. P. (2009). Plant speciescomposition and biofuel yields of conservation grasslands. Ecol. Appl. 19, 2202e2209.

Ajanovic, A. (2011). Biofuels versus food production: Does biofuels production increasefood prices? Energy 36, 2070e2076.

Akala, V., and Lal, R. (2000). Potential of mine land reclamation for soil organic carbonsequestration in Ohio. Land Degrad. Dev. 11, 289e297.

Altieri, M. A., Letourneau, D. K., and Davis, J. R. (1983). Developing sustainable agroeco-systems. Bioscience 33, 45e49.

Anex, R. P., Lynd, L. R., Laser, M. S., Heggenstaller, A. H., and Liebman, M. (2007).Potential for enhanced nutrient cycling through coupling of agricultural and bioenergysystems. Crop Sci. 47, 1327e1335.

Angelini, L. G., Ceccarini, L., Nassi o Di Nasso, N., and Bonari, E. (2009). Comparison ofArundo donax L. and Miscanthus � giganteus in a long-term field experiment in centralItaly: Analysis of productive characteristics and energy balance. Biomass Bioenergy 33,635e643.

Aulakh, M. S., Walters, D. T., Doran, J. W., Francis, D. D., and Mosier, A. R. (1991). Cropresidue type and placement effects on denitrification and mineralization. Soil Sci. Soc.Am. J. 55, 1020e1025.


Balat, M., and Balat, H. (2009). Recent trends in global production and utilization of bio-ethanol fuel. Appl. Energy 86, 2273e2282.

Balvanera, P., Pfisterer, A. B., Buchmann, N., He, J., Nakashizuka, T., Raffaelli, D., andSchmid, B. (2006). Quantifying the evidence for biodiversity effects on ecosystem func-tioning and services. Ecol. Lett. 9, 1146e1156.

Barney, J. N., and Ditomaso, J. M. (2008). Nonnative species and bioenergy: Are we culti-vating the next invader? Bioscience 58, 64e70.

Barney, J. N., and DiTomaso, J. M. (2010). Bioclimatic predictions of habitat suitability forthe biofuel switchgrass in North America under current and future climate scenarios.Biomass Bioenergy 34, 124e133.

Batan, L., Quinn, J., Willson, B., and Bradley, T. (2010). Net energy and greenhouse gas emis-sion evaluation of biodiesel derived frommicroalgae. Environ. Sci. Technol. 44, 7975e7980.

Beale, C. V., and Long, S. P. (1997). Seasonal dynamics of nutrient accumulation and par-titioning in the perennial C4-grasses Miscanthus � giganteus and Spartina cynosuroides.Biomass Bioenergy 12, 419e428.

Bendfeldt, E. S., Burger, J. A., and Daniels, W. L. (2001). Quality of amended mine soilsafter sixteen years. Soil Sci. Soc. Am. J. 65, 1736e1744.

Berg, Å (2002). Breeding birds in short-rotation coppices on farmland in central SwedendTheimportance of Salix height and adjacent habitats. Agric. Ecosyst. Environ. 90, 265e276.

Best, L. B., Campa ,H., III, Kemp, K. E., Robel, R. J., Ryan,M.R., Savidge, J. A., Harmon, P.,Weeks, J., andWinterstein, S.R. (1997).Bird abundance and nesting inCRPfields and crop-land in the Midwest: A regional approach.Wildl. Soc. Bull. 25, 864e877.

Blanco-Canqui, H. (2010). Energy crops and their implications on soil and environment.Agron. J. 102, 403e419.

Blanco-Canqui, H., Lal, R., and Lemus, R. (2005). Soil aggregate properties and organiccarbon for switchgrass and traditional agricultural systems in the southeastern UnitedStates. Soil Sci. 170, 998e1012.

Blanco-Canqui, H., Lal, R., Post, W. M., Izaurralde, R. C., and Owens, L. B. (2006).Rapid changes in soil carbon and structural properties due to stover removal from no-till corn plots. Soil Sci. 171, 468e482.

Blanco-Canqui, H., and Lal, R. (2007). Soil and crop response to harvesting corn residuesfor biofuel production. Geoderma 141, 355e362.

Blanco-Canqui, H., Stephenson, R. J., Nelson, N. O., and Presley, D. R. (2009). Wheatand sorghum residue removal for expanded uses increases sediment and nutrient lossin runoff. J. Environ. Qual. 38, 2365e2372.

Bradshaw, J. D., Prasifka, J. R., Steffey, K. L., and Gray, M. E. (2010). First report of fieldpopulations of two potential aphid pests of the bioenergy crop Miscanthus � giganteus.Fla. Entomol. 93, 135e137.

Brady, N. C., and Weil, R. R. (2008). The Nature and Properties of Soils. Upper Saddle River,N.J.: Prentice Hall.

Bransby, D., McLaughlin, S., and Parrish, D. (1998). A review of carbon and nitrogenbalances in switchgrass grown for energy. Biomass Bioenergy 14, 379e384.

Bressan, R. A., Reddy, M. P., Chung, S. H., Yun, D. J., Hardin, L. S., and Bohnert, H. J.(2011). Stress-adapted extremophiles provide energy without interference with foodproduction. Food Secur. 3, 93e105.

Bullock, J., Pywell, R., Burke, M., and Walker, K. (2001). Restoration of biodiversityenhances agricultural production. Ecol. Lett. 4, 185e189.

Campbell, J. E., Lobell, D. B., Genova, R. C., and Field, C. B. (2008). The global potentialof bioenergy on abandoned agriculture lands. Environ. Sci. Technol. 42, 5791e5794.

Cardinale, B. J., Srivastava, D. S., Emmett Duffy, J., Wright, J. P., Downing, A. L.,Sankaran, M., and Jouseau, C. (2006). Effects of biodiversity on the functioning oftrophic groups and ecosystems. Nature 443, 989e992.


Carroll, A., and Somerville, C. (2009). Cellulosic biofuels. Annu. Rev. Plant Biol. 60,165e182.

Casselman, C. N., Fox, T. R., Burger, J. A., Jones, A. T., and Galbraith, J. M. (2006).Effects of silvicultural treatments on survival and growth of trees planted on reclaimedmine lands in the Appalachians. For. Ecol. Manage. 223, 403e414.

Chamberlain, J. F., Miller, S. A., and Frederick, J. R. (2011). Using DAYCENT to quantifyon-farm GHG emissions and N dynamics of land use conversion to N-managed switch-grass in the southern U.S. Agric. Ecosyst. Environ. 141, 332e341.

Christian, D. P., Niemi, G. J., Hanowski, J. M., and Collins, P. (1994). Perspectives onbiomass energy tree plantations and changes in habitat for biological organisms. BiomassBioenergy 6, 31e39.

Christian, D., Hoffman, W., Hanowski, J., Niemi, G., and Beyea, J. (1998). Bird andmammal diversity on woody biomass plantations in North America. Biomass Bioenergy14, 395e402.

Christian, D. G., and Riche, A. B. (1998). Nitrate leaching losses under miscanthus grassplanted on a silty clay loam soil. Soil Use Manage. 14, 131e135.

Christian, D. G., Yates, N. E., and Riche, A. B. (2006). The effect of harvest date on theyield and mineral content of Phalaris arundinacea L. (reed canary grass) genotypes screenedfor their potential as energy crops in southern England. J. Sci. Food Agric. 86,1181e1188.

Clarens, A. F., Resurreccion, E. P., White, M. A., and Colosi, L. M. (2010). Environmentallife cycle comparison of algae to other bioenergy feedstocks. Environ. Sci. Technol. 44,1813e1819.

Clarens, A. F., Nassau, H., Resurreccion, E. P., White, M. A., and Colosi, L. M. (2011).Environmental impacts of algae-derived biodiesel and bioelectricity for transportation.Environ. Sci. Technol. 45, 7554e7560.

Clark, F. E. (1977). Internal cycling of nitrogen in shortgrass prairie. Ecology 58, 1322e1333.Conant, R. T., Paustian, K., and Elliott, E. T. (2001). Grassland management and conver-

sion into grassland: Effects on soil carbon. Ecol. Appl. 11, 343e355.Costanza, R., d'Arge, R., de Groot, R., Farber, S., Grasso, M., Hannon, B., Limburg, K.,

Naeem, S., O'Neill, R., Paruelo, J., Raskin, R., Sutton, P., and van den Belt, M.(1997). The value of the world's ecosystem services and natural capital. Nature 387,253e260.

Cousens, R. (2008). Risk assessment of potential biofuel species: An application for trait-based models for predicting weediness? Weed Sci. 56, 873e882.

CRP. (2009). Annual Summary and Enrollment Statistics e FY 2009. Washington, D.C.Natural Resources Conservation Service, United States Department of Agriculture.

Crutzen, P. J., Mosier, A. R., Smith, K. A., and Winiwarter, W. (2008). N2O release fromagro-biofuel production negates global warming reduction by replacing fossil fuels.Atmos. Chem. Phys. 8, 389e395.

Cuomo, G., Anderson, B., Young, L., and Wilhelm, W. (1996). Harvest frequency andburning effects on monocultures of 3 warm-season grasses. J. Range Manage. 49,157e162.

Danielsen, F., Beukema, H., Burgess, N. D., Parish, F., Brühl, C. A., Donald, P. F.,Murdiyarso, D., Phalan, B., Reijnders, L., Struebig, M., and Fitzherbert, E. B. (2009).Biofuel plantations on forested lands: Double jeopardy for biodiversity and climate. Con-serv. Biol. 23, 348e358.

Davis, S. C., Anderson-Teixeira, K. J., and DeLucia, E. H. (2009). Life-cycle analysis andthe ecology of biofuels. Trends Plant Sci. 14, 140e146.

de Groot, R. S., Wilson, M. A., and Boumans, R. M. J. (2002). A typology for the classi-fication, description and valuation of ecosystem functions, goods and services. Ecol. Econ.41, 393e408.


de Vries, S. C., van de Ven, G. W. J., van Ittersum, M. K., and Giller, K. E. (2010).Resource use efficiency and environmental performance of nine major biofuel crops,processed by first-generation conversion techniques. Biomass Bioenergy 34, 588e601.

Debolt, S., Campbell, J. E., Smith, R., Jr., Montross, M., and Stork, J. (2009). Life cycleassessment of native plants and marginal lands for bioenergy agriculture in Kentuckyas a model for south-eastern USA. GCB Bioenergy 1, 308e316.

DeHaan, L. R., Weisberg, S., Tilman, D., and Fornara, D. (2010). Agricultural and biofuelimplications of a species diversity experiment with native perennial grassland plants.Agric. Ecosyst. Environ. 137, 33e38.

Djomo, S. N., El Kasmioui, O., and Ceulemans, R. (2011). Energy and greenhouse gasbalance of bioenergy production from poplar and willow: A review. GCB Bioenergy3, 181e197.

Domac, J., Richards, K., and Risovic, S. (2005). Socio-economic drivers in implementingbioenergy projects. Biomass Bioenergy 28, 97e106.

Dominguez-Faus, R., Powers, S. E., Burken, J. G., and Alvarez, P. J. (2009). The waterfootprint of biofuels: A drink or drive issue? Environ. Sci. Technol. 43, 3005e3010.

Donner, S. D., and Kucharik, C. J. (2008). Corn-based ethanol production compromisesgoal of reducing nitrogen export by the Mississippi River. Proc. Natl. Acad. Sci.U.S.A. 105, 4513e4518.

DuPont, S. T., Culman, S. W., Ferris, H., Buckley, D. H., and Glover, J. D. (2010). No-tillage conversion of harvested perennial grassland to annual cropland reduces rootbiomass, decreases active carbon stocks, and impacts soil biota. Agric. Ecosyst. Environ.137, 25e32.

Ellis, E. C., Klein Goldewijk, K., Siebert, S., Lightman, D., and Ramankutty, N. (2010).Anthropogenic transformation of the biomes, 1700 to 2000. Global Ecol. Biogeogr. 19,589e606.

EPA. (2010). Municipal Solid Waste in the United States: 2009 Facts and Figures. EPA530-R-10e012. Washington, D.C. United States Environmental Protection Agency, Office ofSolid Waste.

EPA. (2011). National Primary Drinking Water Regulations. Available online at (accessedOctober 2011). http://water.epa.gov/drink/contaminants/index.cfm#List.

Evanylo, G. K., Abaye, A. O., Dundas, C., Zipper, C. E., Lemus, R., Sukkariyah, B., andRockett, J. (2005). Herbaceous vegetation productivity, persistence, and metals uptakeon a biosolids-amended mine soil. J. Environ. Qual. 34, 1811e1819.

FAO. (2011). The State of Food Insecurity in the World 2011. Food and Agriculture Organiza-tion of the United Nations, Rome. Available online at (accessed January 2012). http://www.fao.org/.

Fargione, J. (2010). Is bioenergy for the birds? An evaluation of alternative future bioenergylandscapes. Proc. Natl. Acad. Sci. U.S.A. 107, 18745e18746.

Fargione, J., Hill, J., Tilman, D., Polasky, S., and Hawthorne, P. (2008). Land clearing andthe biofuel carbon debt. Science 319, 1235e1238.

Fargione, J. E., Cooper, T. R., Flaspohler, D. J., Hill, J., Lehman, C., McCoy, T.,McLeod, S., Nelson, E. J., Oberhauser, K. S., and Tilman, D. (2009). Bioenergy andwildlife: Threats and opportunities for grassland conservation. Bioscience 59, 767e777.

Fargione, J. E., Plevin, R. J., and Hill, J. D. (2010). The ecological impact of biofuels. Annu.Rev. Ecol. Evol. Syst. 41, 351e377.

Fillion, M., Brisson, J., Teodorescu, T. I., Sauvé, S., and Labrecque, M. (2009). Performanceof Salix viminalis and Populus nigra � Populus maximowiczii in short rotation intensiveculture under high irrigation. Biomass Bioenergy 33, 1271e1277.

Fletcher, R. J., Jr., Robertson, B. A., Evans, J., Doran, P. J., Alavalapati, J. R. R., andSchemske, D. W. (2011). Biodiversity conservation in the era of biofuels: Risks andopportunities. Front. Ecol. Environ. 9, 161e168.

http://water.epa.gov/drink/contaminants/index.cfm%23List

http://www.fao.org/

http://www.fao.org/


Florida Exotic Pest Plant Council. (2011). 2011 Invasive Plant List. Available online at(accessed February 2012). http://www.fleppc.org/list/list.htm.

Fog, K. (1988). The effect of added nitrogen on the rate of decomposition of organic-matter. Biol. Rev. Camb. Philos. Soc. 63, 433e462.

Foley, J., DeFries, R., Asner, G., Barford, C., Bonan, G., Carpenter, S., Chapin, F.,Coe, M., Daily, G., Gibbs, H., Helkowski, J., Holloway, T., Howard, E.,Kucharik, C., Monfreda, C., Patz, J., Prentice, I., Ramankutty, N., and Snyder, P.(2005). Global consequences of land use. Science 309, 570e574.

Fornara, D. A., and Tilman, D. (2008). Plant functional composition influences rates of soilcarbon and nitrogen accumulation. J. Ecol. 96, 314e322.

Forseth, I., and Innis, A. (2004). Kudzu (Pueraria montana): History, physiology, and ecologycombine to make a major ecosystem threat. Crit. Rev. Plant Sci. 23, 401e413.

Galatowitsch, S., Anderson, N., and Ascher, P. (1999). Invasiveness in wetland plants intemperate North America. Wetlands 19, 733e755.

Galdos, M. V., Cerri, C. C., Lal, R., Bernoux, M., Feigl, B., and Cerri, C. E. P. (2010).Net greenhouse gas fluxes in Brazilian ethanol production systems. GCB Bioenergy 2,37e44.

Gardiner, M. M., Landis, D. A., Gratton, C., DiFonzo, C. D., O'Neal, M., Chacon, J. M.,Wayo, M. T., Schmidt, N. P., Mueller, E. E., and Heimpel, G. E. (2009). Landscapediversity enhances biological control of an introduced crop pest in the north-centralUSA. Ecol. Appl. 19, 143e154.

Gardiner, M. A., Tuell, J. K., Isaacs, R., Gibbs, J., Ascher, J. S., and Landis, D. A. (2010).Implications of three biofuel crops for beneficial arthropods in agricultural landscapes.Bioenergy Res. 3, 6e19.

Gelfand, I., Zenone, T., Jasrotia, P., Chen, J., Hamilton, S. K., and Robertson, G. P. (2011).Carbon debt of Conservation Reserve Program (CRP) grasslands converted to bioen-ergy production. Proc. Natl. Acad. Sci. U.S.A. 108, 13864e13869.

Gerbens-Leenes, W., Hoekstra, A. Y., and van der Meer, T. H. (2009). The water footprintof bioenergy. Proc. Natl. Acad. Sci. U.S.A. 106, 10219e10223.

Giuliano, W. M., and Daves, S. E. (2002). Avian response to warm-season grass use inpasture and hayfield management. Biol. Conserv. 106, 1e9.

Goldewijk, K. (2001). Estimating global land use change over the past 300 years: TheHYDE database. Global Biogeochem. Cycles 15, 417e433.

Goldewijk, K. K. (2005). Three centuries of global population growth: A spatial refer-enced population (density) database for 1700e2000. Population & Environment 26,343e367.

Gonzalez-Hernandez, J. L., Sarath, G., Stein, J. M., Owens, V., Gedye, K., and Boe, A.(2009). A multiple species approach to biomass production from native herbaceousperennial feedstocks. In Vitro Cell. Dev. Biol. Plant 45, 267e281.

Guo, L. B., and Gifford, R. M. (2002). Soil carbon stocks and land use change: A meta anal-ysis. Global Change Biol. 8, 345e360.

Haberl, H., Erb, K. H., Krausmann, F., Gaube, V., Bondeau, A., Plutzar, C., Gingrich, S.,Lucht, W., and Fischer-Kowalski, M. (2007). Quantifying and mapping the humanappropriation of net primary production in earth's terrestrial ecosystems. Proc. Natl.Acad. Sci. U.S.A. 104, 12942e12947.

Haering, K. C., Daniels, W. L., and Galbraith, J. M. (2004). Appalachian mine soilmorphology and properties. Soil Sci. Soc. Am. J. 68, 1315e1325.

Hanowski, J. M., Niemi, G. J., and Christian, D. C. (1997). Influence of within-plantationheterogeneity and surrounding landscape composition on avian communities in hybridpoplar plantations. Conserv. Biol. 11, 936e944.

Hartemink, A. E. (2008). Sugarcane for bioethanol: Soil and environmental issues. Adv.Agron. 99, 125e182.

http://www.fleppc.org/list/list.htm


Hartman, J. C., Nippert, J. B., Orozco, R. A., and Springer, C. J. (2011). Potential ecolog-ical impacts of switchgrass (Panicum virgatum L.) biofuel cultivation in the Central GreatPlains, USA. Biomass Bioenergy 35, 3415e3421.

Hayes, D. J., Babcock, B. A., Fabiosa, J. F., Tokgoz, S., Elobeid, A., Yu, T., Dong, F.,Hart, C. E., Chavez, E., Pan, S., Carriquiry, M. A., and Dumortier, J. (2009). Biofuels:Potential production capacity, effects on grain and livestock sectors, and implications forfood prices and consumers. J. Agric. Appl. Econ. 41, 465e491.

Heaton, E. A., Dohleman, F. G., and Long, S. P. (2008). Meeting US biofuel goals with lessland: The potential of miscanthus. Global Change Biol. 14, 2000e2014.

Hector, A., Hautier, Y., Saner, P., Wacker, L., Bagchi, R., Joshi, J., Scherer-Lorenzen, M.,Spehn, E. M., Bazeley-White, E., Weilenmann, M., Caldeira, M. C.,Dimitrakopoulos, P. G., Finn, J. A., Huss-Danell, K., Jumpponen, A.,Mulder, C. P. H., Palmborg, C., Pereira, J. S., Siamantziouras, A. S. D., Terry, A. C.,Troumbis, A. Y., Schmid, B., and Loreau, M. (2010). General stabilizing effects of plantdiversity on grassland productivity through population asynchrony and overyielding.Ecology 91, 2213e2220.

Hill, J., Nelson, E., Tilman, D., Polasky, S., and Tiffany, D. (2006). Environmental,economic, and energetic costs and benefits of biodiesel and ethanol biofuels. Proc.Natl. Acad. Sci. U.S.A. 103, 11206e11210.

Hoefnagels, R., Smeets, E., and Faaij, A. (2010). Greenhouse gas footprints of different bio-fuel production systems. Renew. Sust. Energ. Rev. 14, 1661e1694.

Holm, L. (1969). Weeds problems in developing countries. Weed Sci. 17, 113e118.Holzschuh, A., Dormann, C. F., Tscharntke, T., and Steffan-Dewenter, I. (2011). Expan-

sion of mass-flowering crops leads to transient pollinator dilution and reduced wild plantpollination. Proc. R. Soc. B-Biol. Sci. 278, 3444e3451.

Hooper, D., Chapin, F., Ewel, J., Hector, A., Inchausti, P., Lavorel, S., Lawton, J.,Lodge, D., Loreau, M., Naeem, S., Schmid, B., Setala, H., Symstad, A.,Vandermeer, J., and Wardle, D. (2005). Effects of biodiversity on ecosystem functioning:A consensus of current knowledge. Ecol. Monogr. 75, 3e35.

Hoskinson, R. L., Karlen, D. L., Birrell, S. J., Radtke, C. W., and Wilhelm, W. W. (2007).Engineering, nutrient removal, and feedstock conversion evaluations of four corn stoverharvest scenarios. Biomass Bioenergy 31, 126e136.

Houghton, R. (1999). The annual net flux of carbon to the atmosphere from changes inland use 1850e1990. Tellus Ser. B 51, 298e313.

Huang, H., Ramaswamy, S., Al-Dajani, W., Tschirner, U., and Cairncross, R. A. (2009).Effect of biomass species and plant size on cellulosic ethanol: A comparative processand economic analysis. Biomass Bioenergy 33, 234e246.

Huston, M. A., Aarssen, L. W., Austin, M. P., Cade, B. S., Fridley, J. D., Garnier, E.,Grime, J. P., Hodgson, J., Lauenroth, W. K., Thompson, K., Vandermeer, J. H., andWardle, D. A. (2000). No consistent effect of plant diversity on productivity. Science289, 1255.

Hutchings, M. J., John, L. A., and Stewart, A. J. A. (2000). The Ecological Consequences ofEnvironmental Heterogeneity: The 40th Symposium of the British Ecological Society. Oxford:Blackwell Science.

IPCC. (2006). IPCC Guidelines for National Greenhouse Gas Inventories, Vol. 4. InS. Eggleston, L. Buendia, K. Miwa, T. Ngara, & K. Tanabe (Eds.), Hayama, Japan:IGES.

Jakob, K., Zhou, F., and Paterson, A. H. (2009). Genetic improvement of C4 grasses ascellulosic biofuel feedstocks. In Vitro Cell. Dev. Biol. Plant 45, 291e305.

Jakubowski, A. R., Casler, M. D., and Jackson, R. D. (2010). The benefits of harvestingwetland invaders for cellulosic biofuel: An ecosystem services perspective. Restor. Ecol.18, 789e795.


Jakubowski, A. R., Casler, M. D., and Jackson, R. D. (2011). Has selection for improvedagronomic traits made reed canarygrass invasive? PLoS One 6, e25757.

Jaynes, D., Colvin, T., Karlen, D., Cambardella, C., and Meek, D. (2001). Nitrate loss insubsurface drainage as affected by nitrogen fertilizer rate. J. Environ. Qual. 30, 1305e1314.

Jobbágy, E. G., and Jackson, R. B. (2000). The vertical distribution of soil organic carbonand its relation to climate and vegetation. Ecol. Appl. 10, 4e436.

Karlen, D. L., Wollenhaupt, N. C., Erbach, D. C., Berry, E. C., Swan, J. B., Eash, N. S.,and Jordahl, J. L. (1994). Crop residue effects on soil quality following 10-years of no-tillcorn. Soil Tillage Res. 31, 149e167.

Karlen, D. L., Lal, R., Follett, R. F., Kimble, J. M., Hatfield, J. L., Miranowski, J. M.,Cambardella, C. A., Manale, A., Anex, R. P., and Rice, C. W. (2009). Crop residues:The rest of the story. Environ. Sci. Technol. 43, 8011e8015.

Karlen, D. L., Birell, S. J., and Hess, J. R. (2011). A five-year assessment of corn stoverharvest in central Iowa, USA. Soil Tillage Res. 115, 47e55.

Kavdir, Y., Hellebrand, H. J., and Kern, J. (2008). Seasonal variations of nitrous oxide emis-sion in relation to nitrogen fertilization and energy crop types in sandy soil. Soil TillageRes. 98, 175e186.

Keeney, R., and Hertel, T. W. (2009). The indirect land use impacts of United States bio-fuel policies: The importance of acreage, yield, and bilateral trade responses. Am. J. Agric.Econ. 91, 895e909.

Kirschbaum, M. U. F. (2000). Will changes in soil organic carbon act as a positive or nega-tive feedback on global warming? Biogeochemistry 48, 21e51.

Lal, R. (1998). Soil erosion impact on agronomic productivity and environment quality.Crit. Rev. Plant Sci. 17, 319e464.

Lal, R. (2001). World cropland soils as a source or sink for atmospheric carbon. Adv. Agron.71, 145e191.

Lal, R. (2004a). Carbon emission from farm operations. Environ. Int. 30, 981e990.Lal, R. (2004b). Soil carbon sequestration to mitigate climate change. Geoderma 123, 1e22.Lal, R. (2004c). Soil carbon sequestration impacts on global climate change and food secu-

rity. Science 304, 1623e1627.Lal, R. (2009). Soil quality impacts of residue removal for bioethanol production. Soil Tillage

Res. 102, 233e241.Lal, R., Delgado, J. A., Groffman, P. M., Millar, N., Dell, C., and Rotz, A. (2011). Manage-

ment to mitigate and adapt to climate change. J. Soil Water Conserv. 66, 276e285.Landis, D. A., Gardiner, M. M., van der Werf, W., and Swinton, S. M. (2008). Increasing

corn for biofuel production reduces biocontrol services in agricultural landscapes. Proc.Natl. Acad. Sci. U.S.A. 105, 20552e20557.

Landis, D. A., and Werling, B. P. (2010). Arthropods and biofuel production systems inNorth America. Insect Sci. 17, 220e236.

Lardon, L., Hélias, A., Sialve, B., Steyer, J., and Bernard, O. (2009). Life-cycle assessment ofbiodiesel production from microalgae. Environ. Sci. Technol. 43, 6475e6481.

Larson, W. E., Clapp, C. E., Pierre, W. H., and Morachan, Y. B. (1972). Effects ofincreasing amounts of organic residues on continuous corn: II. Organic carbon, nitrogen,phosphorus, and sulfur. Agron. J. 64, 204e209.

Layton, C. N., and Bergstrom, G. C. (2011). Outbreaks of smut caused by Tilletia maclaganiion switchgrass in New York and Pennsylvania. Plant Dis. 95, 1587e1587.

Lemus, R., and Lal, R. (2005). Bioenergy crops and carbon sequestration. Crit. Rev. PlantSci. 24, 1e21.

Lemus, R., Parrish, D., and Abaye, O. (2008). Nitrogen-use dynamics in switchgrass grownfor biomass. Bioenergy Research 1, 153e162.

Leu, M., Hanser, S. E., and Knick, S. T. (2008). The human footprint in the west: A large-scale analysis of anthropogenic impacts. Ecol. Appl. 18, 1119e1139.


Lewandowski, I., Scurlock, J. M. O., Lindvall, E., and Christou, M. (2003). The develop-ment and current status of perennial rhizomatous grasses as energy crops in the US andEurope. Biomass Bioenergy 25, 335e361.

Licht, L. A., and Isebrands, J. G. (2005). Linking phytoremediated pollutant removal tobiomass economic opportunities. Biomass Bioenergy 28, 203e218.

Liebig, M. A., Johnson, H. A., Hanson, J. D., and Frank, A. B. (2005). Soil carbon underswitchgrass stands and cultivated cropland. Biomass Bioenergy 28, 347e354.

Liebig, M. A., Gross, J. R., Kronberg, S. L., Hanson, J. D., Frank, A. B., and Phillips, R. L.(2006). Soil response to long-term grazing in the northern great plains of North America.Agric. Ecosyst. Environ. 115, 270e276.

Linderson, M., Iritz, Z., and Lindroth, A. (2007). The effect of water availability on stand-level productivity, transpiration, water use efficiency and radiation use efficiency of field-grown willow clones. Biomass Bioenergy 31, 460e468.

Lindstrom, M. J. (1986). Effects of residue harvesting on water runoff, soil-erosion andnutrient loss. Agric. Ecosyst. Environ. 16, 103e112.

Liska, A. J., Yang, H. S., Bremer, V. R., Klopfenstein, T. J., Walters, D. T., Erickson, G. E.,and Cassman, K. G. (2009). Improvements in life cycle energy efficiency and greenhousegas emissions of corn-ethanol. J. Ind. Ecol. 13, 58e74.

Lister, R. M., and Ranieri, R. (1995). Distribution and economic importance of barleyyellow dwarf. In C. J. D'Arcy, & P. A. Burnett (Eds.)., Barley Yellow Dwarf: 40 Yearsof Progress (pp. 29e53). St. Paul, MN: APS Press.

Loreau, M., Naeem, S., Inchausti, P., Bengtsson, J., Grime, J., Hector, A., Hooper, D.,Huston, M., Raffaelli, D., Schmid, B., Tilman, D., and Wardle, D. (2001). Ecology eBiodiversity and ecosystem functioning: Current knowledge and future challenges. Science294, 804e808.

Louette, G., Maes, D., Alkemade, J. R. M., Boitani, L., de Knegt, B., Eggers, J.,Falcucci, A., Framstad, E., Hagemeijer, W., Hennekens, S. M., Maiorano, L.,Nagy, S., Serradilla, A. N., Ozinga, W. A., Schaminée, J. H. J., Tsiaousi, V., vanTol, S., and Delbaere, B. (2010). BioScoreeCost-effective assessment of policy impacton biodiversity using species sensitivity scores. J. Nat. Conserv. 18, 142e148.

Love, B. J., and Nejadhashemi, A. P. (2011). Water quality impact assessment of large-scalebiofuel crops expansion in agricultural regions of Michigan. Biomass Bioenergy 35,2200e2216.

Luo, L., van der Voet, E., and Huppes, G. (2009). An energy analysis of ethanol from cellu-losic feedstockecorn stover. Renew. Sust. Energy Rev. 13, 2003e2011.

Lyons, J., Trimble, S., and Paine, L. (2000). Grass versus trees: Managing riparian areasto benefit streams of central North America. J. Am. Water Resour. Assoc. 36,919e930.

Marshall, S. B., Cabrera, M. L., Braun, L. C., Wood, C. W., Mullen, M. D., andGuertal, E. A. (1999). Denitrification from fescue pastures in the southeastern USA fertil-ized with broiler litter. J. Environ. Qual. 28.

Maskina, M., Power, J., Doran, J., and Wilhelm, W. (1993). Residual effects of no-tillcrop residues on corn yield and nitrogen uptake. Soil Sci. Soc. Am. J. 57,1555e1560.

Mathews, J. A., and Tan, H. (2009). Biofuels and indirect land use change effects: Thedebate continues. Biofuels Bioprod. Bioref. 3, 305e317.

McCoy, T. D., Ryan, M. R., Burger, J., L.W., and Kurzejeski, E. W. (2001). Grassland birdconservation: CP1 vs. CP2 plantings in conservation reserve program fields in Missouri.Am. Midl. Nat. 145, 1e17.

McIsaac, G. F., David, M. B., and Mitchell, C. A. (2010). Miscanthus and switchgrassproduction in central Illinois: Impacts on hydrology and inorganic nitrogen leaching.J. Environ. Qual. 39, 1790e1799.


McLaughlin, S. B., Ugarte, D. G. D. L., Garten, C. T., Lynd, L. R., Sanderson, M. A.,Tolbert, V. R., and Wolf, D. D. (2002). High-value renewable energy from prairiegrasses. Environ. Sci. Technol. 36, 2122e2129.

Melillo, J. M., Aber, J. D., and Muratore, J. F. (1982). Nitrogen and lignin control of hard-wood leaf litter decomposition dynamics. Ecology 63, 621e626.

Melillo, J. M., Reilly, J. M., Kicklighter, D. W., Gurgel, A. C., Cronin, T. W., Paltsev, S.,Felzer, B. S., Wang, X., Sokolov, A. P., and Schlosser, C. A. (2009). Indirect emissionsfrom biofuels: How important? Science 326, 1397e1399.

Meyer, W., and Turner, B. (1992). Human-population growth and global land-use coverchange. Annu. Rev. Ecol. Syst. 23, 39e61.

Millennium Ecosystem Assessment. (2005). Ecosystems and Human Well-being: Synthesis.Washington, D.C. Island Press.

Mirza, N., Mahmood, Q., Pervez, A., Ahmad, R., Farooq, R., Shah, M. M., andAzim, M. R. (2010). Phytoremediation potential of Arundo donax in arsenic-contami-nated synthetic wastewater. Bioresour. Technol. 101, 5815e5819.

Mishra, U., Ussiri, D. A. N., and Lal, R. (2010). Tillage effects on soil organic carbonstorage and dynamics in corn belt of Ohio USA. Soil Tillage Res. 107, 88e96.

Mitchell, C., Tilman, D., and Groth, J. (2002). Effects of grassland plant speciesdiversity, abundance, and composition on foliar fungal disease. Ecology 83,1713e1726.

Monti, A., and Zatta, A. (2009). Root distribution and soil moisture retrieval in perennialand annual energy crops in northern Italy. Agric. Ecosyst. Environ. 132, 252e259.

Mooney, D. F., Roberts, R. K., English, B. C., Tyler, D. D., and Larson, J. A. (2009). Yieldand breakeven price of ‘alamo’ switchgrass for biofuels in Tennessee. Agron. J. 101,1234e1242.

Mortensen, J., Nielsen, K., and Jorgensen, U. (1998). Nitrate leaching during establish-ment of willow (Salix viminalis) on two soil types and at two fertilization levels. BiomassBioenergy 15, 457e466.

Mosier, A. R., Duxbury, J. M., Freney, J. R., Heinemeyer, O., and Minami, K. (1996).Nitrous oxide emissions from agricultural fields: Assessment, measurement and mitiga-tion. Plant Soil 181, 95e108.

Mosier, A., Kroeze, C., Nevison, C., Oenema, O., Seitzinger, S., and van Cleemput, O.(1998). Closing the global N2O budget: Nitrous oxide emissions through the agriculturalnitrogen cycle e OECD/IPCC/IEA phase II development of IPCC guidelines fornational greenhouse gas inventory methodology. Nutr. Cycl. Agroecosyst. 52, 225e248.

Mueller, S. A., Anderson, J. E., and Wallington, T. J. (2011). Impact of biofuel productionand other supply and demand factors on food price increases in 2008. Biomass Bioenergy35, 1623e1632.

Mulkey, V. R., Owens, V. N., and Lee, D. K. (2006). Management of switchgrass-dominatedConservation Reserve Program lands for biomass production in South Dakota. Crop Sci.46, 712e720.

Murray, L. D., Best, L. B., Jacobsen, T. J., and Braster, M. L. (2003). Potential effects ongrassland birds of converting marginal cropland to switchgrass biomass production.Biomass Bioenergy 25, 167e175.

Nabity, P. D., Zangerl, A. R., Berenbaum, M. R., and DeLucia, E. H. (2011). Bioenergycrops Miscanthus � giganteus and Panicum virgatum reduce growth and survivorship ofSpodoptera frugiperda (Lepidoptera: Noctuidae). J. Econ. Entomol. 104, 459e464.

Naeem, S., Thompson, L., Lawler, S., Lawton, J., and Woodfin, R. (1994). Decliningbiodiversity can alter the performance of ecosystems. Nature 368, 734e737.

Naeem, S., Bunker, D. E., Hector, A., Loreau, M., & Perrings, C. (Eds.). (2009). Biodiver-sity, Ecosystem Functioning, and Human Wellbeing. Oxford; New York: Oxford UniversityPress.


Natarajan, E., Nordin, A., and Rao, A. N. (1998). Overview of combustion and gasificationof rice husk in fluidized bed reactors. Biomass Bioenergy 14, 533e546.

Nelson, R. G., Ascough, J. C., IIII, and Langemeier, M. R. (2006). Environmental andeconomic analysis of switchgrass production for water quality improvement in northeastKansas. J. Environ. Manage. 79, 336e347.

Ney, R. A., and Schnoor, J. L. (2002). Incremental life cycle analysis: Using uncertaintyanalysis to frame greenhouse gas balances from bioenergy systems for emission trading.Biomass Bioenergy 22, 257e269.

Openshaw, K. (2000). A review of Jatropha curcas: An oil plant of unfulfilled promise.Biomass Bioenergy 19, 1e15.

Papazoglou, E. G., Karantounias, G. A., Vemmos, S. N., and Bouranis, D. L. (2005). Photo-synthesis and growth responses of giant reed (Arundo donax L.) to the heavy metals Cdand Ni. Environ. Int. 31, 243e249.

Papong, S., Chom-In, T., Noksa-nga, S., and Malakul, P. (2010). Life cycle energy effi-ciency and potentials of biodiesel production from palm oil in Thailand. Energy Policy38, 226e233.

Parrish, D. J., and Fike, J. H. (2005). The biology and agronomy of switchgrass for biofuels.Crit. Rev. Plant Sci. 24, 423e459.

Partala, A., Mela, T., Esala, M., and Ketoja, E. (2001). Plant recovery of 15N-labellednitrogen applied to reed canary grass grown for biomass. Nutr. Cycl. Agroecosyst. 61,273e281.

Peacock, L., Herrick, S., and Brain, P. (1999). Spatio-temporal dynamics of willow beetle(Phratora vulgatissima) in short-rotation coppice willows grown as monocultures ora genetically diverse mixture. Agric. For. Entomol. 1, 287e296.

Perlack, R. D., Wright, L. L., Turhollow, A., Graham, R., Stokes, B., and Erbach, D.(2005). Biomass as Feedstock for a Bioenergy and Bioproducts Industry: The Technical Feasibilityof a Billion-Ton Annual Supply. Tech. Rep. ORNL/TM-2006/66. Oak Ridge, TN: OakRidge National Laboratory.

Perry, C. H., Miller, R. C., and Brooks, K. N. (2001). Impacts of short-rotation hybridpoplar plantations on regional water yield. For. Ecol. Manage. 143, 143e151.

Peterson, M. M., Horst, G. L., Shea, P. J., and Comfort, S. D. (1998). Germination and seed-ling development of switchgrass and smooth bromegrass exposed to 2,4,6-trinitrotoluene.Environ. Pollut. 99, 53e59.

Picasso, V. D., Brummer, E. C., Liebman, M., Dixon, P. M., and Wilsey, B. J. (2008). Cropspecies diversity affects productivity and weed suppression in perennial polyculturesunder two management strategies. Crop Sci. 48, 331e342.

Pimentel, D., Hunter, M. S., LaGro, J. A., Efroymson, R. A., Landers, J. C., Mervis, F. T.,McCarthy, C. A., and Boyd, A. E. (1989). Benefits and risks of genetic engineering inagriculture. Bioscience 39, 606e614.

Pimentel, D., Lach, L., Zuniga, R., and Morrison, D. (2000). Environmental and economiccosts of nonindigenous species in the United States. Bioscience 50, 53e65.

Pimentel, D., Marklein, A., Toth, M. A., Karpoff, M., Paul, G. S., McCormack, R.,Kyriazis, J., and Krueger, T. (2008). Biofuel impacts on world food supply: Use of fossilfuel, land and water resources. Energies 1, 41e78.

Pimentel, D., and Patzek, T. W. (2008). Ethanol production: Energy and economic issuesrelated to U.S. and Brazilian sugarcane. In D. Pimentel (Ed.)., Biofuels, Solar and Wind asRenewable Energy Systems (pp. 357e371). New York: Springer.

Pimentel, D., Marklein, A., Toth, M. A., Karpoff, M. N., Paul, G. S., McCormack, R.,Kyriazis, J., and Krueger, T. (2009). Food versus biofuels: Environmental and economiccosts. Hum. Ecol. 37, 1e12.

Piñeiro, G., Jobbágy, E. G., Baker, J., Murray, B. C., and Jackson, R. B. (2009). Set-asidescan be better climate investment than corn ethanol. Ecol. Appl. 19, 277e282.


Plevin, R. J., O'Hare, M., Jones, A. D., Torn, M. S., and Gibbs, H. K. (2010). Greenhousegas emissions from biofuels' indirect land use change are uncertain but may be muchgreater than previously estimated. Environ. Sci. Technol. 44, 8015e8021.

Plieninger, T., and Gaertner, M. (2011). Harnessing degraded lands for biodiversity conser-vation. J. Nat. Conserv. 19, 18e23.

Powers, S. E., Ascough, J. C., IIII, Nelson, R. G., and Larocque, G. R. (2011). Modelingwater and soil quality environmental impacts associated with bioenergy crop productionand biomass removal in the Midwest USA. Ecol. Model. 222, 2430e2447.

Prasifka, J. R., Bradshaw, J. D., Meagher, R. L., Nagoshi, R. N., Steffey, K. L., andGray, M. E. (2009). Development and feeding of fall armyworm on Miscanthus �giganteus and switchgrass. J. Econ. Entomol. 102, 2154e2159.

Quinn, L. D., and Holt, J. S. (2008). Ecological correlates of invasion by Arundo donax inthree southern California riparian habitats. Biol. Invasions 10, 591e601.

Raghu, S., Anderson, R. C., Daehler, C. C., Davis, A. S., Wiedenmann, R. N.,Simberloff, D., and Mack, R. N. (2006). Adding biofuels to the invasive species fire?Science 313, 1742e1742.

Randall, G. W., Huggins, D. R., Russelle, M. P., Fuchs, D. J., Nelson, W. W., andAnderson, J. L. (1997). Nitrate losses through subsurface tile drainage in conservationreserve program, alfalfa, and row crop systems. J. Environ. Qual. 26, 1240e1247.

Renewable Fuels Association. (2011). Ethanol Industry Statistics. Available online at (accessedJanuary 2011). http://www.ethanolrfa.org/pages/statistics.

Reynolds, R. E., Shaffer, T. L., Renner, R. W., Newton, W. E., and Batt, B. D. J. (2001).Impact of the Conservation Reserve Program on duck recruitment in the U.S. PrairiePothole region. J. Wildl. Manage. 65, 765e780.

Robertson, B. A., Doran, P. J., Loomis, L. R., Robertson, J. R., and Schemske, D. W.(2011a). Perennial biomass feedstocks enhance avian diversity. GCB Bioenergy 3,235e246.

Robertson, G. P., Hamilton, S. K., Del Grosso, S. J., and Parton, W. J. (2011b). Thebiogeochemistry of bioenergy landscapes: Carbon, nitrogen, and water considerations.Ecol. Appl. 21, 1055e1067.

Rockwood, D. L., Naidu, C. V., Carter, D. R., Rahmani, M., Spriggs, T. A., Lin, C.,Alker, G. R., Isebrands, J. G., and Segrest, S. A. (2004). Short-rotation woodycrops and phytoremediation: Opportunities for agroforestry? Agrofor. Syst. 61e62,51e63.

Roth, A. M., Sample, D. W., Ribic, C. A., Paine, L., Undersander, D. J., and Bartelt, G. A.(2005). Grassland bird response to harvesting switchgrass as a biomass energy crop.Biomass Bioenergy 28, 490e498.

Ryan, P. (1991). Environmental effects of sediment on New Zealand streams e A review.N. Z. J. Mar. Freshwat. Res. 25, 207e221.

Sarkar, S., Miller, S. A., Frederick, J. R., and Chamberlain, J. F. (2011). Modeling nitrogenloss from switchgrass agricultural systems. Biomass Bioenergy 35, 4381e4389.

Sayre, R. (2010). Microalgae: The potential for carbon capture. Bioscience 60, 722e727.Scherer-Lorenzen, M., Palmborg, C., Prinz, A., and Schulze, E. (2003). The role of plant

diversity and composition for nitrate leaching in grasslands. Ecology 84, 1539e1552.Schilling, K. E., Jha, M. K., Zhang, Y., Gassman, P. W., and Wolter, C. F. (2008). Impact

of land use and land cover change on the water balance of a large agricultural watershed:Historical effects and future directions. Water Resour. Res. 44, W00A09.

Schmer, M. R., Vogel, K. P., Mitchell, R. B., and Perrin, R. K. (2008). Net energy ofcellulosic ethanol from switchgrass. Proc. Natl. Acad. Sci. U.S.A. 105, 464e469.

Schrotenboer, A. C., Allen, M. S., and Malmstrom, C. M. (2011). Modification of nativegrasses for biofuel production may increase virus susceptibility. GCB Bioenergy 3,360e374.

http://www.ethanolrfa.org/pages/statistics


Schuman, G. E., Reeder, J. D., Manley, J. T., Hart, R. H., and Manley, W. A. (1999).Impact of grazing management on the carbon and nitrogen balance of a mixed-grass ran-geland. Ecol. Appl. 9, 65e71.

Searchinger, T., Heimlich, R., Houghton, R. A., Dong, F., Elobeid, A., Fabiosa, J.,Tokgoz, S., Hayes, D., and Yu, T. (2008). Use of US croplands for biofuelsincreases greenhouse gases through emissions from land-use change. Science 319,1238e1240.

Secchi, S., Gassman, P. W., Williams, J. R., and Babcock, B. A. (2009). Corn-based ethanolproduction and environmental quality: A case of Iowa and the Conservation ReserveProgram. Environ. Manage. 44, 732e744.

Semere, T., and Slater, F. M. (2007). Ground flora, small mammal and bird species diversityin miscanthus (Miscanthus � giganteus) and reed canary-grass (Phalaris arundinacea)fields. Biomass Bioenergy 31, 20e29.

Simpson, T. W., Sharpley, A. N., Howarth, R. W., Paerl, H. W., and Mankin, K. R.(2008). The new gold rush: Fueling ethanol production while protecting water quality.J. Environ. Qual. 37, 318e324.

Sissine, F. (2007). Energy Independence and Security Act of 2007: A summary of major provisions.Washington, D.C. Congressional Research Service.

Skärbäck, E., and Becht, P. (2005). Landscape perspective on energy forests. BiomassBioenergy 28, 151e159.

Sleugh, B., Moore, K., George, J., and Brummer, E. (2000). Binary legume-grass mixturesimprove forage yield, quality, and seasonal distribution. Agron. J. 92, 24e29.

Smil, V. (1999). Nitrogen in crop production: An account of global flows. GlobalBiogeochem. Cycles 13, 647e662.

Soetaert, W., & Vandamme, E. J. (Eds.), (2009). Biofuels. Hoboken, NJ: Wiley.Somerville, C. (2006). The billion-ton biofuels vision. Science 312, 1277e1277.Somerville, C., Youngs, H., Taylor, C., Davis, S. C., and Long, S. P. (2010). Feedstocks for

lignocellulosic biofuels. Science 329, 790e792.Spencer, J. L., and Raghu, S. (2009). Refuge or reservoir? the potential impacts of the bio-

fuel crop Miscanthus � giganteus on a major pest of maize. PLoS One 4, e8336.Steinbeiss, S., Bessler, H., Engels, C., Temperton, V. M., Buchmann, N., Roscher, C.,

Kreutziger, Y., Baade, J., Habekost, M., and Gleixner, G. (2008). Plant diversity posi-tively affects short-term soil carbon storage in experimental grasslands. Global ChangeBiol. 14, 2937e2949.

Suer, P., and Andersson-Sköld, Y. (2011). Biofuel or excavation? e Life cycle assessment(LCA) of soil remediation options. Biomass Bioenergy 35, 969e981.

Thornton, F. C., Dev Joslin, J., Bock, B. R., Houston, A., Green, T. H., Schoenholtz, S.,Pettry, D., and Tyler, D. D. (1998). Environmental effects of growing woody crops onagricultural land: First year effects on erosion, and water quality. Biomass Bioenergy 15,57e69.

Tilman, D. (1999). The ecological consequences of changes in biodiversity: A search forgeneral principles. Ecology 80, 1455e1474.

Tilman, D., and Downing, J. (1994). Biodiversity and stability in grasslands. Nature 367,363e365.

Tilman, D., Fargione, J., Wolff, B., D'Antonio, C., Dobson, A., Howarth, R.,Schindler, D., Schlesinger, W., Simberloff, D., and Swackhamer, D. (2001). Forecastingagriculturally driven global environmental change. Science 292, 281e284.

Tilman, D., Hill, J., and Lehman, C. (2006). Carbon-negative biofuels from low-inputhigh-diversity grassland biomass. Science 314, 1598e1600.

Tilman, D., Socolow, R., Foley, J. A., Hill, J., Larson, E., Lynd, L., Pacala, S., Reilly, J.,Searchinger, T., Somerville, C., and Williams, R. (2009). Beneficial BiofuelsdThefood, energy, and environment trilemma. Science 325, 270e271.


Tolbert, V., Todd, D., Mann, L., Jawdy, C., Mays, D., Malik, R., Bandaranayake, W.,Houston, A., Tyler, D., and Pettry, D. (2002). Changes in soil quality and below-groundcarbon storage with conversion of traditional agricultural crop lands to bioenergy cropproduction. Environ. Pollut. 116, S97eS106.

Tom, E. (1994). Nutrient cycling in energy forest plantations. Biomass Bioenergy 6,115e121.

Townsend, A., Howarth, R., Bazzaz, F., Booth, M., Cleveland, C., Collinge, S., Dobson, A.,Epstein, P., Keeney, D., Mallin, M., Rogers, C., Wayne, P., and Wolfe, A. (2003).Human health effects of a changing global nitrogen cycle. Front. Ecol. Environ. 1,240e246.

Trabucco, A., Achten, W. M. J., Bowe, C., Aerts, R., Van Orshoven, J., Norgrove, L., andMuys, B. (2010). Global mapping of Jatropha curcas yield based on response of fitness topresent and future climate. GCB Bioenergy 2, 139e151.

Tsai, W. T., Chou, Y. H., and Chang, Y. M. (2004). Progress in energy utilization fromagrowastes in Taiwan. Renew. Sust. Energy Rev. 8, 461e481.

Tscharntke, T., Klein, A. M., Kruess, A., Steffan-Dewenter, I., and Thies, C. (2005). Land-scape perspectives on agricultural intensification and biodiversity e Ecosystem servicemanagement. Ecol. Lett. 8, 857e874.

U.S. Congress. (2008). Food, Conservation, and Energy Act of 2008 (2nd ed.). H.R. 2419. 11thCongress.

Udawatta, R., Krstansky, J., Henderson, G., and Garrett, H. (2002). Agroforestry practices,runoff, and nutrient loss: A paired watershed comparison. J. Environ. Qual. 31,1214e1225.

United Nations, Department of Economic and Social Affairs, Population Division. (2011).World Population Prospects: The 2010 Revision, Highlights and Advance Tables. Workingpaper No. ESA/P/WP.220.

USDA. (2010). USDA Agricultural Projections to 2019. Rep. OCE- 2010-1. Washington,D.C. United States Department of Agriculture.

USDA-NASS. (2011). Charts and Maps, Field Crops. Available online at (accessed November2011). United States Department of Agriculture e National Agricultural StatisticsService. http://www.nass.usda.gov/Charts_and_Maps/Field_Crops/index.asp.

USDA-NRCS. (2011). PLANTS Profile Database. accessed online at (accessed December2011). http://plants.usda.gov/java/.

van Ruijven, J., and Berendse, F. (2005). DiversityeProductivity relationships: Initial effects,long-termpatterns, and underlyingmechanisms.Proc.Natl. Acad. Sci. U.S.A. 102, 695e700.

VanLoocke, A., Bernacchi, C. J., and Twine, T. E. (2010). The impacts of Miscanthus �giganteus production on the Midwest US hydrologic cycle. GCB Bioenergy 2,180e191.

Venturi, P., and Venturi, G. (2003). Analysis of energy comparison for crops in Europeanagricultural systems. Biomass Bioenergy 25, 235e255.

Venuto, B. C., and Daniel, J. A. (2010). Biomass feedstock harvest from ConservationReserve Program land in northwestern Oklahoma. Crop Sci. 50, 737e743.

Vepsäläinen, V. (2010). Energy crop cultivations of reed canary grassdAn inferior breedinghabitat for the skylark, a characteristic farmland bird species. Biomass Bioenergy 34,993e998.

Vitousek, P., Mooney, H., Lubchenco, J., and Melillo, J. (1997). Human domination ofEarth's ecosystems. Science 277, 494e499.

Vu, A. L., Gwinn, K. D., and Ownley, B. H. (2011). First report of dollar spot caused bySclerotinia homoeocarpa on switchgrass in the United States. Plant Dis. 95, 1585e1585.

Werling, B. P., Meehan, T. D., Robertson, B. A., Gratton, C., and Landis, D. A. (2011).Biocontrol potential varies with changes in biofuel-crop plant communities and land-scape perenniality. GCB Bioenergy 3, 347e359.

http://www.nass.usda.gov/Charts_and_Maps/Field_Crops/index.asp

http://plants.usda.gov/java/


West, T., and Marland, G. (2002). A synthesis of carbon sequestration, carbon emissions,and net carbon flux in agriculture: Comparing tillage practices in the United States. Agric.Ecosyst. Environ. 91, 217e232.

West, T., and Post, W. (2002). Soil organic carbon sequestration rates by tillage and croprotation: A global data analysis. Soil Sci. Soc. Am. J. 66, 1930e1946.

Whan, B. M., Scott, C. H., and Jefferson, T. R. (1976). Scheduling sugar cane plant andratoon crops and a fallowdA constrained Markov model. J. Agric. Eng. Res. 21,281e289.

Whitaker, J., Ludley, K. E., Rowe, R., Taylor, G., and Howard, D. C. (2010). Sources ofvariability in greenhouse gas and energy balances for biofuel production: A systematicreview. GCB Bioenergy 2, 99e112.

Wiens, J., Fargione, J., and Hill, J. (2011). Biofuels and biodiversity. Ecol. Appl. 21,1085e1095.

Wilhelm, W. W., Doran, J. W., and Power, J. F. (1986). Corn and soybean yield responseto crop residue management under no-tillage production systems. Agron. J. 78,184e189.

Williams, P. R. D., Inman, D., Aden, A., and Heath, G. A. (2009). Environmental andsustainability factors associated with next-generation biofuels in the US: What do wereally know? Environ. Sci. Technol. 43, 4763e4775.

Wrobel, C., Coulman, B. E., and Smith, D. L. (2009). The potential use of reed canarygrass(Phalaris arundinacea L.) as a biofuel crop. Acta Agric. Scand. Sect. B 59, 1e18.

Zan, C. S., Fyles, J. W., Girouard, P., and Samson, R. A. (2001). Carbon sequestration inperennial bioenergy, annual corn and uncultivated systems in southern Quebec. Agric.Ecosyst. Environ. 86, 135e144.

Zeri, M., Anderson-Teixeira, K., Hickman, G., Masters, M., DeLucia, E., andBernacchi, C. J. (2011). Carbon exchange by establishing biofuel crops in central Illinois.Agric. Ecosyst. Environ. 144, 319e329.

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[Advances in Agronomy] Volume 117 || Agronomic and Ecological Implications of Biofuels