23
Chapter 12 Biofuel Crops and Greenhouse Gases A. Hastings, J. Yeluripati, J. Hillier, andP. Smith School of Biological Sciences, University of Aberdeen, Aberdeen, UK Introduction Climate change is one of the major concerns for humanity in the twenty-first century. Water vapor, carbon dioxide (CO 2 ), nitrous oxide (N 2 O), and methane (CH 4 ) are the main gases that trap outward going infrared radiation (the greenhouse effect) and keep the planet temperature in the comfort zone for life around 15 C. Of these greenhouse gases (GHGs), CO 2 ,N 2 O, and CH 4 are generated by anthropogenic activity in sufficient quantities to increase their atmospheric concentrations and thus augment the greenhouse effect. The greenhouse forcing impacts of these gases are classified by their long wave radiation absorption rate and their lifetime in the atmosphere normalized to the impact of CO 2 which is unity, CH 4 is 26, and N 2 O is 265 over a 100-year time frame. These three GHGs are released to the atmosphere during anthropogenic economic, industrial, and land management activities. Carbon dioxide is released by burning fossil fuels, N 2 O is released during the production of fertilizers and explosives, and CH 4 is released during the production of fossil fuels and in the processing of waste. Concern about climate change has led to the need to reduce anthropogenic GHG emissions by replacing the energy obtained from fossil fuels for heating, transportation, and electricity generation by alternative energy sources that emit less GHG such as nuclear, hydro, solar, wind, tidal, and bioenergy. In addition, these energy sources can provide a measure of energy security and economic activity. All alternative energy sources that use natural drivers will cause some carbon emissions, either by embedded carbon in the construction materials such as cement and metals, energy used in the manufacture and operating the equipment, or by land-use change. These GHG emissions need to be quantified and amortized over the life of the equipment and apportioned to the energy produced so that their GHG impact can be compared to those of fossil fuel produced energy. This process is known as life-cycle analysis (LCA). In theory, burning biomass for energy should be carbon neutral as the carbon absorbed from the atmosphere by the plant by photosynthesis is returned to the atmosphere during the burning Biofuel Crop Sustainability, First Edition. Edited by Bharat P. Singh. © 2013 John Wiley & Sons, Inc. Published 2013 by John Wiley & Sons, Inc. 383

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Chapter 12

Biofuel Crops and Greenhouse GasesA. Hastings, J. Yeluripati, J. Hillier, and P. SmithSchool of Biological Sciences, University of Aberdeen, Aberdeen, UK

Introduction

Climate change is one of the major concerns for humanity in the twenty-first century. Watervapor, carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) are the main gases thattrap outward going infrared radiation (the greenhouse effect) and keep the planet temperaturein the comfort zone for life around 15 ◦C. Of these greenhouse gases (GHGs), CO2, N2O,and CH4 are generated by anthropogenic activity in sufficient quantities to increase theiratmospheric concentrations and thus augment the greenhouse effect. The greenhouse forcingimpacts of these gases are classified by their long wave radiation absorption rate and theirlifetime in the atmosphere normalized to the impact of CO2 which is unity, CH4 is 26, andN2O is 265 over a 100-year time frame.

These three GHGs are released to the atmosphere during anthropogenic economic, industrial,and land management activities. Carbon dioxide is released by burning fossil fuels, N2O isreleased during the production of fertilizers and explosives, and CH4 is released during theproduction of fossil fuels and in the processing of waste.

Concern about climate change has led to the need to reduce anthropogenic GHG emissionsby replacing the energy obtained from fossil fuels for heating, transportation, and electricitygeneration by alternative energy sources that emit less GHG such as nuclear, hydro, solar, wind,tidal, and bioenergy. In addition, these energy sources can provide a measure of energy securityand economic activity. All alternative energy sources that use natural drivers will cause somecarbon emissions, either by embedded carbon in the construction materials such as cement andmetals, energy used in the manufacture and operating the equipment, or by land-use change.These GHG emissions need to be quantified and amortized over the life of the equipment andapportioned to the energy produced so that their GHG impact can be compared to those offossil fuel produced energy. This process is known as life-cycle analysis (LCA).

In theory, burning biomass for energy should be carbon neutral as the carbon absorbed fromthe atmosphere by the plant by photosynthesis is returned to the atmosphere during the burning

Biofuel Crop Sustainability, First Edition. Edited by Bharat P. Singh.© 2013 John Wiley & Sons, Inc. Published 2013 by John Wiley & Sons, Inc.

383

384 Biofuel Crop Sustainability

process, releasing the chemical energy stored in the plant carbon compounds derived from thesolar energy. This is true in the case of natural vegetation, where in the life cycle of plants,dead vegetation is burnt rather than just decaying; however, this process speeds up the return ofcarbon dioxide to the atmosphere and reduces time constant of the carbon cycle of vegetationand soil. However, emissions are saved by the amount that would have been released by thefossil energy replaced. In the case of crops or forest grown or managed specifically for energythere will be an energy input required in this process and hence some GHG emissions.

Any anthropological intervention in the process of growing vegetation whether it be chang-ing the land cover from one vegetation type to another, disturbing the land by tillage, usingfertilizers, herbicides, and pesticides, or changing the water supply or drainage leads to changesin the soil’s physical and chemical properties. Thus the cultivation of feedstock for bioenergywill create some GHG emissions which need to be compared to emissions from the land usethey replace and any change in carbon inventory to estimate the net impact on atmospheric GHGemissions. In addition to the biosphere GHG emissions, the embedded carbon in the machineryand plant manufacture, energy use in cultivation, transport and processing, and the conversionof the feedstock into a useable fuel need to be added to the GHG cost of the bioenergy.

The sustainability of biofuels has to be judged based upon the net energy they contribute tosociety and the amount of GHG they emit compared to their energy equivalent in fossil fuel. Inaddition, they also have to be judged by their efficient use of resources such as land and wateras these are competed for in the production of food, fiber, and timber or for ecosystem services.

In this chapter we will explore these metrics by the LCA of bioenergy produced from annualand perennial feedstocks and include GHG emission from land-use change. These land-use-change emissions will include the change in carbon stocks in standing vegetation and soils aswell as trace gas emissions of CH4 due to water table changes and N2O emissions from theuse of fertilizers.

Land Cover Change

Annual and perennial crops achieve their maximum growth in one season but slower growingplants, shrubs, and trees exhibit an exponential growth to a maximum implying a slowing ofcarbon accumulation with each season. This is an important consideration to calculate thefrequency of the harvesting of willow in short rotation coppice (SRC) bioenergy production tomaximize yield and carbon capture. For example, carbon stored in willow grown for 30 yearswill be less than that harvested SRC, harvesting every 3 years. However, with a growth timeconstant of 10 years, the third-year growth will be 75% of the first year. Using this exponentialmodel, it is estimated that the incremental carbon capture with SRC harvests would be 24units compared to 9 units when leaving the willow to grow to maturity over the same period(as illustrated in Figure 12.1), the incremental harvest being 15 units.

If we only consider the impact of the growth time constants of various trees on the accu-mulation of carbon in standing vegetation and assume that carbon is assimilated in standingvegetation at a rate that is only related to the growth time constant, the accumulation of car-bon from the atmosphere (−ve) in permanent standing vegetation for various species, pluscarbon emitted to the atmosphere by burning the same amount of coal to produce the energyrepresented by the standing vegetation can be calculated. This can be compared to the carbonemitted from both fossil fuels and from producing and burning biomass from a C4 plant likeMiscanthus and a C3 plant such as willow.

Figure 12.2 compares atmospheric C mitigation under different land use. The first curvefor fossil fuels considers that one unit of carbon equivalent to that which could be produced

12 Biofuel Crops and Greenhouse Gases 385

Above

gro

und d

ry m

atter

Time, years

Tree grown to maturity

Incrementalharvest

Short rotation coppice harvest

Figure 12.1. Graphical depiction of the carbon in standing vegetation of a tree grown to maturity toincremental harvesting by short rotation coppicing. The mitigated carbon at any time is the differencebetween the carbon in the tree if left to grow compared to the cumulative harvested carbon at the sametime (Adapted from Marland and Schlamadinger, 1995).

0–15

–10

–5

0

5

Fossil fuel

C4 fuel

Willow and tossil fuel

Oak and fossil fuel

Beech and fossil fuel

Spruce and fossil fuel

C3 fuel

10

15

20

25

Units o

f cabon s

equeste

red/e

mitt

ed

5 10 15

Years

20 25 30

Figure 12.2. Estimation of the best use of land to mitigate atmospheric carbon. Graph of units ofcarbon sequestered or emitted versus time per hectare of land, considering the rate of absorption ofatmospheric CO2 and the rate of growth of various plants and trees. One unit of carbon represents theamount of carbon that can be fixed by plants or trees on 1 ha of land per year. Curves show the cumulativecarbon emitted to or absorbed from the atmosphere. The curve for fossil fuels shows the accumulationof atmospheric carbon from burning the amount of coal that would replace the biomass grown on 1 ha ofland. The C4 and C3 curves show the impact of using the land for growing Miscanthus and SRC willowbiomass fuels, respectively, replacing coal. The other curves show the impact of growing various speciesof trees, willow, oak, beech, and spruce, with different growth rates, and burning the fossil fuel of thesame energy value as could be grown on the land as a biomass fuel.

386 Biofuel Crop Sustainability

on a unit of land and emitted to the atmosphere each year. By year 30, 30 units would havebeen emitted to the atmosphere, of which 11.4 would have been absorbed by earth systemsand 18.6 would remain in the atmosphere (assuming the 30-year time constant). If the landis used for bioenergy crops such as Miscanthus (C4 crop) then, assuming the carbon cyclingis 100% efficient and obtained at no energy and GHG cost, then after 30 years the use ofbioenergy would have sequestered 11.4 units of carbon. However, SRC willow (C3 crop), usedas a bioenergy crop which has a 10-year growth time constant, will only sequester 5.4 units ofcarbon. These fuels are compared to plantations of oak, beech, and spruce, using the same landbut at the same time burning the same amount of fossil fuel to replace the bioenergy grown onthe same area of land during 30 years. Here we look at the units of carbon stored in the standingvegetation minus the net emissions from burning fossil fuel over the same period. The amountof carbon sequestered is 8.5, 7.1, and 3.7 units, respectively, and depend on the growth timeconstant of the tree of 150, 100, and 50 years, respectively. Willow left unharvested for the 30years would result in net emissions of 9.4 units. From this, it can be seen that perennial andannual bioenergy C4 crops are the most effective at sequestering carbon, trees with growthtime constants greater than 50 years being better than C3 crops bioenergy, such as SRC willowbiomass, with a growth time constant of 10 years.

Land as a Limiting Factor

There is a limited availability of suitable land for conversion to grow bioenergy feedstockscaused by competition for other purposes such as the production of food, fiber, wood, andecosystem services. Thus, it is important that the net energy yield of these feedstocks ismaximized. This net energy should be the gross energy of the fuel produced minus the energycost of production. The starting point for this analysis is finding crops that give the maximumyield of useful products. Crop yields depend on soil conditions, water availability, and climatewhen the optimum agrometric management is used. Thus, different crops will be more suitablein different areas. As an example, the yields of various crops suitable for production, taken fromEurostat, is shown for European countries and the wide variation in yields can be observed inTable 12.1.

Soil Emissions

Quantitative data and evidence for changes of soil organic carbon (SOC) with agriculturalpractices have been acquired from soil analysis from long-term, field-scale farm experiments(Smith et al., 2000), some of which have been ongoing for 150 years, especially in Europeand the United States. Initially, these experiments were designed to see how soil fertility couldbe changed to increase crop yields with various types of fertilizers and farm management.These experiments have recorded changes in SOC from land-use change as some of thesesites had been used for arable agriculture for many centuries prior to the start of the cropexperiments, as in Rothamsted (Poulton et al., 2003). Others had been natural ecosystemslike the Morrow Plot experiments, established on previously C4 grass prairies (Odell et al.,1984). For the Morrow site, there is a 130-year time series showing the reduction in SOCto a new equilibrium which was reached in ±100 years and which suggests an exponentialdecay (e-fold) with a time constant of change of around 30 years (Odell et al., 1984). At thesame site, there are plots that show an increase in SOC from 1974 onward due to the use of

Tab

le12

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rgy

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dry

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gha

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2.9

2.4

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717

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.84.

516

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ustr

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4.5

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52.

745

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215

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813

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72.

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8.7

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327

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and

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92.

647

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Sw

itzer

land

5.9

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442

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387

388 Biofuel Crop Sustainability

Years

Initial soil carbon level Final soil carbon level

Peatland/

Wetland

Forest/woodland

Pasture/

Grassland/

MiscanthusArable land

Peatland/

Wetland

Forest/

Woodland

Pasture/

Grassland/

MiscanthusArable land

Figure 12.3. Diagrammatic representation of the change in SOC with time for a land-use change. Thenew equilibrium is reached in ±100 years which implies an e-fold time constant of change of ±30 years.

low tillage farm management on those plots. This increase has a similar time constant for theincrease. This change of equilibrium is reversible. In Rothamsted, there had been a 105-yearexperiment to convert long-term arable land to a wilderness and deciduous forest (Poultonet al., 2003; Blair et al., 2006). Fitting the published data from the Rothamsted sites (Poultonet al., 2003), the Morrow Plots (Odell et al., 1984), and the Sanborn site (Huggins et al., 1998),with an exponential growth (e-fold) curve, the best fit RMSE (p > 0.001) is achieved with atime constant of 30, 32, and 32 years, respectively.

Guo and Gifford (2002) reviewed 74 publications and tabulated how the SOC changed withland-use change from a high SOC stock use (peat, forest, woodland, wetlands, or grassland) toa low carbon stock land use (arable land) and vice versa. Changes in agricultural managementpractices such as less tillage, manure fertilization in lieu of chemical fertilizers, or incorporatingstraw and crop residue in the soil increase SOC, and increasing tillage and reducing organicadditions to the soil reduce SOC (Smith et al., 2000). However, if no such changes are made,then the SOC remains constant. This process is illustrated in Figure 12.3.

Reductions in SOC that result in CO2 emissions to the atmosphere also release nitrogencompounds that can result in N2O emissions. However, if the same land management systemis used or the same natural ecosystem is maintained, then the soil carbon is in equilibrium andthere is no net emission of carbon and the photosynthetic input balances the soil respiration(Smith et al., 2000). So in the case of bioenergy derived from food crops, if there is no land-useor management change and the same intensive cropping system is used to maintain high cropyields, there will be no SOC changes relative to their cultivation for food crops.

The concern regarding using arable land for growing bioenergy crops, either food or second-generation dedicated bioenergy crops such as perennial grasses and SRC woodland, is that thearable land is taken out of food production. As the world’s population is growing and there isa general expectation and ambition to increase the consumption of animal protein and a widervariety of vegetables, the area of land required to grow food satisfy this diet will increase.This will occur even if crop yield is increased to maximize the efficiency of land use. So thecompetition will be between land used for food and land used for energy crops. Mark Twainsaid, “Buy land as they are not making it anymore”; it is a fixed resource, so it is inevitable that

12 Biofuel Crops and Greenhouse Gases 389

0 5 10

Years

0

20

40

60

80

100

SO

C, M

g h

a–1

120

140

160

180

15 20

Misc all

Init SOC 30

Init SOC 60

Init SOC 120

Init SOC 150

Misc kahle

Figure 12.4. Plot of SOC measured in Miscanthus trial sites in Germany, Denmark, and Irelandplotted against the length of time under Miscanthus (�). Time series from Kahle et al. (2001) is plotted(•). In addition four curves representing the exponential change from initial SOCs of 30, 60, 120, and150 Mg C ha−1 to the assumed natural equilibrium level of 100 Mg C ha−1 with a time constant of30 years are plotted.

if more land is used for bioenergy, then more land will be converted from natural grasslandsand forest to satisfy both the food and fuel need of the world population. This can lead to theexporting of emissions by one country converting food-producing land to grow energy crops,with a GHG saving, to another that converts natural habitats to arable for food production thatis eaten by the country growing the bioenergy feedstock. This is not currently considered ininternational GHG accounting protocols.

If arable land with a low soil carbon is converted to forest to be used for bioenergy, thenthe soil carbon will increase—likewise if converted to perennial grasses like Miscanthus or toshort rotation coppicing of species like willow poplar or eucalyptus. Recent research into soilcarbon changes under Miscanthus plots has demonstrated this.

As seen in Figure 12.4, the experimental SOC measurements, made on European Miscanthustrial sites, fall within the envelope created by the theoretical curves of SOC changes betweeninitial SOC levels of 30 and 150 to equilibrium of ±100 Mg C ha−1 with a time constant of ±30years. The German trial points from Kahle et al. (2001) (annotated as “Misc Kahle”) fall onthe curve that suggests that the SOC is increasing from an initial 60 to an equilibrium level ofaround 100 Mg C ha−1. The SOC level observed at the long-term C3 grassland control plot atthe same site is 60 Mg C ha−1, which had been C3 pasture for centuries before the experimentbegan and was presumed to be at its equilibrium level. To check this, the Kahle et al. (2001)time series of SOC measurements made on Miscanthus trial and the C3 control plots weretested (Figure 12.5) using a student t test and linear regression for significant differences ortrend versus time.

The linear regression shows an increase in SOC with time on the Miscanthus plot R2 =0.57 and a constant value for C3 grass. The student t test indicates a significant difference(p = 0.008) between the two sets of measurements. The available data, while insufficient torigorously test statistically, is suggestive of a trend toward a higher equilibrium level of SOCfor the Miscanthus crop of around 100 Mg C ha−1 on this site with a sandy loam soil, and thatMiscanthus SOC levels are higher than C3 levels. However, data from Schneckenberger and

390 Biofuel Crop Sustainability

30

10

20

30

40

50

60

70

80

90

100

5 7

Plantation age (years)

Miscanthus

C3 grass

Linear(Miscanthus)

Linear (C3 grass)

Soil

org

anic

carb

on, (M

g h

a–

1)

9

Figure 12.5. Soil organic carbon for both Miscanthus trial and the associated C3 grass controls plottedagainst time from land-use change from C3 to Miscanthus. Plot shows a constant C3 SOC value and anincreasing Miscanthus SOC value.

Kuzyakov (2007) on other sites shows no significant SOC difference between Miscanthus andC3 grasses on both sandy and loamy soils.

More recent work by Dondini et al. (2009) on a site in Carlow, Ireland demonstrated asimilar equilibrium level for Miscanthus plot SOC under temperate climate conditions whenexperimental results were compared to the model (RothC) predictions (Figure 12.6).

From the available limited published data, it seems that the equilibrium SOC for Miscanthusplantations is between 100 and 120 Mg ha−1, similar to natural perennial grasslands, so anyconversion from arable land will have a short-term (∼30 years) carbon sequestration effect.Work with SRC willow indicates a similar benefit.

Forest rothC

Arable rothC

Arable data50

19

64

19

66

19

68

19

70

19

72

19

74

19

76

19

78

19

80

19

82

19

84

19

86

19

88

19

90

19

92

19

94

19

96

19

98

20

00

20

02

20

04

20

06

20

08

60

70

80

90

100

Mg

C h

a–

1

110

120

130

Arable with no input rothC

Year

Miscanthus rothC

C3-C data

Miscanthus data

Figure 12.6. Soil C content of different plantations during a period time of 44 years at Carlow,Ireland. Plot shows progression of SOC from forest equilibrium to arable conversion in 1974, conversionto Miscanthus in 1995 with the control plot continuing as arable. Differentiation of original carbon fromthe C3 arable and forest and the C4 Miscanthus is by C isotope analysis.

12 Biofuel Crops and Greenhouse Gases 391

Use of Fertilizers

It is important to consider land-use change when evaluating the GHG neutrality of bioenergysystems and include the net carbon and nitrogen budget, but in this LCA we do not consider N2Oemissions for SOC changes. However, when chemical nitrogen fertilizers are used in the cropmanagement, then nitrous oxide (N2O) emissions due to denitrification are calculated usingthe default tier 1 IPCC emission factor for N2O emissions from N fertilizer application (IPCC,2007). In addition, energy used and N2O released to the atmosphere during the manufacture ofthe chemicals is considered (Patzek, 2008). The N2O emission associated with the manufactureof chemical fertilizers is normally accredited to the chemical industry in GHG emissionestimates (IPCC, 2007) and in the LCA (Shapouri et al., 2002), but as fertilizer is only used asa crop nutrient, this is incorrect as the emissions would not occur if the crops were not grown.N2O is produced primarily from the microbial processes of nitrification and denitrificationin the soil. In well-aerated conditions, N2O emissions from nitrification of ammonium-basedfertilizers can be substantial. In wet soils where aeration is restricted, denitrification is generallythe source of N2O. Research has also shown that a number of individual factors are controllersof nitrification, denitrification, and N2O emissions. Such factors include soil water content,temperature, nitrate or ammonium concentration, available organic carbon and pH. Increasesin the amount of N added to the soil generally increases N2O emissions. The temporal patternof N2O emissions following fertilization is generally that of a large efflux of N2O occurringfor a short time (few weeks after fertilization). After this time, emission rates are reduced tofluctuate around a low baseline level independent of the amount of fertilizer applied (Mosieret al., 1982).

Crop Management

The first part of LCA is to determine the energy used and the GHG emitted during thecultivation, farm management, transportation, crop drying, and other conditioning for eachbioenergy system feedstock. These costs are divided into those annual fixed costs that relateto a hectare of land each year, including crop establishment costs for perennial Miscanthusand SRC willow plantations which are amortized over the life of the plantation, and thosethat relate to the feedstock yield per hectare, such as fertilizer and transportation costs. Thisenables the LCA to account for the variable yields in each country.

Food Crops Grown for Energy

Based upon the mean yield of each crop per country, the carbon and energy cost of farming thefood crops grown for energy are calculated considering that they are grown on arable land withthe same crop management as if grown for food. The SOC is considered to remain constantas current arable land only is considered for energy crops. Soil and the plant respiration areexplicitly ignored at this point and the normal inclusion of roots and plant residue is consideredto maintain the SOC at a constant level. Here we calculate the emissions of food crops usedfor bioenergy such as wheat, maize, oilseed rape (OSR), sugar beet, green maize as food cropsby using the parameters for farm management from St. Clair et al. (2008), who used datafor energy costs of mechanical interventions, herbicide, biocide, insecticide, fungicide, andenzyme carbon and energy costs from (2004). Conventional intensive management with con-ventional mouldboard plough tillage is considered. The energy, carbon, and GHG costs for

392 Biofuel Crop Sustainability

human work days, seed production, machinery manufacture, and fertilizer manufacture usingparameters from Patzek (2008) are also included. This includes the N2O emission from den-itrification using the IPCC default factor of 1% (1 kg N2O-N per 100 kg of N in fertilizerapplied) for arable land, and including the CO2 emissions and N2O emission factor from themanufacture of the fertilizer ammonium nitrate of 2%.

All transportation around the farm and transport to the biofuel/energy processing plant isconsidered. The processing plant is considered to be within 30 km. The energy and GHG costsof farming each crop is broken into a fixed annual cost for the crop and one that is related to theyield. Fertilization is considered as for the intensive chemical fertilization case with only cropresidue being left in the field for wheat, OSR, and sugar beet. For grain maize, stover is left onthe field and incorporated (Patzek, 2008). For green maize, the anaerobic digester residue isreturned to the field as manure, reducing the requirement for chemical fertilizers by 50% (Gerinet al., 2008). The carbon cost of production energy is 21 g C MJ, considering oil is used asthe fuel.

SRC Willow

The SRC willow LCA uses overbark roundwood yields (proxy for SRC willow) using SRCcrop management to optimize production in terms of fertilization with a harvest every 3 years.The biomass fuel is considered to be used in a co-fired coal power station with a mean transportdistance of 200 km. This includes the N2O emission from denitrification using the IPCC defaultfactor of 1% for arable land and including N2O emission factor from the manufacture of thefertilizer ammonium nitrate of 2% (Patzek, 2008). Soil carbon emissions are considered basedupon the conversion of arable land to SRC plantations using factors from Hillier et al. (2009).The plantation life is considered to be 20 years. The carbon cost of production energy is 21 gC MJ, considering oil is used as the fuel.

Miscanthus

The LCA uses modeled yields from MiscanFor (Hastings et al., 2009a,b) to calculate thecrop management energy, and the carbon cost is based upon three scenarios: (1) used as abiomass fuel with current crop management at a large-scale coal power station with a meantransportation distance of 200 km; (2) used locally with current crop management as a biomassfuel or other bioenergy system feedstock with a mean transportation distance of 30 km; and(3) used locally with future potential crop management. The carbon cost of production energyis 21 g C MJ, considering oil is used as the fuel. Current management practice is cropestablishment by micropropagation into a standard arable crop seedbed, harvested each yearfollowing the second/third growing season in the spring after ripening (allowing translocationof nutrients to the rhizome and reduction in moisture content from 50% to about 30%), furtherswath drying in the field, chipping (large baling is probably best), and transportation to theplace of use. Fertilizers are applied to replace nutrients removed at the harvest. The plantationlife is considered to be 15 years. This management scenario is considered for both co-firingremotely and use locally as a furnace fuel for combined heat and power. As micropropagationis energy intensive, the third scenario considers that this is replaced by rhizome propagation,which is becoming the new standard. This case is only considered for local furnace fuel use.These management costs are summarized in Table 12.2.

12 Biofuel Crops and Greenhouse Gases 393

Table 12.2. Summary of on-farm energy and carbon costs of production.

Energy Greenhousecost gas emissions

Transportdistance GJ ha−1 GJ kg C ha−1 kg C

Feedstock Crop management (km) yr−1 Mg−1 yr−1 Mg−1e

Wheat Intensivea 20 9.97 1.40 219 155Barley Intensivea 20 9.97 1.40 219 155Maize Intensivea 20 10.30 1.14 227 125Sugar beet Intensiveb 20 10.88 0.43 239 19Oil seed rape Intensivea 20 10.40 2.34 229 267Willow SRC 3 yrsc 200 2.51 1.68 55 75Willow SRC 3 yrsc 20 2.51 0.57 55 50Green maize Intensived 20 9.60 0.10 211 11Miscanthus Micropropagationc 200 9.07 1.72 199 81Miscanthus Micropropagationc 20 9.07 0.61 199 57Miscanthus Rhizome propagationc 20 5.64 0.61 124 57

aHarvest weight with 14% moisture.bHarvest weight with 75% moisture and 17% sugar.cDry weight.dHarvest weight green.eCO2 equivalent C with N2O equivalent to 296 × CO2.

Conversion Processes and Cost

External energy cost of production for each bioenergy system of converting the feedstock toa useful fuel is calculated based upon published conversion costs. The GHG cost of usingthis external production energy is calculated using the published carbon intensity (CI) of theassociated fuel used. For electricity, we use the current (2004) CI for UK grid sourced energy,which is 134 g CO2 equivalent C MJ−1, and consider the current mix of coal, gas, nuclear,hydro, and wind generation.

Biomass Fuel

Biomass fuels require a dryness of around 15%. In this study, a combination of field dryingto 30% and then undercover storage at the generation plant with air drying is considered.The external energy requirement for drying is considered in the fuel conversion cost. Thetransportation and chopping costs are considered in the farm management component of theLCA. The gross energy at the furnace is calculated considering energy intensity of Miscanthusand SRC willow of 18 GJ Mg−1 of dry matter and subtracting the latent heat of 30% moisture.The net energy is calculated as the gross energy minus the energy used in the feedstockproduction.

Ethanol

Ethanol yields from grain were calculated using a conversion factor of 400 l of ethanol perMg (Patzek, 2008) of dry grain. This includes corrections for losses of 12% of the theoreticalthermodynamics and mass balance conversion to ethanol in the fermentation process. For each

394 Biofuel Crop Sustainability

country, the grain with the highest yield was identified to calculate the maximum possibleethanol yield. Straw, maize stover, and draft are considered by-products with no energy or GHGimpact for on-farm use. Ethanol yields from sugar beet were calculated using the conversionfactor of 105 l of ethanol per Mg of fresh beet, considering a 17% sugar content and a moisturecontent of 75%. Koga (2008) uses a similar conversion factor. The crop parameters used arein agreement with the published crop standards from British Sugar (2008) and due to thehighly industrialized nature of the sugar beet industry in Europe and the large investment inboth breeding and crop to management system to maximize the sugar yield per hectare (Scottand Jaggard, 2000), this represents the quality standard for the EU sugar beet crop. As isstandard practice, the beet tops are ploughed in each year. Potatoes were also considered, butas they have a similar geographic distribution to sugar beet (Tuck et al., 2006) but with loweryields, they were not investigated further. The energy cost of the production of bioethanol is15 GJ kl−1. The carbon cost of production energy is 21 g C MJ−1, considering oil is used asthe fuel.

Biodiesel

For first-generation feedstocks for biodiesel, the oil crops grown in Europe that could be usedwere linseed, sunflower, OSR, hemp, castor, field mustard, or olive; of these, OSR is the mostwidely gown with the highest yield of oil per hectare in Europe. Olive oil was not considered asa biofuel as Europe does not produce a surplus of this valuable food oil. Sunflower is restrictedto Southern Europe at the moment and has a high yield in some climates, so may becomemore used with climate change (Tuck et al., 2006). The conversion factor for biodiesel yieldsfrom OSR is 363.5 l of biodiesel per Mg of rape seed (Karaosmanoglu et al., 1996; Petersonand Hustrulid, 1998; Rathke et al., 2006). The OSR stem and oil seed cake are consideredas by-products with no energy and GHG impact for on-farm use. The energy cost of theproduction of biodiesel is 6.5 GJ kl−1. The carbon cost of production energy is 21 g C MJ−1,considering oil is used as the fuel.

Biogas

Anaerobic digesters have been used for some time on a large scale at sewage plants to producebiogas for heating and electricity generation. This technology is also used on farms to producebiogas from animal excreta and other farm wastes. This biogas has been used for heating ormicrogeneration on the farm and the residue incorporated in the land as an organic fertilizer.To increase the organic feedstock to enable farm plants to export energy commercially, greenmaize is commonly used (Gerin et al., 2008). Green maize use as a feedstock for biogas isanalyzed using a conversion factor of 3.87 GJ gas gross energy per tonne of green maize drymatter. The external energy cost of producing this gas is 5% of the gross energy. The carbon costof production energy is 21 g C MJ−1, considering oil is used as the external fuel. Miscanthusis also considered as an anaerobic digester feedstock with the same conversion factors as forgreen maize, with similar treatment for the residue (Gerin et al., 2008). However, this wouldentail cutting Miscanthus green, before the repartition of the nutrients to the rhizome. Thiswill have an impact on the amount of fertilizer that needs to be added each year to balance theharvest offtake. However, this is offset using the digester residue as a fertilizer and making upthe difference with chemical fertilizers.

12 Biofuel Crops and Greenhouse Gases 395

Cellulosic Ethanol

The production of ethanol from a cellulose feedstock is a process that has been used com-mercially since the First World War (Harris et al., 1945; Saeman, 1945). The first attempt atcommercialization in Germany in 1898 produced 76 l Mg−1 wood, based upon a process thathydrolyzed the cellulose to glucose using dilute acid. This process was improved successivelyduring the two world wars and by 1945 it could produce 211 l Mg−1. During the First WorldWar, a single stage dilute sulfuric acid process was developed in the United States, but itonly produced 105 l Mg−1. However, the impetus of the Second World War allowed furtherdevelopment to increase this yield to 211 l Mg−1, with the ethanol being used in the productionof synthetic rubber. After the war, the plants were closed as they were not profitable in a freemarket, freed from the constraints and needs of total war.

Global warming and the need to reduce GHG emission, plus the increasing shortage of crudeoil, which has driven up energy prices, has helped to create both the political and economicclimate in which cellulosic ethanol can be reconsidered as a practical option. Several pilotplants are already in operation and commercial scale production target dates have been set fora number of plants in construction. The technology used in these cellulosic ethanol plants issteam explosion/acid/enzyme extraction of the glucose from the biomass, then fermentation.They currently convert biomass to ethanol at the rate of 280 l Mg−1 biomass (Sokhansanjet al., 2002; Pimentel and Patzek, 2005).

This LCA for Miscanthus as a feedstock for cellulose ethanol considers the same crop yieldsand management as for its use as biomass fuel with the processing plant a mean 30 km distantfrom the source of the crop. Only the current practice crop management case is considered. Anethanol yield, same as corn stover, of 280 l Mg−1 (Foutch et al., 1980; Hettenhaus and Wooley,2000; Sokhansanj et al., 2002) is used in the model as well as an energy cost of celluloseethanol production of 15 MJ l−1 (Pimentel and Patzek, 2005). The carbon cost of productionenergy is 21 g C MJ−1, considering oil is used as the fuel.

Biorefined Biodiesel

The synthesis of liquid hydrocarbons from coal is an old technology developed by two Germanresearchers Franz Fischer and Hans Tropsch in 1926 (US Patent, 1930). The Fischer–Tropschprocess (FTP) entails gasification of the coal by partial oxidization, hydrolyzation by theaddition of steam, and then recombination of the resultant CO and H in the presence ofcatalysts such as the transition metals: cobalt, iron, and ruthenium or nickel to form liquidhydrocarbons. This technique was developed and used by both Japan and Germany duringthe Second World War but its use decreased thereafter due to the free trade in petroleumproducts. A few companies continue to use the process commercially, SASOIL in SouthAfrica to overcome the embargo during the apartheid years, and Shell in Bintulu used theprocess to produce low sulfur diesel from natural gas. The latter was a pilot gas-to-liquidcommercial project (Price Waterhouse Coopers, 2003), using the catalytic recombination partof the Fischer–Tropsch process (FTP).

This process can use any feedstock containing carbon and hydrogen and is also usedto upgrade tar from tar sands, to produce oil from wood, or biodiesel from livestock orother organic waste. Gasification of waste products such as black liquor and oils from paperproduction is commonly used for steam, heat, and power generation at paper mills (Vattenfall,2005). Recently, an FTP has been added to a waste gasification in a plant in Finland to produce

396 Biofuel Crop Sustainability

Table 12.3. Summary of feedstock conversion rate, fuel energy intensity costs of conversion.

Feedstock Fuel energy Conversionconversion rate intensity energy cost

Feedstock. Biofuel. Unit Value Unit Value Unit Value

Wheat a Ethanol l Mg−1 400 MJ kg−1 35 MJ l−1 15Barley a Ethanol l Mg−1 400 MJ kg−1 35 MJ l−1 15Maize a Ethanol l Mg−1 400 MJ kg−1 35 MJ l−1 15Sugar beetb Ethanol l Mg−1 105 MJ kg−1 35 MJ l−1 15Oil seed rapea Biodiesel l Mg−1 363.50 MJ kg−1 43.70 MJ l−1 6.50Willowc Biomass pu 1 MJ kg−1 18 MJ kg−1 0.82e

Green maized Biogas GJ Mg−1 3.87 MJ kg−1 55.70 Percentageenergy

5g

Miscanthusc Biomass pu 1 MJ kg−1 18 MJ kg−1 0.82e

Miscanthusc Biogas GJ Mg−1 3.87 MJ kg−1 55.70 Percentageenergy

5g

Miscanthusc Cellulosicethanol

l Mg−1 280 MJ kg−1 35 MJ l−1 15

Miscanthusc Biorefinedbiodiesel

l Mg−1 199 MJ kg−1 43.70 MJ l−1 f

aHarvest weight with 14% moisture.bHarvest weight with 75% moisture and 17% sugar.cDry weight assumes 100% conversion, conversion energy cost is latent heat of 30% moisture.dHarvest weight green.eLatent heat of 30% moisture.fConversion enegy cost included in conversion rate as all energy comes from feedstock.g5% of gas is used on site for heating and pump energy.

biodiesel. In Germany, a pilot commercial plant to produce biodiesel from wood and cellulose-rich crops has been commissioned by CHOREN Industries in Freiberg (Blades et al., 2006) inconjunction with Audi and Volkswagen. The plant has been used with a variety of biologicalfeedstocks including wood, straw, and Miscanthus. An LCA was conducted on this plant (Baitzet al., 2004) and reported that if all energy used in the plant was derived from the biomassinput, the ratio of conversion of biomass dry matter to biodiesel was 199 l Mg−1 dry vegetablematter. This gives an effective biodiesel energy output of 5.98 GJ Mg−1 of dry matter.

A summary of the conversion rates is shown in Table 12.3.

LCA Methodology and Boundary Conditions

A full LCA is required to evaluate the sustainability of a bioenergy system and can be dividedinto three parts: farming the crop, turning the crop into fuel, and final energy conversion. Partof the energy input and GHG emissions comes from the farm management strategy employedfor land preparation, planting and seeding, fertilization, pest and weed control, harvesting,storage, drying, preparing and processing the bioenergy feedstock as well as the final usein energy conversion. Sustainability of bioenergy systems requires that the energy used toproduce the fuel is less than the energy harvested and that the GHG cost is less than theequivalent fossil fuel it replaces (Figure 12.7).

Here we present an analysis of the carbon and energy cost for farming the energy cropsconsidering that they are grown on arable land with the same crop management as if grown for

12 Biofuel Crops and Greenhouse Gases 397

Greenhouse gas and energy balance

Photosyntheticcarbon

Transport and processing

Fertilizer, herbicide, etc.

Plough and harvest

N2O denitrification

CO2 plant respiration

CO2 soil decomposition

Figure 12.7. Sustainability balance for bioenergy systems.

food. The SOC is considered to remain constant, so soil respiration is explicitly ignored andthe plant respiration is implicitly included in the harvest yield. The study is made for wheat,maize, OSR, sugar beet, green maize, and roundwood (proxy for SRC willow) plantations,and a perennial grass Miscanthus. We consider the yields for each European country, takenfrom Eurostat, except for Miscanthus which uses modeled results from Hastings et al. (2008)which are summarized in Table 12.1.

This comparative study uses the parameters for farm management from St. Clair et al. (2008),who used data for energy costs of mechanical interventions from Lai (2004) and herbicide,biocide, insecticide, fungicide, and enzyme carbon and energy costs from Lai (2004). Weinclude the energy, carbon, and GHG costs for human work days, seed production, machinerymanufacture, and fertilizer manufacture using parameters from Patzek (2008). This includesthe N2O emission from the manufacture of the fertilizer, ammonium nitrate. All transportationaround the farm and transport to the biofuel/energy processing plant is considered. The energyand GHG costs of farming each crop is broken into a fixed annual cost for the crop and one thatis related to the yield. Fertilization is considered as for the intensive chemical fertilization case,with only crop residue being left in the field for wheat, OSR, and sugar beet. For grain maize,stover is left on the field and incorporated (Patzek, 2008). For green maize, the anaerobicdigester residue is returned to the field as manure, reducing the requirement for chemicalfertilizers by 50% (Gerin et al., 2008). The feedstock production costs are summarized inTable 12.2 and the conversion costs are summarized in Table 12.3.

Three metrics are considered for the comparison of “sustainability” of bioenergy systems.The first is the net yield of energy per hectare or land energy intensity (LEI), the second is CIin terms of g C equivalent GHG emissions per MJ of fuel energy, and the final one is the ratiobetween energy in the fuel and the energy used in production or energy use efficiency (EUE).The resulting metrics for ethanol systems considering feedstocks of wheat, maize, sugar beet,and cellulosic ethanol from Miscanthus are listed for each European country in Table 12.4.

Biodiesel systems using pressed oil seed rape, and biorefined Miscanthus and SRC willoware presented in Table 12.5.

Tab

le12

.4.

Ene

rgy

use

effic

ienc

y(E

UE

),ca

rbon

inte

nsity

(CI),

and

net

ener

gyyi

eld

per

hect

are

for

bio

etha

nolw

ithfo

urfe

edst

ocks

.

Whe

atM

aize

Sug

arb

eet

Mis

cant

hus

cellu

losi

c

Net

yiel

dN

etyi

eld

Net

yiel

dN

etyi

eld

EU

EC

Ien

ergy

EU

EC

Ien

ergy

EU

EC

Ien

ergy

EU

EC

Ien

ergy

Eou

t/E

ing

CM

J−1

GJ

ha−1

Eou

t/E

ing

CM

J−1

GJ

ha−1

Eou

t/E

ing

CM

J−1

GJ

ha−1

Eou

t/E

ing

CM

J−1

GJ

ha−1

Alb

ania

0.87

38−4

0.95

33−2

1.05

24.1

93.

521.

2323

.90

20.1

2A

ustr

ia1

350

1.14

2911

1.14

22.5

519

.43

1.22

24.0

118

.42

Bel

gium

1.09

336

1.17

2915

1.14

22.4

920

.50

1.20

24.3

114

.84

Bos

nia

and

Her

zego

vina

0.70

44−7

0.80

38−5

1.24

23.7

522

.66

Bul

garia

0.87

38−4

0.93

34−2

0.95

26.4

4−2

.51

0.75

35.1

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.98

Cro

atia

0.94

36−2

1.03

312

1.08

23.6

46.

601.

2423

.76

22.5

8C

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s0.

7243

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zech

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ublic

0.99

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1.08

305

1.11

23.0

511

.70

Den

mar

k1.

0733

41.

1322

.76

15.6

41.

1125

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5.09

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onia

0.80

40−5

Finl

and

0.91

37−3

1.06

23.8

75.

12Fr

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1.06

334

1.13

299

1.15

22.3

424

.41

1.21

24.1

117

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man

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0733

51.

1329

91.

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1329

101.

1322

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17.9

11.

1624

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9.34

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0.95

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1.05

313

1.10

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39.

911.

2224

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18.5

4Ic

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land

1.10

337

1.11

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1.15

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9037

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1429

101.

1123

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11.6

11.

2323

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19.9

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tvia

0.87

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1.07

23.7

55.

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nia

0.90

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0.90

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1.07

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26.

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xem

bou

rg1.

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21.

1130

71.

2024

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0.84

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1.04

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53.

221.

2223

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19.4

3M

alta

Net

herla

nds

1.09

336

1.17

2915

1.13

22.6

517

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1.18

24.6

111

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way

0.98

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Pol

and

0.93

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1.05

313

1.09

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18.

27P

ortu

gal

0.65

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1.04

312

1.14

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319

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1.23

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221

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ania

0.83

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80.

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lova

kia

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1.02

311

1.09

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58.

811.

2124

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16.6

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love

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0.97

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1.09

305

1.10

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991.

2323

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21.7

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1429

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0.78

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1.09

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29.

01U

nite

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14.8

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398

Tab

le12

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(CI),

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illow

bio

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ed

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IN

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Net

yiel

den

ergy

EU

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etyi

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out/

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out/

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gC

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out/

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ania

7.50

7.94

124.

287.

717.

1634

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tria

1.86

25.4

019

.90

7.28

8.03

116.

519.

936.

5264

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Bel

gium

2.10

24.0

430

.35

6.79

8.25

100.

169.

846.

5462

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Bos

nia

and

Her

zego

vina

7.79

7.83

135.

907.

717.

1634

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Bul

garia

1.29

30.5

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941.

9216

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9.63

6.54

7.67

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6526

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8313

5.52

7.71

7.16

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chR

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8625

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mar

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4627

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and

1.45

28.7

78.

166.

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ce1.

9824

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118.

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0.61

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6.74

49.5

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erm

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2.07

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228

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6.70

8.29

97.6

710

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6.47

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878.

7575

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308.

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7.08

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6.84

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land

1.96

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5.66

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88.

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1.32

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35.

497.

487.

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tvia

1.46

28.6

28.

487.

797.

1234

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Lith

uani

a1.

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7.83

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2Lu

xem

bou

rg6.

708.

2997

.67

9.75

6.56

60.8

8M

aced

onia

1.73

26.3

215

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7.41

7.98

121.

127.

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taN

ethe

rland

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348.

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ay8.

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9042

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Pol

and

1.89

25.2

320

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7.96

7.07

36.5

0P

ortu

gal

7.67

7.88

130.

829.

266.

6852

.75

Rom

ania

1.20

31.9

83.

14S

lova

kia

1.60

27.3

411

.82

7.04

8.13

108.

189.

476.

6356

Slo

veni

a1.

7726

16.8

37.

697.

8713

1.63

8.74

6.82

45.4

4S

pai

n1.

3629

.79

6.21

7.23

8.05

114.

655.

808.

0919

.43

Sw

eden

1.82

25.6

518

.55

7.26

7.33

30S

witz

erla

nd1.

9824

.69

24.5

46.

378.

4687

.97

9.71

6.57

60.0

6Tu

rkey

1.76

26.0

416

.66

7.71

7.16

34.0

6U

nite

dK

ingd

om1.

9824

.70

24.4

75.

778.

8272

.60

9.31

6.67

53.5

6

399

400 Biofuel Crop Sustainability

Table 12.6. Energy use efficiency (EUE), carbon intensity (CI), and net yield per hectare for biogas.

Green maize Miscanthus

Net yield Net yieldEUE CI energy EUE CI energy

E out/E in g C MJ−1 GJ ha−1 E out/E in g C MJ−1 GJ ha−1

Albania 4.67 6.68 54.53 5.50 8.65 118.66Austria 7.68 4.84 153.74 5.38 8.74 111.22Belgium 7.70 4.83 154.41 5.11 8.96 95.56Bosnia and

Herzegovina5.65 8.54 129.79

Bulgaria 3.12 9.02 26.64 1.77 17.07 8.84Croatia 5.61 5.90 76.93 5.65 8.55 129.43CyprusCzech Republic 6.57 5.32 106.58Denmark 6.86 5.18 117.31 4.03 10.11 52.90EstoniaFinlandFrance 7.28 5 134.45 5.29 8.81 105.57Germany 7.53 4.89 146.24 5.06 8.99 93.17Greece 7.94 4.74 167.57 4.58 9.46 71.49Hungary 5.56 5.93 75.71 5.39 8.73 111.76IcelandIreland 0.38 59.85 −6.13 4.45 9.59 66.84Italy 8.08 4.70 175.52 5.49 8.66 117.96Latvia 5.28 6.14 68.55Lithuania 5.74 5.81 80.57Luxembourg 5.06 8.99 93.17Macedonia 5.40 6.05 71.45 5.45 8.69 115.64MaltaNetherlands 7.59 4.87 149.30 4.85 9.18 83.10NorwayPoland 7.37 4.96 138.67Portugal 5.59 8.59 124.93Romania 4.29 7.10 46.76Slovakia 5.29 6.13 68.86 5.25 8.84 103.24Slovenia 7.32 4.98 136.19 5.60 8.58 125.70Spain 7.67 4.84 153.18 5.35 8.76 109.44SwedenSwitzerland 4.87 9.17 83.88TurkeyUnited Kingdom 1.15 21.01 1.63 4.52 9.52 69.16

A comparison of using green maize and Miscanthus for the generation of biogas in anaerobicdigesters is shown in Table 12.6.

A comparison of various scenarios for the use of biomass derived from Miscanthus andSRC willow is shown in Table 12.7. Local use of Miscanthus and SRC willow in furnaces forcombined head and power or heat only are compared. For Miscanthus, we compare rhizometo vegetative propagation for local use and also for co-firing in a large power station todemonstrate the importance of transportation to the overall GHG emissions. Finally, we showthe potential impact of considering the increase on soil carbon under Miscanthus on the overallCI of the fuel.

Tab

le12

.7.

Ene

rgy

use

effic

ienc

y(E

UE

),ca

rbon

inte

nsity

(CI),

and

net

ener

gyyi

eld

per

hect

are

for

Mis

cant

hus

bio

mas

sin

four

case

s:co

-firin

g20

0km

,loc

alus

eat

20km

ofcr

opfr

omve

geta

tive

pro

pag

atio

n,lo

calu

sein

clud

ing

SO

Cch

ange

s,an

dlo

calu

sew

ithrh

izom

ep

rop

agat

ion

com

par

edto

SR

Cw

illow

.

Mis

cant

hus

co-fi

reM

isca

nthu

slo

calr

hizo

me

Mis

cant

hus

loca

lwith

soil

CM

isca

nthu

slo

cal

SR

CW

illow

loca

l

EU

EN

etyi

eld

EU

EN

etyi

eld

EU

EN

etyi

eld

EU

EN

etyi

eld

EU

EN

etyi

eld

Eou

t/C

len

ergy

Eou

t/C

len

ergy

Eou

t/C

len

ergy

Eou

t/C

len

ergy

Eou

t/C

Len

ergy

Ein

gC

MU

−1G

Jha

−1E

ing

CM

J−1

GJ

ha−1

Ein

gC

MJ−

1G

Jha

−1E

ing

CM

J−1

GJ

ha−1

Ein

gC

MJ−

1G

Jha

−1

Alb

ania

5.83

524

610

.18

426

89.

111.

8426

4.24

9.11

3.84

264.

249.

113.

4672

.25

Aus

tria

5.77

523

110

.06

425

28.

96−0

.28

248.

328.

963.

8824

8.32

10.6

43.

1513

3.72

Bel

gium

5.61

520

09.

764

218

8.58

−3.0

521

4.81

8.58

3.99

214.

8110

.59

3.16

130.

40B

osni

aan

dH

erze

govi

na5.

925

268

10.3

44

291

9.32

0.40

288.

079.

323.

7823

8.07

9.26

3.46

72.2

5

Bul

garia

279

927

4.66

633

3.37

−6.1

129

.25

3.37

7.95

29.2

58.

393.

7052

.32

Cro

atia

5.91

526

710

.34

429

19.

311.

2328

7.28

9.31

3.78

287.

289.

263.

4672

.25

Cyp

rus

4.62

5.83

14.1

0C

zech

Rep

ublic

10.5

93.

1613

0.40

Den

mar

k4.

906

115

8.45

412

77.

03−7

.23

123.

527.

034.

5512

3.52

10.4

13.

2011

8.77

Est

onia

8.72

3.60

58.9

6Fi

nlan

d8.

563.

6555

.64

Fran

ce5.

725

220

9.96

424

08.

83−1

.19

236.

238.

833.

9123

6.23

10.1

23.

2610

3.82

Ger

man

y5.

585

195

9.71

421

38.

52−4

.62

209.

718.

524

209.

7110

.77

3.13

143.

69G

reec

e5.

286

152

9.14

416

77.

831.

1916

3.30

7.83

4.23

163.

304.

915.

5615

.77

Hun

gary

5.77

523

210

.07

425

38.

970.

4624

9.48

8.97

3.88

249.

489.

903.

3093

.85

Icel

and

Irela

nd5.

206

142

8.99

415

77.

65−9

.08

153.

367.

654.

2915

3.36

9.98

3.29

97.1

7Ita

ly5.

835

245

10.1

74

266

9.10

0.83

262.

749.

103.

8426

2.74

8.20

3.76

48.9

9La

tvia

9.32

3.44

73.9

1Li

thua

nia

9.53

3.39

80.5

6Lu

xem

bou

rg5.

585

195

9.71

421

38.

52−2

.02

209.

718.

524.

0020

9.71

10.5

43.

1712

7.08

Mac

edon

ia5.

815

240

10.1

34

261

9.05

−1.9

625

7.77

9.05

3.85

257.

779.

263.

4672

.25

Mal

taN

ethe

rland

s5.

465

175

9.47

419

28.

23−8

.54

188.

168.

234.

1018

8.16

10.3

23.

2111

3.79

Nor

way

9.77

3.33

83.8

7P

olan

d9.

433.

4177

.24

Por

tuga

l5.

885

258

10.2

74

281

9.23

−4.0

227

7.66

9.23

3.81

277.

6610

.26

3.23

110.

47R

oman

iaS

lova

kia

5.69

521

59.

924

235

8.77

0.18

231.

258.

773.

9323

1.25

10.3

83.

2011

7.11

Slo

veni

a5.

895

2.60

10.2

84

2.83

9.24

−127

9.32

9.24

3.80

279.

329.

943.

3095

.51

Sp

ain

5.75

522

310

.03

424

38.

92−2

.95

244.

518.

923.

8924

4.51

7.77

3.91

42.3

5S

wed

en8.

943.

5463

.95

Sw

itzer

land

5.47

517

69.

494

193

8.25

4.09

189.

828.

254.

0918

9.82

10.5

13.

1712

5.42

Turk

ey9.

263.

4672

.25

Uni

ted

Kin

gdom

5.24

614

79.

074

162

7.75

−4.1

815

8.33

7.75

4.26

158.

3310

.29

3.22

112.

13

401

402 Biofuel Crop Sustainability

From the LCA it can be seen that in the European context, the highest energy yield perhectare is achieved by using biomass from perennial grasses or SRC wood. Biomass energysystems also produce the lowest CI and the highest EUE. Local use is important as it minimizesGHG emissions, which are substantially lower than that of coal (33 g C MJ−1) or gas (16 g CMJ−1), even if transported 200 km to a large-scale power station. So, this seems to be the bestoption to reduce GHG with European-grown bioenergy feedstocks.

European ethanol system produces the lowest energy yield per hectare, EUE’s are close tounity, and in all cases with current technology the CI is larger than that of petrol (19) so thatthere is no net GHG saving. For biodiesel, OSR has the lowest energy yields with a CI higherthan diesel. However, the biorefined biodiesel, either from perennial grasses or wood, has alower CI (9) than diesel (22) and an EUE of 4–9, and so does have a net GHG benefit. Biogas,when using feedstocks from high-yielding countries, gives relatively high energy yields, a lowerCI than gas, and a high (4–8) EUE, so in counties with high yields it is a GHG saving option.

GHG Emissions from Indirect Land-use Change

So far in this chapter, we have considered energy crops that could be grown in Europe foruse in Europe and looked at the different emissions resulting from the yields achieved and thefarming methodologies used in each European country. We have considered the case whereagricultural land that is not needed to grow food in Europe is converted to grow bioenergycrops. This is possible as agronometric practices and crop varieties have been optimized inEurope so that sufficient food and fiber can be grown on less land to satisfy the needs of the EUand led to 10% of arable land to be “set aside” to eliminate overproduction. However, the pushto increase the use of bioenergy in the EU in order to reduce GHG emissions and to enhanceenergy security have increased the bioenergy feedstock requirements beyond that which canbe produced on the excess land (Don et al., 2012). The EU’s ambitious objectives for biofuelshave led to an increase in ethanol production from sugarcane in Brazil, palm oil in Africaand Asia, and soya oil production generally. In the United States, the rapid increase in the useof maize to produce ethanol has reduced the amount of maize available for export and thisincreases the international commodity prices, causing hardship and unrest in several countiessuch as Mexico in 2008 (Valentine et al., 2011). This pressure on the demand side has led to anincrease in land conversion to grow displaced food production and the bioenergy feedstocks.This direct and indirect land-use change increases GHG emissions (Searchinger et al., 2008;Popp et al., 2012). In addition, if subsistence farmland is converted to intensively growbioenergy feedstock and additional foodstuffs, this will lead to an increase in GHG emissionsper hectare (Erb et al., 2008, 2012a,b; Popp et al., 2012). Flynn et al. (2012) demonstrated thatthe increase in GHG due to converting land to grow crops such as rape seed, oil palm, and soyain all continents considering the soil type and original land use was considerable. Thus, indirectland change impacts must be given due consideration while formulating bioenergy policies.

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