land use carbon implications of a reduction in ethanol

7/30/2019 Land Use Carbon Implications of a Reduction in Ethanol

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future science group 27ISSN 1758-300410.4155/CMT.11.79 2012 Future Science Ltd

Over the past 10 years, commodity grain prices havedoubled, reaching their highest levels in over 30 years[101]. The rise in prices culminated in the ood pricespikes o 2008 and 2011, where ood riots eruptedin 40 countries. Although the relative increase inood prices in the USA was less severe than in poorernations, the impact o the price spikes has causedoutcry rom interests as diverse as the animal eedlotindustry and the ood security community. From 2007to 2011, meat, milk and egg prices in the USA haveincreased by over 20% and livestock eed costs haverisen by 30% [1]. The number o Americans participat-ing in the Supplemental Nutrition Assistance Programhas increased by 69%, rom 26.3 million in 2006 to44.6 million in 2011. Individual benets are tied to

the ood price index; thereore, increases in ood priceshave contributed to Supplemental Nutrition AssistanceProgram governmental costs swelling to US$60 billionper year [2,102].

Although studies have pointed to a number o ac-tors leading to the increased ood prices, the ethanolindustry, whether deservingly or not, is seen as the majoractor behind the price spikes [3,4]. Several recent studieshave contributed to the poor public opinion o ethanol

by concluding that ethanol is neither a net energysource nor a net reducer o carbon emissions [5,6]. Theimpact o these research reports combined with recentspikes in commodity prices has led to erce politicaleorts to reduce or eliminate subsidies or ethanol [7,8].Opponents o ethanol subsidization won a signicantbattle with Congress recently, voting to eliminate ed-eral blenders tax credits and ethanol import taris [9].Ethanol proponents have deended continued subsidiz-ation o corn grain ethanol as a way to support the bio-uel industry until lignocellulosic second-generationbiouels can be developed. Lignocellulosic ethanol relieson woody, nonood eedstocks, which are consideredto have better net energy returns than rst-generationcorn-grain ethanol. I second-generation biouels can

be developed, they would simultaneously contribute toboth osetting dependence on oreign oil and reduc-ing carbon levels. Yet technical hurdles have stagnateddevelopment o second-generation biouels, orcing theUS EPA to reduce the mandated quantities set out in the2007 expansion o the Renewable Fuels Standard or thesecond year in a row[10]. A recent analysis o ongoingeorts to produce second-generation uels concludesthat the industry will ail to contribute substantially to

Carbon Management(2012) 3(1), 2738

Land use carbon implications o a reduction in ethanol

production and an increase in well-managed pastures

Chad Hellwinckel*1 & Jennier G Phillips2

Background: As the debate over governmental subsidization o ethanol continues, the academic and policy

communities should prepare or a potential reduction o ethanol production, and be aware o the potential

land use impacts. We report a rst-order estimate o carbon implications o the change in land use that

results rom a reduction o ethanol production rom current levels and having well-managed pasture as

an alternative land management option. Method: An integrated biogeophysicalsocioeconomic model is

used to evaluate three levels o potential reductions in ethanol production, along with the possibility o

conversion o cropland to pasture management. Results: Results indicate that up to 10 million ha o cropland

could be converted to pastureland, reducing agricultural land use emissions by nearly 10 teragrams carbon

equivalent per year, a 36% decline in carbon emissions rom agricultural land use.

ReseaRch aRticle

1Agricultural Policy Analysis Center, University o Tennessee, Knoxville, TN 37996, USA2Bard Center or Environmental Policy, Bard College, Annandale, NY 12504, USA

*Author or correspondence: E-mail: [email protected]


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Carbon Management(2012) 3(1) future science group28

Research Article Hellwinckel & Phillips

the EPAs Renewable Fuel Standardtargets even by 2022 [11]. I anothersharp spike in commodity pricesoccurs in the near uture, some havespeculated that ethanol production

mandates could be scaled back oreliminated [103]. In the span o lessthan 3 years the expected role oethanol in the agricultural sector hasgone rom one o rapid growth andlongevity, to one o which the soci-etal benets and technical easibilityare being strongly questioned.

In light o the rapidly changingexpectations regarding the uture oethanol, we believe it is an appropri-ate time to evaluate the land use and

carbon implications o a possiblescaling down o ethanol production.Several studies have investigated theland use implications o the growtho the biouels industry [1214], but

there have been none to date that have investigated theimplications o a drawdown orst-generation biouelsand the non-emergence o second-generation biouels.In this analysis, we investigate such a uture scenarioand the potential o permanent managed pasture as analternative land use that could provide carbon benets.

Although grazing systems have long been associatedwith land degradation in the arid and semi-arid west,new management approaches utilizing some orm orotational grazing are believed to reverse degradationand potentially lead to soil and pasture improvement iwell managed, with implications or soil carbon storage.

The primary management practices associatedwith improved soil carbon sequestration in pasturesare nutrient management and grazing methods.Management-intensive grazing (MIG), also known asintensive rotational grazing or prescribed grazing, is onesuch practice increasingly recognized or its ability toimprove environmental quality in permanent pastures.MIG is a technique involving short-duration (16 days),

high stock density grazing and long rest periods [1517].MIG promotes better pasture utilization [18] and allowspastures to recuperate ater each grazing event, which isthought to pulse carbon into the soil via root slough-ing[19,20]. Paddock rotation, along with balancing cooland warm season grasses and legumes, has been shownunder some circumstances to enable ranchers to increasestocking rates while simultaneously increasing soilorganic carbon (SOC) relative to continuous grazing[21]. The adoption o MIG has been primarily producerled, although evidence o economic benets to dairyproducers in particular [2224] has resulted in increased

acceptance among state-level extension agencies in east-ern and midwestern USA dairy regions. A recent surveyound that 13% o dairies in Maryland, Pennsylvania,New York and Vermont are using MIG [25]. VariousUS Department o Agriculture (USDA) programs to

promote conservation o, or conversion to, permanentpasture or grassland, exist primarily based on the valueo decreasing the potential or soil erosion as well asimproving water quality[26]. Among bee producers inthe western rangelands, MIG is more controversial [27]and or the purposes o this study, our ocus is on therain-ed grazing land east o the 100th parallel in NorthAmerica.

The carbon oset potential o well-managed per-manent pasture has been estimated to be quite large.Globally, non-economic evaluation estimates that150 teragrams carbon per year (TgCyr-1) could be

sequestered in pasturelands[28]

. Within Annex Inations, it is estimated that 70 TgCyr-1 could be seques-tered in pasturelands [21]. Empirical studies within theUSA have estimated that sequestration rates or well-managed pastures range rom 0.21 to 2.9 megagramso carbon per hectare per year (MgCha-1yr-1) [21,26,29,30].Thus, i the 55 million ha o pastureland and range-land in non-arid regions o the USA was converted towell-managed permanent pasture, carbon sequestra-tion could reach 12160 TgCyr-1, potentially osetting110% o total US GHG emissions. Conversion o cro-Conversion o cro-pland to well-managed pastures, which is the ocus othis study, would increase these potential osets. This isa broad range o potential and urther empirical analysisis needed.

Our objective in this article is to evaluate the poten-tial conversion o cropland into pastureland inducedby a reduction o ethanol production, and the resultingimplications upon soil carbon and emissions rom inputuse. As nonprotable cropland is converted to pasture-land, it is expected that carbon emissions associatedwith crop production inputs will decline and soil carbonwill increase. This is necessarily a rst-order assessment,as it does not consider that a decrease in the price ocorn will simultaneously impact eed cost or the con-

nement livestock sector, which has implications orthe demand curve or pasture-raised bee production.

Methodology

The analytical tool used to conduct this analysis is anintegrated socioeconomicbiogeophysical model. Theintegrated model is driven by data on economics, soilattributes, crop rotation, land management and energyconsumption. The economic core o the model is amodied version o the University o Tennessees PolicyAnalysis System model (POLYSYS), which is a partialequilibrium displacement model that iterates annually

Key terms

Second-generation biouels: Biouelsmade rom woody or cellulosic material,which is still under development andrelies on complex enzymes orgasifcation technology.

First-generation biouels: Biouels suchas corn grain ethanol, which rely onlongstanding ermentation technology.

Carbon sequestration: Process oremoving carbon rom the atmosphereand storing it in a reservoir, such as thesoil, where it will not reenter theatmosphere.

Management-intensive grazing:Method o rotational grazing usingrelatively high stock densities, daily toweekly livestock moves and long restperiods or paddock recovery.

Well-managed pastures: Pasturescomposed o high-yielding pasturespecies, usually maintained in avegetative state.


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Carbon in well-managed pastures Research Article

future science group www.uture-science.com 29

and simulates results until the year 2030 [3133]. All pol-icy scenarios are analyzed in comparison with the USDAbusiness as usual baseline projections or the crop andlivestock sectors. POLYSYS has been used to estimatecarbon oset credit supply potential or conservation

tillage and herbaceous grasses used or bioenergy[14,34].POLYSYS is structured as a system o interdepen-

dent modules simulating: crop supply or the continen-tal USA, which is disaggregated into 3110 productionregions; national crop demands and prices; nationallivestock supply and demand; and agricultural income.Variables that drive the modules include planted andharvested area, production inputs, yield, exports, costso production, demand by use, arm price, governmentprogram outlays and net realized income. Managementpractices currently considered in POLYSYS include corn,grain sorghum, oats, barley, wheat, soybeans, cotton,

rice, hay, herbaceous and woody cellulosic eedstocks,aorestation and pastureland. Three levels o tillagemanagement are included or each crop. Conventionaltillage, reduced tillage and conservation tillage aredened, respectively, as leaving less than 15% o theground covered by crop residue, between 15 and 30%ground cover, and greater than 30% ground cover [35].Baseline increases in no-tillage adoption were extendedthrough to 2030 by projecting state-level tillage trendsreported by the Conservation Tillage InormationCenter at a conservative 50% rate. Changes in tillagemix away rom the baseline are determined by relativechanges in protability in alternative scenarios.

The model makes use o over 3500 unique regionalcrop budgets, which are based on regional dierencesin crop production operations. These operation bud-gets list a daily schedule o all machinery and produc-tion inputs used to produce each crop. Both direct andindirect energy and carbon emissions have been tied toeach input o the operation budgets [36]. Direct carbonincludes emissions rom the use o uel on arms, dis-solution o agricultural lime, changes in soil carbonand carbon equivalent (C

eq) emissions o N

2O. Carbon

content o diesel was estimated at 0.81 kg l -1 diesel.Emissions o N

2O resulting rom the application o

nitrogen ertilizer were estimated according to IPCCguidelines [37] and as outlined by Marland et al.[38]. C

eq

emissions o N2O rom the use o nitrogen ertilizers are

estimated using 2.22 tons Ceq

released per ton o nitro-gen applied. Emissions rom lime is 0.06 ton o carbonper ton o limestone applied. Indirect carbon includesCO

2emissions rom ossil uels used in the production,

transport and application o all agricultural inputs havebeen calculated by West and Marland or cultivatedlands [39]. By tying emissions to operations and inputsapplied, the model can estimate changes in productionemissions under assumptions o land use changes.

Several layers o biogeophysical data were integratedto develop a model capable o estimating changes inSOC at the county level. Regional carbon managementresponse curves [40], State Soil Geographic Database(STATSGO) soils data[41] and Landsat land cover data

[42] were integrated to determine potential changes inSOC associated with each unique combination osoil type, crop type and crop management [43]. Theamounts o carbon that could be sequestered underland management practices, such as conservation tillageor pasture conversion, were based on regionally uniquesoil conditions and previous land use. Experimentaldata on the carbon changes under conservation till-age, herbaceous grasses and aorestation to the 30 cmdepth were collected and integrated into the model asdetailed in earlier studies [14,34,43]. Because a signicantamount o cropland is already using conservation till-

age, there is a baseline level o carbon sequestrationalready occurring.Policy-induced changes in land use result in esti-

mated changes in crop production emissions, soil car-bon sequestration and net carbon fux to the atmo-sphere rom agricultural activity. Net carbon fuxincludes changes in soil carbon stocks, and both directand indirect emissions rom the manuacture and useo all crop production inputs. The current study doesnot account or CH

4or N

2O emissions rom livestock.

Cropland can be converted between major croptypes as the relative protability o one crop overreachesanother. Cropland can also be converted to pasturelandi the economic prot o all major crop managementpractices become negative or 3 consecutive years andall xed capital equity is eroded. At this point, pasture-land, which is assumed to return a normal economicprot, becomes a viable economic land use option.Carbon emissions associated with planting and estab-lishing permanent pasture grasses are estimated usingthe same methodology as other management practices.We assume pasture renovation once every 10 years, withmoderate nitrogen and lime applications at seeding butno additional applications. We assume that croplandconverted to pastureland east to the 100th meridian

can sequester carbon. Soil dynamics on more aridwestern lands are more controversial, so our estimatesexclude any sequestration on converted lands west othe 100th meridian [27]. Converted eastern croplandunder pasture management accumulates soil carbon ata rate o 1.85% o the initial regional soil carbon levelper year [44]. This rate does not represent some extremeregional weather or soil conditions, but is only usedto estimate mean conditions. Nationally, soil carbonsequestration averages to 0.41 MgCha-1yr-1, which issimilar to empirical estimates o carbon accumulationunder well-managed pastures [21].


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We analyze three scenarios o ethanol drawdown andcompare them with the extended USDA baseline sce-nario, where corn ethanol production reaches 15 billiongallons by 2020 and then remains constant through2030. To ully investigate the carbon potential o pas-

ture management, this analysis assumes an exogenousdrawdown level o ethanol demand. The three alterna-tive scenarios slowly reduce ethanol production annu-ally until reduced by a total o 25, 50 or 100% by 2025,where production remains steady through to 2030. Analternative would be to allow ethanol to compete withgasoline under an unmandated marketplace. We chosenot to do this or two reasons: uture price o competinggasoline is uncertain, and ethanol may be orcibly shutdown due to a ood price spike event and concern overenergy and carbon balances. By exogenously setting thedrawdown levels, we can give perspective o the range

o uture possibilities. The results will list ethanol pro-duction costs per unit or each scenario or comparisonwith current gasoline production costs. Future scenarioscould endogenously link ethanol demand to energy andeedstock prices.

The economic model solves both crop and livestockmarkets simultaneously; thereore, as commodity pricesdecline the livestock market responds by demandingmore eed or eedlots. Our rst-order analysis does notconsider the supply o cattle raised upon converted crop-land or the tradeos that may occur between eedlotnishing and pasture nishing. Although we discuss thepotential implications o the increased livestock supplyand potential pasture nishing in the discussion, theimplicit eects could be integrated into uture analyses.Our analysis is also limited to conversion o cropland toimproved pasture management and does not considermanagement improvements that may occur on alreadyexisting pasturelands.

Results

In the 2030 baseline scenario year, major crop agricul-ture in the USA emits 39 TgC

eqrom production inputs

and sequesters 12 TgC in the soils o 68 million ha underconservation tillage, to result in a net fux o 27 TgC

eq

rom US agricultural land use to the atmosphere [36,43].As ethanol production is scaled down, corn productionor ethanol eedstocks decline and prices all. Year 2020corn prices decline rom $4.20 per bushel to $2.50 perbushel in the 100% drawdown scenario. Declining cornprices induce conversion o corn cropland to other majorcrops, which in turn reduces other crop prices as sup-ply is increased. In regions where declining crop priceslead to no crop being a protable alternative, croplandis converted to pasture management. The majority othe converting land was previously growing corn, butsome land rom other crops also converts as commodity

prices decline across all crops. In the 100% drawdownscenario, 10.3 million ha o cropland is estimatedto convert to pastureland by 2030. Some amount ocropland is converted to pasture in most regions o thecountry, but the majority o new pasturelands convert

rom previous cornland in the heart o the cornbelt,concentrating on Ohio, Illinois, Iowa, Nebraska andMinnesota(Figure 1).

The new land use equilibrium induced by ethanoldrawdown has a dierent pattern o crop input use thanthe baseline scenario. Corn production is input inten-sive, so in most regions land use movement away romcorn and into other crops or pasture management resultsin a net decline in input use (Figure 2A). Nationally, pro-duction input emissions decline by 5.74 TgC

eqin the

100% drawdown scenario.The new land use equilibrium also has a dierent

pattern o soil carbon sequestration than the baselinesituation. Well-managed pasture sequesters carbon at arate higher than annual crop agriculture; thereore, largeregional conversion to pasture results in net increases insequestration o carbon (Figure 2B). Yet in some regions, ithere is conversion rom no-tillage to more intensive till-age crops, then a net loss o soil carbon can occur. In ourmodel scenarios, we assume cropland converted to pas-ture in western lands does not sequester carbon; there-ore, a transition rom no-tillage cropland to pastureresults in a net decrease in soil carbon accumulation.This could occur in situations where the lost croplandhas a high net primary productivity (NPP) due to irriga-tion and the newly converted pasture has a low NPP dueto dryland management methods. In Figure 2B, losses insoil carbon are most concentrated in western areas andgains in soil carbon occur in eastern areas where we areassuming increased SOC under well-managed pasture.

When both changes in carbon associated with pro-duction inputs and changes in soil carbon accumulationare summed, net carbon fux rom agricultural land useto the atmosphere can be estimated. In most regions netfux is reduced by both a decline in input emissions anduptake o carbon by soils. Large regional reductions innet fux to the atmosphere occur throughout the corn-

belt (Figure 2C). In regions where carbon uptake declined,the impact o lost carbon accumulation is oten osetby larger reductions in emissions associated with inputuse. In very ew regions, the 100% drawdown scenarioresulted in a net fux increase.

Nationally, net carbon fux rom agricultural landuse declines as ethanol drawdown occurs (Figure 3).Approximately hal o the reductions in net fux arerom reductions in input use (-5.74 TgC

eq) and hal are

rom increases soil carbon uptake (-4.17 TgCeq

). Havingwell-managed pastures as a viable economic alternativeto crop agriculture results in a 9, 19 and 36% decline


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in total net carbon fux rom land use agriculture under25, 50 and 100% ethanol production drawdown,respectively(Table 1). Soil carbon increase can occur or2030 years [37], ater which a steady state o SOC isreached in the soil, and no additional accumulationscan occur. Thereore annual net fux reductions willeventually all to only the reductions brought about bydecreased input use.

Ethanol production costs decrease as drawdown levelsincrease due to declines in corn grain eedstock cost(Table 2). When comparing year 2030 ethanol energyequivalent production costs with current gasoline pro-duction costs, ethanol is competitive with gasoline inall drawdown scenarios except the baseline scenario.This indicates that under an unsubsidized and unman-dated marketplace, ethanol would likely be produced at

quantities above the 25% drawdown level. The ethanoldrawdown levels analyzed in this paper would thereorehave to be caused by other movements, such as politi-cal action in response to ood security issues inducedby ood price spike events or concern over net energyand carbon balances. In the current ood and policyenvironment, action beyond removal o mandates is notunquestionable, hence the rationale or investigatingthe larger drawdown scenario. For example the 100%drawdown would not likely occur without legislativeaction to orbid production, or an unoreseen declinein oil prices or oil demand.

Discussion

The results o our analysis indicate that i policy changesand technical ineasibility alter the expected productionpath o ethanol in the USA, conversion o nonprotableagricultural lands to pastures can lead to signicantreductions in land use carbon emissions. This result issignicant in that it indicates that positive movement, interms o carbon emissions, can occur even in the evento a drawdown or dissolution o the biouel industry. Yetthe potential carbon benets o pastureland conversionwill only occur i croplands converted to well-managedpastures, which accumulate soil carbon, are not associ-ated with severe increases in N

2O or CH

4emissions and

are protable or producers. We will discuss these threecritical issues below.

Soil carbon sequestration under permanentpasture/MIG

It is reasonably well established that grazing has a posi-tive impact on soil carbon sequestration [4548]. Studiesusing exclosures indicate that a change in plant spe-cies composition may be partially responsible or theincreased carbon accumulation under grazing relativeto nongrazed grasslands, but positive eedbacks to herb-ivory may infuence belowground carbon ate [49], andmuch remains to be understood regarding the mecha-nisms responsible [50]. Nonetheless, soil carbon seques-tration rates are directly related to NPP [44,51]. Thus,

0

15

510

1020

2040

4080

80+

Hectares (thousands)

Figure 1. Land converted rom crop agriculture to pasture management as a result o a 100% drawdown in corn

grain ethanol demand by 2030. Shown as total hectares converted per Agricultural Statistic District.


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in order to maximize carbon storage under managedpasture, management or high NPP is necessary.

In the bee industry, cow/cal and stocker segmentsmay not warrant as high a level o management o pas-ture as nishing bee cows on grass or grass-ed markets

or dairy, both o which require high quality grass andhigh levels o intake to achieve desired product quality.Under our scenario o land conversion, additional sup-ply o pasture implies greater supply o pastured live-stock. It is unlikely that this pasture would be utilizedentirely by cow/cal producers as this is only one pieceo the bee supply chain and is currently close to equi-librium with the demand or eeder calves. Thus, wenecessarily imply an increase in pastured stockers andnishing bee, displacing some o the livestock currentlygrown out in concentrated animal eeding operations.An associated implication is that some portion o the

new permanent pasture would likely be managed orhigh quality and NPP, with a high likelihood o theuse o MIG.

Some empirical evidence exists in support o thepositive role o MIG in pasture productivity relative tocontinuously grazed pastures. Teague et al. investigatedpaired pastures in three counties in a tallgrass prairieregion o north central Texas, comparing light (14 ani-mal units [AU] 100 ha-1) and heavy (27 AU 100 ha-1)stocking rates grazed continuously to pastures usingMIG (27 AU 100 ha-1), and ound standing biomass atpeak standing crop to be highest on the MIG system(3960 [light stocking], 2696 [light stocking] and 4680[MIG] Kg ha-1) [52]. Older work ound higher stock-ing rate and productivity under six- and 11-paddockrotations compared with continuous grazing in Illinois[53]. Phillip et al. ound a strong interaction betweenstocking rate and rotational requency, with the high-est system eciency using a moderate (6-day) rotationcompared with a more intensive requency o 2 days,with most o the benet coming rom the ability to hayearly season growth compared with continuous graz-ing [54]. However, the impact o MIG on soil carbonsequestration may be a unction o soil processes beyondsimple productivity[18,52], and some evidence has been

ound that MIG promotes soil carbon storage.Little work has been done to investigate soil carbon

sequestration under pastures managed with MIG.Conant et al. sampled soils under pastures in Virginiapaired by grazing method and estimated total soil car-bon to be 22% greater under MIG than in neighbor-ing extensively grazed or hayed pastures [21]. Averagingacross their our sites, they ound a storage rate o0.41 MgCha-1yr-1 using MIG. Teague et al. ound a44% increase in soil organic matter under pasturesmanaged with MIG or 9 years compared with heavycontinuous grazing and 11% increase compared with

Change in emissions (gigagrams Ceq

)


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light grazing[52]. They did not estimate a storage rateor soil carbon using MIG. The rate o soil carbon accu-mulation used in this analysis approximately equalsthe estimate o Conant et al. o 0.41 MgCha-1yr-1 [21].In their work, one site was estimated to sequester soilcarbon at 2.9 MgCha-1yr-1. They note the inherent di-culty in measuring soil carbon storage rates due tospatial variability across sites and soils. Given the lownumber o studies reporting soil carbon sequestrationunder MIG, much work remains to be done. To date,there have been no randomized, replicated studies undercontrolled experimental conditions on MIG. However,

as a pasture management approach, MIG holds promiseto increase soil carbon while providing an economicallyand environmentally benecial livestock system.

Full accounting or GHG emissions rom grazing

As has been pointed out by others [55,56], the ull impacto land conversion to grazing on net GHG emissionsneeds to consider additional GHGs. One option ormanaging pastures or high productivity is by increasingnitrogen supply. This can be achieved through additionso synthetic nitrogen ertilizer, manure or by increas-ing the percentage o legumes in the pasture. All three

Table 1. Cropland converted to well-managed pasture and associated annual emissions o carbon rom

agricultural land use to the atmosphere in 2030 under three scenarios o corn ethanol drawdown.

Scenario Baseline Reduction in corn ethanol

25% 50% 100%

Corn acreage (M ha) 37.5 35.3 32.6 27.2

Pasture conversion (M ha) 0.0 2.0 5.2 10.3

Emissions rom agriculture to the atmosphere (TgCeq

):

From production inputs

From soils

Net fux

39.41 38.01

36.47

33.67

-12.21 -13.17 -14.36 -16.38

27.2 24.84 22.11 17.29

Change in net fux rom baseline (TgCeq

) -2.36 -5.09 -9.91

Change in net fux rom baseline (%) -9 -19 -36The authors assume cropland conver ted to pastureland east o the 100th meridian sequesters carbon at a rate o 1.85% o initial soil carbon per year,which averages to 0.41 MgCha-1yr-1. The authors also assume no carbon accumulation on cropland converted to pastureland west o the 100thmeridian.Positive numbers indicate a carbon release rom agriculture to the atmosphere; negative numbers indicate a carbon capture rom the atmosphere tothe soil.MgC: Megagrams carbon; M ha: Million hectares; TgC

eq: Teragrams carbon equivalent.

2010 2015 2020 2025 2030

Netflux(TgC

eqy

r-1)

30

28

26

24

22

20

18

16

14

12

10

Baseline 25% drawdown 50% drawdown 100% drawdown

Figure 3. Net fux o carbon rom agricultural land use to the atmosphere under baseline and three levels oethanol production drawdown, with well-managed pasture as a viable economic alternative to crop agriculture.

In all three scenarios, the percent drawdown occurs steadily rom 2010 through to 2025 and then remains constant.

As land use adjusts to new economic circumstances, reductions in input use and increases in soil carbon uptake

result in reductions to net fux.

TgCeq

yr-1: Teragrams carbon equivalent per year.


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nitrogen sources have implications or N2O emissions

and are thereore o concern, given the much highergreenhouse warming potential o N

2O compared with

CO2, and could potentially negate the value o the car-bon sink created. However, emissions associated withsynthetic nitrogen application are generally higher thanmanure nitrogen sources and much higher than legumenitrogen sources [57]. Our model assumes pasture reno-vation once every 10 years, with moderate nitrogen andlime applications at seeding but no additional applica-tions. Depending on other actors controlling productionpotential, such as climate and soil type, some strategic useo nitrogen ertilizer may be possible while still achievingthe emissions and sequestration goals [57]. Grazing prac-tices may have a larger impact on overall productivity,but also carry implications or controlling N

2O emis-

sions. There is some evidence that grazing can reducepasture N

2O emissions relative to nongrazed grasslands

[58]; however, net emissions will depend on management.Conventionally, continuous grazing, whereby live-

stock are allowed to move reely through the whole graz-ing area or a season, has been the standard practice, butis increasingly being implicated in pasture degradationand, more recently, in increased N

2O emissions rom

livestock operations. N2O emissions are exacerbated

when soil compact ion occurs, which is a particularproblem near permanent water and mineral points ina continuously grazed pasture, or where animals camp

out under shade [59]. Rotational grazing helps to miti-gate this problem because water and minerals move withthe animals rom paddock to paddock. Under MIG,where animals are kept in small paddocks but moved asrequently as daily, animal impact is evenly distributedthroughout the land, and pastures are allowed to recoveror weeks to months beore livestock return. Thus, com-paction and continuous loading o manure onto specicareas is avoided, decreasing conditions conducive to N

2O

emissions.With respect to CH

4, it is known that enteric CH

4

emissions are generally higher in grass-ed ruminants

than animals consuming grain, as a result o the dier-ences in metabolizable energy intake [60]. Although soil-dwelling methanotrophs consume soil-generated CH

4in

pastures, uptake rates are ar too low to ully compensateor the amount o CH4

that would be released romenteric ermentation at normal stocking rates [61]. Thus,a ull accounting or CH

4emissions in a pasture-based

livestock system would need to be included in estimateso net emissions.

Allard et al. measured CO2, N

2O and CH

4emissions

rom pastures managed intensively (high stocking rateand nitrogen ertilizer applied) and extensively (lowstocking rate and no nitrogen ertilizer) and ound bothto be signicant net C

eqsinks, with the intensively man-

aged pasture exceeding the extensively managed pasture[62]. Recent modeling work by Rotz et al., perormingull lie cycle analysis comparing dairy managementsystems, estimated that a 60-cow dairy would reduce itsnet lie cycle GHG emissions by 1022%, by switchingrom a connement model to a pasture-based system,depending on assumptions regarding soil carbon seques-tration rates [60]. Although our analysis only determinesnet emissions rom land use, these studies suggest that amajor shit in the livestock industry toward increased useo pasture and away rom grain eeding in connementmay help reduce net emission rom the livestock sector.

Economic viability

The emergence and growth o well-managed pasturetechniques has come about only recently. Several casestudy analyses have concluded that well-managed pas-ture systems can be protable [23,54,63,64]. Although thesestudies indicate that producers are receiving more than anormal prot margin, we used the conservative assump-tion that well-managed pastures return zero economicprot, and cropland only converts i there is no alterna-tive protable crop or multiple years. By looking strictlyat economic criteria, well-managed pasture techniquesappear well positioned to become more widespreadunder the scenarios evaluated in this analysis.

Table 2. Corn grain price and ethanol production costs in gasoline energy equivalent terms in 2030 under

baseline and three scenarios o corn ethanol drawdown.

Scenario Baseline Reduction in corn ethanol

25% 50% 100%

Corn grain price (US$ Mt-1

) 152.86 129.64 122.14 109.29Ethanol production cost in gasoline energy

equivalents (US$ l-1):

Feedstock cost

Conversion cost

Distillers grains income

0.65

0.55

0.52

0.47

0.23 0.23 0.23 0.23

0.13 0.11 0.10 0.09

Total cost (US$) 0.75 0.67 0.65 0.60Ethanol costs are listed as the production costs to displace the energy equivalent o one gallon o gasoline. The authors assume gasoline has1.56-times the energy content o ethanol. For comparative purposes, the August 2011 gasoline production cost was US$0.73 per l.


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Yet, due to the recent advancement o well-managedpasture techniques, the major barrier to adoption maynot be lack o economic returns, but lack o inorma-tion armers have not grown up with the knowledge ointensive grazing techniques and agricultural extension

services have been slow to prioritize intensive pasturemanagement as an applicable practice or their regionallivestock armers. Thereore, knowledge barriers mayhinder widespread adoption due to a lack o widelydisseminated inormation on how to initiate improvedpasture management techniques. I ethanol drawdownbegins with no other active eorts toward promotingwell-managed pastures, widespread adoption may notnecessarily ollow.

Due to the potential environmental benets o wide-spread adoption o well-managed pastures, we proposethat the ollowing steps be taken to acilitate sound

growth o the practices: Undertake empirical analyses o pasture systems tourther quantiy the carbon balances and identiy keypractices that maximize the carbon benets;

Educate armers on key pasture management prac-tices through armer-to-armer education programsacilitated through the US Cooperative ExtensionService;

Increase the economic viability o well-managed pas-tures through oering incentives tied to the soilcarbon sequestration ability o pasture practices.

These steps will ensure that appropriate land useoptions are in place in the event that the ethanolindustry experiences a drawdown. Likewise, acilitat-ing sound growth in well-managed pasture techniqueswould also be benecial i successul development o

second-generation biouels occurs. Previous studiesanalyzing land use change as a result o rapid growtho cellulosic eedstocks indicate that pasture improve-ments will be necessary to oset increased competitionor grasslands [65].

Future perspective

As the debate over governmental subsidization o etha-governmental subsidization o etha-subsidization o etha-nol continues, the academic and policy communitiesshould prepare or a potential reduction o ethanol pro-duction and be aware o the potential land use impacts.Agriculture aces many challenges in the near uture.

Climate change impacts combined with increasing uelcosts translate into a high likelihood that agriculture hasentered a new period o history[66]. We could be transi-tioning rom a 40-year period o commodity oversupplywhere prices have been below the cost o production, toa period o scarcity marked by high commodity prices.Ethanol may ace continued diculties rom politicalpressure to reduce nonood uses o our agriculturalresources. I another ood price spike occurs in the nearuture, ethanol mandates will very likely be curtailedor eliminated, with an all-out ban on ethanol being lesslikely, but still possible.

Executive summary

Ethanol situation

Ethanol subsidies have recently been eliminated.

Development o second-generation biouels is lagging behind mandates.

There is some political will to also eliminate ethanol mandates.

High ood prices are bringing ood versus uel issues to the oreront and turning political will against ethanol.

Corn grain ethanol may experience a production drawdown in the near uture, with implications to eedstock demand and agricultural

land use.

Alternative land use

Improved pasture management is an alternative ood use or land and has multiple environmental benets, such as carbon sequestration,

reduced erosion and reduced input use.

Management-intensive grazing has been estimated to sequester rom 0.21 to as high as 2.9 megagrams carbon equivalent per hectare

per year. To date, adoption o management-intensive grazing has been armer led.

Land use carbon potential o transition

First-order analysis indicates that 10 million ha o cropland could convert to well-managed pastures by 2030 i ethanol experiences a 100%

drawdown.

Under 100% drawdown o ethanol, carbon emissions rom agricultural land use would decline by 5.74 teragrams carbon equivalent per

year and soils would absorb an additional 4.17 teragrams carbon equivalent per year.

Preparing or possible transition

More empirical data needs to be collected on the most benecial techniques in pasture management and their carbon sequestration

potentials.

To spur widespread adoption, armer-to-armer education programs would help overcome the barrier o lack o traditional knowledge on

well-managed pasture techniques.

Any uture climate change programs should target the soil carbon benets o well-managed pastures.


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We report a rst-order estimate o the land use carbonimplications o a reduction o ethanol production andhaving well-managed pasture as an alternative manage-ment option. I ethanol production is completely elimi-nated over the next 20 years, well-managed pastures

could potentially oset 10 TgCeq rom the atmospherethrough both reducing land under input-intensive cropagriculture and by increasing soil carbon levels on thenewly established pastures. At ethanol drawdown levelsless than 100%, conversion to well-managed pasturescan stil l make signicant contributions to reducing thenet fux o carbon rom agriculture. Further empiricalstudies should continue to investigate the soil carbon,N

2O, and CH

4implications o improved pasture sys-

tems, such as MIG, in relation to conventional pastureand eedlot systems or livestock production.

Due to the rapid emergence o new pasture manage-

ment techniques, lack o a traditional knowledge base

could be the major barrier to widespread adoption. Wepropose that the US Cooperative Extension Serviceacilitate armer-to-armer education programs to helpdisseminate inormation to armers interested in alter-natives to crop agriculture or conventional pasture man-

agement. Conversion would also be acilitated througharms employing well-managed pasture systems receiv-ing incentives or increases in soil carbon stocks underpossible uture climate programs.

Financial & competing interests disclosure

The authors have no relevant aliations or nancial involvement

with any organization or entity with a nancial interest in or nan-

cial confict with the subject matter or materials discussed in the

manuscript. This includes employment, consultancies, honoraria,

stock ownership or options, expert testimony, grants or patents

received or pending, or royalties. No writing assistance was utilized

in the production o this manuscript.

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