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Authors:

MarlenEve,U.S.DepartmentofAgriculture,OfficeoftheChiefEconomistMarkFlugge,ICFInternationalDianaPape,ICFInternational

Contents:

2 ConsiderationsWhenEstimatingAgricultureandForestryGHGEmissionsandRemovals .........................................................................................................................................................................2‐3

2.1 Scope...................................................................................................................................................................2‐32.1.1 DefinitionofEntity..........................................................................................................2‐32.1.2 DefinitionofSystemBoundaries...............................................................................2‐4

2.2 ReviewofRelevantCurrentToolsandMethods............................................................................2‐122.3 SelectionofMostAppropriateMethodandMitigationPracticestoInclude......................2‐132.4 OverviewofSectors....................................................................................................................................2‐14

2.4.1 CroplandsandGrazingLands...................................................................................2‐162.4.2 Wetlands............................................................................................................................2‐172.4.3 AnimalProduction.........................................................................................................2‐192.4.4 Forestry..............................................................................................................................2‐21

2.5 Land‐UseChange.........................................................................................................................................2‐222.6 Uncertainty....................................................................................................................................................2‐23Chapter2References.............................................................................................................................................2‐24

SuggestedChapterCitation:Eve,M.,M.Flugge,D.Pape,2014.Chapter2:ConsiderationswhenEstimatingAgricultureandForestryGHGEmissionsandRemovals.InQuantifyingGreenhouseGasFluxesinAgricultureandForestry:MethodsforEntity‐ScaleInventory.TechnicalBulletinNumber1939.OfficeoftheChiefEconomist,U.S.DepartmentofAgriculture,Washington,DC.606pages.July2014.Eve,M.,D.Pape,M.Flugge,R.Steele,D.Man,M.Riley‐Gilbert,andS.Biggar,Editors.

USDAisanequalopportunityproviderandemployer.

Chapter 2Considerations When Estimating Agriculture and Forestry GHG Emissions and Removals

Chapter 2: Considerations When Estimating Agriculture and Forestry GHG Emissions and Removals

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Acronyms,ChemicalFormulae,andUnits

CH4 MethaneCO CarbonmonoxideCO2 CarbondioxideCO2‐eq CarbondioxideequivalentsGHG GreenhousegasGWP Globalwarmingpotentialha HectaresHWP HarvestedwoodproductsIPCC IntergovernmentalPanelonClimateChangeN2O NitrousoxideNH3 AmmoniaNO NitricoxideNOx Mono‐nitrogenoxideNO2 NitriteNO3 NitratePDF ProbabilitydensityfunctionUSDA U.S.DepartmentofAgriculture


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2 ConsiderationsWhenEstimatingAgricultureandForestryGHGEmissionsandRemovals

Thischapterdescribesthelinkagesandcross‐cuttingissuesrelatingtosector‐specificandentity‐scaleestimationofgreenhousegas(GHG)sourcesandsinks.Inparticular,thischapterdescribesthecommonelementsthatmustbeconsideredbothwithinanemissionssectororsourcecategoryaswellasacrosssectorsorsourcecategoriesinorderforanentitytoreportaccurateGHGinventoryestimates.

Chapter2isorganizedasfollows:

Scope

ReviewofRelevantCurrentToolsandMethods

SelectionofMostAppropriateMethodandMitigationPracticestoInclude

OverviewofSectors

− CroplandsandGrazingLands

− Wetlands

− AnimalProduction

− Forestry

− Uncertainty

2.1 Scope

InorderforanentitytoaccuratelyinventoryitsdirectGHGemissionsto(andremovalsfrom)theatmosphereandcompareemissionsandremovalsbetweenyears,practices,orentities,itisimportantthatestimationelements—e.g.,definitionsofentityandsystemboundaries—arecommontoallemissionsectorsandsourcecategories.Thesecommonelementsaredescribedinmoredetailinthesectionsthatfollowandinclude: DefinitionofEntity

DefinitionofSystemBoundaries:

− PhysicalBoundaries

− TemporalBoundaries

− ActivityBoundaries

− MaterialBoundaries

2.1.1 DefinitionofEntity

Thedefinitionofanentitywill,toalargedegree,determinethe(spatial)boundsoftheestimationmethodologies.Thiswillprimarilybedrivenbywhatdataalandownerchoosestoinput—i.e.,thedefinitionwillbeuser‐specificandprimarilydependontheuser’sdefinition.1However,itisanticipatedthatthescience‐basedmethodswillbesuitabletoquantifyGHGsourcesandsinksataprocessorpracticescale.Themethodsinthisreportprovideanintegratedassessmentofthenet

1Itshouldbenotedthatthedefinitionofanentityusedinthisreportisnotapolicyorregulatorydefinition,andisonlyprovidedtohelpthelandmanagerdeterminewhatpracticesshouldbeincludedintheestimation.


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GHGemissionsforanentity,alllandsforwhichthelandownerhasmanagementresponsibility.TheyalsoprovidethebasisforanintegratedtooltobeusedbytheU.S.DepartmentofAgriculture(USDA)aswellasbyindividualfarmers,ranchers,forestowners,andotherstakeholderstoevaluatethenetGHGemissionsonparcelsoflandundertheirmanagement.Sowhiletheentitywouldbedefinedasalloftheactivitiesoccurringonalltractsoflandunderthemanagementcontrolofthelandowner,thereportdescribespractice‐levelmethodologiesthatcanbesummedcollectivelytoarriveatanestimatefortheentity.Thedefinitionofentityappliedhereisintentionallybroad,understandingthatanypolicy,registry,ormarketwillprovideitsownnarrowerdefinition.

2.1.2 DefinitionofSystemBoundaries

ThesystemboundariesshouldincludetheGHGemissionsandcarbonsequestrationoccurring(orestablished)onsiteforthesourcecategoryandmanagementpracticeinquestion.Forexample,thisreportdoesnotaddressindirectland‐usechangesoccurringoffsiteorbiogenicGHGfluxrelatedtosubsequentuseofagriculturalorforestryoutputs(e.g.,foodprocessing,pulpandpapermanufacture,biomasscombustion).However,certainoffsitecarbonstorageconsiderations(e.g.,flowofharvestedwoodintoharvestedwoodproducts[HWPs])havebeenconsideredinthereporttomaintainconsistencywithnationalinventoryefforts.

Fourtypesofsystemboundariesareimportantforconsideration:

PhysicalBoundaries

TemporalBoundaries

ActivityBoundaries

MaterialBoundaries

2.1.2.1 PhysicalBoundaries

Physicalboundaries(e.g.,spatial,sectoral)addresstheareaandthemanagementtobeconsideredinthereporting.Settingtheboundariesforwhichemissionsandsequestrationwillbeestimatedismoredifficultthanitfirstseems.Althoughtheremaybemultiplealternatives,clarityandconsistencyareimportant.Therearemanyfacetstoconsider.Onefactoriswhatconstitutesanentityorafarm/ranch/forestoperation;anotheriswhatoperationsareassociatedwiththatentity.Forexample,doestheuseoffertilizeronafarmincludetheprocessesofmanufacturinganddeliveringthatfertilizer?Anotherconsiderationishowtosubdividethatlargerentityintotherelevantsectorsaspresentedintheindividualchaptersinthisreport.Forexample,istheentityentirelygrazinglandorissomeofitinforestmanagement?Finally,theremaybequestionsofhowtoassociatemanagementpracticestothemostrelevantcategoriesforuseoftheaccountingguidelinesprovided,includinganyguidanceonsizelimits,whatconstitutesmanagement,andhowtoaddresschanginglanduses.Definitionsareanimportantpartofsettingboundariesandwillbeprovidedhereaswell.Examplesofmanagementpractices(e.g.,irrigation,tillage,orresiduemanagementforcroplands)areincludedwithinthevarioussectordescriptionsbelow(i.e.,croplandsandgrazinglands,wetlands,animalproduction,andforestry);whenconsideringwhatconstitutesamanagementpractice,anentityshouldnotethatinthecontextoftheseguidelines,amanagementpracticereferstochangesinthemanagementofagriculture,animal,orforestproductionthatimpactGHGemissionsandremovals.

TheobjectiveofthesemethodsistoprovideacompleteestimationofGHGemissionsandcarbonsequestrationwithintheboundariesofanentity.Thisisnotintendedasalifecycleanalysis,aswillbefurtherexplainedbelowinthediscussionofmaterialboundaries.Themethodsaredesignedtobeappliedatthelocalscale,butneedtobeflexibleenoughtobevalidforverylargeentities.The


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methodsaredesignedtoestimatefluxesfortheentiretyofanentity,butmustalsobecapableofevaluatingasinglepractice(e.g.,project)implementedwithinasingleentityoraggregatedacrossmultipleentities.

AsnotedinChapter1,thedefinitionofanentitycanbecomplicated.Forthepurposesofthisreport,usersshouldsimplydelineatethespatialextentofitsentityasthelandareathatisundertheirownershipand/ormanagementcontrolfortheforeseeablefuture.Thisisageneralizedapplicationofthetermentity,andtheusershouldrecognizethatanypolicy,program,orcontractualagreementmaydefinetheuser’sentitydifferentlyandresultinadifferentboundaryoftheentity.Withintheentityboundary,therewillbeavarietyoflandusesthatwillrelyonmethodsfromvariouschaptersinthisreport.Anentityshouldbesubdividedifitincludesdifferentcategoriesoflanduse,suchasgrazinglandandcropland,buttheentireentityshouldfallintosomeland‐usecategory.Norigidlowerboundisspecifiedhereforthearealextentofaland‐usecategorization,but,ingeneral,areasofanacreormoremeritidentification.

Withintheboundariesoftheoverallentity,areasofcroplandwillneedtobeidentified.Beyondjustareasproducingroworclose‐growncropsorhay,croplandalsoincludeslandthatisfallowandareasofhayandpasturethataremanagedinarotationwithothercrops.Wetlands(includingdrainedwetlandsandhydricsoils)andlandunderagroforestrypracticeswherethepredominantproductionactivityiscroppingshouldalsobeconsideredascroplandforthepurposesofthisreport.Finally,areasofcroplandthataresetaside,suchaslandsintheConservativeReserveProgram,areincludedinthismanagementtype.ThemethodsfortheselandsareincludedinChapter3ofthisreport.Thecroplandareasshouldbedelineatedasfieldsorgroupsoffieldsforwhichthebasicrotationsandmanagementpracticesareallsimilar.

Thenextlandmanagementtypetobeidentifiedisgrazingland.Thisislandthatisusedprimarilyforgrazinganimalsandnotaspartofarotationwithothercrops.Thisportionoftheentitywillprimarilybecomprisedofpastureland(whichismoreintensivelymanaged),andrangeland(whichistypicallylessintensivelymanagedandusuallyhasahigherproportionofnativespecies).Wetlands(includingdrainedwetlandsandhydricsoils)andlandmanagedasagroforestryshouldbeincludedinthiscategoryiftheprimaryuseofthetractoflandisforgrazinglivestock.Therewillbeobviousoverlapbetweengrazinglandandforestlandmethodswherethelandmatchesthedefinitionofbothuses.Forexample,ifanyactivemanagementisfocusedonenhancingtreegrowthandtimberproduction,theusershouldidentifytheseareasasforestlandandthemethodswillneedtobeintegratedtoaccountfortheimpactofgrazingmanagementontheforestland.Grazinglandsshouldbedelineatedascontiguousareasthatareunderasimilarstockingrateandsetofmanagementpractices,andthemethodsforgrazinglandsaspresentedinChapter3shouldbefollowed.Inaddition,theGHGestimationmethodsassociatedwiththegrazinganimalsaspresentedinChapter5shouldbefollowed.Developmentofanintegratedtoolthatfollowsthesemethodswillneedtoaccountforthesemanagementinteractions.

Cropland:Aland‐usecategorythatincludesareasusedfortheproductionofadaptedcropsforharvest,includingbothcultivatedandnon‐cultivatedlands.Cultivatedcropsincluderowcropsorclose‐growncropsandalsohayorpastureinrotationwithcultivatedcrops.Non‐cultivatedcroplandincludescontinuoushay,perennialcrops(e.g.,orchards),andhorticulturalcropland.Croplandalsoincludeslandwithalleycroppingandwindbreaks,aswellaslandsintemporaryfalloworenrolledinconservationreserveprograms(i.e.,set‐asides).Roadsthroughcropland,includinginterstatehighways,Statehighways,otherpavedroads,gravelroads,dirtroads,andrailroadsareexcludedfromcroplandareaestimatesandare,instead,classifiedassettlements.


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Forestlandshouldbedelineatedaslandthatisusedprimarilyforwoodybiomassproduction,whetherforsawwood,pulp,biofuels,orotherforestorwoodlandrelatedindustry,orlandthatistreecoveredandmanagedforrecreationalorconservationpurposes.Thiswillincludeareasofagroforestryandsilvopasturewheretheprimarymanagementobjectiveonthelandscapeisforest‐relatedproduction.Anintegratedtoolwouldneedtobeflexibleenoughtoalsocapturetheimpactoftheadditionalcroppingorgrazingactivitiesoccurringontheparcel.Similarly,wetlandareasthatarewoodedorforestedandmanagedprimarilyasforestsandwoodlandswillbeconsideredinthiscategory.Also,becauseharvestingisoneofthemajormanagementpracticesinforestlandandbecauseharvestedwoodmovestoseverallong‐termcarbonpoolsthatundergodifferingratesofdecay,itisimportantthatthemethodsaccountforemissionsfromHWPs,eventhoughtheymaybemovedoutsideoftheboundaryofthefarm/ranch/forestoperation.

TheforestlandmethodsarepresentedinChapter6ofthisreport.Tractsofforestshouldbedelineatedsuchthatanygiventractismadeupoftreesofasimilarstandageandspeciesmix,andthattheentiretractisunderoneuniformsetofmanagementpractices.Onagivenentity,theremaybetreesthatexistoutsideofclearlydefinedforests,suchasorchardsandvineyards,farmsteadshelterbeltsandfieldwindbreaks,andagroforestrypractices.Eventhoughtheselandsmaynotmeetthedefinitionofaforest,thecarbonstorageinthetreesislikelysignificant.Insomecasesitmaybeusefultoevaluateindividualtreesorsmallstandsoftrees(usingmethodspresentedinChapter6).Inothercases,theestimationmayrequireablendingofmethodssuchascroplandmethodsfromChapter3withforestmethodsfromChapter6.

GrazingLand:Aland‐usecategoryonwhichtheplantcoveriscomposedprincipallyofgrasses,grass‐likeplants,forbs,orshrubssuitableforgrazingandbrowsing,andincludesbothpasturesandnativerangelands.Thisincludesareaswherepracticessuchasclearing,burning,chaining,and/orchemicalsareappliedtomaintainthegrassvegetation.Savannas,somewetlandsanddeserts,andtundraareconsideredgrazingland.Woodyplantcommunitiesoflowforbsandshrubs,suchasmesquite,chaparral,mountainshrub,andpinyon‐juniper,arealsoclassifiedasgrazinglandiftheydonotmeetthecriteriaforforestland.Grazinglandincludeslandmanagedwithagroforestrypracticessuchassilvopastureandwindbreaks,assumingthestandorwoodlotdoesnotmeetthecriteriaforforestland.Roadsthroughgrazingland,includinginterstatehighways,Statehighways,otherpavedroads,gravelroads,dirtroads,andrailroadsareexcludedfromgrazinglandareaestimatesandare,instead,classifiedassettlements.

Forestland:Aland‐usecategorythatincludesareasatleast120ft(36.6m)wideand1acre(0.4ha)insizewithatleast10percentcover(orequivalentstocking)bylivetreesofanysize,includinglandthatformerlyhadsuchtreecoverandthatwillbenaturallyorartificiallyregenerated.Forestlandincludestransitionzones,suchasareasbetweenforestandnon‐forestlandsthathaveatleast10percentcover(orequivalentstocking)withlivetreesandforestareasadjacenttourbanandbuilt‐uplands.Roadside,streamside,andshelterbeltstripsoftreesmusthaveacrownwidthofatleast120ft(36.6m)andcontinuouslengthofatleast363ft(110.6m)toqualifyasforestland.Unimprovedroadsandtrails,streams,andclearingsinforestareasareclassifiedasforestiftheyarelessthan120ft(36.6m)wideor1acre(0.4ha)insize;otherwisetheyareexcludedfromforestlandandclassifiedassettlements.Tree‐coveredareasinagriculturalproductionsettings,suchasfruitorchards,ortree‐coveredareasinurbansettings,suchascityparks,arenotconsideredforestland(Smithetal.,2009).


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Wetlandareaswillfallintooneoftwocategories:managedwetlandsornatural,unmanagedwetlands.Manywetlandareasmayhavealreadybeendelineatedinoneoftheabovecategories,andtheirmanagementwillbecapturedthroughestimationforthatcategory.If,however,therearewetlandareasthathavenotalreadybeenincludedinthecropland,grazingland,orforestlanddelineationsabove,thoseshouldbeidentifiedhere.AnaturallyoccurringwetlandthatdoesnothaveactivemanagementbeingappliedinordertoincreaseproductivityorprovideotherenvironmentalserviceswillnotbeincludedintheestimationofGHGfluxes.Thesenatural,unmanagedwetlandsshouldsimplybeincludedinthecategoryof“otherland”asdefinedbelow.Anywetlandareasthatareoutsidetheboundariesofthedefinedareasmentionedaboveandwherethelandmanagerisactivelyapplyingmanagementdecisionsinordertoenhanceproductivityorprovideenvironmentalservicesshouldbedelineatedasamanagedwetlandandincluded.ThisreportprovidesestimationmethodsinChapter4foremissionsfrompalustrinewetlands,2influencedbyavarietyofmanagementoptionssuchaswatertablemanagement,timberorotherplantbiomassharvest,andwetlandsthataremanagedwithfertilizerapplications.Currently,thereareinsufficientdataandtherefore,theGHGfluxeswilllikelynotbeincludedinanentity’sGHGestimationuntiladequatedataexisttoprovidethatestimationwithareasonableandmeasurablelevelofuncertainty.

Settlementswillfallintotwobroadcategories:(1)landwheretheentitymanagerimposesmanagementdecisions;and(2)landwherethemanagerdoesnotregularlyimposemanagementdecisionsthatimpactcarbonbalances.Examplesofsettlementlandthatmaybesignificantfromacarbonmanagementperspectivewouldbedevelopedlivestockfeedyards,dairybarns,poultryhouses,manurepiles,andmanureorrunofflagoons.Examplesofdevelopedlandwheremanagementisnotofconcerntocarbonbalancesishomes,yards,driveways,workshops,roads,andparkingareas.ForpurposesoftheGHGfluxestimation,onlytheareaswithcarbonmanagementimplications(e.g.,animalhousing,manurewastetreatmentareas)needtobeidentifiedwithinthespatialboundarydelineation.TheselivestockandmanuremanagementmethodsarepresentedinChapter5ofthisreport.Theremainingsettlementlandswithoutcarbonmanagementimplications(e.g.,roadsandrailroads)cansimplybeexcludedfromthespatialboundariesanentitychoosestoaccountforwithinthesettlementland‐usecategory.

2Palustrinewetlandsarenontidalwetlandsthatareprimarilycomposedoftrees,shrubs,persistentemergent,emergentmossesorlichens,andallwetlandsthatoccurintidalareaswheresalinityduetoocean‐derivedsaltsisbelow0.5percent.Palustrinewetlandsmusthaveanarealessthan20acres,nothaveactivewave‐formedorbedrockshoreline,haveamaximumwaterdepthoflessthan2m[6.6ft],andhaveasalinitylessthan0.5percent(USGS,2006).

Wetland:Aland‐usecategorythatincludeslandwithhydricsoils,nativeoradaptedhydrophyticvegetation,andahydrologicregimewerethesoilissaturatedduringthegrowingseasoninmostyears.Wetlandvegetationtypesmayincludemarshes,grasslandsorforests.Wetlandsmayhavewaterlevelsthatareartificiallychanged,orwherethevegetationcompositionorproductivityismanipulated.Theselandsincludeundrainedforestedwetlands,grazedwoodlandsandgrasslands,impoundmentsmanagedforwildlife,andlandsthatarebeingrestoredfollowingconversiontoanon‐wetlandcondition(typicallyasaresultofagriculturaldrainage).Provisionsforengineeredwetlandsincludingstormwaterdetentionponds,constructedwetlandsforwatertreatment,andfarmpondsorreservoirsarenotincluded.Naturallakesandstreamsarealsonotincluded.


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Anylandthatisactivelymanagedinsuchawayastoimpactbiomassgrowthorotherwiseimpactproduction‐relatedGHGemissionsshouldhavebeencapturedwithinthespatialboundariesdefinedfortheland‐usecategorieslistedabove.AnyremaininglandshouldbecategorizedasotherlandsorunmanagedlandandwillnotbeconsideredintheestimationofGHGfluxes.Thisincludesthewetlandanddevelopedareasthatwerepreviouslynotedasnothavingactivemanagement—i.e.,unmanagedwetlandsandunmanagedsettlements.Italsoincludesanyotherareaswithintheentityboundarythatrepresentbarren,mined,abandoned,orotherwiseunmanagedland—i.e.,otherland.

Land‐coverchangeissimplyavariationfromyeartoyearinwhatisgrowingonaparcelofland,suchasrotatingcornandsoybeancrops,andisnotconsideredland‐usechange.Incontrast,land‐usechangeisafundamentalshiftinpurposeorproductionofaparcel,suchasashiftfromcroppingtoforestproductionorviceversa.Land‐usechangeneedstobeaccountedforintheannualGHGflux,astheimpact(eitherpositiveornegative)onbiomassandsoilcarboncanbesignificant.Theseland‐usechangemethodsarepresentedinChapter7ofthisreport.

Animalproductionisnotnecessarilyaspatiallydefinedactivitywithintheentity,buthastobeconsideredaspartofthephysicalboundaryofthemanager’soperation.TherearethreemainareasthatneedtobeconsideredasimportanttoestimatingGHGemissionsfromananimalproductionsystem:methaneemissionsfromtheanimals,methaneandnitrousoxideemissionsfrommanagementofmanure,andanyemissionsimpactsrelatedtoanimalhousing.Animalproductioninthechapterisdiscussedbyanimalsystemtype,includingbeef,dairy,sheep,swine,andpoultry.Thecollectivenounforagroupofanimalstypicallyvariesbyspecies,butforthepurposesofthisreport,wewillrefertoanygroupofanimalsofthesameanimaltypethatarekepttogetherunderacommonsetofproductionmanagementpracticesasaherd.Followingthisdefinition,theentity’smanagermayhaveseveraldistinctlydifferentherdsthatmakeuptheentity.GHGemissionsfromanimalproductionwillvarygreatlydependinguponspecies(digestiveprocesses),growthstage,diet,andmanurestorageandmanagement.Timingisalsoachallengeinestimatingemissionsfromtheanimalproductionsector,asemissionsperanimalchangedramaticallyasayounganimalgrowsandmatures,asfeedlotcattlearefinished,orasdairycowscyclebetweengestatingandlactating.Insomecases,itwilllikelybenecessaryfortheusertoestimateemissionsforaherdusingaverageweight,averageage,andotherrepresentativecharacteristicstorepresenttheherdpopulation.Inothercases,itwillbenecessarytogeneralizebyseasons—manuremanagementmaybedifferentinwinterthansummer,animalfeedmixturemayvarybyseasonorbyanimalgrowthstage.Averaging

Settlements:Aland‐usecategoryrepresentingdevelopedareasconsistingofunitsof0.25acres(0.1ha)ormorethatincludesresidential,industrial,commercial,andinstitutionalland;constructionsites;publicadministrativesites;railroadyards;cemeteries;airports;golfcourses;sanitarylandfills;sewagetreatmentplants;watercontrolstructuresandspillways;parkswithinurbanandbuilt‐upareas;andhighways,railroads,andothertransportationfacilities.Alsoincludedaretractsoflessthan10acres(4.05ha)thatmaymeetthedefinitionsforforestland,cropland,grassland,orotherlandbutarecompletelysurroundedbyurbanorbuilt‐upland,andsoareincludedinthesettlementcategory.Ruraltransportationcorridorslocatedwithinotherlanduses(e.g.,forestland,cropland,andgrassland)arealsoincludedinsettlements.

OtherLand:Aland‐usecategorythatincludesbaresoil,rock,ice,andalllandareasthatdonotfallintoanyoftheotherfiveland‐usecategories,whichallowsthetotalofidentifiedlandareastomatchtheidentifiedlandbase.


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andgeneralizinginthiswayshouldbeadequateincapturingtheinformationneededtoprovideareasonableestimateofGHGemissionsaslongasthemanagerappliesassumptionsconsistentlyacrosstheherdsandthroughoutthetimeunderconsideration.Forexample,assuminganaveragefinishweightforfeederanimalsintheherdshouldprovideareasonableGHGestimateaslongastheassumedweightdoesnotchangefromyeartoyear,unlessaspecificmanagementdecision(suchasachangeinanimaldiet)resultsinanactualchangeinfinishingweight,inwhichcasethechangeinaverageswouldbeappropriate.SpecificmethodsforanimalproductionsystemsarepresentedinChapter5ofthereport.Insomecases,suchasmanureappliedtocropland,methodsfromChapter3willbeutilizedaswell.

Occasionally,physicalboundarieswillchangeovertime.Whetheraportionofacroplandfieldisconvertedtoananimalfeedlot,shelterbeltorripariantreesareplantedontoformercropland,orabandonedlandrevertstograzinglandorforestland,thesechangescouldresultintheneedforanewdelineationofparcelboundariesoradissectionofoneparcelintoseveralparcelswithmorethanonemanagementstrategy.Fortheportionoftheparcelwherethischangehasoccurred,theland‐usechangemethods(Chapter7)willbeusedtoestimateGHGfluxes.

Figure2‐1canbeusedtohelplandownersdeterminethelandusecategoryfortheirlandarea,accordingtothedefinitionsabove.

2.1.2.2 TemporalBoundaries

Temporalissuesincludesuchconsiderationsasthefrequencyofthereportedestimates,thetreatmentofactivitiesthatoccurwithinanaccountingperiodbuthavelong‐termimplicationsforcarbonbalances(e.g.,changesinsoilcarbonfollowingachangeintillagepractices),andhowtoaccountforshort‐termmanagementorshort‐termadjustmentstolong‐termmanagementdecisions.Alsosignificantishowtoaddressmovementofspatialboundariesovertimeandwithland‐usechange.ThissectionwillattempttoresolvesomeofthesetemporalissuesaroundGHGemissionestimationandreporting.

ThemethodsreportedhereareintendedtoprovideameansofannualaccountingandreportingofGHGfluxes.Annualchangesinsomeemissionsareeasilyquantified,butforothersitismuchmoredifficult.Carbonstoredintrees,forexample,mayneedtobeestimatedoveralongerperiod,withthechangethenconvertedtoanannualizedestimate.

Thereportmethodologiesassumeanaccountingperiodofonecalendaryear(e.g.,365days)whenestimatingannualizedemissionsinaparticularsectororsourcecategory.

Managementdecisionsalsoaresignificanttotheaccountingtimehorizon.Forexample,aforestmanagementplanmightcallfortimberharvestorthinning.Intheyearofharvest,theannualaccountingwillreflectalossofstandingliveand/orstandingdeadcarbonstocks,yetinthelongertermmanagementstrategy,thenetresultcouldbeanincreaseintotalcarbonstocks.Ifalandmanagerhasamanagementplanthatprescribesforestthinning,butthenharvestsmoreaggressivelythantheplan,considerationshouldbegivenastowhetherthisconstitutesachangeinforestmanagement,whichwouldbediscussedintheforestmanagementmethods(seeChapter6).

Therearealsotimeswhenmanagementhastotakecorrectiveactionortemporarilydeviatefromalong‐termmanagementplan.Thiscouldbethecasewhereacroplandmanagerhasadoptedano‐tillmanagementstrategy,butafterseveralyearshastousetillageoneyearbecauseofweather,pests,orotherextenuatingcircumstances.Inthiscase,themethodswillideallybesensitiveenoughtocapturetheGHGimpactofthedeviationfromthemanagementplan.


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Figure2‐1:DecisionTreeforDeterminingLand‐UseCategoryforLandAreas


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2.1.2.3 ActivityBoundaries

Itisimportanttodistinguishwhichactivitieswithinanentityaresubjecttoaccounting.Thisaccountingsystemisfocusedonland‐basedactivitiessuchastillageandharvesting,andnotonemissionsofGHGsthatarerelatedtofossilfueluse.Thus,emissionsfromtractorfuelorfuelusedforcropdryingarenotcounted,noraretheenergyinputsrequiredtomanufacturefertilizerorfarmtools,ortoheatfarmbuildings—i.e.,indirectGHGemissions(seeChapter1).However,asmentionedinChapter1,wherethereareobviouschangesinthelevelofcombustionduetoachangeinpractices,thatchangeisqualitativelydiscussed.Forexample,ashiftfromconventionaltillagetonotillcanresultinalargereductioninfuelconsumptionbecauseoffewertripsacrossthefield.Theserelationshipsarenotedqualitativelyinthereport,butquantitativemethodsarenotproposed.MethodsforquantifyingemissionsfromstationaryormobilecombustionsareavailablefromotherFederalagencies.

Aspreviouslymentioned,themethodsinthisreportdonotconstitutealife‐cycleassessmentfortwoprimaryreasons.Firsttheactivityboundariesdonotincludeemissionsfromfossil‐fueluse.Second,thetemporalboundariesarefocusedonannualreportinganddonotencompasstherangeofactivitiessuchascapitalinvestment,materialsupplies,anddisposal.

2.1.2.4 MaterialBoundaries

MaterialboundariesincludetheGHGsthataretobeconsideredintheestimationandshouldalsodelineatewhatsourcesofthosegasesareincludedandwhatareexcluded.Alsoincludedinthissectionisadiscussionoftheglobalwarmingpotentials(GWPs)usedthroughoutthereport.Itisimportanttodetermineupfrontwhichgasesareincludedandwhicharenot.Itisalsoimportanttodeterminehowmuchfreedomtheuserhasinwhatisestimatedandwheretheseboundarieslieinordertoensurethatachangeinmanagementthatreducesemissionsinonesectordoesnotinadvertentlycauseemissionstoriseoutsideoftheboundariesbeingreported.

ThereportincludesestimationmethodologiescoveringtheGHGemissionsfromthecroplandsandgrazinglands,wetlands,animalproduction,forestry,andland‐usechangesectors.Withinthesesectorsandsourcecategories,emissionsandremovalsofthemainGHGs—carbondioxide(CO2),methane(CH4),andnitrousoxide(N2O)—areaccountedfor.Itshouldbenotedthatcarbonsequestration(i.e.,increasesincarbonstocks)isestimatedintermsofcarbondioxideequivalents(CO2‐eq).Itshouldalsobenotedthattheanimalproductionchapterincludesdiscussionofammonia(NH3),asthisisanimportantprecursortoN2Oemissionsfrommanuremanagement.EstimatingNH3emissionsisbeyondthescopeofthisreport—NH3isnotconsideredaGHG—butsinceNH3issignificantasaprecursortoN2O,understandingchangesinNH3emissionsresultingfromchangesinmanagementisimportant.

Emissionsandsequestrationvaluesarepresentedinthisreportintermsofthemass(notvolume)ofeachgas,usingmetricunits(e.g.,metrictonsofmethane).Intheintegratedtool,themassesofeachgaswillbeconvertedintoCO₂equivalentunitsusingtheGWPsforeachgasintheInternationalPanelonClimateChange(IPCC)SecondAssessmentReport.

AGWPisanindexusedtocomparetherelativeradiativeforcingofdifferentgaseswithoutdirectlycalculatingthechangesinatmosphericconditions.GWPsarecalculatedastheratiooftheradiativeforcingthatwouldresultfromtheemissionsofonekilogramofaGHGtothatfromtheemissionsofonekilogramofCO₂overadefinedperiodoftime,suchas100years.EmissionsintermsofCO₂equivalents(CO2‐eq)areestimatedbymultiplyingthemassofaparticularGHG(e.g.,CH4,N2O)bytherespectiveGWPforthatparticularGHG.TheGWPsusedinthisreportareshowninTable2‐1below.


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Themethodsinthisreportfocusprimarilyonthedirectemissionsresultingfrommanagementdecisionsmadewithintheboundariesoftheentity—e.g.,withinthefarmandforestgate.Theindirectemissionsrelatedtoinputsintotheentityarenotconsidered.Thereasonforthisisthatthoseemissionswouldlikelybereportedbythemanufacturerproducingtheinputs.Ifonewereconductingafulllife‐cycleassessment,theseemissionswouldneedtobeincluded,butforpurposesoftheemissionsbeingestimatedherewefocusprimarilyontheemissionsresultingwithinthespatialboundaryoftheentity.Theonenotableexceptionthatisaccountedforiswhenmanagementdecisionsontheoperationhaveaspecificrelatedinfluenceonemissionsleavingtheentity’sboundary.AnexampleofthisisindirectemissionssuchasnitrogenthatisappliedwithintheoperationbutthencarriedoffsiteviaerosionorleachingandcontributestoN₂Oemissionsoffsite.Anotherexampletoconsiderisharvestedcommodities.Inthecaseofgrainsorotheragriculturalcommodities,theproductisassumedtobeconsumedwithinarelativelyshortamountoftime,resultinginnonetgainorlossrelatedtoGHGaccounting.HWPsaresomewhatdifferent,asmuchofthatharvestwillendupinlong‐termcarbonpoolseitherasstructures,furniture,orotherwoodproducts,orinlandfills.ThisreportdoesprovideadiscussionofN₂OlossesthatresultfromerosionandleachingoffertilizernitrogenandthecarbonpoolsrelatedtothefateofHWPs.

2.2 ReviewofRelevantCurrentToolsandMethods

ThissectionprovidesanoverviewofthecurrentestimationmethodsorapproachesanentitycouldusetoestimateGHGemissionsandsinksontheirproperty.Thisoverviewisfollowedbyasummaryofeachsector’sproposedmethodologiesforentityGHGestimations.

ThereareseveralapproachesthatafarmerorlandownercanusetoestimateGHGemissionsatanentityscale,andeachapproachgivesvaryingaccuracyandprecision.Themostaccuratewayofestimatingemissionsisthroughdirectmeasurement,whichoftenrequiresexpensiveequipmentortechniquesthatarenotfeasibleforasinglelandownerormanager.Ontheotherhand,lookuptablesandestimationequationsaloneoftendonotadequatelyrepresentlocalvariabilityorlocalconditions.Thisreportattemptstodelineatemethodsthatbalanceuser‐friendliness,datarequirements,andscientificrigorinawaythatistransparentandjustified.

Thefollowingapproacheswereconsideredfortheseguidelines:

Basicestimationequations–Involvecombinationsofactivitydata3withparametersanddefaultemissionfactors.4Anydefaultparametersordefaultemissionfactors(e.g.,lookuptables)areprovidedinthetext,orifsubstantialinlength,inanaccompanyingcompendiumofdata.

3Activitydataaredataonthemagnitudeofhumanactivityresultinginemissionsorremovalstakingplaceduringagivenperiodoftime(IPCC,1997).

4Emissionfactorisdefinedasacoefficientthatquantifiestheemissionsorremovalsofagasperunitactivity.Emissionfactorsareoftenbasedonasampleofmeasurementdata,averagedtodeveloparepresentativerateofemissionforagivenactivitylevelunderagivensetofoperatingconditions(IPCC,2006).

Table2‐1:GlobalWarmingPotentialsUsedintheReport

SpeciesChemicalFormula

Lifetime(years) GWPa

Carbondioxide CO2 Variable 1Methane CH4 12±3 21Nitrousoxide N2O 120 310a GWPsusedare100‐yeartimehorizon,inaccordancewiththeIPCCSecondAssessmentReport(IPCC,2007).


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Models–Usecombinationsofactivitydatawithparametersanddefaultemissionfactors.Theinputsforthesemodelscanbeancillarydata5(e.g.,temperature,precipitation,elevation,andsoilnutrientlevelsthatmaybepulledfromanunderlyingsource),biologicalvariables(e.g.,plantdiversity),orsite‐specificdata(e.g.,numberofacres,numberofanimals).Theaccuracyofthemodelsisdependentontherobustnessofthemodelandtheaccuracyoftheinputs.

Fieldmeasurements–Actualmeasurementsthatafarmerorlandownerwouldneedtotaketomoreaccuratelyestimatethepropertiesofthesoil,forest,orfarmtoestimateactualemissions.Measuringactualemissionsonthelandrequiresspecialequipmentthatmonitorstheflowofgasesfromthesourceintotheatmosphere.Thisequipmentisnotreadilyavailabletomostentities,somoreoftenfieldmeasurementsareincorporatedintoothermethodsdescribedinthissectiontocreateahybridapproach.Afieldmeasurementsuchasasamplemeantreediametercouldbeincorporatedintoothermodelsorequationstogiveamoreaccurateinput.

Inference–UsesState,regional,ornationalemissions/sequestrationfactorsthatapproximateemissions/sequestrationperunitoftheinput.Theinputdataisthenmultipliedbythisfactortodeterminethetotalonsiteemissions.Thisfactorcanhavevaryingdegreesofaccuracyandoftendoesnotcapturethemitigationpracticesonthefarmortheuniquesoilconditions,climate,livestockdiet,livestockgenetics,oranyfarm‐specificcharacteristics,althoughtheycanbedevelopedwithspecificsoiltypes,livestockcategories,orclimacticregions.

Hybridestimationapproaches–Anapproachthatusesacombinationoftheapproachesdescribedabove.Theapproachoftenusesfieldmeasurementsormodelstogenerateinputsusedforaninference‐basedapproachtoimprovetheaccuracyoftheestimate.

2.3 SelectionofMostAppropriateMethodandMitigationPracticestoInclude

Indraftingthereport,anumberofselectioncriteriawereconsidered(e.g.,transparency,consistency,comparability,completeness,accuracy,costeffectiveness,easeofuse).Adescriptionofeachappearsbelow:

Transparency–Theassumptionsandmethodologiesusedforaninventoryshouldbeclearlyexplainedtofacilitatereplicationandassessmentoftheinventorybyusersofthereportedinformation.Thetransparencyofinventoriesisfundamentaltothesuccessoftheprocessforthecommunicationandconsiderationofinformation.

Consistency–Themethodsusedtogenerateinventoryestimatesshouldbeinternallyconsistentinallitselementsandtheestimatesshouldbeconsistentwithotheryears.Aninventoryisconsistentifthesamemethodologiesareusedforthebaseandallsubsequentyearsandifconsistentdatasetsareusedtoestimateemissionsorremovalsfromsourcesorsinks.Consistencyisanimportantconsiderationinmergingdifferingestimationtechniquesfromdiversetechnologiesandmanagementpractices.

Comparability–Fortheguidelinestobecomparable,theestimatesofemissionsandsequestrationbeingreportedbyoneentityarecomparabletotheestimatesbeingreportedbyothers.Forthispurpose,entitiesshouldusecommonmethodologiesandformatsfor

5Ancillarydataareadditionaldatanecessarytosupporttheselectionofactivitydataandemissionfactorsfortheestimationandcharacterizationofemissions.Dataonsoil,croporanimaltypes,treespecies,operatingconditions,andgeographicallocationareexamplesofancillarydata.


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estimatingandreportinginventories.Consequently,ingeneral,themethodsspecifyonemethodforanytechnologyormanagementpractice(i.e.,methodssuggestedinthisreportdonotallowuserstoselectfromamenuofmethods).

Completeness–Themethodsmustaccountforallsourcesandsinks,aswellasallGHGstothegreatestextentpossible.Completenessalsomeansfullcoverageofsourcesandsinksunderthecontroloftheentity.Completenessisanimportantconsiderationtobebalancedwitheaseofuseinreportingappropriatelyforanentitythatmayhaveaminoractivityoranactivitywithseverelylimiteddataavailability.

Accuracy–Arelativemeasureoftheexactnessofanemissionorremovalestimate.Estimatesshouldbeaccurateinthesensethattheyaresystematicallyneitherovernorundertrueemissionsorremovals,asfarascanbejudged,andthatuncertaintiesarereducedasfaraspracticable.

Costeffectiveness–Ameasureoftherelativecostsandbenefitsofadditionaleffortstoimproveinventoryestimatesorreduceuncertainty.Forexamplethereisabalancebetweentherelativecostsandbenefitsofadditionaleffortstoreduceuncertainty.

Easeofuse–Ameasureofthecomplexityoftheuserinterfaceandunderlyingdatarequirements.

Theworkinggroupsdevelopedthefollowingselectioncriteriaforthemitigationpracticesthatcouldbeincludedinthemethods:

1. Thesciencereflectsamechanisticunderstandingofthepractice'sinfluenceonanemissionsource.

2. Publishedresearchsupportsareasonablelevelofrepeatability/consistency(canuseinternationalstudiesifsimilarmanagement,climate,andsoilsasU.S.conditions).

3. Thereisgeneralagreementthatatleastthesignandrangeofresponsesarereasonablywellunderstood.

4. Thereisconsensusoftheauthorsthatthepracticecanbeadequatelyincluded.Toreachconsensus,theauthorsdiscussedissuessuchas:Wouldleavingamitigationpracticeoutmakethereportincomplete?Istherestrongenoughevidencethatthemethodwillholdupforthispracticeforatleastthenextfiveyears?

Thereweremitigationpracticesthatdidnotfulfillthesecriteria,andthosepracticeswerecitedasareasthatrequiremoreresearchinordertofullyunderstandtheeffectofchangesinthepracticetoGHGemissions.TheseresearchgapsareintendedtobecomeareasthatUSDA,non‐governmentalorganizations,universities,andotherresearchinstitutionswillconsiderasimportantareastofocusagricultureandforestryclimate‐changeresearchpriorities.Othertopics,suchasalbedoeffects,werenotconsidered.Currently,withtheexceptionofurbanareas,albedoeffectsarehighlyvariableandaredifficulttoreliablyquantify.

2.4 OverviewofSectors

Thisreportcoversemissionssourcesandsinksfromcroplands/grazinglands,managedwetlands,animalproductionsystems,andforestry,alongwithchangesinlanduse.Figure2‐2canbeusedtohelplandownersdeterminewhichchaptercanbeusedtoestimatetheirGHGsourcesandsinksfromtheirland.


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Figure2‐2:DecisionTreeforDeterminingWhichMethodstoFollowinThisReport


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Figure2‐2:DecisionTreeforDeterminingWhichMethodstoFollowinThisReport(continued)

Thefollowingsectionsprovideanoverviewofthesectorscoveredinthisreport.Foreachsector,theemissionsourcesandsinksareintroducedaswellasthemanagementpracticesimpactingGHGemissions.

2.4.1 CroplandsandGrazingLands

Croplandsincludeallsystemsusedtoproducefood,feed,andfibercommodities,inadditiontofeedstocksforbioenergyproduction.MostU.S.croplandsaredrylands(irrigatedorunirrigated);riceandafewothercropsaregrowninwetlands.SomecroplandsaresetasideintheConservationReserveProgram.Croplandsalsoincludeagroforestrysystemsthatareamixtureofcropsandtrees,suchasalleycropping,shelterbelts,andriparianwoodlots.Grazinglandsaresystemsthatareusedforlivestockproductionandoccurprimarilyongrasslands.Grasslandsarecomposedprincipallyofgrasses,grass‐likeplants,forbs,orshrubssuitableforgrazingandbrowsing;theyincludebothpasturesandnativerangelands(EPA,2011).Savannas,somewetlandsanddeserts,andtundracanbeconsideredgrazinglandsifusedforlivestockproduction.Grazinglandsystemsincludemanagedpasturesthatmayrequireperiodicmanagementtomaintainthegrassvegetationandnativerangelandsthattypicallyrequirelimitedmanagementtomaintain.


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CroplandandgrazinglandsaresignificantsourcesofCO2,N2O,andCH4emissionsandcanalsobeasinkforCO2andCH4(U.S.EPA,2011).N2Oemissionsfromsoilsareinfluencedbylanduseandmanagementactivity,particularlynitrogenapplication.Landuseandmanagementalsoinfluencecarbonstocksinbiomass,deadbiomass,andsoilpools.CropandgrazinglandsystemscanbeeitherasourceorsinkforCO2,dependingonthenetchangesinthesecarbonpools.ThemaininfluencesonnitrogenuseefficiencyandN2Oemissionsarefertilizerrate,timing,placement,andnitrogensource.Tillageintensity,croppingintensity,andtheuseofcroprotationcanhavesignificanteffectsonsoilcarbonstocks.

OthermanagementactivitiesalsoaffectGHGemissionsfromsoils.IrrigationcanimpactCH4andN2Oemissionsaswellascarbonstocks.Burningdecreasesbiomasscarbonstocksandalsosoilorganiccarbonstocksduetodecreasedcarboninputtothesoilsystem.BurningwillalsoleadtoemissionsofCH4andN2Oandothergases(CO,NOx)thatareGHGprecursors.CH4canberemovedfromtheatmospherethroughtheprocessofmethanotrophyinsoils,whichoccursunderaerobicconditionsandgenerallyinundisturbedsoils.CH4isproducedinsoilsthroughtheprocessofmethanogenesis,whichoccursunderanaerobicconditions(e.g.,wetlandsoilsusedforproductionofrice).Bothprocessesaredrivenbytheactivityofmicro‐organismsinsoils,buttherateofactivityisinfluencedbylanduseandmanagement.

TheinfluenceofcropandgrazinglandmanagementonGHGemissionsisnottypicallythesimplesumofeachpractice’seffect.Theinfluenceofonepracticecandependonanotherpractice.Forexample,theinfluenceoftillageonsoilcarbonwilldependonresiduemanagement.Theinfluenceofnitrogenfertilizationratescandependonfertilizerplacementandtiming.Becauseoftheseinterconnections,estimatingGHGemissionsfromcropandgrazinglandsystemswilldependonacompletedescriptionofthepracticesusedintheoperation,aswellasancillaryvariablessuchassoilcharacteristicsandweatherorclimateconditions.ItisalsoimportanttonotethattrendsinGHGemissionsassociatedwithachangeincropandgrazinglandmanagementcanbereversedifthelandownerrevertstotheoriginalpractice.Forexample,afarmermightswitchfromconventionaltillagetono‐tillfor10yearsandseeanincreaseinsoilcarbonsequestration;if,however,thefarmerthenrevertstoconventionaltillage,thegainsinsoilcarbonwillbequicklylostasthestoredsoilcarbonisreleasedbackintotheatmosphereasCO2,negatingtheGHGmitigationoftheprevious10years.However,reversalswillnotnegatetheGHGmitigationforCH4orN2Othatoccurredpriortothereversion.IfemissionsarereducedforCH4orN2O,theemissionreductionispermanentandcannotbechangedbysubsequentmanagementdecisions.

Thetextbox,ManagementPracticesImpactingGHGEmissionsfromCroplandsandGrazingLands,liststhemostsignificantmitigationpracticesdiscussedinChapter3.Additionalmitigationpracticesarediscussedinthechapter,buttheseoftenhavesparseorconflictingevidenceinsupportoftheirmitigationeffects.Therefore,thetextboxliststhemorerobustlysupportedpractices.

2.4.2 Wetlands

WetlandsoccuracrosstheUnitedStatesonmanylandforms,particularlyinfloodplainsandriparianzones,inlandlacustrine,glaciatedoutwash,andcoastalplains.TheNationalWetlandsInventorybroadlyclassifieswetlandsintofive

ManagementPracticesImpactingGHGEmissionsfromCroplandsandGrazingLands

NutrientManagement(SyntheticandOrganic)

TillagePractices CropRotationsandCroppingIntensity Irrigation ResidueManagement Set‐Aside/ReserveCropland WetlandRiceCultivation LivestockGrazingPractices ForageOptions Silvopasture


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majorsystems,including(1)marine,(2)estuarine,(3)riverine,(4)lacustrine,and(5)palustrine(Cowardinetal.,1979).Thesesystemsarefurtherclassifiedbymajorvegetativelifeform.Forexample,forestedwetlandsareoftenclassifiedaspalustrine‐forested.Similarly,mostgrasslandwetlandsareclassifiedaspalustrinewetlandswithemergentvegetation(e.g.,grassesandsedges).Wetlandsalsovarygreatlywithrespecttogroundwaterandsurfacewaterinteractionsthatdirectlyinfluencehydroperiod,waterchemistry,andsoils(Cowardinetal.,1979;Winteretal.,1998).Allthesefactorsalongwithclimateandland‐usedriversinfluenceoverallcarbonbalanceandGHGflux.

GrasslandandforestedwetlandsaresubjecttoawiderangeoflanduseandmanagementpracticesthatinfluencethecarbonbalanceandGHGflux(Faulkneretal.,2011;Gleasonetal.,2011).Forexample,forestedwetlandsmaybesubjecttosilviculturalprescriptionsandintensityofmanagement,andhence,thecarbonbalanceandGHGemissionsshouldbeevaluatedonarotationbasis.Incontrast,grasslandwetlandsmaybegrazed,hayed,ordirectlycultivatedtoproduceaharvestablecommodity.AllthesemanipulationsinfluencetheoverallGHGflux.Thisreportwillfocusprimarilyonrestorationandmanagementpracticesassociatedwithriverineandpalustrinesystemsinforested,grassland,andriparianecosystems;althoughothermajorwetlandssystemsaresignificantintheglobalcarboncycle(e.g.,estuarine),thesewetlandssystemshavereceivedthemostattentionintermsofimplementationofrestorationandmanagementpracticestoconservewetlandshabitatsandsustainecosystemsservices(BrinsonandEckles,2011).Wetlandsthathavebeendrainedforacommodityproduction,suchasannualcrops,arenotconsideredwetlandsinthisguidance.Therefore,managementofdrainedwetlandsisaddressedinothersectionsoftheguidance,suchasinChapter3.

Wetlandemissionsarelargelycontrolledbythedegreeofwatersaturationaswellasclimateandnutrientavailability.Inaerobicconditions,commoninmostuplandwetlandecosystems,decompositionreleasesofCO2,andCH4emissionsaremoreprevalentinanaerobicconditions.Typically,wetlandsareasourceofCH4,withestimatedglobalemissionsof55to150millionmetrictonsCH4peryear(Blainetal.,2006).N2Oemissionsfromwetlandsaretypicallylow,unlessanoutsidesourceofnitrogenisenteringthewetland.Ifwetlandsaredrained,N2Oemissionsarelargelycontrolledbythefertilityofthesoil.WetlanddrainageresultsinlowerCH4emissionsandanincreaseinCO2emissionsduetooxidationofsoilorganicmatterandanincreaseinN2Oemissionsinnutrientrichsoil.Ontheotherhand,thecreationofwetlandsgenerateshigherlevelsofCH4andlowerlevelsofCO2(Blainetal.,2006).

Biomasscarboncanchangesignificantlywithmanagementofwetlands,particularlyinpeatlands,forestedwetlands,orchangesfromforesttowetlandsdominatedbygrassesandshrubsoropenwater.Peatlandscoverapproximately400millionhectaresorthreepercentofthegloballandsurface,accountingfor450billionmetrictonsofstoredcarbon(Couwenbert,2009).Emissionsfrompeatlanddegradationandfiresareestimatedat2billionmetrictonsofCO2‐eqperyear(IPCC,

ManagementPracticesImpactingGHGEmissionsfromWetlands

SilviculturalWaterTableManagement ForestHarvestingSystems ForestRegenerationSystems Fertilization ConversiontoOpenWetland ForestTypeChange WaterQualityManagement WetlandManagementforWaterfowl ConstructedWetlandsforWastewater

Treatment Land‐UseChangetoWetlands ActivelyRestoringWetlands ActivelyRestoringScrub‐GrassWetlands ConstructingWetlands PassiveRestorationofWetlands


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2011).Inforestedwetlands,therecanalsobesignificantcarbonindeadwood,coarsewoodydebris,andfinelitter.Harvestingpracticeswillalsoinfluencethecarbonstocksinwetlandstotheextentthatthewoodiscollectedforproducts,fuel,orotherpurposes.WetlandsarealsoasourceofN2Oemissions,primarilybecauseofnitrogenrunoffandleachingintogroundwaterfromagriculturalfieldsand/orlivestockfacilities.N2OemissionsfromwetlandsduetonitrogeninputsfromsurroundingfieldsorlivestockfacilitiesareconsideredanindirectemissionofN2O(deKleinetal.,2006).DirectN2Oemissionscanalsooccurifmanagementpracticesincludenitrogenfertilizationofthewetlands.

Thetextbox,ManagementPracticesImpactingGHGEmissionsfromWetlands,liststhemanagementpracticesinwetlandsthathaveaninfluenceonGHGemissions(CH4orN2O)orcarbonstockchanges,andwillbecoveredinmoredetaillaterinthereport.Individualsectionswilldealwithdifferenttypesofwetlandsincludingforested,grassland,andconstructedwetlandsthatcouldoccurinagriculturalandforestryoperations.Themethodsarerestrictedtoestimationofemissionsonpalustrinewetlandsthatareinfluencedbyavarietyofmanagementoptionssuchaswatertablemanagement,timberorotherplantbiomassharvest,andwetlandsthataremanagedwithfertilizerapplications.

2.4.3 AnimalProduction

GHGemissionsfromanimalproductionsystemsconsistofthreemaincategories:entericfermentation,housing,andmanuremanagement.Thethreecategoriesaredescribedinthesectionsthatfollow.Discussionaboutentericfermentationandhousingareaddressedtogetherinthisreport.

2.4.3.1 EntericFermentationandHousing

Entericfermentationreferstothemethaneemissionsresultingfromanimaldigestiveprocesses,whilehousingemissionsrefertoGHGemissionsfrommanurethatisstoredwithinthehousingstructure(i.e.,manurestoredunderabarnfloor).GHGemissionsarisingfrommanurestoredinhousinghavesimilaremissionstomanurethatismanagedinstockpiles.MorediscussiononhousingmanureemissionscanbefoundinSection2.4.3.2andChapter5.

Forentericfermentation,CH4‐producingmicro‐organisms,calledmethanogens,existinthegastrointestinaltractofmanyanimals.Ruminantanimals(hoofedmammals)thathavethreeorfourchamberedstomachs(andchewcudasapartofthedigestiveprocess),producemuchmoreCH4thandootheranimalsbecauseofthepresenceandfermentativecapacityoftherumen(thefirststomachinaruminantanimal).

Intherumen,CH4formationisadisposalmechanismbywhichexcesshydrogenfromtheanaerobicfermentationofdietarycarbohydratecanbereleased.Controlofhydrogenionsthroughmethanogenesisassistsinmaintenanceofanefficientmicrobialfermentationbyreducingthepartialpressureofhydrogentolevelsthatallownormalfunctioningofmicrobialenergytransferenzymes(Martinetal.,2010).CH4canalsoarisefromhindgutfermentation,butthelevelsassociatedwithhindgutfermentationaremuchlowerthanthoseofforegutfermentation.AlthoughanimalsproduceCO2through

ManagementPracticesImpactingGHGEmissionsfromEntericFermentationand

Housing

DietaryFat GrainSource,GrainProcessing,Starch

Availability FeedingCo‐ProductIngredients RoughageConcentrationandForm LevelofIntake FeedAdditivesandGrowthPromoters NovelMicroorganismsandTheirProducts Genetics


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respiration,theonlygasofconcerninentericfermentationprocessesisCH4.Infieldstudies,respirationchambersequippedwithN2OandNH3analyzershaveconfirmedthatentericfermentationdoesnotresultintheproductionofN2OorNH3(Reynoldsetal.,2010).

Thetextbox,ManagementPracticesImpactingGHGEmissionsfromEntericFermentationandHousing,listsseveralofthepracticesthatcanmodifyentericfermentationemissions.Mostofthepracticesrelatetodietcomposition.ThesepracticesarecoveredingreaterdetailinChapter5.

2.4.3.2 ManureManagement

Storageofanimalmanure(dungandurine)isapopularmanagementpracticebecauseitreducestheneedtobuycommercialfertilizer,allowsformorecontrolovermanureapplication,andhaslowerdemandsonfarmlabor.ThetreatmentandstorageofmanureinmanagementsystemscontributestotheGHGemissionsoftheagriculturalsector.Anaerobicconditions,asfoundinmanylong‐termstoragesystems,produceCH4throughanaerobicdecomposition.N2Oisproducedeitherdirectly,aspartofthenitrogencyclethroughnitrificationanddenitrification,orindirectly,asaresultofvolatilizationofnitrogenasNH3andnitrogenoxides(NO,NO2,orNO3)andrunoffduringhandling.

Animalmanurecanbeclassifiedas:

Slurry,wherethedrymatterisgreaterthan10percent;

Solid,wherethedrymatterisgreaterthan15percent;or

Liquid,wherethedrymatterislowerthan10percent.Thefoursolidmanurestorage/treatmentpracticesare:(1)temporarystack;(2)long‐termstockpile;(3)composting;and(4)thermo‐chemicalconversion.Theeightmainliquidmanurestorage/treatmentpracticesare:(1)anaerobicdigestion;(2)nutrientremoval;(3)anaerobiclagoon/runoffholdingpond/storagetanks;(4)aerobiclagoon;(5)constructedwetland;(6)sand‐manureseparation;(7)combinedaerobictreatmentsystem;and(8)solid‐liquidseparation.GreateranalysisofeachofthesesystemsisprovidedinChapter5.

ThemagnitudeofCH4andN2Oemissionsthatresultfromanimalmanureisdependentlargelyontheenvironmentalconditionsthatthemanureissubjectedto.CH4isemittedwhenoxygenisnotavailableforbacteriatodecomposemanure.Storageofmanureinponds,tanks,orpits,asistypicalwithliquid/slurryflushingsystems,promoteanaerobicconditionsandtheformationofCH4.Storageofsolidmanureinstacksordrylotsordepositionofmanureonpasture,range,orpaddocklandstendtoresultinmoreoxygen‐availableconditions,andlittleornoCH4willbeformed.OtherfactorsthatinfluenceCH4generationincludetheambienttemperature,moisturecontent,residencytime,andmanurecomposition(whichisdependentonthedietofthelivestock,growthrate,andtypeofdigestivesystem)(U.S.EPA,2011).

TheproductionofN2Ofrommanagedlivestockmanuredependsonthecompositionofthemanureandurine,thetypeofbacteriainvolved,theoxygenandliquidcontentofthesystem,andtheenvironmentforthemanureafterexcretion(U.S.EPA,2011).N2OoccurswhenthemanureisfirstsubjectedtoaerobicconditionswhereNH3andorganicnitrogenareconvertedtonitratesandnitrites(nitrification),andifconditionsbecomesufficientlyanaerobic,thenitratesandnitritescan

ManagementPracticesImpactingGHGEmissionsfromManureManagement

Thermo‐ChemicalConversion AnaerobicDigestion LiquidManureStorageandTreatment‐

Sand‐ManureSeparation LiquidManureStorageandTreatment–

Solid‐LiquidSeparation


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bedenitrified(reducedtonitrogenoxidesandnitrogengas)(Groffmanetal.,2000).N2Oisanintermediateproductofbothnitrificationanddenitrificationandcanbedirectlyemittedfromsoilasaresultofeitheroftheseprocesses.Drywastehandlingsystemsaregenerallyoxygenatedbuthavepocketsofanaerobicconditionsfromdecomposition;thesesystemshaveconditionsthataremostconducivetotheproductionofN2O(USDA,2011).

SomemanuremanagementsystemscaneffectivelymitigatethereleaseofGHGemissionsfromlivestockmanure.Thetextbox,ManagementPracticesImpactingGHGEmissionsfromManureManagement,listsseveralofthepracticesthatcanmodifymanuremanagementemissions.

2.4.4 Forestry

ForestsystemsrepresentasignificantopportunitytomitigateGHGsthroughthesequestrationandtemporarystorageofforestcarbonstocks.ForestsremoveCO2fromtheatmospherethroughphotosynthesisandstorecarboninforestbiomass(e.g.,stems,root,bark,leaves).RespirationreleasesCO2totheatmosphere.Netforestcarbonstocksincreaseovertimewhencarbonsequestrationduringphotosynthesisexceedscarbonreleasedduringrespiration.OtherGHGsarealsoexchangedbyforestecosystems—e.g.,CH4frommicrobialcommunitiesinforestsoilandN2Ofromfertilizeruse.

Harvestingforestsreleasessomesequesteredcarbontotheatmosphere,whiletheremainingcarbonpassesinHWPs,thefateofwhich(e.g.,combustionforenergy,manufactureofdurablewoodproducts,disposalinlandfills)determinestherateatwhichthecarbonisreturnedtotheatmosphere.

Therearemanyforestryactivities(i.e.,managementpractices)relevanttoreducingGHGemissionsand/orincreasingcarbonstocksintheforestrysectorincludingestablishingand/orre‐establishingforest,avoidedforestclearing,andforestmanagement.Moreinformationoneachisincludedbelow.

TheChapter6describesmethodsforthevarioussourcecategoriescontributingtotheGHGfluxfromforests.Thesesourcecategoriesincludeforestcarbonaccounting—e.g.,livetrees,understory,standingdead,downdeadwood,forestfloororlitter,forestsoilorganiccarbon—establishing,re‐establishing,andclearingforest,forestmanagement,HWPs,urbanforestry,andnaturaldisturbances(e.g.,forestfires).Thissubsectionbrieflydescribesthesesourcecategories.DescriptionsofthecurrenttoolsandmethodsusedtoestimateGHGfluxfromthesesourcecategoriesisdiscussedlaterinChapter6.

ForestCarbon.Accountingforforestcarbon(i.e.,forestbiomass)typicallydividestheforestintoforestcarbonpools—e.g.,livetrees,understory,standingdead,downdeadwood,forestfloororlitter,forestsoilorganiccarbon—thedefinitionsforwhicharedevelopedaroundacommonsetinusebyanumberofpublications,whicharefurtheroutlinedinChapter6.Themethodsforestimatingthekeyforestcarbonpoolsarewelldevelopedandfairlystandard.

Establishing,Re‐Establishing,andClearingForest.Inadditiontoforestlandremainingforestland,therearethreedistinctprocessesthatcansignificantlyalterforestcarbonstocks,andaretermed:

ManagementPracticesImpactingNetGHGEmissionsfromForestry

EstablishingandReestablishingForest AvoidingClearingForest StandDensityManagement SitePreparationTechniques VegetationControl Planting NaturalRegeneration Fertilization SelectionofRotationLength HarvestingandUtilizationTechniques FireandFuelLoadManagement ReducingtheRiskofEmissionsfromNatural

Disturbances ShortRotationWoodyCrops


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forestestablishment(i.e.,afforestation),forestre‐establishment(i.e.,reforestation),andforestclearing(i.e.,deforestation).Eachoftheseprocessesaltersstocksofcarboninabovegroundandbelowgroundcarbonpools.Establishmentinvolvestheintentionalplanting(orallowingthenaturalprocessofsecondarysuccession)onlandthatwasnotpreviouslyforest.Reestablishmentisreturninglandthatwasrecentlyforestbackintoforest.Ineithercase,establishingforestwillgenerallyincreasethecarbonstocksinabovegroundandbelowgroundcarbonpoolsovertime.Forestclearingistheremovaland/orconversionofaforestsystemintoanotherlandcover(cropland,grazingland,etc.)andisthemostsignificantsourceofGHGemissionsfromforests.

ForestManagement.Forestmanagementdescribestherangeofpracticesemployedbylandownerstomeettheirobjectives(e.g.,timberproduction)whilesatisfyingbiological,economic,andsocialconstraints.Anumberofthepracticesusedbyforestmanagerstoachievetheirobjectivesimpactthecarbondynamicsinforestseitherbyenhancingforestgrowthoracceleratingthelossofforestcarbon.Themanagementpracticesinclude:standdensitymanagement(e.g.,underplanting,pre‐commercialandcommercialthinning);sitepreparationtechniques(e.g.,mechanicalmethods,chemicalapplication,prescribedburning);vegetationcontrol;planting(e.g.,plantingdensity,speciesselection,geneticimprovement);naturalregeneration;fertilization(e.g.,nitrogenandphosphorousfertilizerapplication);selectionofrotationlengths;harvestingandutilizationtechniques;fireandfuelloadmanagement;reducingtheriskofemissionsfrompestsanddisease;andestablishingbiomassplantations(i.e.,shortrotationwoodycrops).

HarvestedWoodProducts.Aproportionofthewoodcarbonharvestedfromforestsendsupinsolidwood,paper,orotherproducts,whicharecollectivelyknownasHWPs.Thecarboncontainedintheseproductscanremainstoredforyearsordecadesdependingontheenduse,andmayeventuallybecombusted,decay,orbedivertedtolandfills.

UrbanForestry.Urban(orurbancommunity)forestdescribesthepopulationoftreeswithinanurbanarea.Urbantreesdirectlystoreatmosphericcarbonaswoodybiomassandalsoaffectlocalclimate(e.g.,secondaryeffects).ThemaintenanceofurbantreesalsoaffectsGHGemissionsinurbanareas(i.e.,indirecteffects).

NaturalDisturbances.Naturaldisturbancesinforestsystems(e.g.,forestfires,pestsanddisease,storms)cansignificantlyimpactforestcarbonstockseitherdirectlyinthecaseofcombustionfromforestfiresorindirectlybyconvertinglivebiomasstodeadorconvertingstandingtreestodowneddeadwoodandacceleratingdecomposition.

Thetextbox,ManagementPracticesImpactingNetGHGEmissionsfromForestry,liststhemanagementpracticesrelevanttoreducingGHGemissionsand/orincreasingcarbonstocksintheforestrysectorincludingestablishingand/orreestablishingforest,avoidingforestclearing,andimprovingforestmanagement.

2.5 Land‐UseChange

Convertinglandparcelsfromoneland‐usecategorytoanothercanhaveasignificanteffectonaparcel’scarbonstocks.Forexample,carbonstockgainscanberealizedbyconvertingcroplandsoilstowetlandsorforestland,whilecarbonstocklossesoftenresultfromaconversionfromforestlandstograzinglands.Aland‐usecategorizationsystemthatisconsistentandcomplete(bothtemporallyandspatially)isneededinordertoassesslanduseandland‐usechangestatuswithinanentity’sboundaries.Allofthelandwithinanentity’sboundaryshouldbeclassifiedaccordingtothefollowingland‐usetypes:cropland,grazingland,forestland,wetland,settlements(e.g.,residentialandcommercialbuildings),andotherland(e.g.,baresoil,rock);seedefinitionsprovidedabove.Individualparcelareasshouldsumtothetotallandareabeforeandafterland‐usechange.


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Inmanycases,themethodsproposedtoestimatecontributionstotheGHGfluxresultingfromland‐usechangearethesameasthoseusedtoestimatecarbonstockchangesintheindividualcroplandandgrazingland,wetland,andforestrychapters;although,inspecificcases,guidanceisalsoprovidedonreconcilingcarbon‐stockestimatesbetweendiscretedatasetsandestimationmethods(e.g.,reconcilingforestsoilcarbonestimatesandcroplandsoilcarbonestimatesforland‐usechangefromforestlandtocropland).ThemethodsforquantifyingGHGfluxfromland‐usechangeareintendedforuseattheentityscaleonlandsmanagedtoenhancetheproductionoffood,feed,fiber,andrenewableenergy.Methodsarecurrentlynotprovidedforestimatingemissionsfromenergyusedwhenconvertinglandusefromonecategorytoanother.Neitheraremethodsprovidedforland‐usechangefromsettlementsorthe“otherland”categorytocropland,grazingland,wetlandorforestland.ThemethodshavebeendevelopedforU.S.conditionsandareconsideredapplicabletoagriculturalandforestryproductionsystemsintheUnitedStates.Thissubsectionbrieflydescribesthesourcecategoriescovered.FurtherdescriptionsofthecurrenttoolsandmethodsusedtoestimateGHGfluxfromthesesourcecategoriesarediscussedlaterinChapter7.

AnnualChangeinCarbonStocksinDeadWoodandLitterDuetoLandConversion.Liveanddeadbiomasscarbonstocksandsoilorganiccarbonconstituteasignificantcarbonsinkinmanyforestandagriculturallands.Followingland‐useconversion,theestimationofdeadbiomasscarbonstockchangesduringtransitionperiodsrequiresthattheareasubjecttoland‐usechangeontheentity’soperationbetrackedforthedurationofa20‐yeartransitionperiod.

ChangeinSoilOrganicCarbonStocksforMineralSoils.Soilorganiccarbonstocksareinfluencedbyland‐usechange(Aaldeetal.,2006)duetochangesinproductivitythatinfluencecarboninputsandtochangesinsoilmanagementthatinfluencecarbonoutputs(DavidsonandAckerman,1993;Ogleetal.,2005;PostandKwon,2000).Themostsignificantchangesinsoilorganiccarbonoccurwithland‐usechange,particularlyconversionstocroplands,duetochangesinthedisturbanceregimesandassociatedeffectsonsoilaggregatedynamics(Sixetal.,2000).

SpecificmitigationpracticesarenotexplicitlydescribedinChapter7;however,avoidingland‐useconversionsthatresultinsignificantcarbonlossescouldmitigatenetGHGemissions(e.g.,avoidingtheconversionofforestlandstograzinglands).

2.6 Uncertainty

QuantifyingtheuncertaintyofGHGemissionsandreductionsfromagricultureandforestrypracticesisanimportantaspectofdecisionmakingforfarmersandlandownersastheuncertaintyrangeforeachGHGestimatecommunicatesourlevelofconfidencethattheestimatereflectstheactualbalanceofGHGexchangebetweenthebiosphereandtheatmosphere.Inparticular,afarm,ranch,orforestlandownermaybemoreinclinedtoinvestinmanagementpracticesthatreducenetGHGemissionsiftheuncertaintyrangeforanestimateislow,meaningthathigherconfidenceintheestimatesexists.Thisreportpresentstheapproachforaccountingfortheuncertaintyintheestimatednetemissionsbasedonthemethodspresentedinthisreport.6AMonteCarloapproach

6TheIPCCGoodPracticeGuidance(IPCC,2000)recommendstwoapproaches—Tier1andTier2—fordevelopingquantitativeestimatesofuncertaintyforemissionsestimatesforsourcecategories.TheTier1methoduseserrorpropagationequations.Theseequationscombinetheuncertaintyassociatedwiththeactivitydataandtheuncertaintyassociatedwiththeemission(orother)factors.Thisapproachisappropriatewhereemissions(orremovals)areestimatedastheproductofactivitydataandanemissionfactororasthesumofindividualsub‐sourcecategoryvalues.TheTier2methodutilizestheMonteCarloStochasticSimulationtechnique.Usingthistechnique,anestimateofemission(orremoval)foraparticularsourcecategoryisgeneratedmanytimesviaanuncertaintymodel,resultinginanapproximatePDFfortheestimate.


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wasselectedasthemethodforestimatingtheuncertaintyaroundtheoutputsfromthemethodologiesinthisreport,asitiscurrentlythemostcomprehensive,soundmethodavailabletoassesstheuncertaintyattheentityscale.Limitationsanddatagapsexist;however,asnewdatabecomeavailable,themethodcanbeimprovedovertime.ImplementationofaMonteCarloanalysisiscomplicatedandrequirestheuseofastatisticaltooltoproduceaprobabilitydensityfunction(PDF)7aroundtheGHGemissionsestimate.8Fromtheprobabilitydensityfunction,theuncertaintyestimatecanbederivedandreported.

Chapter2References

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Wheresufficientandreliableuncertaintydatafortheinputvariablesareavailable,theTier2methodisthepreferredoption.

7TheintegralofaPDFoveragivenintervalofvaluesistheprobabilityforarandomvariabletotakeonsomevalueintheinterval.Thatis,thePDFisafunctiongivingprobability“densities”anditsintegralgivesprobabilities.AnarrowerPDFforanestimateindicatessmallervariancearoundthecentral/mostlikelyvalue,i.e.,ahigherprobabilityofthevaluetobeclosertothecentral/mostlikelyvalue.Theuncertaintyforsuchanestimateislower.

8GiventhecomplexityofMonteCarloanalysisandthenecessityforatool,theapproachpresentedhereisnotintendedfordevelopmentbyalandowner,ratheritisintendedforuseindevelopingatoolthatalandownerwouldusetoassessuncertaintyestimates.


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thefarmscale.Animal,4:351‐365.Ogle,S.M.,F.J.Breidt,andK.Paustian.2005.Agriculturalmanagementimpactsonsoilorganic

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