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Modeling Soil Organic Carbon Storage and Its Dynamics in Croplands of China

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Modeling Soil Organic Carbon Storage and Its Dynamics in Croplands of China

    Modeling Soil Organic Carbon Storage and

    Its Dynamics in Croplands of China AgriculturalSciencesinChina

    2010,9(5):704712

    Availableonlineatwww.sciencedirect.com

    

    一扩

    ScienceDirectMay2010

    ModelingSoilOrganicCarbonStorageandItsDynamicsinCroplandsof

    China

    TANGHua-jun,QIUJian-jun,WANGLigang,LIHu1,LIChang

    sheng2andEricvanRanst3

    InstituteofAgriculturalResourcesandRegionalPlanning,ChineseAcademyofAgriculturalSciences,Beijing100081,P.R.China

    InstitutefortheStudyofEarth,OceansandSpace,UniversityofNewHampshire,Durham,NH03824.USA

    DepartmentofGeologyandSoilScience(WE13)/LaboratoryofSoilScience,GhentUniversity,GentB9000,Belgium

    Abstract

    Soilorganiccarbon(SOC)isoneofthecentreissuesrelatedtonotonlysoilfertilitybutalsoenvironmentalsafety.

    AssessingSOCdynamicsincroplandshasbeenachallengeinChinaforlongduetothelackofappropriatemethodologies

    anddatasources.AsallalternativeapproachforstudyingSOCdynamics,process

    basedmodelsareadoptedtomeetthe

    needs.Inthispaper,aprocessbasedmodel,DeNitrification

    DeComposition(DNDC),wasappliedtoquantifytheSOC

    storageandthespatialdistributionincroplandsofChinain2003,withthesupportofanewlycompiledcounty.1evelsoiY

    climate/landusedatabase.ThesimulatedresultsshowedthatthetotalSOCstorageinthetoplayerf0.30cm1ofthe

    1.18x10hacroplandsofChinais4.7

    5.2PgCin2003withanaveragevalueof4.95PgC.TheSOCstorageinthe

    northeasternprovinces(1.3PgC)accountsforabout1/4ofthewholenationaltotalsduetotheirdominantlyfertilesoils

    withhighorganicmattercontent.SOCdensityrangesfrom3.9to4.4kgCm,withanaverage

    of4.2kgCm',alevelis

    muchlowerthantheworldaverageleve1.ThemodelresultsalsoindicatedthathighratesofSOClossesoccurredinthe

    croplandswiththemostcommoncroppingpatternsinChinaaslikesinglesoybean>maize>paddy>cotton>winterwheat

    andcomrotation.TheresultsreportedinthispapershowedthattherewasstillagreatpotentialforimprovingSOCstatus

    inmostcroplandsofChinabyadoptingproperfarmingpracticesandland

    usepattern.Therefore,longtermpolicyto

    protectSOCisurgentlyneeded.

    Keywords:China,cropland,DNDCmodel,soilorganiccarbon

    lNTRODUCTION

    SincetheIndustrialRevolution,humankindcameto

    realizethegreatimpactsofanthropogenicactivities

    onearthecosystems.CarbonrC1releasedfromter

    restrialecosystemstotheatmospherehasexceeded

    theearthecosystem'scapability(Sunela1.2001)

    andtherelationwithglobalchangesisincreasingly

    andattractsmoreworldwideattentions.Itisesti

    matedthatthetotalterrestrialsoilorganiccarbon

    (SOC)reservoirisbetween1395and2200Pg(1Pg=

10g),whichis23timeslargerthanthatinthe

    bioticpoolwith500.600Pgandatmosphericpool with750Pg(SuandZhao2002).Eyenverylittle changethathappensinSOCpoolmaygreatlyinflu

    encetheglobalcarboncycle.TheSOCstoragein theglobalagro-ecosystem(140??170Pg)nearlyac-

    countsfor10%ofthetotalterrestrialSOCstorage (Buringheta1.1984)andplaysanimportantrolein

    ecosystem theagriculturalproductionandagro

    conservatiOn.ButthedeclineOfS0Cwitharateof Received2November,2009Accepted2March,2010 c0Tresp0ndenceTANGHua-jun,Professor,Tel:+861082109395,Email:hjtang@mail.caasnetcn

    ~2010,CAASAllfightsreservedPublishedbyElsevierLtd.

    doi:10lO16/$1671?2927(09)60146-2

    ModelingSoilOrganicCarbonStoragean

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    0.8Gtyr.duetolandcultivation(Aguilareta1. 1988)notonlyunderminesagriculturalsustainable developmentbutalsoaffectstheenvironmentalhealth (Eswaraneta1.1993;Freibauereta1.2004;Lal 2004).Asalargecountry,Chinaownsaverylarge percentageoftheworld'scroplandsandrural population.Thesocialandeconomicstabilityofthe nationlargelydependsonagriculturaldevelopment, andSOCisoneofthekeyfactorsthataffectagri

    culturalproduction,nutrientavailabilityandsoil stability,andhencethedeclineofSOChasbrought anunprecedentedtensiontotheChineseagriculture

    (PanandZhao2005).EstimatetheSOCstorageand identifyitschangingtrendsundercurrentcropping systemsarehencehighlydesirable.Duringthepast decades,agreatnumberofstudieshavebeencon

    ductedtoestimateSOCstorageandchangefrom soilsatlargerspatialscales(WangandZhou1999; Wangeta1.2000;Jinela1.2001:Yueta1.2005). Forexample.Jineta1.(2001)discussedthevariabil

    itvOfS0CofChinesesoilswithsoiltaxonomic categories.WuandCai(20061analyzedthechanges inSOClevelusingrobuststatisticsofthesecond nationalsoilsurveydatabaseofChina.Fieldexperi

    mentsorsamplingsintimeintervalsalsohavebeen widelyemployedtoevaluatetheCsequestrationata countyorsmallerscale(Huangeta1.2006). Meanwhile,regionalornationalCstockestimation havebeenanincreasinglytrendusingS0Cdatabase linkedtothedifferentarearesolutionofsoilmapping unitsofgeographicalinformationsystem(GIS)da

    tabase(Shieta1.2005).However.theestimatesin SOCstockderivedfromtheseresearcheshavebeen debatedwidelybecauseofthelimitofthedata sourcesandinconsistentmethods(Yueta1.2007). Inaddition,sinceSOCishighlydynamicinspace andtimedrivenbycomplexcombinationsofclimate, soilandmanagementconditions,quantifyingtheSOC dynamicsatregionalscalethroughsoilsurveydata andfieldexperimentswerenotverystraightforward. Infact,modelsofferthepossibilitytosimulatethe

intricateprocessesinthesoilandthechangeofcar

    bonstorage,whichisbecomingamainstreamin agriculturalstudiesinmanycountriesfZhangeta1. 20061.Themodelswiththebasicprocessesof physics,chemistryandbiologybeingembedded,such asCENTURY,DNDC(DeNitrification

    DeComDosition),NCS0IL,RothC(Rothamstedcar

    bonmode1),etc.,havebeenwidelyappliedforSOC inventoryorstorageinmanyregions(Smitheta1. 1997).ForthisstudyonregionalSOCdynamicsfor China.weselectedtheDNDCmode1duetoitslim

    itedrequirementforinputparametersaswellasits successfulapplicationsinC:hinaandothercountries (Cai1996;LiCSeta1.2003;Browneta1.2002; Pathaketa1.2005:Qiueta1.2005).Formerstudies haveindicatedtheS0Cdeclineatnationalscalein China,andhaveproposedstrategiestoreducethe lossofS0CinChinesecroplands(Tangeta1.2006), andthestudyreportedinthispaperisacontinuous efforttoidentifySOCchangetrendsandspatialdis

    tributionsincroplandsofChinawiththesupportof anewlybuiltdatabase.

    MATERIALSANDMETH0DS

    DNDGmode

    DNDCisabiogeochemicalmodeloriginallydeveloped forpredictingcarbonsequestrationandnitrogen cycling.Itconsistsofsixsubmodels,whichsimu?

    latesoi1climate,plantgrowth,decomposition, nitrification.denitrification,andfermentation,

respectively.DNDCsimulatesplantgrowthbytrack

    ingphotosynthesis,respiration,waterandNdemand, Callocation,cropyield,andlitterproduction.The modeledlitterrrootandabovegroundresidue)pro

    ductionisoneofthemajorprocessescontrollingthe soilCdynamics.IntheDNDCmodel,SOCresidesin fourmajorpools:plantresiduesor1itter.microbial biomass,humads,andactivehumus.Eachpoolcon

    sistsofoneormoresubpoolswithdifferentproperties. Thedailydecompositionrateforeachsub-poolisregu-

    latedbypoolsize.Assoonasthelitterisincorporated inthesoil.DNDCwillpartitionthelitterintothevery labile.1abileandresistantsoillitterpoolsbasedonC/N ratioofthe1itter.Eachofthelitterpoolhasaspecific decompositionratethoughsubjecttotemperature, moistureandfreeNavailabilityinthesoiIprofile. Duringthesimulateddecompositionoflitter.partof thelitterCisconsumedastheenergysourcebythe soilmicrobesandhencebecomescarbondioxide(co) @2010.CAASAllrightsreseP,,edPublishedbyElsevierLtd 706TANGHua-junetal

    thatisfinallyemittedintotheatmosphere;partofthe litterCisturnedintothemicrobialbiomass.After deathofthemicrobes,thehumadsfromthemicrobial remainswillfurtherdecomposeandbecomepassive humus.EmissionofCOfromdecompositionisone ofthemajorprocessesleadingtolossofSOC.Since croplitterproductionisamajorfactoraffectingthe SOCdynamics,thephysiologicalandphenologypa

    rametersforthemajorcropswidelyplantedinChina

    havebeencalibratedandstoredaslibrarydatain DNDC.Inaddition,thefarmingmanagementprac

    ticesspecificforChina,suchasmidseasondrainage forpaddyrice,application

    asacommonfertilizerfor

    ofammoniumbicarbonate

    almostallcropsetc.,have

    beenparameterizedinDNDCtomakethemodelmore suitablefortheChineseagroecosystems(Lieta1.

    2006).TheDNDCmodelcanbedownloadedforfree viatheinternet(http://www.dndc.sr.unh.edu/Pubs. htm1).Detaileddescriptionsofthemodel'sdevelop

    mentandstructurewerepublishedbyLiandFrolking (1992)andLi(2000).

    SuitabilityoftheDNDCmodelforChina

    Duringthepasttwodecades,theDNDCmodelhas beenindependentlytestedandappliedforsoi1CandN studiesinNorthAmerica,Europe,Oceania,andAsia, includingafewvalidationsforChina.Thetestsdem- onstratethatDNDCiscapableofcapturingthebasic patternsandmagnitudesofSoCvariationsfLieta1. 1994.2001).Fromthereported1iteratures,11long

    termexperimentswereselectedandconductedtotest theDNDCmodelacrosstypicalagriculturalecosys

    temsinChina(Fig.1).ThemeasuredSOCdynamics' datasets,containingrelevantclimate,soilproperties,crop Table1CharacteristicsofthesitesforvalidationsofDNDCinChina

    rotation,andmanagementdatafromthesesitesfTable 1),wereusedforthevalidationsofDNDCmode1.The testresultsshowedthattheDNDCmodelgenerallyhad

    goodperformancesinsimulatingtheSOCdynamics andcapturingpatternsofSOCchanges(Lieta1.1997; LiCSfa1.2003;Haneta1.2004;WangandQiu

    2004;Zhangeta1.2006).Recently,furthervalidation testswereconductedinthestudy(Wangeta1.2008), inwhichsixlongterm(20yr)SOCdatasetsfrom

    Northeast,North,Northwest,CentralSouth,East,and SouthwestChinawerecollectedforvalidationtests.

    describedsixvalidationstests Insummary,theabove

    supporttheconclusionsreportedbyotherresearchers inChinathatDNDCiscapableofquantifyingSOCin theagroecosystemsacrossthewholeChina.

    Datainputandmethodsformodelsimulation

    Amajorchallengeinapplyinganecosystemmodelat regionalscaleisassemblingadequatedatasetsneeded toinitializeandrunthemode1.Thedatasetsconsist f{??一

    /}

    Fig.1LocationsofcroplandsitesforvalidationtestsinChina. ~2010,CAASAllrightsmserv~lPublishedbyElsevierLid ModelingSoilOrganicCarbonStorageandItsDynamicsinCroplandsofChina707

    ofseveralsubdatasetsincluding(1)adatasetofcrop types,includingphysiologicaldataoftypicalcrops, croppingdata(plantingdateandharvestdate),maxi- mumyield,etc.;(2)anagriculturaldataset,including sowingacreagesofallkindsofcrops,nitrogenfertil

    izeruse,effectiveacreagesofirrigationandcropland acreages,livestockandagriculturalpopulationat countylevelin2003;(3)aclimatedataset,including dailyweatherdatafor2003(precipitation,maximum

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