4Crop Response to Climate Ecophysiological Models

59BookID182985_ChapID4_Proof#1-12/10/2009AbstractTopredictthepossibleimpactsofglobalwarmingandincreasedCO2onagriculture,scientistsusecomputer-basedmodelsthatattempttoquantifythebest-availableknowledgeonplantphysiology,agronomy,soilscienceandmeteorologyinordertopredicthowaplantwillgrowunderspecificenvironmentalconditions.Thechapterreviewsthebasicfeaturesofcropmodelswithemphasisonphysiologi-calresponsestotemperatureandCO2andexplainshowmodelsareusedtopredictpotentialimpactsofclimatechange,includingoptionsforadaptation.Theclosingsectionreviewsmajorissuesaffectingthereliabilityofmodel-basedpredictions.Theseincludetheneedforaccurateinputs,thechallengesofimprovingtheunder-lyingphysiologicalknowledge,andtheneedtoimproverepresentationsofgeneticvariationthatlikelywillaffectadaptationtoclimatechange.4.1IntroductionEcophysiologicalmodelswerethedominanttoolsusedtoestimatethepotentialimpactofclimatechangeinagroecosystemsintheThirdandFourthAssessmentReportsoftheIPCC(Gitayetal.2001;Easterlingetal.2007)andarewidelyusedelsewhereinclimatechangeresearch.Thesemodels,alsoknownas“cropmodels”or“simulationmodels”,attempttoencapsulatethebest-availableknowledgeonplantphysiology,agronomy,soilscienceandagrometeorologyinordertopredicthowaChapter4CropResponsetoClimate:EcophysiologicalModelsJeffreyW.WhiteandGerritHoogenboomD.LobellandM.Burke(eds.),ClimateChangeandFoodSecurity,AdvancesinGlobalChangeResearch37,DOI10.1007/978-90-481-2953-9_4,©SpringerScience+BusinessMedia,B.V.200J.W.White()USAridLandAgriculturalResearchCenter,USDA-ARS,21881NorthCardonLane,Maricopa,AZ85224email:[e-mail]griculturalEngineering,165GordonFutralCourt,TheUniversityofGeorgia,Griffin,GA30223-1731email:[e-mail]182985_ChapID4_Proof#1-12/10/2009BookID182985_ChapID4_Proof#1-12/10/2009plantwillgrowunderspecificenvironmentalconditions.Themodelsare“ecophysi-ological”becausetheyusemathematicaldescriptionsofphysiological,chemicalandphysicalprocessestosimulatecropgrowthanddevelopmentovertime.Physiologicalprocessesconsideredmayincludephotosynthesis,respiration,growthandpartition-ing,developmentofreproductivestructures,transpiration,anduptakeofwaterandnutrients.Chemicalandphysicalprocessescaninvolvesoilchemicaltransformations,energyflows,anddiffusionofgasesintoandoutofleaves,amongothers.Topredictcropgrowth,themodelrequiresthatinitialconditionsbespecified,suchasthesoilnutrientandwaterstatus,theplantingdateanddensity.Dataontemperature,solarradiation,precipitation,orotherweatherparametersarethenusedtoestimatehowthedevelopmentandgrowthofthecropprogressoverthecroppingseason.Mostmodelsoperateatdailytimesteps,startingatplantingandendingatthepredictionofharvestorphysiologicalmaturity,dependingonthecrop.Informationonirrigations,fertilizerapplications,tillageevents,pests,diseases,orotherfactorsalsomaybeconsidered.ThefirstecophysiologicalmodelsweredevelopedbyDeWit(1965)intheNetherlandsandDuncanandcolleaguesintheUnitedStates(Duncanetal.1967).Thesemodelswereprimarilyusedasresearchplatformstoquantitativelytestbasichypothesesaboutplantgrowthanddevelopment(Loomisetal.1979).Ascomput-ingpowerincreasedandunderstandingofbasicprocessesimproved,morefactorswereconsidered,suchasthedynamicsofspecificnutrientsinthesoilandplantandtheeffectsofpestsanddiseases.Modelsareavailableforallmajorannualcropsandmanyminorcrops(e.g.,Jonesetal.2003).Currentmodelstypicallyrunonapersonalcomputeroraworkstationandcansimulateacroppingseasoninlessthan1s.Theresponsivenessofthemodelstoclimateandotherenvironmentalvariables,aswellastocropmanage-ment,allowthemtobeeasilyadaptedtosimulateresponsestoprojectedclimateconditions,suchasobtainedfromgeneralcirculationmodels.Thischapterfirstreviewshowecophysiologicalmodelsfunctionwithemphasisonthephysiologicalresponsesthataremostrelevanttoclimatechangeresearch.Wethendiscusshowthemodelsareappliedinclimatechangeresearchandidentifychallengesandopportunitiesforimprovingthemodelsperseandhowtheyareappliedtoclimatechangeresearch.Theoverallobjectiveistohelpreadersunderstandhowthefeaturesofecophysiologicalmodelsaffectprojectionsofpotentialimpactsofclimatechange.ReadersseekingfurtherinformationshouldconsulttextssuchasHayandPorter(2006)foranoverviewofthephysiologicalassumptionsandTsujietal.(1998)orHanksandRitchie(1991)fordetailsonmodelingbothplantandsoilprocesses.4.2OverviewofEcophysiologicalModelsAsimulationusingabasicmodelmightstartwithasetofinitialconditionsspecifyingwherethecropisgrown,theinitialstatusofwaterandnutrientsinthesoils,andtheparametersneededtorepresentthephysiologicalcharacteristicsofthecrop.614CropResponsetoClimate:EcophysiologicalModelsBookID182985_ChapID4_Proof#1-12/10/2009Foranannualcrop,themodelloopsthroughaseriesofsubroutinesthatestimateplantorsoilprocessesonanhourlyordailybasis,outputtingintermediatevaluesatspecifiedintervals(Fig.4.1).Ineachcycle,themodelcheckswhetherthecrophasreachedmaturityoraharvestdata,inwhichcasetheyieldandadiverserangeofsummarydatamaybeoutput.Normally,theoutputofthesemodel