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Purdue Methods for Corn Growth Plant Growth Facility

3-1-2010

Optimizing Greenhouse Corn Production: WhatIs the Best Lighting and Plant Density?Robert EddyPurdue University, robeddy@purdue.edu

Daniel T. HahnPurdue University, dhahn@purdue.edu

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Recommended CitationEddy, Robert and Hahn, Daniel T., "Optimizing Greenhouse Corn Production: What Is the Best Lighting and Plant Density?" (2010).Purdue Methods for Corn Growth. Paper 13.http://docs.lib.purdue.edu/pmcg/13

ThisdocumentisbasedonmaterialsoriginallypostedtothePurdueUniversityHLADepartmentPlantGrowthFacilitywebsite:http://www.hort.purdue.edu/hort/facilities/greenhouse/CornMethod.shtml

Whatisthebestlightingandplantdensity?Inbredandmutantcornlinesgrownindoorsoftendon’tyieldadequateseed,slowingprogressoftheproject.Thedifferencebetween75and100seedsonanearmayseemnegligiblecomparedtoahybridearwith600seeds,butjustmaymakethedifferencebetweenhavingenoughseedforthenextroundofbreedingornot.Weaddresslightingandplantdensitytogetherinthisdocumentbecauseoftheirrelationshiptolightreachingthelowercanopy,whichhasbeenshowntocorrelatetoseedyield.We’velearnedthehardwaythatthesamelightingthatproducesexcellentvegetativegrowthmaynotproduceadequateseedyieldiftheplantsaretoocloselyspaced.Earsabort,silksfailtoemergefromearsoremergelongafterpollenshed.Itisgenerallyacceptedthatifotherenvironmentalstressesarereduced,thelimitingfactorincornyieldislight.Webelievethegrowingsystemthatweproposeeliminateswaterandnutrientstress,somaximizinglightshouldbeafocustoimproveseedyield.Thisisachallengeforplantgrowthfacilities.Overthecourseofaday,wehavemeasureda40%lossindailylightintegral(solaraccumulation)inourmodernglassgreenhousesduetoglazingandsuperstructure.WetooklightintensityreadingsinsideacornfieldonanovercastJulyday(1250µmol/m2/s)andweresurprisedtomeasure314µmol/m2/satthelowestleavesofthestalks.Inagreenhouse,wemaygetathirdofthatintensity.Inagrowthroom,wherelightsourceisdirectlyabovewithlittlepenetrationintothetallcanopyfromthesides,we’vemeasuredlightatsoilsurfacebelow10µmol/m2/s.Fieldresearchthatsupplementedlighttolowercanopy(OttmanandWelch,1988)increasedkernelsperearby14%andnumberofearsintheplotby25%.Thiswasaccomplishedbyaddingonly121µmol/m2/s.Fromthis,wesuggestthatalotcouldbegainedbylightingandplantspacingstrategiesthatincreaselighttolowercanopy.Noneofourstudiescomparedlightingorplantdensity,butwewillreportonwhatwehaveobserved,studieswehavecollaboratedwith,andconsensusfromotherfacilities.Itisbynomeanscomprehensive.PlantspacingandconfigurationWebelievetheminimumdistancebetweenthestalksinarowshouldbe30.5‐cm(12‐inch).Thisisfurtherapartthanmostfieldcornisplantedbut—again—plantgrowthfacilitieshavelowerlightthanoutdoors.Thehigherthedailylightintegralyoucanprovidewithsupplementallighting,thecloseryoumaybeabletopositiontheplants.Thoughuntested,theremaybea

benefitfromspacingtheplantsfurtherduringacriticalperiodof2‐3weeks.Prine(1971)reportedthat,infieldtestsdoneoverthreeseasons,arapidabortionofearsoccurred4daysbeforesilksemergedto8daysaftersilkemergenceunderunfavorablelightconditions.Otegui(1997)determinedkernelnumberperplantwasrelatedtotheamountofinterceptedlightduringthesilkingperiodand15daysprior.Onetrickweborrowfromfieldproductionisthetwin‐rowconfiguration.Tworowsarespacedsothatthestalksineachroware30.5cmapart(sameasinter‐rowspacing),then76‐91cm(30‐36inch)betweenthestalksandthoseofthenexttwinrow.The91cmdistanceisenoughforresearcherstoaccesstheplantsandtogetaladderinforreachingtassels.ControlledPharmingVentures,anundergroundplantgrowthfacilityinsouthernIndiana,hascomparedevenlyspacedrowsagainsttwinrowsinagrowthroom.Eventhoughtheplantdensitywascontrolled,thetwinrowsyieldedmoreseed(personalcommunication).Theseresultsagreewithseveralfieldcornstudies(Jones,2007).SupplementallightingintensityanddurationSupplementallightingistypicallyusedforgrowingcorninagreenhouse.Itisnotanabsolutenecessity.Oneofthemostexperiencedcorngrowers,DickChristensen,formerlyofPioneerHi‐Bred,reportsgrowingcorninambientNorthCarolinagreenhouselightsowninNovemberthatyieldedadequatelyfortheproject.Butforoptimumseedproduction,northerngreenhouseswillrequireartificiallighting.Recommendationsfortheintensityofsupplementallightrangefrom250‐750µmol/m2/satadistanceofonemeterbelowthelights.Specializedcorngrowthroomswithoutsunlightarecapableof500‐2000µmol/m2/s.Atourgreenhouses,weprovide150‐250µmol/m2/ssupplementallightingingreenhousesand1000µmol/m2/sinourcornchamber.Notethattheseintensityrecommendationsareatcanopylevelofthecrop.Spacingandconfigurationofplantswoulddeterminelightreachinglowercanopy.Lamptypeistypicallyamixofmetalhalideandhighpressuresodiumoronlymetalhalide.USDAGreenhouseManager,NathanDeppe,cautionsthatrelativehumiditymustbekeptabove40%whenusinghighsupplementallightintensity.Allgrowersagreethatpollencanbekillediftasselsareallowedtooclosetothelights.SeeourdocumentWhatotherideasforimprovingseedyield?formoredetails.Mostfacilitiesreportusingaphotoperiodof14hours.ThePlantGrowthChamberHandbooksuggestsupto20hoursduringthevegetativephase.Weused16hoursforallstagesofgrowthinourexperiments.Severalfacilitymanagershaveseendamagetoleavesundersupplementallightingof24hours,soitisnotrecommended.We’vedocumentedthat24hourlightingexacerbatescalciumdeficiencysymptomsonseedlingcorn(seeFigure2).MethodstoimprovelightintensityHavingalightsystemthatraisesandlowers(seeFigure1)isanexcellenttoolformaximizinglight,ifavailable.Anothereffectivetechniqueistogrowthecornontablesclosertothelightwhileplantsareshort,thenmovethemtothefloor.Thistakesconsiderabletime,especiallywithourproposedsystemthatwouldrequiremovingthedripirrigationsystem.Oneresearchreportedanincreaseinyieldbyremovingtasselsafterpollinationsothatlightscouldbeloweredclosertotheplantsduringthegrain‐fillperiod(personalcommunication).Iftrue,thismayworkbecauseofincreasedlightduringthecriticalwindowreportedbyPrine.

AnewstandardmaybewarrantedRecommendingalightintensityforcornatcanopylevelmayneedtobereconsidered.Sinceseedyieldincreasedwhensupplementallightwasappliedtolowercanopyinafield,onewouldexpectasimilarbenefitinagreenhouse.Becauseplantspacing,typeoffacility,photoperiodandotherfactorsimpactlightreachinglowercanopy,anewlightingstandardmayneedtobedevelopedthatreportsdailylightintegralreachingthelowercanopy.Untilthatvaluecanbedeterminedempirically,wesuggestgrowerstrytoachieveaminimum1.5moles/dayatlowestleaf.Thiscorrespondstoauniformintensityatthisheightof30µmol/m2/sfor14hoursperday.Withsupplementallightingof150µmol/m2/sonemeterbelowlightsinaglassgreenhouse,wewereabletoachieve1.7‐4.4moles/dayatlowestleafforsevendaysinearlyMarchduringseedripeningstage.Itwasenoughlightforverygoodseedyieldofprimaryear(583seeds/ear),butsecondaryearsaborted.

Figure1.Left:Spacingwith30­cmbetweenstalkswithinthetwinrow(foreground)and76cmspacingbetweenthetwinrows.Right:LightbanksatControlledPharmingVenturesraiseandlowertooptimizelight.

Figure2.Seedlingdamagefrom24­hourlighting.

Figure3.Aportableloggingunittracksdailylightintegralandotherdataatlowestleaflevel.