Effect of Post-Infiltration Soil Aeration at Different Growth Stages on Growth and Fruit Quality of Drip

16 Pages·2015·0.25 MB·English

RESEARCHARTICLE
Effect of Post-Infiltration Soil Aeration at
Different Growth Stages on Growth and Fruit
Quality of Drip-Irrigated Potted Tomato
Solanum lycopersicum
Plants ( )
YuanLi1,2,3,4,ZongxiaJia1,5,WenquanNiu1,2,3,4*,JingweiWang1,2,3,4,MingzhiZhang3,4
1 InstituteofSoilandWaterConservation,NorthwestA&FUniversity,Yangling,712100,Shaanxi,China,
2 InstituteofSoilandWaterConservation,ChineseAcademyofSciences&MinistryofWaterResources,
Yangling,712100,Shaanxi,China,3 CollegeofWaterResourcesandArchitecturalEngineering,Northwest
A&FUniversity,Yangling,712100,Shaanxi,China,4 InstituteofWater-savingAgricultureinAridAreasof
China,NorthwestA&FUniversity,Yangling,712100,Shaanxi,China,5 DezhouProspectingandDesigning
InstituteofWaterConservancy,Dezhou,253000,Shandong,China
*[email protected]
Abstract
OPENACCESS
Soilhydraulicprinciplessuggestthatpost-infiltrationhypoxicconditionswouldbeinduced
Citation:LiY,JiaZ,NiuW,WangJ,ZhangM(2015)
intheplantroot-zonefordrip-irrigatedtomatoproductioninsmallpotsfilledwithnaturalsoil.
EffectofPost-InfiltrationSoilAerationatDifferent
GrowthStagesonGrowthandFruitQualityofDrip- Nopreviousstudyspecificallyexaminedtheresponseoftomatoplants(Solanumlycopersi-
IrrigatedPottedTomatoPlants(Solanum cum)atdifferentgrowthstagestolowsoilaerationundertheseconditions.A2×6factorial
lycopersicum).PLoSONE10(12):e0143322.
experimentwasconductedtoquantifyeffectsofnopost-infiltrationsoilaerationversusaer-
doi:10.1371/journal.pone.0143322
ationduring5differentperiods(namely27–33,34–57,58–85,86–99,and27–99daysafter
Editor:HaibingYang,PurdueUniversity,UNITED
sowing),ongrowthandfruitqualityofpottedsingletomatoplantsthatweresub-surface
STATES
trickle-irrigatedevery2daysat2levels.Soilwasaeratedbyinjecting2.5litersofairinto
Received:June15,2015
eachpotthroughthedriptubingimmediatelyafterirrigation.Resultsshowedthatpost-infil-
Accepted:November3,2015 trationaeration,especiallyduringthefruitsetting(34–57DAS)andenlargement(58–85
Published:December2,2015 DAS)growthstages,canpositivelyinfluencetheyield,rootdryweightandactivity,andthe
nutritional(solublesolidsandvitaminCcontent),taste(titratableacidity),andmarketquality
Copyright:©2015Lietal.Thisisanopenaccess
articledistributedunderthetermsoftheCreative (shapeandfirmness)ofthetomatofruits.Interactionsbetweenirrigationlevelandpost-infil-
CommonsAttributionLicense,whichpermits trationaerationonsomeofthesefruitqualityparametersindicatedaneedforfurtherstudy
unrestricteduse,distribution,andreproductioninany
onthedynamicinterplayofairandwaterintherootzoneoftheplantsundertheconditions
medium,providedtheoriginalauthorandsourceare
ofthisexperiment.
credited.
DataAvailabilityStatement:Allrelevantdataare
withinthepaperanditsSupportingInformationfiles,
andfromtheFigsharedatabaseathttp://dx.doi.org/
10.6084/m9.figshare.1560001.
Introduction
Funding:ThisworkissupportedjointlybyChina863
Plan(2011AA100507)andtheNational111Projectof ItiswellknownthatmesophyticplantrootsaccesssoilO (inairordissolved)bydiffusive
2
China(No.B12007). masstransfer.At298°KthediffusioncoefficientforO inwateris2.6×10−5cm2s-1compared
2
to0.176cm2s-1inair[1,2].ThisimpliesthatunderthesameO concentrationgradientthedif-
CompetingInterests:Theauthorshavedeclared 2
thatnocompetinginterestsexist. fusivemasstransferiscloseto6800timesgreaterinairthaninwater.
PLOSONE|DOI:10.1371/journal.pone.0143322 December2,2015 1/16
SoilAerationonGrowthandFruitQualityofTomato
Plantrootsthereforedependprimarilyontheoxygensupplyfromsoilairwhichcanbecon-
tinuallyreplenishedbyexchangewiththeatmosphere,ratherthanfromoxygendissolvedin
thesoilsolution.
Tomato(SolanumlycopersicumL.)iscultivatedinChinaundersmall(0.1to0.2ha),low-
cost,structureswithremovalplasticcovers[3,4].Container(orpot)productionsystemsthat
usenaturalsoilmediaarelessexpensiveandcommoninChina'sprincipaltomatoproduction
provinces(namelyShandong,Xinjiang,Hebei,andHenan).Sincewaterandairoccupythe
sameporespaceofthesoilvolumeinthepots,theirsoilsaturationlevelsarereciprocally
related.Increasingwatersaturationimpliesdecreasingairsaturationandvice-versa.Inthis
context,formulatingirrigationtiming,level,andfrequencyforpottedplantsneedstotakeinto
accountmeetingcropwaterandnutrientrequirementsaswellaspreventingoxygen-deficient
conditionsintherootenvironment.Thesechoiceswoulddependonmanyfactorssuchasthe
irrigationmethod,irrigationwaterquality,soiltype,andcropspecies.
Soilhydraulicsdictatethatgravitationaldrainagefrompotscantakeplaceonlyifthesoil
layeratthebottomofthepotsissaturated(Richard'soutflowlaw)andtheprofiledepthinthe
potexceedsthesoilbubblingpressure.Asaresult,thesoilhydraulicsincontainersisdifferent
fromnaturalsoilprofiles,andpotproductionsystemsarepronetovaryingperiodsofexposure
tolowoxygenlevels(hypoxia)orlackofoxygen(anoxia)intherootzonefollowingirrigation.
Finersoiltextureswouldposeahigherriskbecauseoftheirhigherbubblingpressureand
slowerpost-infiltrationinternaldrainageandredistributionthancoarsesands.Smallpots
requirelesssoilandoccupylessspaceundercoveredproduction.Ontheotherhand,they
wouldprovidelesssoilvolumeforrootexpansionandhigherriskofexposuretohypoxiafol-
lowingirrigation.Inthiscase,toppingand/orcompleteorpartialpruningoflateralshootsand
trusses(especiallyforindeterminatecultivars)areusedtolimitshootgrowthandrootexpan-
sionandimprovefruitsizeandquality[5,6].
Severalstudiesintheliteraturesupporttheideasintheprecedingdiscussion.Bhattaraietal.
[7]presentedanin-depthreviewofstudiesshowingthatirrigationwithaeratedoroxygenated
water(termedasairgationandoxygation)oradditionofhydrogenperoxide[8,9]would
increasedissolvedO contentandoffsetthenegativeeffectsofhypoxiafollowingirrigation.
2
Wangetal.[10]demonstratedthatpartitioningtherootsystemofmaizeplantsincontainers
dividedintotwocompartmentsandalternatelyirrigatingthem,lessenedthepossibleeffectof
hypoxicoranoxicconditionscomparedtosinglecompartmentpots.
Subsurfacedrip(ortrickle)irrigationofpottedplantsnotonlyrequireslesswaterbutkeeps
thesoilsurfacepartiallysaturatedandopentodiffusionofatmosphericair.Also,thesaturated
root-zonevolumebelowtheleveloftheemitterscanbecontrolledbyvaryingtheirrigation
rateandfrequency[11].Dependingonspecies,rootsofmesophytescantoleratevaryingperi-
odsofhypoxiaoranoxiaandmayevenacclimatizeanddevelopgreatertolerancefollowing
exposure[12,13].Sensitivitytolowrhizospheresoilaerationforagivenspeciesmayalsochange
overtime,andthereforeplantresponsemayalsodependondifferentgrowthstagesofthe
crop.Underhypoxicconditionsintherootzone,above-groundsymptomsmaynotbeappar-
entalthoughphysiologicalchangeshaveoccurredthatcandecreasegrowthanddevelopment
andloweryield.Rootzonehypoxiacausesstomatalclosure[14],andthisinturnresultsinless
gasexchangewithleaves,lowerphotosynthesisandtranspirationalongwithreducedwater
andnutrientuptake.Otherassociatedeffectsarereducedrootmassandleafexpansion,and
visiblelossofleafchlorophyllandprematureleafsenescence[15,16,17,18].
Tomatoplants(Solanumlycopersicum)areoneofthemostvulnerablemesophytestohyp-
oxiaintherootenvironment[19].Highvulnerabilityincorporatestheconceptsoflowsensitiv-
ity(i.e.lownegativeresponsethresholds)andlowresilience(i.e.abilitytoadjust,recover,or
resistaperiodofexposure).Therearenoreportsintheliteratureontheinter-relationshipof
PLOSONE|DOI:10.1371/journal.pone.0143322 December2,2015 2/16
SoilAerationonGrowthandFruitQualityofTomato
thesetwoaspectsofvulnerabilityoftomatoplantstorootzonehypoxianorreportsonplant
characteristicsandenvironmentalfactorsthatcontributeto,orareassociatedwith,highvul-
nerability.RaoandLi[20]reviewedstudiesonnegativeeffectsofrootzonefloodingontomato
plants.Sensitivityoftheplantsaccordingtotheirgrowthstagewereintheorderflowering
stage>fruitingsettingandfruitgrowthstage>seedlingstage>fruitripeningstagebutthis
orderdependedondurationofexposuretohypoxicconditions.Negativeresponsesincluded
reducedplantheight,leafarea,leafchlorophyllcontent,fruitset,andrespirationrate.
Aliteraturesearchreturnedfewstudiesontheeffectsofroot-zonehypoxiaontomatofruit
marketqualityandnutritionalvalue[11,21,22].Thesestudiesindicateaeratedirrigation
(termedairgation)canincreaseshootgrowthalongwithyield,hardness,andnutritionalvalue
oftomatofruit.Asimilarpaucityofstudiesexistsontomatorootgrowthresponsetohypoxia.
Aerationthroughsubsurfacetrickleirrigationtubesstimulatedrootgrowth[23,24,25]andarti-
ficialaerationhasbeenshowntopromoterootmetabolismandgrowth[26,27].Meeketal.[28]
reportedhigheryieldsoftomatoeswererelatedtohigheroxygencontentsinthesoilrootzone
beforeandduringthefruit-enlargingstage.
Theforegoingdiscussionindicatesthatpost-infiltrationaerationmaybebeneficialforsub-
surfacedrip-irrigatedpottedtomato(Solanumlycopersicum)productionusingnaturalsoil.
Also,thatthisbenefitmayberealizedwithaerationrestrictedtospecificgrowthstages.An
ongoingresearchprogramatNorthwestAgricultureandForestUniversity,Yanling,China
addressesissueswithdrip-irrigatedproductionofvegetablesincontainers[11,27].Todate,no
studyhasspecificallyexaminedthesensitivityoftomatoplants(Solanumlycopersicum)tolow
soilaerationatdifferentgrowthstagesandhowthismayimpactrootandfruitgrowth,devel-
opment,andquality.However,suchinformationwouldhavehighpracticalvalue,ifitshown
thatpost-infiltrationaerationisneededonlyatspecificgrowthstagesoftomatoplantstoover-
comethenegativeeffectsofhypoxiaintherootzoneundersub-surfacetrickle-irrigation.
Thisobjectiveofthisstudywastoquantifyeffectsofnopost-infiltrationsoilaerationversus
aerationduring5differentperiods(namely27–33,34–57,58–85,86–99,and27–99daysafter
sowing)onpottedtomatoplants(Solanumlycopersicum)thatweresub-surfacetrickle-irrigated
every2daysat2levels.Specifically,weexamineddataonyield,rootgrowthandactivity,and
themarketandnutritionalvalueofthefruits.
MaterialsandMethods
Sitedescription
Theexperimentwasconductedunderarain-shelterattheKeyLaboratoryofWaterandSoil
EngineeringforDryRegionsatNorthwestA&FUniversityYangling,Shaanxi,Chinabetween
April7andJuly15,2011.Thelocationissemi-aridwithanaverageannualrainfallof572.5
mm,anaverageannualsunshineof2163.8hoursand210frost-freedays.
Experimentaldesign
OnApril20,3-weekoldtomatoseedlingsofthevariety“TianzeChunlei”weretransplantedto
144experimentalpots.Eachpotcontainedtopsoilcollectedfromthe0cmto20cmdepthof
theKeyLaboratoryfarmland(aLousiltyclayloamclassifiedasInceptisolbasedontheU.S.
soiltaxonomy).Threelitersofwaterwereaddedtoeachpotaftertransplanting.Thepotshad
anupperinnerdiameterof29cm,abottominnerdiameterof22cmandadepthof24.5cm
andwerefilledwithsoilto22.5cmtoachieveadrybulkdensityof1.3gcm-3.Thetotalvolume
(V)ofsoilinthepotswas9.8litercalculatedasthevolumeofatruncatedrightcircularconeof
largediameter=25.2cm(R),smalldiameter22cm(r),andheight22.5cm(h)usingthefor-
mulaV=[πh(R2+r2+Rr)]/3.Theweightofsoilineachpotwas12.75kg.Thefieldcapacity,
PLOSONE|DOI:10.1371/journal.pone.0143322 December2,2015 3/16
SoilAerationonGrowthandFruitQualityofTomato
topsoilinitialmoisture,totalnitrogen,andorganicmattercontentswere230gkg-1(23%by
weight),23.8%,0.98gkg-1and9.51g(cid:1)kg-1,respectively.Thetotalporosity(n)ofthesiltyclay
loamsoilinthepotswasestimatedas1minustheratioofthedrybulkdensity(ρ )totheparti-
b
cledensity(ρ ).Usingthemeasuredρ =1.3gcm-3andtakingρ =2.60gcm-3givesanesti-
p b p
matedn=0.50Every2days,startingApril27(27daysaftersowing),72potswereirrigatedat
0.6to0.7ofthegravimetricfieldcapacity(lowlevel)andtheother72potsat0.7to0.8offield
capacity(highlevel).Thisimpliestheweightofwaterinthepotsatthelowirrigationlevelran-
gedfrom1.76(=0.6×0.23×12.75kg)to2.05kg(0.7×0.23×12.75kg).Similarly,weightof
waterinthepotsatthehighirrigationlevelrangedfrom2.05kgto2.35kg.Thevolumeof
waterneededforthe2irrigationlevelswasapproximatedthroughweighing[29]andrecorded
foreachpot.Thefivepost-infiltrationaerationperiodsbydateanddaysaftersowing(DAS)
were:(1)theseedlingstagebetweenMay4and10or27to33DAS,(2)thefloweringandfruit
settingstagebetweenMay10andJune3or34–57DAS,(3)thefruitenlargingstagebetween
June3andJuly1or58–85DAS,(4)thefinalfruitripeningstagebetweenJuly1and15or86–
99DAS,and(5)thewholegrowingperiodbetweenMay4andJuly15or27to99DAS.During
thesepost-infiltrationaerationperiods,airwasinjectedintothepotsthroughtheburieddrip
irrigationtubeswithanaircompressoratarateof2.5litersperpot.Thisrateapproximated
50%ofthesoilporosityineachpot.Ano-aerationcontrolwasincludedforatotalof6experi-
mentaltreatments.Foreachirrigationlevel,eachofthe6treatmentswasappliedtoablockof
12pots.Thetomatoplants(Solanumlycopersicum)wereprunedtosinglestems,andwere
toppedaftertheappearanceof4trusses.Exceptirrigationandaeration,theothermanagement
measureswerethesameforallpots.
Threepotsfromeachtreatmentblockweretaggedforripefruityield,fruitcharacteristics,
andothernon-destructivemeasurements.Theremaining9potsineachblockwereincluded
fordestructivemeasurementsatendofthefirstthreegrowthperiods(namely27–33,34–57,
and58–85DAS).Atend57and85DAS,threepotswererandomlysampledfromeachtreat-
mentblockfordestructivemeasurementsofrootdryweightandrootvigor.Therootsofthe
plantswereremovedandwashedthroughasieve.Rootactivitywasmeasuredona0.5-gpor-
tionsoffreshroottipsusingthetriphenyltetrazoliumchloride(TTC)method[30].Thistestis
basedonliverootsreducingcolorless2,3,5-triphenyltetrazoliumchloride(TTC)toredtriphe-
nylformazan(TPF).Thelatteristhenextractedafterafixedincubationperiodandmeasured.
RootactivitywasexpressedasthemassTPFproducedinmgpergfreshrootperhour.Thedry
weightofthewashedrootswasthenmeasured.Thiswasalsodoneforthe3taggedplantsat99
DASafterthefinalfruitswereharvested.
Thevolumeofwaterforthe38irrigationsappliedtothe3taggedpotsforeachtreatment
weretotaledandaveragedtoobtainameanvalueofwaterappliedperpot(n=18)forthelow
andhighirrigationlevels.
Fruitqualitymeasurements
Fullyripefruitsonthetaggedplantswereprogressivelyharvestedandweigheduntil99DAS.
Thesizeandhardnessofthefirst8ripefruitsharvestedfromthefirsttrussweredetermined.
Axialandlateralfruitdiameterofeachfruit(mm)weremeasuredusingaVerniercaliper.Fruit
hardness(Nmm-2)wasmeasuredintheequatorialareaofeachfruitusingaKMH-51pene-
trometer(KiyaSeisakushoCo.Ltd,Tokyo,Japan).
Thetasteandnutritionalpropertiesofthefirstripefruitharvestedfromthefirsttrussof
eachtaggedplantweredetermined.Thefruitwasslicedandblendedafterremovingtheskin
andseeds.Ahand-heldATAGO-P32temperature-compensatedrefractometer(ATAGOCo.
Ltd,Tokyo,Japan)wasusedtodirectlyreadthe%solublesolids(as°Brix)oftheblendedfruit
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SoilAerationonGrowthandFruitQualityofTomato
atroomtemperature[31].Titratableacids(%byweight)weredeterminedbydilutinganali-
quotoftheblendedfruitandtitratingagainst0.1MNaOHusingphenolpthaleinasanindica-
tor.The%byweighttitratableacidswasestimatedas(mlNaOH×acidfactor=0.0064)
dividedbymlaliquotofblendedfruit.Becauseskinandseedsmakeuplessthan1%oftomato
fruitfreshweight,theseparametersmeasuredinweight%oftheblendedfruitcanbetakenfor
practicalpurposesas%byweightoffreshfruit[3,32].VitaminCcontent(mgper100gfresh
fruit)wasdeterminedbymolybdenumbluecolorimetry[33].Thismethodisbasedonthereac-
tionofascorbicacid(VC)withammoniumphospho-molybdateinthepresenceofSO 2-and
4
PO 3-generatingthebluemolybdenum.Thisbluemolybdenumhasthemaximumabsorption
4
at760nm.ThisvitaminCassaymethodisaccurate,repeatable,andinsensitivetotheinterfer-
enceinthepresenceofcommonreducingsugars.
Statisticalanalysis
Theexperimentaldesignwastreatedasa2×6factorialwith3replicatesforstatisticalanalyses.
Accordingly,thedatacollectedforeachoftheobservedexperimentalvariableswasanalyzed
usingthegenerallinearmodelY =μ+α +β +(αβ) +ε whereY denotesthevariable
ijk i j ij ijk ijk
observedonthekthreplicate(k=1,2,3)fortheithirrigation(i=1,2)andjthaerationtreat-
ment(j=1,2...6).Hereμdenotestheoverallmeanofthevariable,α theeffectofirrigation,
i
β theeffectofaeration,(αβ) theirrigation×aerationinteractioneffect,andε theassociated
j ij ijk
randomerror.Thefittingofthemodelwasdoneusing2wayANOVAroutineoftheSPSSsoft-
warepackage(IBM,Armonk,NewYork).IftheANOVAresultsforagivenresponseshowed
nosignificantirrigation×post-infiltrationaerationeffect,theaerationtreatmentmarginal
meanswereseparatedbytheDuncanmultiplerangetest.At-testwasusedtocompareirriga-
tiontreatmentmarginalmeans.Ifsignificantinteractioneffectswereobtained,thesimpleeffect
aerationtreatmentmeansofateachirrigationlevelwereseparatedbytheDuncanmultiple
rangetest.
Results
Freshfruityield,solublesolidsandplantgrowth
About5to6medium-sizedhigh-qualityfruitswereharvestedfromeachpotasaresultofthe
heavypruningofthestemsandcullingofthetrusses.Neitherpost-infiltrationaerationnorirri-
gationleveltreatmentssignificantlyimpacted(P(cid:3)0.05)freshfruityieldofthepottedsingle
tomatoplants(Table1).TheANOVAshowedtherewasnoirrigation×post-infiltrationaera-
tioninteractioneffect.Nevertheless,freshfruityieldsforallthepost-infiltrationaeratedplants
werehigherthanthosethatreceivednoaerationtreatment.Forthelowirrigationtreatment,
themeanyield(n=3)ofthenon-aeratedplantswas616gperplantcomparedtothemean
yieldfortheof688gperplant(about12%higher)forthepotsthatwereaeratedfortheentire
periodof27–99daysaftersowing.Correspondingvaluesforthehighirrigationtreatmentwere
633and693gperplant(about9%higher).Themeanyield(n=18)acrossallaerationtreat-
mentswas674gperplantatthelowirrigationleveland680gperplantatthehighirrigation
level.
Eventheshortperiodsofpost-infiltrationaerationtendedtoincreasefreshfruityield.As
showninTable1aerationfrom27to33DASresultedina10%yieldincreasefrom616to680
gperplantforthelowirrigationlevel.Forthehighirrigationlevel,therewasacorresponding
8%increasefrom633to683gperplant.Lowerincreasesof6%and4%overthenoaeration
treatmentwereobtainedwithaerationfrom86to99DAS(Table1).Maximumyieldsof709
and710gperplantwereobtainedforpost-infiltrationaerationduring58–85daysaftersowing
correspondingtothefruitsettingperiod(Table1).
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SoilAerationonGrowthandFruitQualityofTomato
Table1. Fruityield,above-groundplantdryweight(gperplant),plantheight(cm)andsolublesolidscontentofthefirstripefruitfromthefirst
trussofpottedsingletomatoplantsfor6post-infiltrationaerationtreatments(i.e.noneor2.5literaerationappliedduring5differentperiods)at99
DAS. Potsweresubsurfacedrip-irrigatedat2-dayintervalstomaintainthesoilat60to70%or70to80%ofvolumetricfieldcapacity(denotedaslowand
highirrigationlevel).
Aerationperiod,daysafter Fruityield,(gperplant) Plantdryweight,(gper Plantheight,(cm) SolubleSolids(°Brix)
sowing plant)
Irrigationlevel Low High Mean Low High Mean Low High Mean Low High Mean
(n=6) (n=6) (n=6) (n=6)
None 616a 633a 625a 30.7b 36.0a 33.3c 78.2d 79.1c 78.6c 4.67a 4.73a 4.70a
27–33 680a 683a 681a 40.2ab 41.0a 40.6abc 80.5d 84.5b 82.5b 5.00ab 5.20abc 5.10abc
34–57 695a 704a 699a 42.2a 52.3a 47.3a 88.8ab 88.8a 88.8a 5.13ab 5.73bc 5.43cd
58–85 709a 710a 709a 44.1a 51.5a 47.8a 90.8a 88.0a 89.4a 5.47b 5.80c 5.63d
86–99 654a 659a 657a 36.1ab 37.9a 37.0bc 82.2cd 83.1b 82.7b 4.87ab 4.93ab 4.90ab
27–99 688a 693a 691a 40.5ab 49.2a 44.9ab 85.0bc 82.2b 83.6b 5.13ab 5.40abc 5.27bcd
OVERALLMEAN 674 680 677 39.0ab 44.6 41.8 84.2 84.3 84.3 5.04 5.30 5.17
Notes:Irrigationandinteractioneffectswerenotsignificant(p>0.05)inANOVA.Aerationtreatmentmeansacrossirrigationlevels(n=6)notfollowedby
thesameletteraresignificantlydifferentatthe5%level.
doi:10.1371/journal.pone.0143322.t001
Ingeneral,abovegroundplantdryweightandplantheightat99DAS(Table1)mirrored
theyieldresponsetothetreatments.Thiswouldbeexpectedsincethesethreevariablesrepre-
sentanintegratedmeasureofthetreatmenteffectsontheplantovertheentiregrowthperiod.
The2-wayANOVAshowednosignificantinteractionbetweenirrigationlevelandpost-infil-
trationaerationtreatments.Overallmeanabovegroundplantdryweightforthehighirrigation
levelwas14%higherthanthelowerlevel(Table1).Aswasfoundforfreshfruityield,post-
infiltrationaerationevenforshortperiodsresultedinabovegrounddryweightandplant
heightincreasesalthoughtheseincreaseswerestatisticallynon-significant.Also,highest
increasesforplantdryweightandheightovertheno-aerationtreatmentoccurredforthelon-
gerperiodsofpost-infiltrationaeration.
The2-wayANOVAresults(Table1)indicatedahighlysignificanteffect(P=0.004)of
post-infiltrationaerationeffectonsolublesolidscontent(as°Brix)ofthefreshfruits.Irrigation
leveleffectswereborderlinesignificant(p=0.058),andtherewasnosignificantinteraction
betweenthetwoexperimentaltreatmentfactorson°Brix.TheLSD forcomparingirrigation
0.05
meanvalues(n=18)forsolublesolidscontentacrossallaerationtreatmentswas0.26.The
overallmeans(Table1)fortheirrigationtreatmentonsolublesolidscontentvalueswere5.04
versus5.30°Brix.
Solublesolidsvaluesatthehighirrigationlevelweregreaterthanthoseatthelowlevelfor
allaerationtreatments(Table1).Solublesolidscontentrespondedpositivelytopost-infiltra-
tionaerationduringtheflowering(34–57DAS)andfruitsettingstages(58–85DAS).Valuesat
thelowirrigationlevelforthesetreatmentswere10%and17%higherthanwithoutaeration.
Correspondingvalueswere21%and23%atthehighirrigationlevel(Table1).Themeansfor
thesetreatmentswerenotsignificantlydifferent(P>0.05)thanthoseforcontinuousaeration
treatmentforbothirrigationlevels.
Rootdryweightandactivity
Table2showstheresultsofmeasurementofrootdryweightat58,85,and99DAS.The2-way
ANOVAshowedirrigationleveltreatmentshadnosignificanteffectonrootdryweightonany
ofthesedatesandtherewerenoirrigation×aerationinteractions.Theaerationtreatment
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SoilAerationonGrowthandFruitQualityofTomato
Table2. Rootdryweight(gperplant)ofpottedsingletomatoplants(n=3)measuredat57,85,and99daysaftersowing(DAS)forthe6post-infil-
trationaerationtreatments(i.e.noneor2.5literaerationappliedduring5differentperiods)atthelowandhighirrigationlevels(i.e.subsurface
drip-irrigationtomaintainsoilat60to70%and70to80%ofvolumetricfieldcapacity).
Aerationperiod,daysaftersowing Rootdryweight(gperplant)measuredatgivenDAS
irrigationlevel Low High
DAS 57 85 99 57 85 99
None 2.89a 3.52b 3.94c 3.14a 3.81b 4.13b
27–33 3.30a 3.89ab 4.37abc 3.31a 4.23ab 4.77ab
34–57 4.07a 4.72ab 5.28ab 4.16a 4.98ab 5.85a
58–85 3.09a 4.98a 5.55a 3.22a 5.18a 6.30a
86–99 3.05a 3.68ab 4.02bc 3.21a 4.18ab 4.74ab
27–99 3.90a 4.74ab 5.22abc 4.22a 5.13a 5.81a
OVERALLMEAN 3.38 4.26 4.73 3.54 4.58 5.27
Notes:Irrigationandinteractioneffectswerenotsignificant(p>0.05)inANOVA.Aerationtreatmentmeansateachirrigationlevelnotfollowedbythesame
letteraresignificantlydifferentatthe5%level
doi:10.1371/journal.pone.0143322.t002
effectsweresignificantforallthreedates.TheaerationtreatmentmeansinTable2representa
1-wayANOVAontherootdryweightobservationsatagivendateateachirrigationlevel.
Althoughnotsignificantlydifferenttherootdryweightmeansatthehighirrigationlevelwere
greaterthanatthelowirrigationlevelforallaerationtreatments(Table2).Aswouldbe
expecteddryrootweightvaluesconsistentlyincreasedwithageoftheplants.Aerationtreat-
menteffectsweremorepronouncedforobservationsat58and99DAS.Aerationapplication
betweenfrom58to85DASsignificantlyenhancedrootdryweightforbothirrigationlevelson
thesedates.
The2-wayANOVAshowedbothirrigationlevelandsoilaerationtreatmentssignificantly
affectedrootactivityobservationsat58,85,and99DAS.Also,theirrigation×aerationeffects
weresignificantforthese3dates(Table3).Rootactivitywasmarkedlyhigherat85DAScom-
paredtoobservationsat58and99DAS.At57DAStherootactivityforallaerationtreatment
Table3. Irrigation×post-infiltrationaerationinteractiononrootactivity(asmgtriphenylformazanpergfreshrootperhour)ofpottedsingle
tomatoplants(n=3)measuredat57,85,and99daysaftersowing(DAS). Aerationtreatments(i.e.noneor2.5literaerationappliedduring5different
periods)atthelowandhighirrigationlevels(i.e.subsurfacedrip-irrigationtomaintainsoilat60to70%and70to80%ofvolumetricfieldcapacity).
Aerationperiod,daysaftersowing Rootactivity(TPFpergfreshrootperhour)forirrigationlevelatgivenDAS
DAS 57 85 99
irrigationlevel Low High t-test Low High t-test Low High t-test
None 7.4c 7.8d * 11.6e 11.8d ns 6.7c 6.9c ns
27–33 8.3b 8.8c * 12.5d 12.4c ns 6.8c 6.7c ns
34–57 9.4a 10.4a ** 13.5b 14.7b ** 9.2a 9.2b ns
58–85 7.4c 9.3b ** 12.9c 15.1a ** 9.4a 9.6a ns
86–99 6.9d 7.7d ** 11.6e 11.8d ns 6.7c 6.8c ns
27–99 8.4b 9.3b * 14.9a 15.3a * 8.6b 9.1b *
OVERALLMEAN 6.8 7.6 ** 11.0 11.6 ** 6.8 6.9 ns
Notes:Aerationtreatmentmeansateachirrigationlevel(n=3)notfollowedbythesameletteraresignificantlydifferentatthe5%level.Thet-testwas
usedtocompare2irrigationtreatmentmeans(n=3)foreachaerationtreatmentperiod.Theasteriskindicatessignificantlydifferentmeans(*for
p(cid:3)0.05)and(**forp(cid:3)0.01,otherwisenotsignificant(ns).
doi:10.1371/journal.pone.0143322.t003
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Table4. Irrigation×post-infiltrationaerationinteractionontitratableacidityandvitaminCcontent(freshweightbasis)ofthefirstripefruitfrom
thefirsttrussofpottedsingletomatoplants(n=3). Aerationtreatmentswerenoneor2.5literaerationappliedduring5differentperiods.Potsweresub-
surfacedrip-irrigatedat2-dayintervalstomaintainthesoilat60to70%or70to80%ofvolumetricfieldcapacity(denotedaslowandhighirrigationlevel).
Aerationperiod,daysaftersowing TitratableAcidity(weight%) VitaminCContent(mg/100g)
Irrigationlevel Low High t-test Low High t-test
None 0.79a 0.82a ns 55.0a 42.8a *
27–33 0.76b 0.78b ns 69.4b 59.3b *
34–57 0.62c 0.65d ns 67.7b 59.2b *
58–85 0.65c 0.73c * 59.8a 71.5c *
86–99 0.65c 0.64d ns 57.8a 64.9b *
27–99 0.62c 0.69c * 60.5a 64.4b ns
OVERALLMEAN 0.68 0.72 ** 61.7 60.4 ns
Notes:Aerationtreatmentmeansateachirrigationlevel(n=3)notfollowedbythesameletteraresignificantlydifferentatthe5%level.Thet-testwas
usedtocompare2irrigationtreatmentmeans(n=3)foreachaerationtreatmentperiodandacrossaerationtreatments(n=18).Theasteriskindicates
significantlydifferentirrigationmeans(*forp(cid:3)0.05),(**forp(cid:3)0.01,otherwisenotsignificant(ns).
doi:10.1371/journal.pone.0143322.t004
atthehighirrigationweresignificantlygreaterthancorrespondingvaluesforthelowirrigation
level(Table3).
TitratableacidityandvitaminCcontent
ANOVAresultsfortitratableacidityandvitaminClevelsshowedhighlysignificantirrigation
×aerationeffects(p=0.02andp<0.01respectively).Post-infiltrationaerationeffectswere
highlysignificant(p(cid:3)0.01)forbothresponsevariables,aswastheirrigationleveleffect,but
onlyfortitratableacidity.Thepost-infiltrationaerationeffectsateachirrigationlevelonthese
twofruitnutritionalpropertiesarepresentedinTable4.
Theoverallmean(n=18)for%titratableaciditywassignificantlyhigher(0.68%versus
0.72%withLSD =0.02)atthehighirrigationlevel.Ontheotherhandtherewasnosignifi-
0.05
cantdifferenceintheoverallmeanvitaminCcontent,whichwasslightlyloweratthehighirri-
gationlevel(61.7versus60.4mg/100gwithLSD =2.5).AsshowninTable4,titratable
0.05
aciditymeans(n=3)wereconsistentlygreateratthehighirrigationlevelforallaerationtreat-
mentsbutweresignificantlydifferent(LSD =0.04)onlyforaerationduringfruitenlarge-
0.05
ment(58–85DAS)andduringtheentiregrowthperiod(27–99DAS).
Theresults(Table4)furthershowthatatbothirrigationlevels,titratableaciditywassignifi-
cantlyhigherforpost-infiltrationaerationduringtheearliergrowthstages(27–33DAS)and
forthenoaerationtreatmentrelativetothelaterstages.Forthelowirrigationlevel,vitaminC
contentwasalsohigherfortheaerationtreatmentduringtheearliergrowthstages(27–33DAS
and34–57DAS)thanforthenoaerationandaerationatthelaterstages.Ontheotherhand,
vitaminCcontentwasmaximumatthehighirrigationlevelforaerationduringthefruit
enlargementstage(58–85DAS).
Shapeandhardness
TheANOVAresultsforexperimentaltreatmenteffectsonthefruitaxialandlateraldiameters,
andhardness(measuredonthefirst8ripefruitsharvestedfromthefirsttrussesof3pottedsin-
gletomatoplants)shownosignificantirrigationnorirrigation×post-infitrationaerationeffect
(Table5).Althoughtheirrigationtreatmentdifferenceswerenon-significant,means(n=3)
foreachaerationtreatmentwerehigheratthehighirrigationlevel(Table5).Overallmean
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SoilAerationonGrowthandFruitQualityofTomato
Table5. Axialandlateraldiameter,andhardnessmeasuredonthefirst8ripefruitsharvestedfromthefirsttrussesof3pottedsingletomato
plantsfor6post-infiltrationaerationtreatments(i.e.noneor2.5literaerationappliedduring5differentperiods). Potsweresubsurfacedrip-irrigated
at2-dayintervalstomaintainthesoilat60to70%or70to80%ofvolumetricfieldcapacity(denotedaslowandhighirrigationlevel).
Aerationperiod,daysaftersowing Axialdiameter,(mm) Lateraldiameter,(mm) Hardness,(Nmm-2)
Irrigationlevel Low High Mean(n=16) Low High Mean(n=16) Low High Mean(n=16)
None 37.7a 38.4a 38.0a 53.2a 55.7a 54.5a 2.7a 2.9a 2.8a
27–33 44.0ab 45.5ab 44.7b 56.8a 58.2a 57.5a 3.6b 3.7ab 3.7b
34–57 48.4b 51.3b 49.9b 59.8a 60.6a 60.2a 3.8b 4.1b 3.9b
58–85 47.0ab 50.2b 48.6b 58.9a 62.2a 60.5a 4.0b 4.0b 4.0b
86–99 43.7ab 44.9ab 44.3b 54.9a 55.7a 55.3a 3.6b 3.6ab 3.6b
27–99 47.2ab 48.2b 47.7b 58.1a 60.1a 59.1a 3.9b 4.0ab 3.9b
OVERALLMEAN 44.6 46.4 45.5 56.9 58.8 57.9 3.6 3.7 3.6
Notes:Irrigationandinteractioneffectswerenotsignificant(p>0.05)inANOVA.Aerationtreatmentmeansacrossirrigationlevels(n=16)notfollowedby
thesameletteraresignificantlydifferentatthe5%level.
doi:10.1371/journal.pone.0143322.t005
axialdiameter(n=48)acrossaerationtreatmentswas44.6mmand46.4mmforthelowand
highirrigationlevels.Correspondingvaluesforlateraldiameterwere56.9and58.8mm,and
3.6and3.7Nmm-2forfruithardnessmeasuredaspenetrometerresistance.
Theaxialdiameterandhardnessoffruitsfromthenon-aeratedplantswassignificantly
lower(P(cid:3)0.05)thanthosefromtheirpost-infiltrationaeratedcounterparts.Themeanaxial
diameter(n=16)acrossthelowandhighirrigationlevelsforthenon-aeratedplantfruitswas
38.0mmandsignificantlylessthanthevaluesforalltheotherpost-infiltrationaerationtreat-
ments.Post-infiltrationaerationduring34–57DASresultedina31%increaseinaxialdiame-
ter,followedbyincreasesof28%and26%foraerationduringthe58–85DASand27–99DAS
stagesrespectively(Table5).Fruithardnessrespondedsimilarlytothepost-infiltrationaera-
tiontreatments.Aerationduringthe34–57DASand58–85DASstagesgavemeanvalues
(n=16)of3.9and4.0Nmm-2.Bothvalueswere43%higherthanthehardnessof2.8Nmm-2
forthenon-aeratedplantfruits(Table5).Aerationtreatmentshadnosignificanteffectonlat-
eraldiameter(Table5).Nevertheless,thedifferencesbetweentheaerationtreatmentmeans
acrossirrigationlevelsforlateraldiameter(n=16)showedasimilarpatternasfortheaxial
diameterandhardness(Table5).
Discussion
Freshfruityield
Thenon-significantirrigationeffectonfreshfruityieldindicatedadequatesoilwateravail-
abilityatboththelowandhighlevels.UsingresultsreportedbyRawlsetal.[34],theesti-
matedvolumetricwatercontentatfieldcapacityofsiltyclayloamsoilinthepots=0.50,and
volumetricwatercontent=0.21atsoilwaterpotentialof-1.5MPa(consideredastheperma-
nentwiltingpoint).Givenatotalvolumeof9.8litersoilinthepots,thesepropertiesimply
plantavailablewaterbetween0.9and1.4literatthelowirrigationlevel(i.e.0.6to0.7offield
capacity),andbetween1.4and1.9literatthehighirrigationlevel(i.e.0.7to0.8offield
capacity).Between27–99DAS,themean±standarddeviation(n=18)forthetotalvolumes
ofwaterappliedperpot=36.9±2.2literforthelowirrigationand39.3±4.4literforthe
highirrigation.Thisimpliesanaverageirrigationrateofabout512cm3perpotperdayfor
thelowirrigationleveland546cm3perpotperdayforthehighirrigationlevel.Transpira-
tionratesaveraged300to350cm3perdayoverthegrowingperiodforsinglepottedtomato
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plantsgrownundersimilarconditions[35].Hermantoetal.[36]reportedsimilarratesof0.3–
0.4literplant-1day-1forgreenhouseproducedtomatounderdripirrigation.Soilwaterstress
wasthereforeunlikelyforboththelowandhighirrigationlevelsduringthegrowthperiodin
thisexperiment,andwouldmostlikelyexplaintheobservedweakeffectofirrigationlevels
onfreshfruityield.
Nopreviousstudyhadspecificallyexaminedtheresponseofsub-surfacedrip-irrigatedpot-
tedtomatoplantsatdifferentgrowthstagestopost-infiltrationsoilaeration.Increasinglevels
ofdripirrigationatagivenfrequencywouldsupplymoresoilwateravailablefortranspiration,
andgenerallythiswouldincreasegrowthandyield.Ontheotherhandincreasingdrip-irriga-
tionlevelsalsoresultinlowerlevelspost-infiltrationsoilaeration.Rawlsetal.[34]reporteda
geometricmeanbubblingpressureof33for689samplessiltyclayloamsoils.Sincetherewas
22.5cmdepthofsoilinthepots,itwouldbeexpectedthattherewouldbelittletendencyfor
gravitationaldrainagefromthepots,andthatthesoilinthevicinityofthesub-surfacedrip
emitterswouldbeclosetosaturationimmediatelyafterirrigation.Sinceredistributioninfiner
texturedsoilsisgenerallyslow,thissaturatedzonewouldbeexpectedtopersistforsometime
afterirrigation.Thisextentofthiszonewouldalsoincreasewithincreasingirrigationvolumes
requiredtocompensateforconsumptiveusebytheplantsovertime,andmaintainthetarget
volumetricsoilwatercontent.Anypositiveeffectofpost-infiltrationaerationwouldberelated
primarilyonhowwelltheinjectedairstreampermeatesthiszoneandpromotesenhancedroot
activityandoverallplantgrowthanddevelopment.
Rootdryweightandactivity
Theresultsonrootdryweightandactivitytendtosupportthisconclusion.Thetaprootof
tomatotransplantsareusuallybrokenandthisresultsinafibrous-likesystemasaresultofthe
anincreaseddensityofthelateralsinthefirstfewinches[37].Fortransplantsinthefield,they
observedcloseto10shortlateralspercmaveragedovertheupper15cmofthetaprootfor
tomatoplants4weeksaftertransplantinginthefield.Theselateralsbranchedprofuselyresult-
inginthesurfacesoilina30cmradiusaroundtheplantthoroughlyramifiedwithrootlets.For
subsurfacedripirrigationinthefieldwiththeemitterdirectlybeneaththeplantrowHanson
andMay[38]foundtomatoplantrootswereconcentratedaroundthedriplines.Dresbøll
Thorup-Kristensen[39]foundthatduringshort-termhypoxiainpartoftherootsystem,potted
tomatoplantsshowedincreasedactivityinthenon-affectedrootstocompensateforsubopti-
malconditions.Post-infiltrationaerationwouldmorelikelyamelioratehypoxicconditions
above,ratherthanbelow,theemitter.Inthisstudy,therootactivitywasmeasuredonroottip
samplestakenfromtheentirerootsystem.Thismostlikelyexplainsthesignificantandrather
complicatedinteractionbetweenpost-infiltrationaerationandirrigationlevelonrootactivity
asthesizeoftherootsystemincreasesovertimeintheconfinedvolumeofthepots.Italso
explainstheconsistentmarkeddifferencesbetweenthenoneand27–99DASaerationtrea-
ments(Table3).
Theseresultsalsoindicatethatthesensitivityofthepottedtomatoplantrootsmaychange
astherootssystemdevelopsovertime.Niuetal.[27]showedthatsoilaerationincreasesthe
oxygencontentinthesoil,andsignificantlyenhancerootactivityandrootabsorptioncapacity.
Thisresearchshowsthatpost-infiltrationsoilaerationincreasedrootactivityespeciallyduring
thefruitsetting(34–57DAS)andenlargement(58–85DAS)growthstages.Aerationfrom86
to99DASalmostnochangeofrootactivity,androotactivityofaeratedatthewholegrowth
stagewaslowerthanaeratedatfruitsetting(34–57DAS)andenlargement(58–85DAS)
growthstages.Thisisfullyshowsthemainstageofrootneedsoxygenisfruitsetting(34–57
DAS)andenlargement(58–85DAS)growthstages.
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