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Agric.WaterManage.(2016),http://dx.doi.org/10.1016/j.agwat.2016.01.012

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Agricultural Water Management

j o u r n a l h o m e p a g e :w w w . e l s e v i e r . c o m / l o c a t e / a g w a t

Combined effects of deﬁcit irrigation and crop level on early nectarine trees

JM. De la Rosa

^a

, MR. Conesa

^a

, R. Domingo

^a

, E. Aguayo

^b

, N. Falagán

^b

, A. Pérez-Pastor

^a,∗

aTechnicalUniversityofCartagena(UPCT),DepartmentofPlantProduction,PaseoAlfonsoXIII,48,ETSIA,30203Cartagena,Murcia,Spain

bUPCT,DepartmentofFoodEngineering,PaseoAlfonsoXIII,48,30203Cartagena,Murcia,Spain

a r t i c l e i n f o

Articlehistory:

Received11September2015

Receivedinrevisedform15January2016 Accepted23January2016

Availableonlinexxx

Keywords:

Fruitthinning RDI

Signalintensity Trunkgrowth Waterstressintegral Yield

a b s t r a c t

Athree-yearlongexperimentwasimplementedinanearlynectarine(PrunuspersicaL.Batschcv.Flanoba) commercialorchardtoevaluatetheeffectsofdeficitirrigationanddifferentcroplevelsonvegetative growth,plantwaterstatus,andfruityieldandquality.Threeirrigationtreatmentswereassessed:(i) control,fullirrigation(TCTL);(ii)normalpracticeofthefarmer(TFRM);and(iii)regulateddeficitirrigation (TRDI),whichinvolvedirrigatingthecropatthesamelevelasthecontrol(TCTL)duringthecriticalperiodsof thefirstyearandat60%TCTLduringpostharvest.Inthelasttwogrowingseasonstheirrigationwassched- uledtomaintainthesignalintensity(SI)ofmaximumdailytrunkshrinkage(SIMDS=MDSTRDI/MDSTCTL)at differentwaterstresslevelsdependingonthephenologicalstage:SI=1.0(non-waterstress)andSI=1.4 (moderatewaterstress).Besides,duringthelasttwoseasons,theinteractionsbetweenTCTLandTRDIwere studiedatfivedifferentcroplevels,whichwereobtainedbycontrollingthedistancebetweenfruitsleft onthebranches:fromverylow(16cmbetweenfruits)toveryhigh(8cmbetweenfruits).Cropwateruse efficiency(WUE)ofTRDIwashigherthaninTCTLandTFRM,increasingbyaround25%in2010and2011,and around74%thefinalyear.Interestingly,TFRMincreasedtheWUEfromthefirstyearbymorethan30%.

Theyield/annualincreaseintrunk-cross-sectionalarea(TCSA)ratioincreasedinTRDIwithrespectto theothertreatmentsastheexperimentprogressed,reachingdifferencesof53%.Vegetativegrowthwas clearlysensitivetodeficitirrigationwithastrongcorrelationbetweentheincreaseinthewaterstress integralobtainedbymiddaystemwaterpotential(stem)andthereductioninTSCA.Incontrast,fruit productionandqualitywerenotaffectedbywaterdeficit.Asregardstheinteractionbetweencroplevel andwaterdeficit,fruitfirmnesswastheonlyfruitqualityparameterstudiedthatpresentedsignificant differences,thehighestvaluescorrespondingtothefruitsfromTRDItreesandthelowestcroplevel.In earlynectarinetrees,thepostharvestperiodcanbeconsideredasanon-criticalperiodforapplyingRDI strategiesbutonlywhenthewaterstressintegralappliedisoflowintensityinMayandJune(much lowerthan9MPaday),inordertolimitthedecreaseinvegetativegrowthandsonotaffectthefollowing harvests.

1. Introduction

Peachandnectarinetrees(PrunuspersicaeL.Batsch)aretwoof themaindeciduousfruitspeciesgrowninSpainwithanaverage productionof1,175,500tperyearintheperiod2010–2012(FAOT- SAT,2015).Extra-earlyvarietiesaremainlycharacterizedbytheir highexportvalue,beingamongtheﬁrsttobemarketeddueto theirattractivecolourandtaste(Alcobendasetal.,2012).Inareas

∗ Correspondingauthorat:Dpto.ProducciónVegetal,ETSIA—UniversidadPolitéc- nicadeCartagena,Avda.PaseoAlfonsoXIII,48,E-30203Cartagena,Murcia,Spain.

Fax:+34968325793.

E-mailaddress:[email protected](A.Pérez-Pastor).

ofwaterscarcity,itisnecessarytouseirrigationtechniquesefﬁ- ciently,notonlytosavewater,butalsotoincreaseproductivityand obtaingood-qualityfruits(FereresandSoriano,2007).

Generally,growersscheduleirrigationaccordingtoexperience, althoughtheyarealsoconditionedbythevolumeofwateravailable (low in many areas suffering from water scarcity), the irriga- tionsysteminstalledandthedifferentagriculturaltechniquesof theirfarms.Thus,whilefarmersoftenachievehighefficienciesin water use, theysometimesapplytoomuch water, usuallydur- ingfruitgrowthtoobtainfruitofmaximumsize,butalsoduring thepostharvestperiodinearlymaturingfruittrees.Theywould thereforebenefitfromprotocolstoachievegreaterefficiencyby optimizing theapplied water usingsoil and plantwater status indicatorstocontrolirrigationwaterleaching.

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Deficitirrigation(DI)hastraditionallybeendefinedasanirriga- tionstrategyinwhichtheamountofwaterappliedislowerthan thatneededtofullysatisfythecropwaterrequirements.DIaims toincreasewater useefficiency(WUE)byeliminatingirrigation eventsthathavelittleimpactonyield.However,thisapplication canalso have otherbenefitsrelated with (i)decreasingnitrate leaching,(ii)reducing theenergy usedduringirrigations (since mostirrigationequipmentispressurized),and(iii)maximizingthe competitivenessoftheagriculturalsector.Moreover,earlystud- iesreportedimprovedfruitqualityduetoahighermaturityindex asresultofanincreaseinthephenoliccompositionoffruit,espe- cially in thecase of extra earlyvarieties witha short ripening time(Buendíaetal.,2008;Falagánetal.,2015).Inlatevarieties ofnectarineunderRDI ThakurandSingh(2013)founda higher concentrationofsugars,higherlevelsoftotalphenols,andhigher antioxidant,ascorbicacidandanthocyaninlevels.Differencesfrom thelevelsobtainedinacontroltreatmentincreasedwiththesever- ityofRDI.

OneofthemostimportantDIstrategiesdevelopedinfruittrees isregulateddeficitirrigation(RDI,Chalmersetal.,1981),whereby waterrestrictionsareappliedinnon-critical periods,whenfruit growthislesssensitivetosoilwaterdeficit,whilecoveringthefull waterrequirementsduringtherestofthegrowingseason(Buesa etal.,2013;Mitchelletal.,1989).Inthis sense,StageIIoffruit growth(slowfruitgrowthrate)andthepostharvestperiodaresuit- abletimesforreducingirrigationinextra-earlynectarinetrees(De laRosaetal.,2015).Postharvestisthelongestnon-criticalperiod ofthegrowingseason,andisimportantbecauseitiswhencar- bohydratereservesaccumulateandfloraldifferentiationprocesses occur(HandleyandJohnson,2000).Therefore,RDImustbeman- agedcarefullyinordertoavoidreductionsinbloomandfruitload (Pérez-Pastoretal.,2015).RDIhassuccessfullybeenstudiedina widerangeoffruitcrops(seereviewsofRuiz-Sánchezetal.,2010 andPérez-Pastoretal.,2015).Instonefruits(e.g.,nectarine),RDI hasbeenusedtocontrolvegetativegrowth,decreasingcompetition betweenvegetativeandfruitgrowth(Ruiz-Sánchezetal.,2010).

However,aseverewaterdeﬁcitmayresultinaseriousreduction ofvegetativegrowth,reducingthenumberoffruitspertrees(by decreasingthetreesize),orevencausedisordersinthefollowing harvest(Naor,2014).Tosolvethis,plantwaterstatusneedstobe controlledbyusingindicatorswhensuchstrategiesareapplied.

Recently,continuousmeasurementsofplantwaterstatusthrough theuseoftrunkdiameterfluctuations(TDF)havebeenusedfor irrigationschedulinginrealtimewithhighprecision,thusreduc- ingthepossibledangersofRDIappliedduringthewaterdeficit periods(FernándezandCuevas,2010;Ortu ñoetal.,2010).Maxi- mumdailyshrinkage(MDS),whichcoverscyclesofshrinkingand swellinginducedbychangesintranspiration(Corelletal.,2014)is consideredoneofthemostsensitivewaterstressindicators(Dela Rosaetal.,2014).However,thefactthatMDSintegratestheeffects ofweatherconditionsandthesoilwateravailabilitypromotedthe useofMDSsignalintensity(SI_MDS,GolhamerandFereres,2004)as asuitableirrigationschedulingtechnique(DelaRosaetal.,2015;

Puertoetal.,2013).

Theresponseofnectarineyieldtowaterdeﬁcitmustbecon- sideredtogetherwithitsresponsetoclimaticconditionsandfruit thinningpractices(Naoretal.,2005).Infact,ascroploadincreases, theseasonal growthof trunkdiameter and treebiomass accu- mulationmaybereducedas aresultof increasedcarbohydrate partitioningtowardsfruit(BermanandDeJong,1997).However, Intriglioloetal.(2014)reportedthatcroploadreductioncouldbe employedtoalleviatethedetrimentaleffectsthatlong-termRDI strategieshaveontreegrowth.

Earlyreportsassessedthecombinationofwaterdeﬁcitandcrop levelinfruittrees(Alcobendasetal.,2012;Intriglioloetal.,2014;

Lopezetal.,2007;Naoretal.,2013).However,toourknowledge,

thisworkrepresentsthefirsttimethattheaboveinteractionhas beenstudiedusingtheconceptualapproach ofSIMDS forirriga- tionmanagement,whilebeingcomparedwithgrowers’irrigation practices. For these reasons,a three-year long experiment was implementedinanearlynectarinecommercialorchard,toeval- uatetheeffectsofthedeficitirrigationonvegetativegrowthand croplevelusingtheSI_MDS,seekingtomaintaintheyieldandfruit qualitystandardsnecessarytoincreasegrowers’benefits.

2. Materialsandmethods 2.1. Experimentalsite

Thestudywasperformedduringthreeconsecutivegrowingsea- sons(2009–10;2010–11and2011–12)inacommercialorchard locatedinMurcia(38^◦8N;1^◦ 13W).Eachgrowingseasonwas takentobeginontheﬁrstdayofpost-harvestandendonthelast dayof harvestofthefollowingyear.Theexperimentalplothad anareaof2haofseven-year-oldearlynectarinetrees(P.persicaeL.

BatschcvFlanoba)graftedontohybridGF677rootstockataspacing of5.5m×3.5m.Atthebeginningoftheexperimentthetrunkdiam- eterofthetreesaveraged14.2cm,withoutdifferencesbetween treatments.Thesoil,withanaveragedepthof1.55m,hadlowavail- ablepotassium (236mgkg⁻¹), soluble phosphorus(6.6mgkg⁻¹) andorganicmatter(0.8%)contents,aclayloamtextureandhigh levelsofchlorideandsodium(4.37and8.87,respectively,inaque- ousextract1:2).Theelectricalconductivity(EC)oftheirrigation watervariedbetween1.5and2.5dSm⁻¹,accordingtothesource used(irrigationcanal,welloramixofboth),withmaximumlevels ofchlorideandsodiumofaround12.6and13.4meqL⁻¹,respectively.Usualhorticulturalpractices(eg.,weedcontrol,fertilization, pruning,fruitthinningandgirdling)werecarriedoutbythetech- nical department of thecommercialorchard. Theweather was typicallyMediterranean,withhot,drysummersandmild,wetwin- ters.Annualaveragetemperatureswere17.9,17.3and17.6^◦Cfor the2009–10,2010–11 and 2011–12 seasons,respectively, with themaximumtemperature(43.8^◦C)occurringinthesummerof 2009.Rainfallwasmainlydistributedbetweenautumnandspring, amountingto296, 256and 290mm, respectively,for thethree seasonsstudied.

A drip irrigation system was installed, with two lines per treerowspaced1.2mand 9.33pressure-compensatedemitters (1.6Lh⁻¹)pertreeplacedevery75cm.

2.2. Irrigationtreatments

Duringthethreeconsecutivegrowingseasonsoftheexperi- ment,threeirrigationtreatmentsatcommercialcroplevel,were carriedout:(i)Control,TCTL,irrigatedat110%ofETc(maximum cropevapotranspiration)duringthewholeseasoninordertoavoid limitingsoilwaterconditions;theETcwasdeterminedfromthe cropreferenceevapotranspiration(ET₀ Penman–Monteith,Allen etal.,1998);(ii)farmertreatment(TFRM),irrigatedaccordingtothe farmer’snormalpractice;thisinvolvedapplyingirrigationwater aboveT_CTLlevelsduringtheﬁrstseason,andreducingtheirriga- tionamountasthestudyprogressedasinthecaseofTRDI(Fig.1);

and(iii)regulateddeﬁcitirrigation,T_RDI,irrigatedfortheﬁrstsea- son(2009–10)at110%ofETcduringthecriticalperiods(second rapidfruitgrowthperiodandtwomonthsafterharvest)andat60%

ofT_CTLduringlatepostharvest(fromJulyuntiltheendofthegrow- ingseason).Theirrigationschedulingprotocolofthis treatment variedeachseasonaccordingtotheinformationobtainedfromthe MDSandmidday(12.00hsolartime)stemwaterpotential(_stem) measurementsinthepreviousyear.Therefore,duringtheﬁnaltwo seasons(2010–11and2011–12)theirrigationwasscheduledto

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Fig.1. Monthlyvaluesofirrigation(A)forthethreeirrigationstrategies:TRDI( ),TCTL( )andTFRM( )andwaterstressintegralvalues(SSTEM,B)forTFRM( ) andTRDI( ).

maintainthesignalintensity(SI)ofthemaximumdailyshrink- ageofthetrunk(MDS,SIMDS=MDSTRDI/MDSTCTL)dependingonthe phenologicalstageatdifferentwaterstresslevels:SI=1.0(non- waterstress)duringthefruitgrowthandearlypostharvest(May) andSI=1.4(moderatewaterstress)duringlatepostharvestperiod (fromJulyuntiltheendofthegrowingseasonin2010–11,andfrom theendofMayuntiltheendoftheseasonin2011–12)(DelaRosa etal.,2015).

ETcwasdeterminedastheproductofreferencecropevapotran- spiration(ET₀),thecropcoefﬁcientsproposedbytheAgricultural InformationSystemofMurcia(www.siam.es)forthisareaadjusted forthetreesize(FereresandGoldhamer,1990),andanadditional leachingfractionapplieddue tothesalinenatureoftheirriga- tionwater.Theleachingfractionwasdeterminedbythemethod describedbyMaasandHoffman(1977),measuringtheelectrical conductivityoftheirrigationwater.

Irrigationwasscheduledweeklywithafrequencythatvaried from1to2timesperdayinspring-summerto1–7irrigationsper weekfortherestoftheyear.Thestarttimeoftheirrigationwas thesameforalltreatments,andwasduringthenight(between3 and5a.m.).Thenumberofirrigationswasthesameinallirrigation treatmentsandtheamountsofirrigationwaterappliedwerevaried byvaryingtheruntime.

Theexperimentaldesignconsistedof3replicatespertreatment, randomlydistributedwithintheorchard.Eachreplicatehadthree adjacenttreerowsand15treesperrow.Measurementsweretaken

fromthetreesinthecentralrow,withtheothertreesservingas borders.

2.3. Fruitthinningtreatments

Theeffectofdifferentcroplevelsonproductionandqualitywas evaluatedin2011and2012inT_CTL andTRDI.Fivedifferentcrop levelswereachievedbyleavingdifferentdistancesbetweenfruits onthebranch:(i)verylow(16cmbetweenfruits);(ii)low(14cm betweenfruits);(iii)normalorcommercial(12cmbetweenfruits);

(iv)high(10cmbetweenfruits);andv)veryhigh(8cmbetween fruits). In addition,malformed, poorly positionedor verysmall fruitswereeliminatedinalltreatments.Eachtypeofthinningwas performedonthreerepresentativetreesrandomlyselectedwithin eachtreatment.Allsubsequentmeasurements(production,num- beroffruits,fruitsize,solublesolids,ﬁrmness,acidityandmaturity index)wereperformedindividuallyoneachtree.

2.4. Measurements

2.4.1. Weather

An automatic weather station located close to the orchard providedclimaticdata:airtemperature,relativehumidity,solar radiation,rainfallandwindspeed.Theweatherstationwascom- posedofananemovane(Young,model05103-5,USA),radiometer (KippandZonen,modelCMP6,Netherlands),pluviometer(Thies-

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Clima, model 5.4031.30.006 Germany), datalogger (Campbell, modelCR100)andthermo-hygrometer(Vaisala,modelHMp45AC, Finland).

2.4.2. Plantwaterstatus

Midday(12.00hsolartime)stemwaterpotential(stem)was measuredevery7–10daysinoneleafpertreeonthesametrees thatweremonitoredwithlinearvariabledisplacementtransducers (LVDT),enclosingtheleavesinfoil-coveredplasticandaluminum envelopesforatleast2hbeforethemeasurement.Measurements weremadeusingapressure chamber(SoilMoistureEquipment Corp.,Model3000)accordingtotheproceduredescribedbyHsiao (1990).

Thewaterstressintegralwascalculatedmonthlyfromthemid- daystem waterpotentialvalues(S_stem,MPaday),asinMyers (1988):

S_STEM=

i=t i=0

_¯

STEMi,i+1−STEMCTLi,i¯ +1

n (1)

where t is the number of measurements of each treatment;

STEMi,i¯ +1 is the mean stem values for any interval i, i+1;

STEMCTLi,i¯ +1 isthemeanvaluesforTCTL atthatinterval;andn, thenumberofdaysintheinterval.

Trunk diameter ﬂuctuation was monitored in six trees per treatment (two trees per replicate), using LVDT sensors (SolartronMetrology,BognorRegis,UK,modelDF±2.5mm,preci- sion±10␮m)installedonthenorthernsideoftrunks,30cmabove thegroundandmountedonholdersbuiltofaluminiumandinvar (analloycomprising64%Feand35%Ni,whichhasminimalther- malexpansion).Measurementsweretakenevery30s,and10min meanswererecordedbyaCR1000datalogger(CampbellScientiﬁc, Inc., Logan, USA), connected to an AM16/32 multiplexer pro- grammedtoreportmeanvaluesevery10min.SeveralTDF-derived indices were calculated according to Goldhamer and Fereres (2001): maximum (MXTD) and minimum (MNTD) daily trunk diameter,maximumdailytrunkshrinkage(MDS=MXTD−MNTD) and trunk daily growth rate(TGR, calculated as thedifference betweenMXTDoftwoconsecutivedays).

2.4.3. Treeandfruitgrowth

Trunkperimeterwasmeasuredevery2–3monthswithatape measureonﬁvetreesperreplicateatamarkedlocationabout0.3m fromthesoilsurface. Trunkcross-sectional areawasestimated fromthecirclearea.TheannualincreaseinTCSA(TCSA)wascal- culatedasthedifferencebetweentwoTCSAmeasurementsmade attheendofharvestintwoconsecutiveyears.Pruningdryweight wasdeterminedannuallyduringwinterdormancyandsummer inﬁvetreesperreplicate.Shootgrowthwasmeasuredevery1–3 weekswithatapemeasureon20shootsperreplicateselectedat thebeginningoftheexperiment.

Fruitdiameters(perpendiculartothefruitsuture)weremea- suredin30randomlyselectedfruitsperreplicateevery3–7days duringfruitgrowthandatharvesttimeusinganelectronicdig- italcalliper.Fruitweightbeforeharvestwasestimatedfromthe diametermeasurementsusingtheequationpreviouslydetermined (Fw(g)=0.065+0.0029Fd^2.56(mm)r²=0.999).Fruitdailygrowth ratewascalculatedasthedifferencebetweentwoconsecutivefruit weightsdividedbythenumberofdaysbetweenmeasurements.

2.4.4. Yielddeterminationsandfruitquality

Maturenectarinefruitswereharvestedon4–6pickingdates, startingatthebeginningofMayeach year,withtheexactcom- mercialpickingdatesdependingontheyear.Thetotalnumberof fruitsoneachoccasionwasweighedandcountedfromtentrees

ofeachreplicate.Averagefruitweightwascalculatedbyweighing andcountingthefruitspertree.Croploadwasdeterminedasthe ratioofthenumberoffruitstoTCSA,andcroplevelasthenum- beroffruitspertree.Theyield/TCSAratio(kgoffruitproducedper unitofTCSA)hasbeendeﬁnedasyieldefﬁciency(Ebeletal.,1995;

González-AltozanoandCastel,1999).

Fruitqualitywasdeterminedinsamplesof20fruitsperreplicate fromeachharvestdate.Immediatelyafterharvesting,allsamples weretransportedtothelaboratoryinabout1h,wheretheywere analyzed.Totalsolublesolids(TSS)weredeterminedinfruitjuice byusingahandrefractometer(AtagoN1,Tokyo,Japan).Thetitrat- ableacidity(TA)ofthefruitjuicewasdeterminedbytitrating5mL ofjuicewith0.1molL⁻¹NaOHandexpressedasapercentageof malicacid.ThematurityindexwascalculatedastheTSSTA⁻¹.Flesh ﬁrmnesswasdeterminedonboth sidesofthefruitwithanFT- 327penetrometer(Effeggi,Milan,Italy)withapistondiameterof 7.9mm(0.5cm²),afterremovingtheepidermisoftheequatorial zoneonbothsidesofthefruit.

Water use efﬁciency (WUE) was determined as the ratio betweenyieldandthetotalamountofwaterapplied(irrigation), yield efﬁciency ratio as kgof fruit produced per unit of trunk cross-sectional area(kgcm⁻²)and carbon partitioning between vegetativeandproductivegrowthaskgoffruitproducedpertrunk cross-sectionalareaincrease(kgcm⁻²).

2.4.5. Statisticalanalysis

Analysisofvariance(ANOVA)wasusedtodiscriminatethemain treatmenteffects.MeanswerecomparedwithaDuncanmultiple rangetestat95%conﬁdence level.Allanalyseswereperformed usingStatgraphicssoftware(StatgraphicsPlusforWindowsVer- sion4.1).Relationships betweencropleveland production and qualityparameterswereexploredthroughlinearregressionanal- yses. Analysisof covariance was usedto determinedifferences betweenlinearregressions.

3. Results

The averagemonthly amountof water appliedin the three irrigationtreatments,togetherwiththewaterstressintegralmea- suredfrommiddaystemwaterpotential(S_stem),arepresented in Fig.1. Thewater applied in T_CTL was 681mm, 617mm, and 719mmforthethreegrowingseasons(2009–2010,2010–2011, and2011–2012),respectively.TheTRDItreatmentreceived17,15 and37%lesswaterthanthecontrolinthethreeseasons,respectively.Incontrast,theT_FRMtreatmenthadmorewaterappliedthan TCTL (about 20and 5%)duringtheﬁrsttwo years,and 10%less duringthethirdgrowingseason(Fig.1andTable1).

S_stem values increased as the experiment progressed and dependedonthereductioninthewaterappliedinTRDIandTFRM

withrespecttoTCTL(Fig.1).Thehighestvaluewasreachedinthe secondyearinSeptember(aroundof23MPaday).Duringtheﬁnal year,thevaluesofS_stemweresimilartothoseofthetwoprevi- ousyearsbutremainedhighforlonger,withvaluesabove9MPa daypermonthfromJunetoOctober,correspondingtolessthan 60mmmonth⁻¹ of irrigationwater applied,while control trees receivedmorethan100mmmonth⁻¹.

Thetrunkgrowthrate(TGR)ofwell-wateredtreespresented two different periods. First, from February to April (around 30␮md⁻¹),coincidingwiththebeginningofleafemergenceand thensecondlyfromharvesttoAugust,correspondingtothehigh- esttrunkgrowthrate values oftheseason (around60␮md⁻¹) (Fig.2B,C). TreesfromTCTL presentedsimilarTGRvaluesduring each yearthroughouttheexperiment.T_FRM treespresentedthe highestvaluesofMXDTintheﬁrstyear,whileinthesecondyearthe valuesweresimilartoTCTL.TGRparticularlydecreasedduringthe

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Pleasecitethisarticleinpressas:DelaRosa,JM.,etal.,Combinedeffectsofdeﬁcitirrigationandcroplevelonearlynectarinetrees.Agric.WaterManage.(2016),http://dx.doi.org/10.1016/j.agwat.2016.01.012

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Table1

Amountsofirrigationwaterapplied,watersavingrelativetocontrol,productionparameters(Yield,croplevelandfruitweight),vegetativegrowth(pruningandannualincreaseintrunk-cross-sectionalarea-TCSA)andefﬁciency parameters(wateruseefﬁciency-WUE,croploadandyieldperTCSA)forthethreeirrigationstrategies(TCTL,TRDIandTFRM)andforeachseason(2009–2010,2010–2011and2011–2012).

Irrigation Productionparameters Vegetativegrowth Efﬁciencyparameters

Absolute(mm) Saving(%) Yield(kgtree⁻¹) Croplevel(n^oFtree⁻¹) Fruitweight(g) Pruning(kgtree⁻¹) DTCSA(cm2y−1) WUE(kgm⁻³) Cropload(kgcm⁻²) Y×DTCSA⁻¹(kgcm⁻²)

2009–10 TCTL 681 38.8 371 105 12.1a 20.4b 3.0a 0.22 1.9a

TRDI 565 17 40.9 392 104 11.3a 16.4a 3.8b 0.23 2.5b

TFRM 817 −20 42.2 387 109 15.5b 22.6b 2.7a 0.23 1.9a

ANOVA – – ns ns ns 0.008 0.018 0.006 ns 0.032

2010–11 TCTL 617 53.9 494 109 12.5b 27.1b 4.5a 0.26 2.0a

TRDI 522 15 56.3 509 111 10.9a 22.8a 5.6b 0.28 2.5b

TFRM 654 −6 58 511 113 14.6b 25.7b 4.6a 0.27 2.2a

ANOVA – – ns ns ns 0.011 0.021 0.025 ns 0.044

2011–12 TCTL 719 43.5 392 111 14.8b 24.1c 3.1a 0.18a 1.8a

TRDI 454 37 47.7 433 110 11.5a 17.2a 5.5b 0.22b 2.8b

TFRM 648 10 44.4 401 111 14.7b 21.5b 3.6a 0.19a 2.0a

ANOVA – – ns ns ns 0.001 0.002 <0.001 0.037 0.01

Average TCTL 672 45.4 419 108 13.1b 23.9b 3.5a 0.22 1.9a

TRDI 514 23 48.3 445 109 11.2a 18.8a 4.9b 0.24 2.6b

TFRM 706 −5 48.2 433 111 14.9b 23.3b 3.5a 0.23 2.1a

ANOVA – – ns ns ns 0.006 0.011 <0.001 ns 0.008

ns,notsignificant.MeansforeachcolumnfollowedbydifferentletteraresignificantlydifferentatP<0.05,accordingtoDuncan´ısmultiplerangetestafterirrigationeffectswereshowntobesignificantbyANOVAtestwith P<0.05.

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Fig.2. (A)Seasonalevolutioninreferencecropofevapotranspiration(ET0, ),middayairvapourpressuredeficit(VPDmd, )andrainfall( );(B)maximumdaily trunkdiameter(MXDT)and(C)trunkdailygrowthrate(TGR)forTRDI( ),TCTL( )andTFRM( ).Eachpointcorrespondstothedailyaverageof6sensors.White (TRDI)andgray(TFRM)starsindicatesignificantdifferencesfromTCTLatP<0.05.Verticaldashedlinesanddottedlinesmarkthewaterdeficitperiodandharvestperiods, respectively.

summerseason(byabout53%)comparedwithT_CTLinthelastyear studied,leadingtoanoveralldecreaseof32%inTGR,(Fig.2B,C).

TRDIexhibitedadecreaseinMXDTvaluesaccordingtothewater deﬁcitapplied,withatotalreductionofaround45%intrunkgrowth withrespecttothecontrolinthethreeyearsofthestudy(Fig.2B).

TGRvalues decreasedgraduallywiththedecreaseofsoil water contentduringthemid-summerperiod,causedbythedecrease inappliedwater(Fig.1),whileintheothertreatmentsitgrewby around50␮md⁻¹.However,inAugust/Septemberrainfallledto occasionalincreasesinthesevalues(Fig.2A,C).

Thetrunk-cross-sectionalarea(TCSA)showedthehighestval- uesinTFRM,matchingcontrolvaluesinthethirdyear.Thepattern ofTCSAwassimilartothatofTGR andMXDTexplainedabove.

T_RDIonlypresentedlowervaluesthantheothertwotreatments afterthreecyclesofdeficitirrigation(Fig.3A).However,theannual increaseintrunk-cross-sectionalareagrowthmeasuredattheend ofeveryharvestwassignificantlylowerinT_RDIfollowingthefirst yearofdeficitirrigationthaninT_CTL(Table1).Thistrendcontinued untiltheendoftheexperimentalperiod,reachingmaximumdiffer- encesof29%inthethirdyear.InT_FRMthevaluesfellwithrespectto thecontrol,leadingtosignificantlylowervaluesthaninthecontrol attheendofthethirdyear(Table1).

Theweightofallthebranchesremovedinsummerandautumn pruningduringtheexperimentalperiodinthedifferentirrigation treatments is shown in Fig. 3 and Table 1. During the experiment,pruningweights wereslightly higherin summerthan in autumn (Fig. 3B). T_FRM presented the highest values from the beginningofthestudy(22%higherthancontrol),althoughthedif-

ferencesbecamelesspronouncedastheexperimentprogressed.

TRDIshowedsigniﬁcantdifferencesonlyinthewinterpruningof thethirdyear(23%lessthancontrolandfarmer)(Fig.3B).How- ever,themeanvalueswerealwayslowestintheRDItreatment.

Theshootlengthpresentedasigmoidtrendduringtheexperimen- talperiod,withonlyoneexponentialgrowthperiodbetweenthe beginningofMayandmid-June(Fig.4).Thesecondslopeofthe curvewasduetotheharvest.Therewerenosigniﬁcanteffectsof thedifferentirrigationstrategiesonshootlengthduetothehigh variabilityofthedataobtained(Fig.4).

Fruitdiametergrowthforthethreeyearsofthestudy(Fig.5A,B) tendedtoreﬂect thethreegrowthstagestypicalofstonefruits.

Despitetheearlyripeningofthiscultivarandthecontinualincrease infruitfreshweight,therewasaclearslowingdowninthesec- ondstage,correspondingtoligniﬁcationoftheendocarp,although thiswaslessevidentinthethirdyear.Thedurationofthesestages averaged25daysfromfullbloomforstageI,10daysforstageII and15–20daysforstageIII(Fig.5).Nodifferencesbetweentreat- mentsweredetectedsincetherewasnowaterstresslevel,dueto thesimilaramountsofwaterreceivedbythetrees(Fig.1).

Whenthetrunkandfruitgrowthrateswerecompared,acertain parallelismwasobserved.Whilethefruitgrowthratewasincreas- ingatarateof0.1and1.5gperday,thetrunkgrowthratewas maintainedataround40␮mday⁻¹,butinterestingly,whenFGR reached4gperdayinthethirdfruitgrowthstage,TGRshowed minimumvalues,ofaround10␮mday⁻¹(Fig.6).Later,whenthe fruitswereharvested,thetrunkgrewfaster(TGR≈50␮mday⁻¹).

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Fig.3.(A)Seasonalevolutionofthemeantrunkcross-sectionalarea(TCSA)duringthethreegrowingseasonsand(B)pruneddryweightforTRDI(white),TCTL(black)and TFRM(gray).DifferentlettersaresigniﬁcantlydifferentaccordingtoDuncan´ısmultiplerangetest(P<0.05).Eachbarandpointcorrespondstothemeanoffourreplications (ﬁvetreesperreplication)±SE.Dottedlinesdelimittheharvestperiods.

Fig.4.Seasonalpatternsofshootlengthduring2009(A),2010(B)and2011(C)forTRDI( ),TCTL( )andTFRM( ).Eachpointcorrespondstothemeanoffour replications(ﬁvetreesperreplicationandtwoshootpertree)±SE.

Harvestingwasdividedinto adifferentnumber ofpicksper year(5,4and 6,respectively),starting aroundtheend ofApril (120DOY).Totalyieldinthecontroltreatment,was38.8,53.9and 43.5kgtree⁻¹forthethreeseasons.Thefruitweightdecreasedwith thedateofharvest—from110gperfruit(ﬁrstpick)tolessthan100g (lastpick)(Fig.7).Theyieldwashigherinthesecondyear,dueto thehighernumberoffruitpertree,becauseofalessfruitthin-

ningandconsequentlyyieldincreased28%(Table1).Theaverage ofnumberoffruitpertreerangedbetween383and408,intheﬁrst andthethirdyear,and504fruitpertreeinthesecondyear.The mainfruitsizesforeachofthetreatmentscorrespondedtoclassB (around55%)andC(around30%),andonlya10%forsizeA,with nodifferencesbetweentreatments(datanotshown).

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Fig.5. Seasonalpatternsoffruitdiameter(A)andfruitfreshweight(B)fortheexperimentalyears2010,2011and2012forTRDI( ),TCTL( )andTFRM( ).Each pointcorrespondstothemeanoffourreplications(thirtyfruitperreplication)±SE.Dottedlinesdelimittheharvestperiods.DOY:dayoftheyear.

Fig.6. Seasonalpatternsoftrunkgrowthrate(TGR;A,BandC)andfruitgrowthrate(FGR;D,EandF)duringfruitgrowthandharvestfortheexperimentalyears2010(A andD),2011(BandE)and2012(CandF)forTRDI( ),TCTL( )andTFRM( ).Eachpointcorrespondstothemeanoffourreplications±SE.Dottedlinesdelimitthe harvestperiods.DOY:dayoftheyear.

Thedifferentirrigationtreatmentsprovidedsimilaryields,crop loadsandfruitweights.However,whendatawereanalyzedaccord- ingtoharvestdate,theyieldandnumberoffruitshowedsigniﬁcant differencesbetweenT_FRMandtheothertreatmentsforthesecond harvestdateinthelastyear(Fig.7).

Cropwateruseefficiency(WUE)ofT_RDIwashigherthanthat ofTCTL andTFRM,byaround25%in2010and2011,andaround 74%thefinalyear(Table1).Interestingly,T_FRMincreaseditsWUE fromthefirstyearbymorethan30%.Theproductiveefficiencywas significantly(22%)higherinTRDIthaninthecontrolandfarmer

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Fig.7. Fruitfreshyield(A,BandC),numberoffruitpertree(D,EandF)andmeanfruitfreshweight(G,H,andI)ateachharvestdatein2010(A,DandG),2011(B,EandH) and2012(C,FandI)forTCTL(black),TRDI(white)andTFRM(gray).Eachbarcorrespondstothemeanfourreplications(ﬁvetreesperreplication)±SE.DOY:dayoftheyear.

treatments,butonlyattheendoftheexperiment(Table1).The yield/TCSAratioalwayspresentedhighervaluesinT_RDIthanin theothertreatmentsastheexperimentprogressedreachingdiffer- encesof53%(Table1).

Fruit qualitydetermined in nectarinefruitscollectedonthe mainharvestdateineachyearpointedtonosigniﬁcanteffecton weight(Fig.7),fruitdiameter,ﬁrmness,acidityorsolublesolids betweenirrigationtreatments(Table2).

Whendifferentrelationshipsbetweentheannualwaterstress integralandothervariablessuchastrunkdiameter,pruningdry mass,yieldandfruitqualitywerestudied,thehighestcoefﬁcients ofdeterminationobtainedwerewithtrunkdiameter(Fig.8).

Regardingtheinteractionbetweencroplevelandwaterdeﬁcit, Fig.9showstherelationshipobtainedbetweenthedifferentcrop levelsandthemainyieldcomponentsandqualitytraitsassessed inthisstudyforT_CTL andTRDI duringthelasttwogrowingsea- sons(2010–2011and2011–2012).Asexpected,highercroplevels (numberoffruitspertree)promotedhigheryields(kgpertree⁻¹) (Fig.9A,B)forthetwoirrigationtreatments.Fruitqualitywasalso affected,theaveragefruitweightdecreasingbyaround4.5gfor eachextra100fruitspertree(Fig.9C,D),whileTSSandthetitrat- ableaciditydecreasedonaveragebyaround0.15%and0.35gL⁻¹, respectively,withnosigniﬁcantdifferencesbetweentheirrigation treatments(Fig.9G–J).

Fruitﬁrmnesswastheonlyfruitqualityparameterstudiedthat presented signiﬁcantdifferences betweenirrigationtreatments,

thehighestvaluesobtainedcorrespondingtofruitsfromTRDItrees andlowercroplevel(Fig.9EandF).

4. Discussion

Theyieldresponseofnectarinecv.‘Flanoba’wasinsensitiveto deficitirrigationuntilareductionof37%ofirrigationwaterwas appliedcomparedwiththecontrol(T_CTL),correspondingtoSI_MDS valuesofaround1.5duringpostharvestasmeasuredbytheLVDT sensors.Thisunderlinestheconsiderablescopeforsavingwater andallowsanincreaseofwateruseefficiency(WUE)of70%com- paredwithwell-wateredtrees.Moreover,apositiveeffectonthe managementofTFRMwasalsoobserved,sinceinthetwolastgrow- ingseasonstheamountofwaterappliedaveraged1600m³ha⁻¹ lessthanthatappliedinthesametreatmentduringthefirstseason (Table1).Thisimprovementwasduetoanagronomiccomparison madebetweentreatmentsbythefarmer(noeffectonfruityieldand qualitywhentheirrigationwaterwasreducedastheexperiment progressed).OfnoteisthatpostharvestirrigationschedulinginT_RDI duringthethree-yearsassayedneitheradvancednordelayedthe harvestdateswithrespecttoT_CTL.Furthermore,thephysicochem- icalcharacteristicsofthefruitevaluatedwerenotalteredbydeficit irrigation(Fig.5).

Theseﬁndingsunderlinethefactthatthepostharvestperiodin anearlynectarinevarietycanbeconsideredanon-criticalperiod fortheapplicationsofRDIstrategies,ascantheﬁrstandsecond

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Table2

Averagefruitdiameter,totalsolublesolids,Titratableacidity,maturityindexandﬁrmness)forthethreeirrigationstrategies(TCTL,TRDIandTFRM)andforeachseason (2009–2010,2010–2011and2011–2012).

Season Averagefruitdiameter(mm) TotalSolubleSolids(%) Titratableacidity(mgL⁻¹) Maturityindex Firmness(kg0.5cm⁻²)

2009/2010 TCTL 60.4 8.5 11.4 7.3 5.0

TRDI 60.1 8.3 10.7 7.8 4.5

TFRM 60.8 8.4 10.7 7.9 4.7

ANOVA ns ns ns ns ns

2010/2011 TCTL 60.9 7.9 9.7 8.1 4.1

TRDI 60.9 8.1 10.0 8.1 3.6

TFRM 61.0 7.7 9.6 8.0 3.3

ANOVA ns ns ns ns ns

2011/2012 TCTL 60.9 8.7 11.2b 7.8 5.8

TRDI 60.9 9.0 10.9ab 8.3 6.1

TFRM 60.9 8.8 10.6a 8.3 5.9

ANOVA ns ns 0.046 ns ns

ns,notsignificant.MeansforeachcolumnfollowedbydifferentletteraresignificantlydifferentatP<0.05,accordingtoDuncan´ısmultiplerangetestafterirrigationeffects wereshowntobesignificantbyANOVAtestwithP<0.05.

Fig.8.Relationshipbetweenannualwaterstressintegralandvegetativegrowth(Pruningdrymass—A;Trunkdiametergrowth—D),productivitygrowth(Yield—B;Fruit weight—E)andfruitquality(Solublesolids—C;Totalacidity—F).EachpointcorrespondstoanaverageperyearfortheirrigationstrategiesTRDI(),TCTL(䊏)andTFRM().

fruitgrowthstagesaccordingtopreviousstudiesinpeach(Ruiz- Sánchezetal.,2010),innectarine(ThakurandSingh,2012)and inapricottrees(Pérez-Pastoretal.,2015).Inthissense,threshold valuesofstemofabout−1.5and−2.0MPaduringthepostharvest wererecommendedtoensurenoimpairment ofbloomfertility (Gironaetal.,2005)andtolimittheoccurrenceofdoublefruits (Naoretal.,2005),respectively.Moreover,inourearly-ripening nectarinecultivarawaterstresslevelwasverydifﬁculttoimple- mentduringthefruitgrowthperiod,sinceitcoincidedwithlow waterdemandandseveralrainfallevents(fromMarchtobegin- ningof April).However,it waspossibletoapplya waterstress 15-daysafterripeningwithoutnegativelyaffectingtreeyield,as mentionedbyPérez-Pastoretal.(2009)inapricotandGironaetal.

(2005)inpeachtrees,whileimprovingthefruitqualityatharvest andaftercoldstorageinbothcrops(Lópezetal.,2011;Pérez-Pastor etal.,2007).WhenRDIisapplied,itisessentialnotonlytoiden- tifythesenon-criticalperiodsbutalsotodeterminetheintensity

andthetimingofthewaterstressimposedwithinanynon-critical period(postharvestinourcase)toavoidadverseeffects onthe followingharvestandonvegetativegrowth.

Vegetativegrowthwassensitivetodeﬁcitirrigation,asmany researchershavereportedindeciduousfruittrees(Bolandetal., 1993;Casparietal.,1994;Gironaetal.,2005;Pérez-Pastoretal., 2014; Rahmatiet al.,2015).Thiswas conﬁrmedin ourexperi- mentbythestrongcorrelationbetweentheincreaseinthewater stressintegralobtainedbystemandthereductioninTSCA(Fig.8).

Furthermore,duringthe firsttwo growingseasons,thevegeta- tivegrowthwasreducedinT_RDI,correspondingtowatersavings ofaround15%,althoughduringthethirdyear,thisreductionwas greaterataround40%involving37%watersaving,duetothemore prolongedreductionofwaterappliedcomparedwiththefirsttwo growingseasons,inbothcaseswithoutpenalizingtheyieldand quality,asaboveindicated.Chalmersetal.(1984)foundthatdeficit irrigationappliedfromtheearlystagesoffruitgrowthuntilthe

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Fig.9. Relationshipbetweencropleveland:yield(AandB);Fruitweight(CandD);Firmness(EandF);Totalsolublesolids(GandH)andTitratableacidity(IandJ)forthe irrigationstrategiesTRDI()andTCTL(䊏)andfortheexperimentalyears2011(A,C,E,GandI)and2012(B,D,F,HandJ).Eachpointrepresentstheaverageofthreereplicates (1treeperreplication)±SE.

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endofshootgrowthaffectedvegetativegrowthbyinhibitingshoot development,butdidnotaffectthefinalyieldorfruitsize.How- ever,whentheintensityanddurationofthewaterstressimposed aresevere,thevegetativegrowthmayreducethetotalyieldpertree byreducingthenumberoffruitsduetothereductionintreesize (Pérez-Pastoretal.,2014).Inapricottrees,theauthorsdetermined thecorrectintensityandtimingtoavoidanynegativeinfluenceof thewaterdeficitduringthenon-criticalperiod(post-harvest),and suggestedthatRDIledtoyieldreductionsasaconsequenceofthe decreaseinthenumberoffruitspertreeduetothereductionin vegetativegrowth,butonlywhenwaterdeficitspromotedwater stressintegralvalueshigherthan140MPaday,whichprovideda watersavingof>46%withrespecttowell-watered-trees.

More particularly, the nectarine cultivar studied presented highvegetativegrowthjustafterharvest(fromMaytoJune),as Figs.2and6show,andasindicatedbythepruningweight,which washigherinearlysummerthaninautumn,increasingwiththe leveloftheirrigationwaterapplied(Figs.3and8).Theseresults agreewithpreviousreportsinalmond(Romeroetal.,2004), in pear(Mitchelletal.,1989),andinpeach(Bolandetal.,1993;Girona etal.,2005;Johnsonetal.,1992).Controllingvegetativegrowthcan alsobepositive inthesensethatdeficitirrigationreduceslabor costs(Lópezetal.,2008).However,awaterdeficitappliedfromthe endofMayinvolvedasubstantialreductioninvegetativegrowth andwaspotentiallyharmfulbecauseofthedecreaseintreesize and,hence,thepossibilityoflowersubsequentyields.Ourfindings showedthat waterstressintegraland trunkgrowthratevalues registeredin June must belower than 10MPa dayand around 50␮mday⁻¹,respectively(Figs.1and2),inordertonotaffectveg- etativegrowth.Thecompetitionbetweenvegetativegrowthand fruit(BevingtonandCastle,1985)inthedaysprecedingharvest canbeseeninFig.6.However,suchcompetitionisonlypossible duringtheshortperiodoffruitgrowthandripening(50days),since throughoutpostharvest,vegetativegrowthdoesnotcompetewith fruitgrowth.Ruiz-Sanchezetal.(2010)indicatedthataclearsep- arationbetweenthemainperiodsofvegetativegrowthandfruit growthisanadvantageousfeatureforthesuccessfulimplementa- tionofRDIinfruit.Inaddition,thenon-criticalpost-harvestperiod coincideswiththemonthsofgreatestevaporativedemand,sothe marginforsavingwaterishigh.Moreover,thesignificantlyhigher valuesoftheratiobetweenyieldandTCSAinTRDI thaninthe T_CTLandT_FRMduringthethreeyearsoftheexperimentindicated thatcarbonpartitioningwasmainlydedicatedtofruitgrowthat theexpenseofreducedvegetativegrowth.

Croplevelaffectedthetotalyieldandfruitquality,sothatfruit thinningcanbeconsideredasatechniqueforimprovingfruitcom- position(Alcobendasetal.,2012).Asexpected,theaveragefruit weightdecreasedwithhighercroplevels,duetothehighercom- petitionbetweenfruitsforphotoassimilates(BermanandDeJong, 1997)andthelowerleaf:fruitratio(GrossmanandDejong1995).

Besides,TSSdecreasedasthecroplevelincreased,asfoundinpeach (Lopezetal.,2012).Howeverthebehaviourofbothﬁrmnessand titratableaciditywascontrarytosomeresultspublishedforapri- cot(Southwicketal.,1995)andsweetcherrytrees(Useniketal., 2008).Thesedifferencesmightbeduetotheearlymaturationof thenectarinetreesstudiedinthisexperiment.

Theirrigationtreatments(TRDIandTCTL)didnotalterrelations betweencroplevelandfruityieldandquality.Onlyfirmnesswas significantlygreaterinT_RDI treeswithalowercroplevel.Inthis sense,Alcobendaset al.(2012)suggestedotherfactors,suchas exposuretosunlight,shouldbetakenintoconsiderationinorder tocompensatethepossiblenegativeeffectsofdeficitirrigationon fruitsize.

Asobservedinthiswork,thepostharvestperiodinearlynec- tarine trees can beconsidered as non-critical for applyingRDI strategies,althoughthewaterstressintegrallevelappliedshould

belowerthan9MPadaypermonthduringthemonthsfollowing harvest(MayandJune),whenvegetativegrowthisgreatestinthis crop.Inotherwordsamildwaterstressmustbeappliedsincethis iswhenvegetativegrowthisgreatest.Higherwaterstresslevels wouldnegatively affectthesubsequentharvestbyreducingthe numberoffruitspertree.Afterthisperiodthewaterstressintegral levelcanbehigher,coinciding withtheperiodofgreaterwater demand(fromJulytoSeptember).

Acknowledgements

ThisworkwassupportedbytheSpanishMinistryofScienceand Innovation(AGL2010-19201-C04-04)andEuropeanprojectLIFE+

IRRIMAN(LIFE13ENV/ES/000539).MaríaR.Conesaacknowledges herFPUfellowshipfromtheSpanishMinistryof Education.We thanktheFrutasEstherSACompanyforallowingustousetheir facilitiestocarryoutthetests.

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