ContentslistsavailableatSciVerseScienceDirect
European
Journal
of
Agronomy
j our na l h o me p a g e :w w w . e l s e v i e r . c o m / l o c a t e / e j a
Changes
of
soil
properties
and
tree
performance
induced
by
soil
management
in
a
high-density
olive
orchard
Riccardo
Gucci
a,∗,
Giovanni
Caruso
a,
Claudio
Bertolla
a,
Stefania
Urbani
b,
Agnese
Taticchi
b,
Sonia
Esposto
b,
Maurizio
Servili
b,
Maria
Isabella
Sifola
c,
Sergio
Pellegrini
d,
Marcello
Pagliai
d,
Nadia
Vignozzi
daDip.diColtivazioneeDifesadelleSpecieLegnose,UniversitàdiPisa,ViadelBorghetto80,56124,Pisa,Italy bDip.diScienzeEconomico-EstimativeedegliAlimenti,UniversitàdiPerugia,ViaSanCostanzo1,06126,Perugia,Italy cDip.diIngegneriaAgrariaeAgronomiadelTerritorio,UniversitàdiNapoliFedericoII,ViaUniversità100,80055,Portici,Italy dCRA-CentrodiRicercaperl’AgrobiologiaelaPedologia,PiazzaD’Azeglio30,50121,Firenze,Italy
a
r
t
i
c
l
e
i
n
f
o
Articlehistory:
Received12September2011
Receivedinrevisedform20February2012 Accepted1March2012
Keywords: OleaeuropaeaL. Oilquality Plantcover Soilmacroporosity Tillage
Waterinfiltration
a
b
s
t
r
a
c
t
Long-termeffectsofplantcoversonyieldandoilqualityinoliveorchardsarepoorlyknown.Wecompared performanceofOleaeuropaeatreesgrownundereithertillage(CT)orpermanentnaturalcover(NC)in asandy-loamsoiloverfiveyearsanddeterminedchangesinsoilproperties.Thesoilwastilledfromthe yearofplantinguntiltheendofthesecondgrowingseason,whenbothsoilmanagementtreatments wereestablished.TheCTtreatmentwaskeptweed-freeusingaharrowwithverticalblades(0.10m depth),whereastheNCwasobtainedbylettingthenaturalfloragrow.Treeswerefullyirrigateduntil year3afterplanting,whendeficitirrigation(about50%offull)wasstartedforbothsoiltreatments. Trunkcrosssectionalarea(TCSA)ofNCtreeswas77and87%tothatofCTtreesattheendofthe2006 and2010growingseasons,respectively.FruityieldandoilyieldofNCtreeswere65and69%tothoseof CTones,respectively(meansoffiveyears),however,whenexpressedonaTCSAbasis,theyresulted87 and95%,respectively.ThefruitnumberofNCtreeswaslowerthanCTones,whereastheoilcontentwas similar.Therewerenodifferencesinfreeacidity,peroxidevalue,spectrophotometricindexes,andfatty acidcomposition,butphenolicconcentrationsoftheNCtreatmentwereslightlyhigherthanthoseofCT oils.Soilmacroporosityinthetopsoilwas5.2and2%fortheNCandCTtreatments,respectively.Water infiltrationrateinCTplotswaslowerthaninNConesbecauseofsoilsurfacecrusting;NChadhigher valuesoftotalorganiccarbonandtotalextractablecarbonthanCT,whereasthehumiccarboncontent wasunaffected.
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
Waterscarcityandsoildegradationaremajorthreatsto agri-culturalproductionintheMediterraneanbasin,whereover95%of totalolivetreesaregrown.Soilmanagementcanmarkedlyaffect soilproperties(Gómezetal.,1999,2009;Hernándezetal.,2005) andmoisture(Hernándezet al.,2005)although responsesvary dependingonsoiltype,slope,equipmentused,andenvironmental conditions.
Abbreviations:ANOVA,analysisofvariance;CT,tillage;DW,dryweight;ET0, ref-erenceevapotranspiration;FW,freshweight;HC,humiccarbon;Kfs,fieldsaturated hydraulicconductivity;LAI,leafareaindex;LSD,leastsignificantdifference;MI, maturationindex;NC,naturalcover;PLWP,pre-dawnleafwaterpotential;TCSA, trunkcrosssectionarea;TEC,totalextractablecarbon;TOC,totalorganiccarbon; VOO,virginoliveoil.
∗Correspondingauthor.Tel.:+390502216138;fax:+390502216147.
E-mailaddress:rgucci@agr.unipi.it(R.Gucci).
Conventional tillage causes soil losses, runoff, structure degradation,accelerationof organicmattermineralization with consequentformationofcompactedlayersandnegativeeffecton porosityalongtheprofile(Gómezetal.,2004,2009;Morenoetal., 2009;Pagliaietal.,2004;Rodrıguez-Lizanaetal.,2008).Compacted layersdecreasewaterinfiltrationwhich,inturn,increasesrunoff onslopesandwaterlogginginflatareas.Theeffectsoftillageare timedependent:aftertillageporosityandwaterinfiltrationinitially increase,buttheloosestructuredoesnotpersistduetocompaction, aggregateinstability,andsurfacesealingdrivenbyexternaland internalforces (Zhaietal., 1990).It hasbeenshown that posi-tiveeffectsoftillageonwaterinfiltrationintheinterrowarelost withineightweeks,buttheylastlongerinthezonebeneaththe treecanopyinaclay-loamsoil(Gómezetal.,1999).Allthese pro-cessesinevitablyleadtoplantstress,depletioninsoilfertility,and increasingdependenceonchemicalinputsforplantprotectionand fertilizationwithpotentiallynegativeeffectsonyieldandproduct quality.
41 (2012) 18–27 19
Inrecentyearsthere isevidenceof anincreasingoccurrence ofheavyrainfalleventsassociatedwithclimatechange(Brunetti etal.,2001;IPCC,2007)thatfurtherexposesthesoiltoerosionand degradation(Phillipsetal.,1993;Nearingetal.,2004).Sandy-loam soilsareparticularlysusceptibletocrustingduetotheimpactof raindropswhenthesoilisbareanddry,withresultingcloggingof poresbydispersedclayorslakedfragments(Dexter,1997).Ithas beenobservedthatsinglerainfallsofhighintensityaresufficient todeterminetheabovechanges,whereastheimpactofsuccessive eventsisless(ZhangandMiller,1996).Inspiteofallthese prob-lems,periodictillageisstillthemostcommonlyadoptedmethod tocontrolweedsinoliveorchards(Gómezetal.,2003;Ramosetal., 2011).
Theuseofaplantcoveriscurrentlytherecommendedpractice forprotectionoftheorchardfloor.Thepresenceofacovercrop notonlyhaspositiveeffectsonsoilproperties(Gómezetal.,2004, 2009),butalsodeterminesbetterbiochemicalfertility(Hernández etal.,2005)andgreaterbacterialbiomassanddiversity(Moreno etal.,2009)thantilledsoils.Apermanentplantcoverdecreasessoil erosion,compaction,surfacecrusting,improvestrafficcorridors, andincreaseswaterinfiltrationandaccumulationoforganicmatter downthesoilprofile(Gómezetal.,2004,2009;Pagliaietal.,2004; SchutterandDick,2002).Olivegrovesmanagedwithgrasscover havelowersoillossesandaloweraverageannualrunoffcoefficient thanoneswhereweedsareeliminatedbyeithertillageor herbi-cideapplications(Gómezetal.,2004;Taguasetal.,2010).Onthe otherhand,completesodcoveringtheorchardfloorcompeteswith treerootsforwaterandnutrientsand,hence,mayreducegrowth andyieldoftrees(Atkinson,1980).Forinstance,grassesandweed groundcoversreducedvegetativegrowth,yieldandleafnitrogenof twopeachcultivarscomparedtoherbicidetreatment(Tworkoski andGlenn,2001).Littleinformationisavailableonthelong-term responseofyieldtosoilmanagementinoliveorchards.Although thereissomeevidencethatanaturalcoverdoesnotreduceyield comparedtoconventionaltillageunderrainfedconditions(Gómez etal.,1999;Hernándezetal.,2005)morestudiesareneededto quantifytheeffects,ifany,ofplantcoversonyieldandoilquality. Theseeffectsarelikelytobemediatedbywateravailability.Gómez etal.(1999)reportedasignificantdecreaseinyieldofolivetrees whenthesoilwasmanagedbytillageplusherbicideinayearof verylowprecipitation.
Olivetreesforoilproductionaretraditionallynotirrigated,but inrecentyearsirrigationhasbeenextensivelyusedtostimulate growthduringthetraining phase andincrease yieldonce trees attain maturity.Deficit irrigationis currentlyexpanding dueto thegrowingconcernabouttheefficientuseofwater.Deficit irri-gationconsistsinsupplyinglesswaterthanthatneededtomeet thefullrequirementsofthecrop.Manyrecentstudieshaveshown theadvantagesofdeficitirrigationpracticesintheoliveorchard, astheyachieveconsiderablewatersavingswhilemaintaininghigh yields(Carusoetal.,2011;Guccietal.,2007;Laveeetal.,2007; Morianaet al.,2003).The controlleddistributionofsuboptimal volumesofwaterisalsobeneficialtoobtainoilswithhigh concen-trationsofphenoliccompoundsandlongshelf-life(Motilvaetal., 2000;Servilietal.,2007).
Moststudiesontheeffectofdifferentsoilmanagementpractices havebeenconductedintraditional,rainfed,matureoliveorchards focusing mainly on either soil physical or chemical properties (Gómezet al.,1999,2004).Inthis workwe useda comprehen-siveapproachtocontrastahigh-densityoliveorchardmanaged withanaturalplantcoverwithonetilledto0.1mdepthintermsof plantperformanceandsoilcharacteristicsoverfivegrowing sea-sons.In particular,theobjectivesweretodetermineeffectson: (i)soil(macroporosity,waterinfiltrationrate,fractionsoforganic carbon content) and (ii) vegetative growth, yield components (flowering,fruitset,fruitweight,oilaccumulation,fruitnumber),
andoilquality(freeacidity,peroxidevalues,spectrophotometric indexes,phenolicconcentrationsandfattyacidscomposition)of deficit-irrigatedtreescultivatedeitherwithanaturalplantcover as the orchard floor or tilled to 0.1m depth in a sandy-loam soil.
2. Materialsandmethods
2.1. Plantmaterialandsite
Weusedanolive(OleaeuropaeaL.cv.Frantoio)orchardplanted, at a densityof 513treesha−1 inApril 2003,onflat landat the
VenturinaexperimentalfarmofUniversityofPisa,Italy(43◦10′N; 10◦36′E)between2004and2011.Culturalpracticeswereaimedat keepinglabourandchemicalinputtoaminimum.Minimum prun-ingcriteriawereusedforcanopymanagement(Carusoetal.,2011) andpruned woodwasshredanddistributedonthesoilsurface usingaVKD170mulcher(Nobili,Bologna,Italy).
Priortoplanting147tha−1 ofcowmanurewereappliedinto
thesoilprofile.Inthefirstyeareachtreereceivedabout15gofN, P2O5andK2O.Since2005(3rdyearafterplanting)fertilizerswere
distributedonlyviatheirrigationsystemforatotalof25,50,85, 25,50and35gofN,P2O5andK2Opertreein2005,2006,2007,
2008,2009and2010,respectively.
Alltreeshadbeenfullyirrigatedsinceplantinguntilthe2006 growingseason, when deficit irrigation wasstarted using sub-surface drip lines (Caruso et al., 2011). Trees received about halfthevolumeneededtofullysatisfytheirrequirements, cor-responding to469, 677, and 893m3ha−1 in 2006, 2007, 2008,
respectively;in2009and2010,duetosummerrains,thewater appliedwasonly23and12%tothatofwellirrigatedtrees(497and 109m3ha−1 in2009and2010,respectively).Thewater
require-mentofwellirrigatedtreeswascalculatedaccordingtoDoorenbos and Pruitt (1997) using a crop coefficient of 0.55. The coeffi-cient of ground cover wasadjusted annuallyaccording to tree size(0.6,0.8,0.9,1for2006,2007,2008,and2009–2010, respec-tively).
Theclimateat thestudysite wassub-humidMediterranean (Nahal,1981;Carusoetal.,2011).Theclimaticconditionsoverthe studyperiodweremonitoredusingaweatherstationiMETOSIMT 300(PesslInstrumentsGmbH,Weiz,Austria)installedonsitesince May2006.Referenceevapotranspiration(ET0),calculated
accord-ingtothePenman–Monteithequation,was948,993, 1101and 1001mmin2007,2008,2009and2010,respectively.Annual pre-cipitationwas708,1107,771and1140mmin2007,2008,2009 and2010,respectively(Fig.1).Rainsduringsummermonthswere 160mm(2006),39mm(2007),74mm(2008),87mm(2009)and 140mm(2010),asreportedinFig.1.
2.2. Soiltypeandmanagement
The soil was a deep (1.5m) sandy-loam(Typic Haploxeralf, coarse-loamy,mixed, thermic)(SoilSurvey Staff,2006) consist-ingof600g/kgsand,150g/kgclayand250g/kgsilt.ThepHwas 7.9,averageorganicmatter1.84%andcation exchangecapacity 13.7meq/100g,allmeasuredat0.4mdepth.Thesoilwashighin CaandMg,mediumforN,K,NaandlowinP.
20 41 (2012) 18–27
Fig.1. Monthlyprecipitation(mm)attheexperimentalsiteinVenturina,Italy,from 2007through2010.
Thepercentage ofsoil surface covered by thenatural cover wasmeasuredat10 differentpositions(below thetreecanopy andintheinterrow)alongthreetransects(totalof30positions) in February, May,July and October 2007 by using a 1m2 grid
(1m×1m)subdividedinto100squares.Theplantcoverwas com-pleteinalltheNCplotsduringthewetmonths,buttypicallydried outinthesummertorecovernaturallyuponlatesummerrainfall. Soilmoistureat0.06mdepthwasmeasuredatthreelocationsper soilmanagementtreatmenttwiceadayin2007and2010usinga ML2xThetaProbe(Delta-TDevice,Cambridge,UK).
2.3. Soilporosityandstructure
Inordertocharacterizesoilstructure,verticallyorientedthin sections(55mm×85mm)wereobtainedfrom undisturbedsoil samples collectedin May 2010 at different depths (0–0.1 and 0.1–0.2m)alongtheprofileofthetwosoilmanagementsystems (sixthinsectionspertreatmentanddepth).Theundisturbed sam-plesweredriedbyacetonereplacement(Miedemaetal.,1974)and impregnatedundervacuumwithapolyester resin.The impreg-natedblocks were cut into 60mm high×70mm wide×30m thickverticallyorientedthinsections(Murphy,1986).Twoimages ofthe0–0.1mlayerweretakenforeachsoilthinsection:one repre-sentativeofthesectionasawholeandtheotherat0–5mmdepthto evaluatesoilcrusting.Theimageswereanalyzedusingthe Image-ProPlussoftware(MediaCybernetics,SilverSpring,MD,USA),total porosityandporedistributionwerecalculatedfrommeasurements ofporeshapeandsize(theinstrumentbeingsetuptomeasure poreslargerthan50m).Ashapefactor [perimeter2/(4area)]
wasusedtodivideporesintothreeclasses:regular(rounded,shape factor 1–2), irregular (shape factor 2–5), and elongated (shape factor>5),correspondingapproximatelytotheclassificationused byBoumaetal.(1977).Poresofeachshapegroupwerefurther subdividedintosizeclassesaccordingtoeithertheirequivalent diameter(regularandirregularpores),ortheirwidth(elongated pores)(Pagliaietal.,1984).Thinsectionswerealsoexaminedusing aZeiss ‘RPOL’microscopeat25×magnificationtoobservesoil structure.
2.4. Waterinfiltrationrate
Steady-state infiltration tests were performed in situ using a thin-walled metal ring of 0.3m diameter, partially inserted (40mm)intothesoiltocauseaslittledisturbanceofthesurfaceas possible.Topreventthecloggingofthesoilsurfaceduetocareless waterapplication,onepieceofcheeseclothwasplacedunderthe wateroutlettip.AGuelphPermeameter(Model2800–Soil mois-tureEquipmentCorp.,SantaBarbara,USA)wasusedtomeasure therateatwhichthewaterenteredthesoil.Themeasurements werecarriedoutinMay2010withfourreplicatesforeach treat-ment,aboutsixmonthsafterthelasttillage(CT)whentheinter-row soilsurfacewassealedduetothecompactingeffectofwinterand springrainfalls.Ahydraulicheadof25mmwasusedineachtest andfieldsaturatedhydraulicconductivity(Kfs)calculated
accord-ingtoEq.(2).AccordingtoGuelphPermeametertechnique,Kfswas
calculatedusingRichards’analysis(Reynolds,1993):
Kfs=
C(X,Y)R
[2H2+a2C+2H/˛] (1)
whereCisthedimensionlessshapefactorofthemeasuringwell thatdependsprimarilyontheH/aratioandsoiltexture/structure properties,(XorY)Risthesteady-stateflowratedependingon whetherthecombinationreservoir(X)ortheinnerreservoir(Y)of permeameterwasused,Histhehydraulicheadofwaterinthering, aistheradiusofthering,and˛isasoiltexture/structureparameter (Elricketal.,1989).TheCfactorvalue(Reynolds,1993)usedinthe calculationwasobtainedaccordingtotheempiricalequationof
Zhangetal.(1998)forsandysoils.
Sincethemetalringpreventedthefield-saturatedcomponent oflateralflow,Eq.(1)wasmodifiedasfollows:
Kfs=
C(X,Y)R
[a2C+2H/˛] (2)
2.5. Soilorganiccarbonfractioning
Atthesametimeandpositionofundisturbedsoilsampling,bulk sampleswerecollectedtoevaluateorganiccarboninbothsoil man-agementtreatments.Totalorganiccarbon(TOC)wasdeterminedby oxidationat170◦C,withpotassiumdichromateinpresenceof sul-phuricacid.Theexcesspotassiumdichromatewasmeasuredout byMöhrsalttitration(YeomansandBremner,1988).
Totalextractablecarbon(TEC)andhumiccarbon(HC)organic matter fractioning were determined according to the official methodoftheItalianSocietyofSoilScience(SequiandDeNobili, 2000).TheTECwasobtainedby0.1MNaOH+0.1MNa4P2O7(1:10
soil to solution ratio) at 65◦C for 24h. The humic and fulvic acids(HAandFA,respectively)wereseparatedfromtheextract by acidification to pH 2.0 with H2SO4. The purification of FA
fromnon-humicsubstanceswascarriedoutbyadsorptiononto polyvinylpyrrolidonecolumns.ThepurifiedFAfractionwasthen combinedwiththeHAfractiontogivethehumifiedcarbon(HC). ThequantificationofTECandHCintheextractswasperformedby K2Cr2O7+H2SO4hotoxidation(YeomansandBremner,1988).
2.6. Leafwaterpotentialandvegetativegrowth
Treewaterstatuswasdeterminedbymeasuringpre-dawnleaf waterpotential(PLWP)onsixtreespertreatmentevery7–10days duringthevegetative seasonusing apressure chamber(Caruso etal.,2011).
41 (2012) 18–27 21
Table1
Theeffectofsoilmanagementoncanopyvolumeofyoungolivetrees(cv.Frantoio).Valuesaremeans±standarddeviationsofsixoreighttreespertreatment.Leastsignificant differences(LSD)betweensoilmanagementsystemswerecalculatedafteranalysisofvariancewithineachyear(p<0.05).
Treatment Canopyvolume(m3)
January2006 November2007 November2008 December2009
Naturalcover 7.42±2.13 12.76±2.86 15.19±2.67 21.27±7.15
Tillage 9.69±1.10 23.60±3.17 27.16±4.07 30.48±6.99
LSD(0.05) 2.22 3.74 4.17 8.90
Theaveragecanopyvolumewascalculatedfrommeasurementsof heightandwidthofthecanopytakeninNovember2007,November 2008and December 2009, assuminganelliptic shape. Theleaf areawasdetermineddestructivelyattwodatesin2007.Fourtrees wereharvested,woodandleavesseparatedandtheirfreshanddry weightsdetermined.Theleafareaofasubsamplewasdetermined, priortooven-dryingat50◦C,byscanningthefreshlycutleaves andusingthe“UTHSCSAImageTool”program(UniversityofTexas, HealthScienceCenter,TX,USA).Theregressionsbetweenleafarea, leafdryweightandwooddryweightandbranchdiameterwere usedtoestimatethetotalleafareaofeachtree,fromwhichtheleaf areaindex(LAI)wascalculated.
2.7. Fruitset,yieldcomponentsandoilquality
Thetotalnumberofone-year-oldshoots,thenumberof flow-eringshootsbearingatleastoneinflorescenceandthenumberof inflorescencesweremeasuredinspringonthreeselectedbranches pertreeofsixtreespertreatment,aspreviouslyreported(Caruso etal.,2011).Fruitletspresentoneachselectedbranchwerecounted about30daysafterfullbloomandfruitsetexpressedasthenumber offruitsperinflorescence.Atharvest,50–100fruitswererandomly sampledtomeasureaveragefruitweightandmaturationindex accordingtostandardmethodology(Guccietal.,2007).Thetotal numberoffruitspertreewascalculatedbydividingthecropyield bytheaveragefruitweight(Carusoetal.,2011).
Theoilcontentofthefruitmesocarpoffivefruitspertreewas measuredbynuclearmagneticresonanceusinganOxfordMQC-23 analyzer(OxfordAnalyticalInstrumentsLtd.,Oxford,UK)(Caruso etal.,2011).Theoilyieldofindividualtreeswascalculatedafter measuringthemesocarpoilcontentonadryweightbasis,thefruit freshyield,thepulp/fruitratio,andtheratiobetweendryandfresh weight,aspreviouslyreported(Guccietal.,2007).
Harvestoccurredon20Novemberin2006,6November2007,21 October2008,19October2009and25October2010.Eachtreewas harvestedindividuallybyhandandfinalcropyieldwasexpressed onthebasis ofTCSA toaccount fordifferencesin treesizeand vegetativegrowth.
About250ccofoilwereobtainedusingalaboratoryscalesystem fromabout3.5kgoffruits,whichwerecrushedbyahammermill, theresultingolivepastemalaxedat25◦Cfor20min,andtheoil separatedbycentrifugation(Servilietal.,2007).Theoilswerethen filteredandstoredinthedarkat8◦Cuntilanalysis.Thefreeacidity, peroxidevalue,fattyacidscompositionandUVabsorption charac-teristicsat232and270nmoftheoilsweremeasuredinaccordance withtheEuropeanOfficialMethods(UE1989/2003modifyingthe ECC2568/91).Thetotalphenolsandortho-diphenolswere deter-minedbytheFolin-CiocalteumethodaccordingtoMontedoroetal. (1992).
2.8. Experimentaldesignandstatisticalanalysis
Eachtreatmentwasassignedto36trees,dividedintothreeplots of12treeseach.Eachplotincludedthreerowsoftrees.Toavoid bordereffectsonlythecentralrowofeachplotwasusedandall
measurementsandsamplesweretakenontheinnertreesofthe centralrow.Treatmentmeanswereseparatedbyleastsignificant difference(LSDtest)afteranalysisofvariance(ANOVA)usingfive orsixreplicatetrees.Sincetreesizewasnotuniformbetween treat-mentswhendifferentsoilmanagementswereputintoaction,the TCSAmeasuredinApril2004wasusedasacovariateinthe anal-ysisofcovariance(MedCalcsoftware,Mariakerke,Belgium).Soil macroporosityandorganicmatterfractionsdatawereanalysedby 2×2factorialANOVAwithsixreplicates.
3. Results
3.1. Treeperformance
ThePLWPofCTtrees,measuredduringtheirrigationperiod, wasoftensignificantlylower(morenegative)thanthatofNCtrees (Fig.2).Inthelastfouryearsofthestudy,thecumulatedleafwater potentialofCTtreeswasonaverage13%lowerthanthatofNCtrees withdifferencesrangingfrom7to20%in2009and2007, respec-tively.ThesoilhumidityofNCplotsmeasuredat0.06mdepthwas significantlygreaterthanthatofCTonesduringsummermonths of2010,butdifferencesdisappearedsinceautumn2010(Fig.3). Thesedataareconsistentwithsoilhumidityvaluesmeasuredat 0.5mdepthbeneaththetreecanopy(1.1mfromthetrunk),which werehigherintheNCthanintheCTtreatment(datanotshown).
TheTCSAofNCcultivatedtreeswassmallerthanthatoftrees growinginCTplots.Differenceswereestablishedearlyaftersoil treatmentshadbeenputintoactionandtheeffectwasevidentat theendofeachofthefivegrowingseasons(Fig.4).Significant dif-ferencesinleafareapertreebetweenthetwosoilmanagement systemswerefoundatthebeginning(35.3and57.2m2forNCand
CT,respectively)andend(45.8and68.6m2forNCandCT,
respec-tively)ofthefourthyearafterplanting.Thesevaluescorresponded toaLAIof1.81and2.92forNCandCT,respectively(beginningof 2007)and2.36and3.67forNCandCT,respectively(endof2007). ThecanopyvolumeofCTtreeswassignificantlyhigherthanthat ofNCtreesby23,46,44and30%in2006,2007,2008and2009 (Table1).
22 41 (2012) 18–27
Table2
Yield,yieldcomponents,yieldefficiency(fruityield/TCSAoroilyield/TCSA),andmaturationindex(MI)ofyoungolivetrees(cv.Frantoio)subjectedtotwodifferentsoil managementsystems.Valuesaremeansofthree(2006–2008)ortwo(2009–2010)years.Leastsignificantdifferences(LSD)atp≤0.05werecalculatedafterANOVAwithin eachperiod(n=4–6treespertreatment).
Soilmanagement Years Fruityield
Naturalcover 2006–2008 9588 12,602 4617 6077 2269 2903 2.13 3.17 71.4
Tillage 16,342 14,818 10,252 8901 3470 3062 1.70 2.47 71.0
LSD(0.05) 3445 4408 2472 2396 805 855 0.24 0.86 1.15
Naturalcover 2009–2010 18,013 11,047 8636 5124 3371 2172 2.29 2.48 61.1
Tillage 25,148 12,423 14,278 6858 4555 2308 1.87 2.24 65.4
LSD(0.05) 6903 2267 5115 1935 849 565 0.37 1.04 4.90
TCSA:trunkcrosssectionalarea;FW:freshweight;DW:dryweight.
Table3
Freeacidity,peroxidevalue,K232,K270,totalphenols,ortho-diphenols,andfattyacidscompositionofvirginoliveoils(VOO)fromolivetrees(cv.Frantoio)subjectedtotwo
differentsoilmanagementsystems.ValuesaremeansoffourdifferentVOOreplicates(n=4).Differentlettersindicateleastsignificantdifferencesatp≤0.05afteranalysis ofvariance(ANOVA)withineachyear.DataoffattyacidsweretransformedbyarcsinetransformationpriortoANOVA.
Soilmanagement Year Freeacidity
Naturalcover 2006 0.25 10.2 1.775 0.123 520 133 N.A. N.A. N.A. N.A.
Tillage 0.25 12.7 1.975 0.125 443 132 N.A. N.A. N.A. N.A.
Naturalcover 2008 0.37 9.7 1.730 0.295 605 205 13.3a 73.5 8.4 0.6b Tillage 0.40 10.2 1.645 0.141 530 192 12.8b 74.4 7.9 0.7a
Naturalcover 2009 0.34 7.2 2.000 N.A. 702a 325a 14.0 73.0 7.9 0.6
Tillage 0.31 5.3 1.897 N.A. 505b 238b 14.2 73.4 8.0 0.7
Naturalcover 2010 0.23 9.3 1.875 0.109 130 65 N.A. N.A. N.A. N.A.
Tillage 0.20 9.6 1.888 0.107 119 60 N.A. N.A. N.A. N.A.
N.A.:notavailable.
pigmentedthanthosepickedfromtheCTtrees (Table2).There weresignificantdifferencesinfreshweightbetweentreatments: fruitsfromtheCTtreatmentweresmallerthanthosefromtheNC treatment(Table2).
Soilmanagementdidnotinfluencefreeacidity,peroxidevalue, K232,andK270inanyoftheyearsofstudy(Table3).Thefattyacid
compositionoftheoilshoweda significantincrease inpalmitic acidattheexpenseoflinolenicacidoftheNCtreatmentonlyin oneoutoftwoyears.Otherfattyacids(myristic,palmitoleic, mar-garic,eptadecanoic,stearic,arachic,eicosenoic,behenic,lignoceric) presentinoliveoilsarenotreportedinTable3,astheydidnotdiffer betweensoilmanagementtreatments.Totalphenolic concentra-tionsoftheNCtreatmentwereslightlyhigherthanthoseoftheCT one,althoughdifferencesweresignificantonlyin2009(Table3).
3.2. Soilpropertiesandwaterinfiltration
Soil porosity, determined according to micromorphometric methods(Pagliai,1988), waslow inbothtreatments (Fig.6).In particular,NCandCTsoilscanbeclassifiedasdense (macroporos-itybetween5and10%)andverydense(macroporositylowerthan
5%),respectively.Soilmacroporositywassignificantlyaffectedby soilmanagementonlyatthesurface(0–0.10m)whereNCshowed highervalues thanCT.Thisdifferenceresultedmainlyfromthe higherfrequencyofirregularporesandelongatedpores,which dra-maticallydecreasedinCT.Macrophotographsoftheupperpartof soil(0–5mm)andthecorrespondingporesizedistributionofthe twosoilmanagementsconfirmedtheabovedifferencesand evi-dencedthepresenceofacompactsurfacecrustintheCTtreatment only(Fig.7).
ThewaterinfiltrationrateofNCtreatmentwassimilartowhat
FAO(1990)considersastandardsteadyrateforsandyloamsoils (20–30mmh−1)(Fig.8).Onthecontrary,theinfiltrationrate
mea-suredinCTplotswasabouteighttimeslowerthanthatintheNC treatment,inagreementwiththelowvalueofmacroporosityatthe surfaceofCTsoil.
Totalorganic carbon and TEC in NCplots werehigher than in CT ones, the former at both depths, the latter only at the 0–0.1mdepth(Table4).TheTEC valuessignificantly decreased at 0.1–0.2m depth in both management systems. The humic fraction, the more resistant pool of soil organic matter (Tate, 1987), was quite low and unaffected by soil management (Table4).
Table4
Effectofsoilmanagementonthedifferentfractionsofsoiltotalorganiccarbon(TOC).Differentletterswithineachcolumnindicatesignificantdifferencesbetweensoil managementtreatmentsanddepthsafteranalysisofvariance(p<0.05).
Soilmanagement Depth(m) TOC(%) TEC(%) HC(%)
Tillage 0–0.1 1.14b 0.55b 0.19a
0.1–0.2 1.04b 0.31c 0.12b
Naturalcover 0–0.1 1.33a 0.68a 0.18a
0.1–0.2 1.35a 0.38c 0.10b
41 (2012) 18–27 23
Fig.2. Seasonalcourseofpre-dawnleafwaterpotential(PLWP)ofolivetrees sub-jectedtodifferentsoilmanagementin2007(A),2008(B),2009(C),and2010(D). Symbolsaremeansofsixtrees.Verticalbarsrepresentleastsignificantdifferences atp≤0.05,calculatedafteranalysisofvariancewithineachdateofmeasurement. Horizontallinesindicatetheirrigationperiod.H,harvest.
Fig.3.Seasonalchangesinsoilmoisture,measuredat0.06mdepth,ina high-densityoliveorchardmanagedeitherbynaturalplantcoverortillage.Symbolsare meansoftwomeasurements(dawnandsolarnoon)ofthreereplicatetrees dur-ing2010and2011.Verticalbarsrepresentleastsignificantdifferencesatp≤0.05, calculatedafteranalysisofvariancewithineachdateofmeasurement.
24 41 (2012) 18–27
Fig.5.Numberoffloweringshootsandfruitsetofolivetrees(cv.Frantoio) sub-jectedtotwodifferentsoilmanagementsystems.Fruitsetwasmeasuredabout30 daysafterfullbloomandexpressedasnumberoffruitsper100inflorescences. Mea-surementsweremadeeveryspring,beforethebeginningofirrigation.Valuesare meanof5–6replicatetrees.Differentlettersindicateleastsignificantdifferences betweentreatmentsafteranalysisofvariance(ANOVA)withineachyearatp≤0.05. DataoffruitsetweretransformedbyarcsinetransformationpriortoANOVA.
4. Discussion
Soilmanagement hada majorimpactonsoilphysical prop-erties.The NCtreatment had greatersoil macroporosity in the 0–0.1mupperlayerandwaterinfiltrationratethanCTplots.The dramaticdecreaseinsoilmacroporosityoftheCTtreatmentwas essentiallyduetoasignificantreductioninelongatedand irregu-larpores,whicharecriticalforrootpenetration,watermovement andgasdiffusion.Thevegetationcoverlikely protectedthesoil surfacefromtheraindropimpact,thusreducingmechanical disrup-tionofsoilaggregatesandpreservingthecontinuityofelongated pores(Paninietal.,1997).Therewasalsoevidenceofsoil crust-ingintheCT treatment,which waspresumablyresponsiblefor thelowvaluesofinfiltrationrate.Theseresultsconfirmthe occur-renceofsurfacesealingandlowinfiltrationintilledsoils(Gómez
Fig.6. Totalmacroporosity(pores>50m)values(n=6),expressedasapercentage ofareaoccupiedbyporesofthethreeshapegroups(regular,irregularand elon-gatedpores),attwodifferentdepths(0–0.1mand0.1–0.2m)innaturalcover(NC) andtillage(CT)treatments.Differentlettersindicateleastsignificantdifferences betweentreatmentsandsoildepthsafteranalysisofvariancewithineachshape groupatp≤0.05.
et al., 2004; Moreno et al., 2009) despite the fact that our CT treatmentwasintendedtobelessaggressivethanconventional tillage. Conventional tillage of oliveorchards typically involves mechanical disturbance of the 0–0.2m layer, theuse of heavy equipment(mouldboardploughorchiselplough),periodicdisking orharrowing(Gómezetal.,2009;Morenoetal.,2009),whereaswe
41 (2012) 18–27 25
Fig.8.Waterinfiltrationratemeasuredintheinterrowofahigh-densityolive orchardduringthesixthgrowingseasonafterestablishmentofdifferentsoil man-agement.Histogramsaremeansoffourreplicates(bars=standarddeviations).
triedtominimizedisturbancebylimitingtillageto0.1mdepthand abstainingfromusingrotarytillers.
ThebaresoiloftheCTplotswasvulnerabletocrustingand, therefore,susceptibletowaterlogging.Olivetreesaresensitiveto hypoxiaconditionswhichmaynegativelyinfluencetreegrowth andproduction(Araguesetal.,2004;Datetal.,2006),butthe peri-odsof waterloggingthat occurredinpartof theCTareainthe autumnof2008and2010duetotheabundantprecipitationsof NovemberandDecemberweretoobrieftoaffecttreeperformance (Fig.1).Theincreasingnumberofheavyrainfallevents(Brunetti etal., 2001)exacerbatestheproblemof soilcrustingand com-pactionintilledsoils.Overthe2006–2010periodthere wasan annualaverageof7.5heavyrainfallevents(intensitybetween15 and40mmh−1)intheexperimentalarea,atleasttwoofwhich
in theautumn.In 2010 therewere 11 events, fiveof which in theautumn.WhensurfacesealingoftheCTtreatmentoccurred andhinderedwaterinfiltration,evenrainfalleventsofmoderate intensity(3–15mmh−1)couldcausewaterlogging.
Thedifference ininfiltration ratebetweenNC and CT treat-mentswasmuchgreaterthanthatreported(about2-fold)between conventionaltillageandabarleycropcoverinaclay-loamafter sevenyearsofdifferentiatedsoilmanagement(Gómezetal.,2009). Besidesdifferencesinsoiltypeandtimeofmeasurementafterlast tillagethedifferenceswereportedwereprobablyamplifiedby hav-ingmeasuredinfiltrationonlyinthemiddleoftheinterrow.Inolive orchardssoilpropertiesandhydrologicalparametersinthezone beneaththetreecanopyaredistinctfromthoseintheinterrow. Inparticular,ithasbeenshownthatwaterinfiltrationbeneaththe canopywasaboutfourtimesthatoftheinterrowinaclay-loam soilinsouthernSpain(Gómezetal.,1999).
SoilstructureispositivelyaffectedbyTOCcontent(Arandaetal., 2011;Hernándezetal.,2005;Hernanzetal.,2002),butitis neces-sarytoquantifythedifferentfractionsofTOCtobetterevaluatethe effectofsoilmanagement(VittoriAntisarietal.,2010).Infact,we foundthatwhileTOCwasdifferentbetweenNCandCTtreatments atbothdepths(0–0.1and0.1–0.2m),differencesinTECwere sig-nificantonlyinthemoresuperficiallayer,andHCwasunaffected bysoilmanagementinbothlayers.Theuseofplantcovers deter-minesanincreaseofeasilymineralizableorganicmatter,namely freshherbaceousplantresiduessuchasleaves,rootdebrisand exu-dates(Berryetal.,2002).Suchfractionenhancesbiologicalactivity, thusfavouringsoilaggregateformation(TisdallandOades,1982). Thisisparticularlyimportantinweaklystructured,coarsetextured soilsandwasclearlyshownbyourmacroporosityresults.Underthe pedo-climaticconditionsofourstudy,fiveyearsofnaturalplant coverwerenotsufficienttoaffecttheHCcontentofthe0–0.2m
topsoil.Thisisnotsurprisingbecauselongerperiodsare neces-sarytoincreasethesoilcontentoforganicmatteralongtheprofile underMediterraneanclimateconditions.Gómezetal.(1999)did notfinddifferencesintheorganicmatterofthe0–0.09mtopsoil beneatholivecanopiesbetweenconventionaltillageandnotillage (plusherbicide)after15years.Theformationofstableorganic com-poundsislargelydeterminedbyeithersoilorganicmatterturnover orsoilminerals(Buurmanetal.,2009).ThelowvalueofHCwe measuredinbothsoilmanagementtreatmentswaslikelydueto therapidturnoveroforganicmatterinthetopsoilandtothe spe-cifictexturalcharacteristics.Theabundanceofthelabilefractions versusthehumifiedonessuggestedthatthissoilhadapoor humi-ficationcapacity(VittoriAntisarietal.,2010).
Thepresenceofa permanentsodreduced trunkgrowthand thenumberoffruitspertreewithrespecttoCT-cultivatedtrees. DifferencesinTCSAandcanopyvolumebetweentreatmentswere apparenteveryyearanddeterminedagreaterLAIandfruiting sur-faceoftheCTmanagement,whichcanexplainwhyCTtreeshad more fruitsthan NCones.Inolivetrees fruityield ispositively correlatedwithtotalfruitnumber(Guccietal.,2007;Trentacoste etal.,2010),whichisnotalteredbythinningasinthestandard commercialpracticeofotherfruittrees.Theeffectonfruitnumber wasstillsignificantwhenthelargersizeofCTcanopieswastaken intoaccount.Althoughitisimpossiblefromourdatatodetermine whatcausedthedrasticreductioninfruitnumber/TCSAfortheNC treatment,wehypothesizethatitwasduetoreducedshootlength ratherthanfruitset(Fig.5).Changesininitialfruitsetorfruitlet abscissionhavebeenreportedtooccuronlywhenseverewater deficitdevelops(Guccietal.,2007),butthedifferencesinPLWPwe measuredbetweenNCandCTtreesweretoosmalltoaffectfruit abscission.TheoverallnegativeeffectofNConfruitoroilyieldwas largelydiminishedandnolongersignificantwhenyieldefficiencies (yield/TCSA)werecalculated,indicatingthatdifferencesincanopy sizeweremainlyresponsiblefortheloweryieldofNC-growntrees.
Gómezetal.(1999)didnotfindanyyielddifferencesbetweenolive treesgrownwithconventionaltillageornotillageunderrain-fed conditions.
TheincreaseinfruitweightandmaturationindexfortheNC treatmentareconsistentwitheffectsduetocroplevelratherthan treewaterstatus(Guccietal.,2007;Trentacosteetal.,2010).In addition,thesmalldifferencesinmaturationindexorplantwater statusdidnotappearrelevanttoaffectoilquality.Aclearnegative correlationbetweentreewaterstatusandoilphenolic concentra-tionshasbeenreported(Motilvaetal.,2000;Servilietal.,2007) but, in ourstudy,the PLWPof NCtrees was never lowerthan that of CT ones (Fig. 2). It remains to be ascertained whether thehigherpolyphenolsconcentrationoftheNCtreatment mea-suredeveryyear(althoughsignificantonlyin2009)isconfirmed overlongerperiodsand,ifso,whythisincreasesincecannotbe explainedbytreewaterstatusorstageofripening.Phenolsand ortho-diphenolsareveryimportantforqualitycharacterizationof virginoliveoil(VOO)sincetheyarecloselyrelatedtotheirsensory andhealthproperties(Servilietal.,2004).Oilsofbothsoil treat-mentsexceededthe200mgkg−1value,currentlyconsideredthe
thresholdabovewhichphenoliccompoundsexerttheir nutraceu-ticaleffectsasantioxidants,exceptin2010,whenabundantrains duringfruitdevelopmentdeterminedlowphenolicconcentrations intheoil(Servilietal.,2007).
26 41 (2012) 18–27
rootsystemsoftrees.Hence,theestablishmentofpermanent cov-ersshouldnotberecommendedinthefirsttwoyearsafterplanting butdelayedtothethirdorfourthyeardependingontreegrowth. Anaturalplantcoversignificantlydecreasedthenumberoffruits andyield,butdidnotaffectyieldefficiency,mesocarpoilcontentor oilquality;theseeffectsdidnotdependonagreaterwaterdeficit developinginNCtreesbasedonPLWPandsoilmoisture measure-ments.
Acknowledgments
We are grateful to Michele Bernardini, Rolando Calabrò, Maurizio Gentili,and StefaniaSimoncini for excellent technical assistance. We also thank Netafim Italia for the supply of the subsurfaceirrigationsystem.ResearchsupportedbyUnaprol-Italy (projectReg.UEno.2080/2005andno.867/2008)andPRIN2004 “CarbonCycleinTreeEcosystems”(projectno.2004074422 004).
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