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Effects of organo-mineral glass-matrix based

fertilizers on citrus Fe chlorosis

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European Journal of Agronomy · January 2013

DOI: 10.1016/j.eja.2012.07.007

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Europ.J.Agronomy44 (2013) 32–37

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

Effects

of

organo-mineral

glass-matrix

based

fertilizers

on

citrus

Fe

chlorosis

Biagio

Torrisi

a,∗

, Alessandra

Trinchera

b

, Elvira

Rea

b

, Maria

Allegra

a

,

Giancarlo

Roccuzzo

a

_,

_Francesco

_Intrigliolo

a

a_Consiglio_per_la_Ricerca_e_la_{sperimentazione}_in_Agricoltura_–_Centro_di_ricerca_per_{l’Agrumicoltura}_e_le_Colture_Mediterranee_(CRA-ACM),_C.so_Savoia_190,₉₅₀₂₄_Acireale,_Italy

b_Consiglio_per_la_Ricerca_e_la_{sperimentazione}_in_Agricoltura_{– Centro}_di_ricerca_per_lo_studio_delle_Relazioni_tra_Pianta_e_Suolo_(CRA-RPS),_Via_della_Navicella_2-4,₀₀₁₈₄_Roma,_Italy

a

r

t

i

c

l

e

i

n

f

o

Articlehistory: Received9March2012

Receivedinrevisedform6July2012 Accepted17July2012

Keywords: Fechlorosis Orange

Glass-matrixbasedfertilizer Driedvinevinasse

a

b

s

t

r

a

c

t

SeveralcitrusorchardsdevelopsymptomsofFedeficiencywhencultivatedincalcareousandalkaline soils.Inafieldtrialanewtypeoffertilizer,theglass-matrixbasedfertilizer(GMF,aby-productfrom ceramicindustries)wasapplied.GMFisabletoreleasenutrients,particularlyFe,onthebasisof plant-demand,beingnutrientsnotsolubleinwater,butonlyinacidicormetalcomplexingsolutions.Inour experiment,theeffectivenessofGMFwastestedon“Tarocco”orangetreesoftwentyyears,severely sufferingfromFechlorosis,alsobymixingGMFwithmeatmeal(MM)ordigestedvinevinasse(DVV), thuscomparingthesetreatmentstotheconventionalFe-chelatefertilizationandtheFe-unfertilized control.

TheGMF+DVVmixtureshowedtobeabletosupplyadequatelymicronutrients(particularlyFe)onlong term,reducingthechlorosissymptoms,increasingtheleafSPADindex,Feconcentrationanddecreasing Feindex.Nosignificanteffectonyieldandfruitqualitywasnoticed.Ourresultsindicatedthatthese innovativeformulates,andinparticularglass-matrixbasedfertilizermixedwithdigestedvinevinasse, couldbeusedasan“environmentalfriendly”fertilizer,allowingnotonlytoreducetheuseofchemicals (suchasFe-chelate),butalsotore-useindustrialwastesandorganicresidueswhichgavean“adding value”tothesenovelorgano-mineralformulates.

1. Introduction

Fechlorosisisthemostcomplexphenomenonincitrusorchard andoneofmajorabioticstressesaffectingfruittreecropsinthe Mediterraneanarea(Abadíaetal.,2011;Pestanaetal.,2003).One ofthemostcommonsymptomsistheleafbladeyellowing, start-ingfromapicalleaves,whichmayprogressandturnintonecrosis (TagliaviniandRombolà,2001).Itexhibitsatemporalandspatial variability,requiringanefficientdiagnosissystem.Fechlorosisis mainlycausedbylowFeavailabilityinsoil,duetothepresenceof highamountofactivelimeandhighsoilpH(LindsayandSchwab, 1982).

Ingeneral,tolerantgenotypesofcitrusrootstocks displayan enhancedabilitytoreduceFe(III)atrootlevel(bytheFCRenzyme), releasingprotonsintotherhizosphereunderlowexternalFe avail-ability(Bienfait,1988;Manteyetal.,1994;Pestanaetal.,2011), reducingand/orchelatingsubstancessuchasphenolsandflavins (WelkieandMiller,1993;Susìnetal.,1994).StrategyIalsoincludes morphological changes, such as the developmentof root hairs

∗Correspondingauthor.Tel.:+390957653132;fax:+390957653113.

E-mailaddress:biagiofrancesco.torrisi@entecra.it(B.Torrisi).

andtransfercellsandincreasedratesofprotonsexcretion( Lòpez-Millanetal.,2001).

LowFeavailabilityinducesmorphologicalchangesinroot epi-dermalcellsthataresimilartothoseinducedbyPdeficiency.When Feislimiting,root-hairformationand elongationincreases.The extraroothairsthatresultfromlimitedFeavailabilityareoften locatedinpositionsthatareoccupiedbynon-haircellsunder nor-malconditions(Lòpez-Bucioetal.,2003;RömheldandMarschener, 1981).

ThepreventionandcureofFechlorosisinfruittreeshavebeen traditionallyapproachedthroughtheuseofsyntheticFechelates (Lucena,2003).SoilapplicationofFechelatesaimstoenhancing Fe availability for the following uptake at root level and rep-resents an efficient prevention tool, due to the mechanism by whichitisabsorbedbytheroots,transportedandutilizedbythe leaves.

ItshouldberemarkedthatFechelatesgenerallyappliedtosoil arewater-solubleandthuseasilyleachedoutfromtherhizosphere if excessive irrigationregimes are applied, or during the rainy season(RombolàandTagliavini,2006).Moreover,alikely under-estimatedproblemrelatedtosyntheticchelatesistheirpotential to bind also undesired heavy metals (Grˇcman et al., 2001). In addition,thecostfortreatingorpreventingFechlorosisincitrus orchardswiththeuseofsyntheticFechelatesisveryhigh,astobe

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Table1

Mainphysicalandchemicalparametersof0–30cmsoil(meanvalues).

Parameter Value

applicableonlytohighvaluecrops,correspondingtomorethan 400D_ha−1₍_Rombolà_and_Tagliavini,₂₀₀₆_).

Glass-matrixbased fertilizer (GMF),obtainedby alteringthe crystallinestructureofamineralnaturalsubstancethrougha phys-ical process by mixing different salts and oxides, represents a newtypologyoffertilizer,characterizedbythespecificattitudeto releasenutrientsonthebasisofplant-demand,beingnutrientsnot solubleinwater,butonlyinacidicorinmetalcomplexingsolutions (∼99%),similartothoseexudedbyplantroots(Pintonetal.,2007;

Trincheraetal.,2009).

TheGMFabilitytoreleaselargeamountsofmacroand micro-elements,inparticularFe,whenappliedaloneorincombination withsmallamountsoforganicamendments,wasalreadytested in laboratory under different extractive conditions (0.2% and 2% citric acid;0.1% and 1% HCl) (Trinchera et al.,2009, 2011), confirming its attitude to solubilize nutrients in presence of complexingacidic solutions. Onthebasis of suchprevious lab-oratoryresults, inthis fieldtrialthesefertilizersweretestedin fieldasasuitablealternativetosyntheticFechelatestocureFe chlorosis.

The aim of our workwas to evaluate if glass-matrix based fertilizer, alone orin combination withtwo alternative organic materials,couldactonthepreventionandtreatmentofnutrient deficiencyand,inparticular,ofFechlorosisinfieldconditions,in comparisonwiththeuseofacommonsyntheticFe-chelate fertil-izer.

2. Materialsandmethods

2.1. Orcharddescription

The research was realized in a farm located in the Eastern Sicily(Italy),wheretwentyyearsold“Tarocco”orangetrees[Citrus sinensis(L.) Osbeck]graftedonsourorangerootstock[C. auran-tium(L.)]werecultivated witha plantingdistanceof6m×4m

(416treesha−1_)._The _area_is_{characterized}_by _high_summer_and

low winter temperatures. The rainfalls are concentrated in the autumn–winterseason.Duringtheexperimentalperiodtotal rain-fallhadtypicalvaluesofthisMediterraneanregion.Theirrigation wascarriedoutwithtwomicro-sprinklersperplantwithan aver-ageannualwatersupplyof3360m3_ha−1_._Soil_of_citrus_orchard_was

asandy-loamysoil,withalowcontentoforganicmatter,high con-tentsofactivelimeandtotal calciumcarbonate,lowcontentof availableFe(Suppl.Ord.G.U.No.248,21.10.1999,MethodIX.3). Mainchemical–physicalsoilparametersarereportedinTable1 (soilsampledat0–30cmofdepth,layermostexploredbycitrus roots).

Before treatments (early spring season, 2008), plant leaves showedtypicalsymptomsofFedeficiencybygreendiscoloring,in particulartheintervenialleafyellowing,startingfromapicalleaves. Treescanopyshowedsymptomsof Fechlorosisthroughoutthe year,buttheyweremoreevidentinspring,whenshootgrowthis fasterandthebicarbonateconcentrationinthesoilsolutionbuffers

Table2

Elementalcomposition(gkg−1₎_of_fertilizers_utilized_in_different_treatments_(a),_and amountofnutrients(gtree−1₎_distributed_yearly_during_the_trial_(b).

N PasP2O5 KasK2O Fe

a_In_all_GMF_treatments,_the_three_years’_Fe_amount₍₄₅_g)_was_distributed_in_the

firstyear;noFeadditioninthecontrol.

thesoilpHin therhizosphere androotapoplast(Rombolàand Tagliavini,2006;TorrisiandIntrigliolo,2009).Resultsreportedin thispaperarerelatedtothreeyearsoffieldtrial(2008–2010).

2.2. Experimentaldesign

The trial was realised by adopting a system with two ran-domizedblocks;withineachblock3plantspertreatmentwere identified,foratotalof6indexplantspertreatment.Toevaluate theeffectofthreeGMFtreatments,incomparisonwithastandard treatmentwithaFe-chelatefertilizerandaFe-untreatedcontrol, fivetreatmentswereapplied:GMF(100%glassmineralfertilizer, powderedat0.1mm),GMF+DVV(80%glassmineralfertilizer+20% digested vine vinasse, powdered at 0.1mm), GMF+MM (80% glassmineralfertilizer+20%meat-meal,powderedat0.1mm),NK fertilizercontainingFe-EDDHA [ethhylenediamine-di(o-hydroxy-phenylacetic) acid],and thecontrol Test(treatmentwithout Fe supply).

Besides,main parameters of DVV and MM were also deter-mined: pH (8.4 and 6.4), Corg (155gkg−1 and 415gkg−1), Ntot (41gkg−1 _and ₈₁_g_kg−1_), _P₂_O₅ ₍₉_g_kg−1 _and ₁₂₅_g_kg−1_), _K₂_O

(16gkg−1 _and ₁₀_g_kg−1_), _Fe₂_O₃ _(no _detectable _content _and

1.5gkg−1_), _{respectively.} _No_detectable _amount_of_heavy _metals

wererecordedinGMF,DVVandMM(Table2).Topreparethe fer-tilizingmixtures,GMFandorganicmatrices(DVVandMM)were driedinaovenat40◦_C_for₁₈_h,_weighted_and_then_mixed_at_the

ratioGMF/organicmatrix=80/20(w/w).

AllthetreesreceivedthesameNPKamount(370gN,200gP2O5 and300gK2Opertree),appliedeachyearonthe2nddecadeof March.In thecontroltreatmentand in allothertreatments, to completetheannualrequirementsofN,PandK,singlenutrient fertilizers wereadded asurea, simple superphosphate and sul-phateofpotash,respectively.ThetotalFethreeyears’request(45g pertree)wasappliedinonerateatthebeginningofthefirstyear (2nddecadeofMarch)foralltheGMFtreatments,whereastheFe chelateonewasfractionatedinyearlyapplications(15gpertree peryear),addedonthe2nddecadeofMarch.Treatmentswiththe additionofDVVorMMalonewerenotperformedbecauseofthe negligibleFesupplyrespecttothataddedwithGMFfertilizer(see Table2).

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waterandnutrientuptake)withoutdamagingthem,topromotethe mechanismof“plantdemand”.Thechosendepthwasthatofan ordinarysoiltillageinthearea.

2.3. Treenutritionalstatus

Everyyear,nutritionalstatuswasdeterminedbyfoliar analy-sisperformedon20leavesoftheindextreescollectedinOctober fromnonfruitbearingterminalshootsoftheyear’sspringflush on6treespertreatment(Embletonetal.,1973),accordingtoa standardpracticefordeterminingcitrusnutritionalstatusinSicily (Intriglioloetal.,1999).

Leaveswerewashedwithdistilledwater,ovendriedat65◦_C_for

24h,untiltheyreachedconstantweight.Arepresentative subsam-plewasmill-groundandnitrogen(N,ingkg−1₎_was_determined

bymicro-Kjeldahldigestionprocedure.Leafsubsampleswerealso analyzedforphosphorus(P,ingkg−1_),_potassium_(K,_in_g_kg−1_),

calcium(Ca, in gkg−1_), _magnesium _(Mg, _in _g_kg−1₎ _and _Fe _(Fe,

inmgkg−1₎_content_by_Inductively_Coupled_Plasma_Spectrometry (ICP-OESOptima2000DV,PerkinElmer,Italy),afterdry-ashingof samplesinmufflefurnaceat550◦_C_for₁₂_h_and_dissolution_in_a

1%(v/v)solutionofhyperpureHNO369%(PanreacQuimicaSAU, Barcelona,Spain).

2.4. EstimationofFedeficiencyandSPADindex

Everyyear,fortheestimationofFedeficiency,20leavespertree weresampledfromnon-fruitbearingshoots,inthe2nddecadeof May,whentheleaveswerewelldevelopedandthesymptomsof Fechlorosis,ifpresent,becomeeasilyanalyticallyevaluable.The leavesweretreatedasaboveandanalyzedforFe(mgkg−1₎_by ICP-OES.

SPADvaluewasestimatedusingtheportableinstruments SPAD-502chlorophyllmeter(Minolta,Osaka,Japan),usingthesame20 leavespertreealready sampledfortheestimationof iron defi-ciency,beforetheywereovendried.TheSPADreadings,expressed asSPADunits,weretakenfromthemidareaofthefullyexpanded springleaves(Intriglioloetal.,2000;Pestanaetal.,2005).

2.5. Yieldandfruitquality

Everyyear,totalyieldpertreewasrecordedatcommercial har-vest(February)and,onasub-sampleof50fruitscollectedfromthe outerpartofthecanopy,thefruitmeanweightandfruitphysical andchemicalparametersweredetermined.Fruitweight,firmness, widthofthecentralaxisandpeelthicknessweremeasured accord-ingtoWardowskietal.(1979).Furthermore,foreachsub-sample juicecontent,totalacidity(TA)andtotalsolublesolids(TSS)were determined. Vitamin C was determined by high-performance liquid chromatography (HPLC) (Rapisarda and Intelisano, 1996).

2.6. Statisticalanalysis

Datawereevaluatedfortheanalysisofvariance(ANOVA)by

SPSS-10package(SPSS,Chicago,USA);Duncan’smultiplerangetest wasusedformeanseparation.

3. Results

Visualsymptomsofthecitrusleaves,sampledafterthreeyears ofexperiment,showedclearlytheeffectsofdifferenttreatments onFechlorosis.LeafgreennessintheFechelatefertilizertreatment showedtheovercomingoftheFechlorosis,aspredictable,whereas intheothertreatmentsleavesmaintainedthetypicalintervenial leafyellowing. Onlytheleavessampledfromtreestreatedwith

Fig.1. Leavessampledafterthreeyearsoftheexperiment:differentlevelsof chloro-sisareshown,asaresultofthedifferentfertilizationtreatments.

GMF+DVVshowedanincreasedgreencolourinalltheyearsof testing,thussuggestingapositiveactionofthismixtureon chloro-sisevenuntilthreeyearsaftertreatment(Fig.1).

ResultsofleafanalysesandSPADareshowninTable3,asmean valuesofthreeyears’experiment.

PlantstreatedwiththemixtureGMF+DVVandFechelate, com-paredtoGMF,GMF+MM and thecontrol,showeda significant increaseofSPADindex.

Moreover, a positive effect on Fe (Table 3) was found in the different treatments. As expected, after three years of experiment, fertilization with Fe-chelate gave the highest val-ues of Fe contents, but it was comparable to what obtained after addition of GMF+DVV. The other fertilization treat-mentsgaveresultscomparabletocontroltreatmentwithoutFe supply.

IthasbeenproposedtoidentifyFedeficiency,notonlybyFe con-centrationinleaves,butalsoanalysingtheconcentrationofother elements.Inthiscontext,P/Feratio(PandFe␮gg−1_d.w.)_is consid-eredtobeanusefulindextoevaluatechlorosisduetoFedeficiency. Theratioincreaseswhenthechlorosisbecomessevere( Álvarez-Fernándezetal.,2005;Chouliarasetal.,2004)duetotheincrease ofplantPuptakeand/orthedecreaseofFeuptake.K/Caratio(Kand Ca␮gg−1_d.w.)_gave_similar_information₍_Chouliaras_et_al.,_2004; Wangetal.,2008;El-Jendoubietal.,2011),butrelatedtotheeffect ofcalciumexcessinthesoilcationexchangecomplex.TheFeindex, [(10P+K)50]/Fe(wherePandKg100g−1_d.w.,_Fe_␮g_g−1_d.w.),_is

Table3

Leafmacronutrient(gkg−1_),_Fe_(mg_kg−1₎_content_and_SPAD_index._Leaf macronu-trientarereferredtoleavessampledinOctober,FeandSPADtoleavessampledin May.Meanvaluesofthreeyears±standarderrorinparenthesis;n=18.

Treatment N P K Ca Mg Fe SPAD

GMF 26.4b 1.29 11.7c 43.6ab 1.75ab 64a 47.6a (±0.4) (±0.01) (±0.5) (±1.1) (±0.04) (±8.2) (±3.5)

GMF+DVV 25.1a 1.32 9.3b 46.7bc 1.84b 73ab 67.0b (±0.4) (±0.02) (±0.4) (±1.5) (±0.06) (±7.7) (±1.9)

GMF+MM 25.5ab 1.31 10.2b 42.1a 1.67a 63a 52.6a (±0.5) (±0.03) (±0.6) (±1.9) (±0.03) (±6.7) (±2.9)

Fechelate 25.6ab 1.33 7.3a 48.1c 1.86b 80b 73.4b (±0.4) (±0.03) (±0.5) (±2.1) (±0.06) (±8.9) (±1.6)

Test 26.2ab 1.32 9.1b 44.2abc 1.65a 64a 50.6a (±0.5) (±0.02) (±0.7) (±1.7) (±0.05) (±6.0) (±2.6)

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0,00

GMF GMF+MM Fe chelate Test

a

Fig.2.LeafP/Feratio,K/CaratioandFeindex(meanvaluesofthreeyears).Mean separationatp<0.05byDuncan’smultiple-rangetest.Meanswiththesameletter arenotsignificantlydifferent.

anotherimportantindexforevaluatingFedeficiency(Köseo˘glu, 1995;Wangetal.,2008).

OurdatashowedtheincreaseofP/Feratio,K/CaratioandFe index(Fig.2)inGMF,GMF+MMandcontroltreatments,andthe decreaseinGMF+DVVandFe-chelateones.

OfparticularinterestisthebehavioroftheSPADduringthethree years.Fig.3showsthat,atthethirdyear,theSPADvalueobtained forGMF+DVVtreatmentwasquitesimilartothatofFe-chelateone. Thesedifferenceswerejustevidentinthesecondyear,indicating asortofFeslowreleaseinthesoilbyGMF-DVV.

Concerningtheyieldandqualityoffruits,onlythemeanvalues ofthreeyears (Table4)werereported,sincetheannual perfor-mancesweresimilarduringthethreeyearsofstudy.

Nosignificantdifferenceswerenoticedasfarasyieldandfruit qualityparameters wereconcerned(Table4).Anupwardtrend ofmaturityindex(TSS/TA)inGMF+DVVtreatmentwasnoticed, mainlyduetoalowervalueoftotalacidity(TA)infruitjuice.

0,0

Fig.3.SPADindex(meanvalues,calculatedforeachyearofexperiment).Mean separationatp<0.05(small letters)andp<0.001(capitalletters)byDuncan’s multiple-rangetest.Meanswiththesameletterarenotsignificantlydifferent.

4. Discussion

TreatmentsGMFandGMF+MMshowedaSPADindexrather lowwhencomparedwiththecorrespondingmeasuredleafFe con-tent.ThismaybeduetoaFeinactivationeffect,inparticularin theleafapoplast(asanexample,throughaprocessof alkaliniza-tion):asamatteroffact,ahighconcentrationoffoliarFecannot alwaysbeconsideredasareliableindicatortodiagnoseFechlorosis (Römheld,2000).

Inourexperiment,visiblesymptomsofchlorosisduetohigh contentofsoilactivelimethatstronglyinfluencednotonlyFe,but alsoothernutrientsuptake,werefoundincorrespondencewith sub-optimaloroptimalleafFecontent.Intheso-called“chlorosis paradox”(Moralesetal.,1998;Pestanaetal.,2003),chloroticleaves withlowSPADindexshowtotalleafFeconcentrationsimilartothat ofFesufficientleaves.Inourexperimentthis“paradox”wasfound, sinceplantswithlowerSPADindexhowevershowedafairlygood Fecontentinleaves(Table3).

ThebeneficialeffectoforganicmatteronFechlorosisprevention dependsonthedirectFechelatingabilityofthehumicandfulvic acidsandthebiostimulationexertedbyorganiccomponentson boththesoilmicrobialactivitiesandtherootgrowth(Shenkerand Chen,2005).Inparticular,previousstudiesshowedthatplantroots developmentwaspositivelyinfluencedbythepresenceofparticles ofaddedorganicmaterials,whichhavealsotheabilitytoattract rootstowardsthem,increasingmucigelexcretion(Trincheraetal., 2010)andacidicrootexudates(Oburgeretal.,2009),sotobeable tosolubilizenutrientsfromGMF+DVVmixture.

Datafromtheliterature(Intriglioloetal.,2000)suggestthat SPAD index is correlated with leaf-N-concentration,but in our studywedidnotfoundthisindication.Infact,severelychlorotic leaves,withlowSPADvalues,hadhigherNcontent.Thiscorrelation ispreferentiallyfoundinplantswithagoodnutritionalstatus, with-outstrongbioticorabioticstresses,andtheabsenceofassociation couldalsobeduetothefactthatleafNallocationisnotexclusive ofpigment-proteinreactioncentercomplexandthatgrowth envi-ronmentplaysacentralrole(Jifon etal.,2005).Asalsoshowed in Table3,theNcontentof theplantstreated withGMF+DVV andFechelatewhichshowedgreenerleaves(thatimplieshigher SPADindex)was25.1and25.6gkg

−1

ds,respectively,whilefor treat-mentGMF,whichgavechloroticleaves(lowerSPADindex),itwas 26.4gkg

−1

ds.TheGMF+MMtreatmentgaveaNleafconcentration correspondingto25.5g kg−

1

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Table4

Yieldandfruitqualitycharacteristics(meanvaluesofthreeyears±standarderror,n=18).

GMF GMF+DVV GMF+MM Fechelate Test

ThehighKconcentrationsinGMFandGMF+MMleavescannot beexplainedbydifferencesinKsuppliedwithfertilization,since itwasequallydistributedinalltreatments.Probably,itsincrease wasduetoanincreaseofATPasesactivityofrootplasma mem-brane,directlyinvolvedinprotonsexcretion(Marschner,1995). ThehighKconcentrationmaybealsoassociatedtothe accumu-lationoforganicacidsthatoccursunderFedeficiency(Belkhodja etal.,1998;WelkieandMiller,1993).Onthecontrary,with treat-ment Fe-chelate we found a reduction of K uptaken by plant. Urrestarazuetal.(1994)alsopointedoutthatplantstakeKmuch morethanFeandexcessiveamountsofKcouldinhibittheFeuptake andtranslocationinplants,leadingtoFedeficiency.Somerecent studiesshowedthat,whenthechlorosissymptomsoccurred, cor-respondinghighKcontentsinchloroticleaveswerefound(C¸elik andKatkat,2007;Lietal.,2001).Thisrelationshipbetween potas-siumandFemaybeattributedtothenormalizationeffectofKon Feabsorptionandtranslocationintotheshoots(Lietal.,2001).

ThelowervaluesofP/FeandK/CaratiosandofFeIndexobtained after addition of the organo-mineral fertilizer GMF+DVV con-firmedthehypothesizedmechanismofnutrientreleasebasedon plantdemand,alreadydescribedbyTrincheraetal.(2010),which takeplacebyincreasingplantrootexudationandfavouringthe releaseofnutrientsbythemixture.Thedriedvinevinasse, consti-tutedmainlybyhumo-similarorganiccompounds,isparticularly abletocomplex mineralnutrientscontainedin GMFand mak-ingthemavailableforthefollowingrootuptake;conversely, in GMF+MM,thismechanismisnoteffectivebeingMMconstituted mainlybysimpleproteins,notabletocomplexorchelatenutrients fromGMF.

TherationaleforthedecreaseoffruityieldinFedeficienttrees hastobefoundinthedecreasedassimilatorypowercausedbyFe chlorosis(Álvarez-Fernándezetal.,2006).Inourcase,inspiteofthe evidentchloroticleafysymptoms,almostallthevaluesofnutrient inleaveswereintheoptimumrange,withtheonlyexceptionof magnesium(Embletonetal.,1973).Forthisreasonnocleareffect onyieldandfruitqualitywasnoticed.

5. Conclusions

Resultsobtainedattestedthattheconsideredorgano-mineral fertilizersincreasedsignificantlythenutrientrelease fromGMF, favoringthefollowingnutrientuptakebyplants.Inparticular,foliar K,Ca,MgandFeseemedtobepositivelyaffectedbytheorganic matteradditiontoGMFatdifferentextent.

InrelationtoFechlorosisofcitrusplants,allevidencesallowed toaffirmthatthemixtureGMF+DVVisthemostpromising for-mulate able tofront Fe deficiency of citrus in field conditions, byincreasingplantFeuptakeand related photosynthetic activ-ity.Theabilityofthespecificaddedorganiccomponents,mixed tothealumino-silicatematerial, tocomplex mainnutrient ele-ments,makesthem,andFeinparticular,moreavailabletoplants: the mixtures of GMF and used organic matrices seems to be

particularlyeffectiveas“environmentalfriendly”fertilizers,since theyallownot onlytoreducetheuseofchemicals,but alsoto re-useagro-industrialwastesandorganicresidueswhichgavean “addingvalue”tothesenovelorgano-mineralformulates.Atthe end,sincethereportedexperienceisrelatedtoamedium-term period,itshouldbeconsideredthepotential“residual”Fethatthe proposedmixturescouldsupplytoplantonlongterm:thisaspect needstobefurtherinvestigated.

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