I•COMMON NUTRIENTDISORDERS OF CITRUSS

Table of conTenTs

1. INTRODUCTION

2. DEFICIENCYSYMPTOMS 1

2.1 NITROGEN(N) 1

2.2 POTASSIUM(K)DEFICIENCY 2

2.3 PHOSPHORUS(P)DEFICIENCY 4

2.4 MAGNESIUM(Mg)DEFICIENCY 5

2.5 CALCIUM(Ca)DEFICIENCY 6

2.6 MANGANESE(Mn)DEFICIENCY 7

2.7 COPPER(Cu)DEFICIENCY 8

2.8 ZINC(Zn)DEFICIENCY 9

2.9 MOLYBDENUM(Mo)DEFICIENCY 10

2.10 IRON(Fe)DEFICIENCY 11

2.11 BORON(B)DEFICIENCY 12

3. MULTIPPLEDEFICIENCYSYMPTOMSINTHESAMETREE 14

4. TOXICITYSYMPTOMS 15

4.1 NITROGEN(N)TOXICITY 15

4.2 PHOSPHORUS(P)TOXICITY 15

4.3 POTASSIUM(K)TOXICITY 16

4.4 SODUIM(Na)TOXICITY 16

4.5 BORON(B)TOXICITY 17

5. REFERENCES 18

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II• COMMON NUTRIENTDISORDERS OF CITRUSS

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III•COMMON NUTRIENTDISORDERS OF CITRUSS

1InTRoDUcTIon

ManycitrusorchardsinAsiaandtherebyBhutanarelocatedinslopelandareaswherethesoilsareinfertilewithlowsoilorganicmattercontent.Mostlythesesoilsarealsolowincalciumandmagnesium.Manyofthefarmerstendtooverlooktheimportanceof chemical fertilizers thoughmost orchard owners used organicmanure such asfarmyardmanure(FYM).Asaresult,manyorchardsmaysufferfromanimbalanceofnutrientsavailability.Whenthishappens,thereisadeclineinbothquantityandqualityofyieldandmanytreessufferfromnutrientdisorders.

PracticallyinBhutan,citrusnutrientmanagementisstilltraditionalandtheuseoffertilizersisdeterminedbywhatisaffordableandnotbywhatthecropdemands.Veryfewfarmersusechemicalfertilizersandthesinglemostfrequentlyusedfertil-izerisureaalonefollowedbyfewfarmersusingsuphala.

Allcropsneedadequatesupplyofboththemacroandmicronutrients.Cropremovalofthetraceelementsisverysmallcomparedtothemajornutrients.However,thesenutrientsplayacriticalroleintheproperfunctioningofthetree.

Nutrientbalanceisanimportantfactorintheappearanceofdeficiencysymptomsbecause deficiencies may be caused by an excess of one element rather than ashortageofanother.Deficienciesofsomenutrientscausestresssymptomsinyoungleaves.Thisistrueforboron(B),calcium(Ca),copper(Cu),zinc(Zn),manganese(Mn)andiron(Fe).Otherelementsinducesymptomsinleavesofanyage.Suchisthecaseofnitrogen(N)andsulfur(S).Magnesium(Mg),potassium(K),andmolybdenum(Mo)showvisiblesymptomsmostlyinmatureleaves.Visualsymptomsofnutritionaldisordersofcitrusremainanimportantwarningsignalofproblems,andtheirrecog-nitionremainsanimportantfacetofcitrusmanagement.Deficiencysymptomsoccurfirstononlyafewtreesorevenonafewshootsinanentireorchard,thusgivingawarningofpotentiallyseriousdeficiencyinthefuture.

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IV• COMMON NUTRIENTDISORDERS OF CITRUSS

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1•COMMON NUTRIENTDISORDERS OF CITRUSS

2 DefIcIencY sYMPToMs

2.1 NITROGEN (N)

Citrushaveahighnitrogen(N)requirement.Nitrogendeficiencydramaticallyaffectstreegrowthandproduction.Thoughseverenitrogendeficiencyisrare,thesymptomsare:

The main visible symptoms:

Reductioninyield•Yelloworpalegreenleaves,leavesnarrow,uprightandslightlyrolled•Leavesdropearlier thanusual (caution:samesymptomscanbeexhibitedby•thenematodes)Foliageisthinduetoleaffall,•Twigsdiebackgivingthetreeabrushyappearance•Treeslackvigor.•

Nitrogen deficit citrus leaves showing yellowing accompanying N withdrawal from leaves subtending

new growth.

Twigs from trees maintained on low N (left) and adequate

N (right). A= green terminal leaves

B=yellowing, C= defoliation

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2• COMMON NUTRIENTDISORDERS OF CITRUSS

Possible causes of nitrogen deficiency:

Lack of available N in the soil due to:

Leachingheavyrainfall,over-irrigationwithhighlyporoussoil.•Denitrificationinwaterloggedsoil–temporarydeficiencycanberelievedbydry•weather.

Remedial actions:

Nitrogenfertilizerssuchasammoniumnitrate,urea,ammoniumsulphate,am-•moniumphosphateandcompoundormixedNPKfertilizerscanbeusedtocor-rectitsdeficiency.Ureacanbeusedbothasfoliar(lessthan10kgN/ha)andsoilapplication.•

Fertilizer placement:

Formaturetreesbroadcastingofnitrogenousandmixedfertilizersisthemain•method.Foryoungtrees,fertilizersneedtobespreadwithinthereachoftheirrootsys-•temsbybroadbandsystemrunningfromabout15cmfromthetrunktoabout50cmbeyondthecanopy.

Caution:Ammoniumsulphateislessliabletoleachingbuttheytendtomakethesoilmoreacidicafteryearsofregularusewhileammoniumnitrateisverymobileandmoveseasilytotherootsbutiseasilylostthroughleaching.

2.2 POTASSIUM (K) DEFICIENCY

KdeficiencyiswidespreadinAsiaanditsdeficiencyoccurswhenitslevelis<1.4%.Potassiumhasmoreeffectonfruitqualitythananyotherelements.

The main visible symptoms of K deficiency:

Fadingstartsasblotches•Blotchesfirstappearaspaleyellowwhichdeepenstobronzeatlaterstage•Older leavesarepersistent (contrast toNandMgdeficiencies,which induce•prematuresheddingofleaves)Afterextendedperiodsoftime,thechloroticleaftipsturnbrown,givinganap-•pearanceofleafscorchor“tipburn”Foliagedrab,•Treesexcessivelydroughty•Smallfruitwithlowlevelsofsugar&acidity,skinisthinandsmooth,tendsto•

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3•COMMON NUTRIENTDISORDERS OF CITRUSS

colorearlyandsplitseasilyCreasingismoreprominent•Severedeficiencyreducesyieldbycausingheavyflowerandfruitdrop.•

Potassium deficiency symptoms are usually most prominent in the spring. Brown irregular patches and yellow blotching appear near the apex of the leaf, while the base of

the leaf is last to lose its colour. Leaf fall follows. Note the bare lower twigs.

Possible causes of potassium deficiency:

InsufficientKsupplyinthesoil•Leachinginacidsandysoils•Soilswithveryhighconcentrationofcalcium(Ca)&magnesium(Mg)•HeavyapplicationofN•Lackofsoilmoisture•Insomecalcareoussoils,thereisadecreaseinKuptake.•

Remedial actions

Potassiumchloride(MoP)andsulphate,mixedorcompoundNPKfertilizersare•thecommonlyusedsourcesofK.Foliarapplicationsorspraysofpotassiumnitratearesometimesmoreeffective•whereheavysoilslimitthepenetrationofKtotherootzone,however,repeatedapplicationsarerequired.

Fertilizer placement:

Potassiumdoesnotmovefreelyinsoilsandisslowtoreachtherootsandso•broadcastingisineffectiveBandingisthebestwaytoapplypotashfertilizers.Deepplacement(15-20cm)•ensuresgooduptakeastherootsgrowthoughtheband.

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4• COMMON NUTRIENTDISORDERS OF CITRUSS

Fruit in the centre (normal), fruits on the left and right with high levels of N and no P respectively.

Large puffy P-deficient orange fruit with thick peel (right), healthy fruit (left)

2.3 PHOSPHORUS (P) DEFICIENCY

Phosphorusdeficiencyisrarelyfoundincitrusanywhereintheworld.EvensoilswithlowtotalPcontentgenerallyprovideadequateamountsforintensivelygrowncitrus.Occursonlyiftheleaflevelsfallbelow0.07%

The main visible symptoms of P deficiency:

Reducedgrowthandyield•Prematuredefoliation•Reducedsizeofnew leavesthatdevelopadullbronzedgreencastandshed•readilyFruitsare•

coarsewiththickpeels*palecolor*spongyfruit*excessivelyacidityofjuicemayoccur.*

Remedial actions

Pdeficiencyinlightsandyormucksoilcanbereadilycorrectedinafewmonths•bysoilapplication.Inheavysoils,surfaceapplicationsmaynotbeeffective,andsoilinjectionmay•berequiredtogetPintotherootzone.Superphosphate, triple superphosphate, or ammonium phosphate (MAP, DAP)•andNPKcompoundfertilizersarethemiainsourcesofP.Poultryandanimalmanure,ifusedathighratesforatleast4-5yearscontribute•tosoilphosphorussupplies.

Fertilizer placement:

Phosphorusdoesnotmovefreelyinsoilsandisslowtoreachtherootsandso•broadcastingisineffective

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5•COMMON NUTRIENTDISORDERS OF CITRUSS

Toavoidrepeatedrootdisturbance,applyenoughsuperphosphatefor3-4years•inonedressing.Asurfacebandclosetothedripringiseffectiveinlighttex-turedsoils.Organicmatterimprovesphosphorusmovement.•Sodcultureandmulchesencouragesrootstoforagenearthesurface.•

Caution:Reservesbuildupinthesoilaftermanyyearsofregularphosphorususeandcanbeeitheromittedforseveralyearsorappliedeverysecondorthirdyear.Leafanalysisisthebestwaytomonitorcontinuingneeds.

2.4 MAGNESIUM (Mg) DEFICIENCY

CitrusissensitivetoMgdeficiency.Magnesiumdeficiencysymptomsappearprimarilyonmatureleavescontaininglessthan0.2%Mg.

The main visible symptoms of Mg deficiency:

Chlorosisonmargins&tipsofleaves&inthepartoftheleafbetweenveins•Mainlyinoldleavesorinthebottomofafruitingtwig•Youngleavesremaingreen•Inseverecases:•

leavesmayfallearly*whole leafblademaydie (except theveinswhichremaingreenandthe*greenpartlookslikeaninverted“V”)

Fruitsgenerallysmallwithlowsugarcontent,lesscoloredfruit,canbemore•subjecttobiennialbearingIfdeficiencyisnotcorrecteditweakensthetrees.•

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6• COMMON NUTRIENTDISORDERS OF CITRUSS

Mg deficiency in orange trees results in a distinct yellow pattern in the older leaves.

The yellowing begins near the edge and towards the apex, leaving a triangle of green at the base of the leaf or an

inverted “V” of green in a chlorotic leaf.

Onacidsoils,pHmaintenancewithdolomitelimegenerallyprovidesadequate•MgforthetreeandeliminatestheneedforsolubleMgsaltsFoliarapplicationsofmagnesiumnitrate@1kg/100Lwhenspringflushleaves•are½to2/3expanded.

2.5 CALCIUM (Ca) DEFICIENCY

Calciumdeficiencysymptomsareextremelyrareascalciumisgenerallythedomi-nantnutrientincitrusleaves.Calciumdeficiencyisusuallyassociatedwithstronglyacidicsoils,andaclimatewithmanycloudyorrainydays.Calciumdeficiencysymp-tomsappearwhentheconcentrationofcalciumintheleavesislowerthanthecriti-calvalueof2.5%.

The main visible symptoms of Ca:

Mottling/fadingalongmargins•Affected leaves abscise rap-•idlyTreesextremelystunted•Leaf levels of less than 1%•Caareassociatedwith

Stuntedgrowth*Poorrootdevelopment*Diebackoftwigs*Yellowingofleafmargins*andinterveinalareas.

Possible causes of Magnesium deficiency:

Dueto lowsoilMgreserve,high levelsof•soil K competing for uptake or transloca-tionfromleavestofruitwithheavycrops,Leachinginacidsandysoils•LeachingofaddedMginsoilswithpH4.5•to5.0UnbalancedconditionwithexcessiveKand•Cacontent.

Remedial actions

Mgdeficiencycanbecorrectedwithsoil•applicationofmagnesiumsulphateordo-lomite.

Mottling along margins of Ca deficient orange leaves.

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7•COMMON NUTRIENTDISORDERS OF CITRUSS

Possible causes of Calcium deficiency

NativeCaleachinginacidicsoils•ContinuoususeofammoniumcontainingfertilizeracceleratesCalossfromsoils•UseofMoPandsulphurcauselossesofsoilCa•Inhighlysalinesoilswithhighconcentrationofsodium•

Remedial actions

ThoselowinCaareusuallyassociatedwithlowpHandwhenlimeisappliedto•raisesoilpH,anamplesupplyofCaisprovided.OthersourcesofCaareirrigationwater,especiallyfromdeepwells,fertilizers•suchascalciumnitrateandsuperphosphate.

2.6 MANGANESE (Mn) DEFICIENCY

Manganesedeficiencyiswidespread,butoftenonlyoftransientoccurrence.Likeanyotherheavymetals,Mndeficiencyoccursinyoung,enlargingleaves.Inspring,whenthesoilisstillcool,andinsummer,whenleafexpansionisveryrapid,temporaryMndeficiencypatternsarefound.Mostlytheygoawaywithoutanyattention.Onlyper-sistentandseverepatterndevelopmentofmostofthefoliagerequirescorrection.

The main visible symptoms of Mn deficiency:

SymptomsverysimilartoZincdeficiency•Interveinalchlorosis(palegreencolor)•Showslightgreenmottleonadarkgreenbackground•Often the pattern appears like a series of inverted “horseshoes” around the•peripheryoftheleafLeafsize&shapenormal•Internodesnotshortened•Occuronlyinyoungenlargingleavesandnotinoldones•OccursifsoilpH>7.5•

Full size orange leaves with light and dark green mottle pattern from Mn deficiency.

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8• COMMON NUTRIENTDISORDERS OF CITRUSS

Possible causes of Manganese deficiency:

Manganesedeficiencysymptomsoccuronlyonyoungleaves.•WhenconcentrationofMninleafis<25mg/kg•Deficiencyoccursinbothacidicandalkalinesoils,dueto•Leachinginacidicsoils•Insolubilityinthealkalinesoils•

Remedial actions

Mndeficiencyisbestcorrectedbyfoliarsprayofmanganesesulphate(100g/100L)•and500gureaisoftenaddedtoimproveuptakeofMn.Inhumidclimates,finelygroundMnOisveryeffectiveinsprays.•Analternativetofoliarsprayisthesoilapplicationof200-400kg/haofmanga-•nesesulphateUn-neutralizedMnSO4attherateof8-14kg/haperyearisgenerallyincludedin•apostbloompesticidalsprayinsomepartsofthewesternworld.

2.7 COPPER (Cu) DEFICIENCY

Copperdeficiencyunlikeanyotherheavymetalsisnotassociatedwithaleafchlo-rosis.TheCudeficientleavesareabnormallydarkgreenandsmallerthannormal,exceptforafewgiant leavesfoundonvigorousS-shapedbrancheswhichemergefromstuntedbushytrees.

The main visible symptoms of Cu deficiency

Twigsdiebackandmultiplebudsformnearthejuncturewithlivewood•Themostreliablesymptomsarethebrowngumpocketswhichdeveloponthe•flatsidesofangularyoungshoots.Newshootsmayproducenarrow,elongatedleavessimilartopeachleaves•Multiplebudsorsproutsmayformatnodes•Ifconditionismoderate,fruitdevelopmentisnormal;withmoreseveredefi-•ciency,fruitdevelopsbrownlesions,therigidpeelmaysplitandfruitdrops.

Cu deficit in citrus with elongated leaf

& twig dieback (left) and young twigs with gum pockets (right)

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9•COMMON NUTRIENTDISORDERS OF CITRUSS

Possible causes of copper deficiency:

InsufficientavailableCuinthesoils•

Remedial actions

Copperoxideortribasiccoppersulfateisusedinsprays.•CareshouldbetakennottoapplyexcessiveamountofCuasitstoxicitydam-•agestherootsystemandleadstodroughtytreeswithsparsefoliage,verysmallleavesandstubbyfeederroots.CopperspraysusedforfungicidalpurposesreadilycontrolCudeficiency•

2.8 ZINC (Zn) DEFICIENCY

Zincdeficiencyoccurseverywherecitrusisgrown.Itproducesadistinctiveyellowmottleonleavesthatarereducedinsize.

The main visible symptoms of Zn deficiency

Interveinalchlorosisofyoungleavesattheshoottip,•Youngleavesbecomesmall&narrowwithshortenedinternodesknownas“little•leaf”,“mottleleaf”and“resetting”(caution:samesymptomsmaybeexhibitedbycitrusblightandtristeza)Oldleavesremainnormal•Continuedstressleadstodefoliationandtwigdieback,fruitssmall,misshapen•andbleachedtowhitishcolor.Yieldslow.•

Strong chlorosis from Zn deficiency in small

attenuated orange leaves

Possible causes of zinc deficiency

InsufficientZn(<25mg/kg)•CalcareoussoilswithhighsoilpH(closetopH8)andpoorlyaeratedsoils•Fungusdiseases(rootrot&footrot)•DuetosoildepletionorformationofinsolubleZncompounds•Relatedtoheavyprecipitation•

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10• COMMON NUTRIENTDISORDERS OF CITRUSS

ExcessivePorNcaninduceoraggravateZndeficiency•Applicationoflarge&frequentamountsofpoultrymanureinthesoil•Zndeficiencyoftenaccompaniesothermetaldeficiencies.ZnandMnorZnandFe•oftenco-existsonthesameshootsandtheresultingchlorosismaybebaffling.

Remedial actions

Annualfoliarsprayofzincsulphate(150g/100L)onspringflushleaveswhenthey•areabouttwo-thirdsfullsize.Forlargeareas,soilapplicationof80-120kg/haofzincsulphatemaybebroad-•castandincorporatedintothetopsoilsoitreachesthefeederrootssinceitisveryimmobilefromthepointofapplication.

2.9 MOLYBDENUM (Mo) DEFICIENCY

Molybdenumisanunusualnutrientelementinseveralways.Itisrequiredinsmalleramountsthanotheressentialelements,anditsavailabilityinthesoilincreaseswithpH.Modeficiencyisrareinmostorchards.

The main visible symptoms of Mo deficiency

Mo deficiency causes a•“yellowspot”todeveloponfullymaturedleaves.Leaves produced in the•spring develop one to sev-eral large yellow-orangespotsinlatesummer.Spots occur at random on•leaves and gradually be-come gum-impregnated,turn reddish brown andbulge on the underside ofthe leaf. During the au-tumn,leavesdropprematurely,leavingathinlyfoliatedtree.Spotsdevelopbrowncentreswithorangehalos•Spotsmayoverlaporcoalesce•Severeinacidsoils•

Possible causes of molybdenum deficiency

Unavailableinacidicsoils•ItsavailabilityinthesoilincreaseswithpH•

Yellow spots from Mo deficiency in mature leaves.

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11•COMMON NUTRIENTDISORDERS OF CITRUSS

Remedial actions

Sprayswithsodiummolybdate(6g/100L)foundtopreventthesymptoms•IflowpH,correctitbyusinglimingmaterials•

2.10 IRON (Fe) DEFICIENCY

FedeficiencyisacommonproblemandlikeZndeficiency,itoccurseverywherecit-rusisgrown.Fedeficiencyisofrareoccurrenceonneutraloracidicsoils.MostFedeficiencyoccursoncalcareoussoilsandistermedlime-inducedchlorosis.However,Fetoxicityisnotknowntobeaproblemincitrusproduction.

The main visible symptoms of Fe deficiency

Theusual symptomsare verydistinctiveandconsist of yellowed leaveswith•greenmidribandlateralveins.Thisoccursonlyonyoungleavesbutmaypersistintomaturitywithoutshorten-•ingthelifeoftheleafChlorosispunctuatedbyafinenetworkofgreenveins•Severedeficiency-leaveslightyellowtonearlywhite.•

Fe-deficient young orange leaves with loss of chlorophyll and only the main veins and the midrib remaining green.

Possible causes of Fe deficiency:

AssociatedwithhighsoilpHorsometimesknowas“lime-inducedchlorosis”•Excessiveirrigation•Prolongedwetsoilconditions,orpoordrainageorhighwatertableoralowsoil•temperaturecanfurtheraggravatetheproblemLowsoiltemperature•Soilsalinity•Othersituationsnotclearlyunderstood.•

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Remedial actions

Oneeffective controlmeasure is to includecareful irrigation (avoidoverwa-•tering)andtheselectionoftolerantrootstock(don’tplantPoncirustrifoliatarootstocksinproblemsoilsasitismoresensitivetoFedeficiencythansweetorange,roughlemon)Foliarspraysofironsulphateorironchelateareeffective(latereffectiveonly•forfewtreesandnotonalargescale)

2.11 BORON (B) DEFICIENCY

The main visible symptoms of B deficiency

Dull,lusterlessleafcolor•Corkinessofleafveins•Shortinternodes,drabcolor,yellowveinssimilartogirdling,thickenedleaves,•corkyvenation,andbucklingoftheleafbladealongthemidribGumdeposits in thepeelare the rather specificsymptomsandcorkspots in•albedooffruit.(caution:fruitinjuredbyspinedcitrusbugareoftenwronglydiagnosedas‘borondeficient’)Bloommaybeexcessivebutunfruitfulnessresultsfromexcessivesheddingof•youngfruitPoordevelopmentofflower’spollentubeleadingtosubsequentpollinationfailure•Fruitsabnormalinshape“ashardasstones”andsuchfruitslackinjuice.•

B-deficit citrus with dull lusterless leaf color (left) & young B-deficient fruit with

gum deposits in peel and premature development of

rind color (right).

Possible causes of B deficiency:

IfBoroncontentoftheleafislessthan25mg/kg,•Iscommoninhigh-rainfallareaswithhightemperature(morethan33oC),on•acidicsoils(pHlowerthan5)withacoarsetextureasitishighlysolubleandleachesouteasily.Itismorelikelytooccurindryyearsespeciallyincalcareoussoils(pHhigherthan7.5)•Canalsobe found in soilswithheavyapplicationsofnitrogenandpotassium•fertilizersHeavylimeapplications•

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Remedial actions

Applicationofborax,awhitecrystallinesalt(5-10kg/ha)•Foliarapplicationof0.25%ofboraxsolutioncanbeappliedrepeatedlyevery10•daysuntilthedeficiencyiscorrected.Incalcareous soils, sulfur shouldbeapplied@2mt/ha to reduce the soilpH•andincreasethesolubilityofboroninthesoilsolution.(Caution:Citrusisverysensitivetoexcessboronandthereforeapplyaboronfertilizerorsprayonlyifyouaresureofitsdeficiency).

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14• COMMON NUTRIENTDISORDERS OF CITRUSS

3MUlTIPPle DefIcIencY sYMPToMs In THe saMe TRee

Incalcareous(limestone)soil–multipledeficienciesofeg.Fe,Mn,Znmayoc-•cur.Difficulttodiagnosemultipledeficienciesfromvisiblesymptoms,therefore•Leafanalysisimportant•

Upper row: left –normal leaf; two leaves on the upper right shows Mn deficiency;

Lower row: two leaves on the left show combined Zn & Mn deficiency. Three

leaves on the right show combined Mn, Cu and Zn deficiencies.

Zn & Mn deficiency

Mn deficiency

Mn,Cu, Zn def

Normal

Multiple deficiency symptoms- Fe, Mn and Zn occurring together in a tree grown in calcerous soils. Some young leaves are conspicuous whitish yellow color, showing Fe

deficiency; while other show typical symptoms of Zn and Mn deficiency.

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15•COMMON NUTRIENTDISORDERS OF CITRUSS

4ToXIcITY sYMPToMs

Toxicities caused by excesses ofmost essential elements are not too common incitrus.Thosenutrientsassociatedwithsalineandsodicproblems(sodium,chlorideandsulfur)mayoftencausetoxicitybutitresultsfromthesalineorsodicconditionsinthesoil.

4.1 NITROGEN (N) TOXICITY

Symptoms of N toxicity

Excessivesummer/autumnflusheswithdarkgreenleaves•Poorqualityfruit•Withthickpeel•LowlevelofTSSwhichcontributetothesweetflavor•Delayedcolorbreak•Shortstoragelife•

Excessive growth of summer/autumn flushes which have dark green leaves are symptoms of N toxicity.

4.2 PHOSPHORUS (P) TOXICITY

Too much phosphorus does not cause any loss in yield or fruit quality, but canaccentuatetheeffectsofZndeficiencyintrees

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16• COMMON NUTRIENTDISORDERS OF CITRUSS

4.3 POTASSIUM (K) TOXICITY

Symptoms of K toxicity

KreducesthenormaluptakeofMg(ToomuchKcanaccentuateMndeficiency)•therefore,KtoxicitysymptomsaresimilartoMgdeficiencysymptomsDelaysmaturity,causesorangetobecomecoarse,large,moreacidicandless•juicyFruitareusuallywith:•roughpeel•highacidity•Therindthickensandbecomesroughandre-greeningincreases•

Fruits on the right rows (C & D) have high K status. The fruits are larger than the normal ones (rows A & B) but the surface peel rough and they

have higher acidity.

Excess Potassium

4.4 SODUIM (Na) TOXICITY

Sodium toxicity is ofmajor importance in arid and semiarid areas or where Na-containingfertilizersorgroundwaterareused.

Symptoms of Na toxicity

Irregularyellowmottling•Tipandmarginalleafnecrosis•HeavyleafdropisoftenthefirstsignofNatoxicity.•

Na-toxicity in orange leaves with tip and marginal necrotic spots.

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17•COMMON NUTRIENTDISORDERS OF CITRUSS

4.5 BORON (B) TOXICITY

Borontoxicitysymptomsappearinleaveswithgreaterthanabout250mg/kgofBandindryareaswheretheirrigationwatercontainsmorethan0.5mg/kgofB.

Symptoms of B toxicity

Symptomsusuallyoccurinoldleaves•Scorchingoryellowingofmarginsandtipsandmottling•Formationofsmallbrownish,resinouspustulesontheundersideofleaves•Severetoxicity–prematureleafdropofforwilttodeath•Unlesstoxicityissevere,thereisnoadverseeffectonthefruit.•

Last word

Theabovetablesaregeneralrecommendationsonly(fromLiterature).•Thebestrecommendationscanbemadeonlyaftersoilandplantanalysisat•theSoilandPlantAnalyticalLaboratory(SPAL),NSSC.Thisisespeciallyimportantforcashcrops.•

B toxicity on citrus with older leaves showing scorching or yellowing on the margins and tips, sometimes with little brown spots.

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18• COMMON NUTRIENTDISORDERS OF CITRUSS

5RefeRences

Bennett,W.F.1983. NutrientDeficiencies&ToxicitiesinCropPlants.CollegeofAgriculturalSciencesandNaturalResources.TexasTechUniversity,Lubbock.APSPRESS.TheAmericanPhytopathologicalSociety.St.Paul,Minnesota.

Food& FertilizerTechnologyCenter.2003.CitrusProduction:AManual forAsianFarmers.

R.G.Weir,SpecialChemist.AgfactH2.AC.3,firstedition1987,MagnesiumandMan-ganesedeficienciesincitrus.NSWAgriculture.

R.G.Weir,SpecialChemist.AgfactH2.AC.2,thirdedition2003,IronandZincdefi-cienciesincitrus.NSWAgriculture.

Zekri,Mongi andObrezaThomas,A.Extension (SL202) Instituteof FoodandAg-ricultureSciences.MacronutrientDeficiencies inCitrus:Calcium,Magnesium,andSulfur1.UniversityofFlorida

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