Soil Acidity And Alkalinity, Lime And Liming

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Title:
Soil Acidity And Alkalinity, Lime And Liming
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Fact sheet
Creator:
Hanlon, Edward A.
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University of Florida Cooperative Extension Service, Institute of Food and Agriculture Sciences, EDIS
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Gainesville, Fla.
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Collected for University of Florida's Institutional Repository by the UFIR Self-Submittal tool. Submitted by Melanie Mercer.
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"December 199"
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"RF-AA002"

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University of Florida Institutional Repository
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SoilAcidityandAlkalinity,LimeandLiming1 TheInstituteofFoodandAgriculturalSciencesisanEqualOpportunity/AffirmativeActionEmployerauthorizedtoprovideresearch,educational informationandotherservicesonlytoindividualsandinstitutionsthatfunctionwithoutregardtorace,color,sex,ornationalorigin. FloridaCooperativeExtensionService/InstituteofFoodandAgriculturalSciences/UniversityofFlorida/JohnT.Woeste,DeanE.A.Hanlon2SOILpH ImportanceofSoilpHBecauseoftheinfluenceofpHonavailabilityof plantnutrients,thepHofasoilisprobablyitsmost importantsinglechemicalcharacteristic.Whensoil pHistoolowortoohighforoptimumplantgrowth, thepHcanberaisedbyapplyingalimingmaterialor loweredbyapplyinganacid-formingmaterial. DeterminingsoilpHisthefirststepinany fertilizationprogram.pHofFloridaSoilsMostFloridasoilsareacid,withpH'sranging between4.0and6.5.Themostacidareunlimed flatwoodssoils,havingpH'sof3.0-5.0.However, therearemanysoilsinFloridathatcontainnaturally occurringcalciumcarbonateandhavepHvalues above7.0.Thesesoilsgenerallyarefoundinthe vicinityofthecoastorinthemarlsoilareasof southernFlorida. Termsfrequentlyusedtodescribethe approximatesoilpHrangesareindicatedinTable1. Table1. SoilpHDescriptions stronglyacid <5.0 moderatelyacid 5.0-6.0 slightlyacid 6.0-6.5 nearneutral 6.5-7.5 slightlybasic 7.5-8.0 moderatelybasic 8.0-8.5 stronglybasic >8.5SOURCESOFSOILACIDITYSoilsinhumidregionsnaturallybecomemore acidwithtimeduetoleachingofthebasiccations, primarilycalcium,magnesium,potassium,and sodium.Inaddition,asthebasiccationsaretakenup byplantstheyarereplacedwithhydrogen, contributingfurthertosoilacidity.Decompositionof organicmatteralsocontributestothenatural tendencyforsoilstobecomemoreacidwithtime. Manyfertilizerscontainammoniumnitrogen whichreleaseshydrogenwhennitrifiedinthesoil. Applicationofsignificantamountsofsuchfertilizer willlowerthesoilpH.BUFFERCAPACITYResistancetochangeinpHisreferredtoas buffercapacity.Thebuffercapacityofsoilisdirectly relatedtothesoil'scationexchangecapacity.Sandy soilstendtohavesmallbuffercapacitiesandclayey soilsorthosehighinorganicmatterhavelargebuffer capacities. Ifjustenoughlimingmaterialwereaddedto neutralizetheacidinthesoilsolution,moreacid wouldmovefromtheexchangecomplextothesoil solution.Asaconsequence,thepHrisewouldbe negligiblysmallandwouldremainnegligiblysmall untilenoughlimewereaddedtoappreciablydeplete theexchangeable(reserve)acidity. 1.ThisdocumentwaspublishedDecember1992asRF-AA002,FloridaCooperativeExtensionService.Formoreinformation,contactyour countyCooperativeExtensionServiceoffice. 2.ExtensionSoilScientist,CooperativeExtensionService,InstituteofFoodandAgriculturalSciences,UniversityofFlorida,Gainesville.

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SoilAcidityandAlkalinity,LimeandLiming Page2 Thisbufferingeffectisequallyimportantin preventingarapidloweringofsoilpH.Forexample, Hionsareproducedbysoilbiochemicalchangesand theadditionofcertainfertilizers.Thisincreasesthe numberofHionsinthesoilsolution.Almost immediately,however,thisaciditybecomesadsorbed onsoilcationexchangesites,againresultinginlittle changeinthesoilsolutionpH.Thesetwoexamples showthatthebasisofbuffercapacityliesinthe adsorbedcationsoftheexchangecomplex.INFLUENCEOFpHONPLANT NUTRIENTAVAILABILITYPlantsdifferinthepHrangeoverwhichtheymay grow.ThisisdueprimarilytotheeffectofpHonthe availabilityofvariousplantnutrientsinthesoilat differentpHlevels.Instronglyacidmineralsoils(pH below5.0),aluminum,iron,zinc,copper,and manganeseavailabilityincreasesandtheseionsmay reachlevelsthataretoxictoplants.Stronglyacid soilsareusuallydepletedofthenutrient bases--calcium,magnesium,andpotassium--sothat plantsmaybeunabletoobtainthequantitiesofthese nutrientsnecessaryforpropergrowth.Also,reduced availabilityofphosphorusandmolybdenumoccursat lowsoilpH. SoilpHissoimportantinplantnutritionthatits influenceoneachofthecropnutrientswillbe discussedbrieflybelow.NitrogenTheeffectofpHonnitrogenavailabilityisan indirectone.Navailabilityinsoiliscloselyassociated withtheactivityofmicroorganismswhichcarryout nitrogentransformationsanddecomposeorganic matter.ThemostfavorablepHrangeforthese microorganismsis6.0to8.0.PhosphorusTheavailabilityofphosphorusisquitecomplex andtoalargeextentreducesthepHrangeinwhich cropscanbeeconomicallyproduced.AtpHlevels below5.5,insolubleironandaluminumphosphates formandthephosphorusisessentiallyunavailableto plants.AtpHvaluesabove7.5theformationof insolubletricalciumphosphatebecomesanimportant factorinreducingtheavailabilityofsoilphosphorus. Thegreatestavailabilityofsoilphosphorusinmineral soilsisbetweenpH5.5and6.5.PotassiumTheavailabilityofpotassiumislessinfluencedby soilpHthanthatofmostoftheotherelements.CalciumItisincorrecttosaythatpHinfluencescalcium availability,becauseitisprimarilythecalcium concentrationinthesoilthatinfluencespH.When thesoilexchangecapacityislargely(e.g.90%) saturatedwithbases(calciumgenerallybeingthe mostabundant),thepHwillusuallybehigh(e.g.6.5) and,whentheexchangeableCaislow(e.g.50%)the pHwillusuallybelow(e.g.4.5).Calciumdeficiency ishighlyunlikelyifsoilpHisabove5.5,either naturallyoraftercorrectionwithlime. PleasenotethattheMehlichI(doubleacid) extractantremovesmorethanjustexchangeableCa fromthesoil.Sincecalciumphosphatesarealso solubilizeditispossibletohaveahighCasoiltest andarelativelylowpH.Anylimestoneparticleswill alsobesolubilizedbytheextractingacid.MagnesiumMagnesium,likeCa,isoneofthebasicions whoseconcentrationinfluencesthesoilpH.Whenthe soilisaciditisusuallybecausethebaseshavebeen leachedout,andMgwillusuallybelow.Situations occur,however,wherepHisadequateforgoodplant growthbuttheMgcontentofthesoilislow.Insuch casesfertilizerMgshouldbeappliedinsomeform otherthandolomitetoavoidtheadverseeffectof over-limingonothernutrients.SulfurLikenitrogen,theavailabilityofsulfurisvery muchrelatedtotheactivitiesofsoilmicroorganisms. IfthepHisfavorableforthemicroorganismsitwill alsobefavorableforsulfuravailability.Sulfurisvery mobileinsoilandtendstoleachquitereadily.Many ofthebases(calcium,magnesium,potassium)leach outofthesoilassulfates.IronIronisquitesolubleinanacidsoilandbecomes increasinglylesssolubleasthepHincreases.When thesoilpHismuchabove6.2,thesolubilityofironis seriouslyreducedandcertainplantsmaysufferFe

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SoilAcidityandAlkalinity,LimeandLiming Page3 deficiency.Ifthesoilbecomestooacidandishighin phosphorus,theironcombineswithphosphorusto forminsolubleironphosphate.ManganeseTheavailabilityofmanganeseisverymuchlike thatofiron.AssoilpHincreasestheavailabilityof manganesedecreases.Floridasoilsaregenerallylow inMnandmanycropsinFloridashowMndeficiency abovepH6.2.Inotherareasofthecountry,Mnmay betoxicinstronglyacidsoils.ZincZincavailabilityalsodecreaseswithincreasingsoil pH.UsuallyapHabove6.5istoohighforsoilslow inzinc,especiallyforcropswithahighzinc requirement.Cropresponsestosoilapplicationsof zinchavebeenmeasuredwhenthepHrangedfrom 6.0to6.5.Wherezincdeficiencyisaproblemand thepHofthesoilishigh,mostcropsrespondto nutritionalsprayscontainingzinc.CopperLikezinc,copperisquiteavailableatacidpHs, becomesincreasinglylessavailableasthepHrises, andisalmostunavailableabovepH7.5.Invegetable fieldsandcitrusgroveswherecoppersprayshave beenusedyearafteryear,thecopperlevelshavebuilt uptotoxicconcentrationsandcoppertoxicityis avoidedbylimingthesoiltoapHbetween6.5and 7.0.BoronBoronismostavailablebetweenpH'sof5.0and 7.0.Above7.0theavailabilitydecreasesveryrapidly untilapHofabout8.5.Above8.5theavailability againincreases.Boronisneededinsuchsmall quantitiesthatthereisanarrowmarginbetweena concentrationinthesoilthatisdeficientandonethat istoxic.MolybdenumMolybdenumistheonlymicronutrientthatis moresolubleathigherthanatlowerpHlevels. Limingoftenconcurrentlysolvesmolybdenum deficiencies.Molybdenummaybecometoxicinsome alkalinesoils.MEASURINGSOILpHThepHtestisanimportantdiagnostic determinationmadeonthesoil.Itisusedinmaking limingrecommendationsandtoaidinevaluatingthe availabilityofvariousplantnutrients.SoilpHismost frequentlymeasuredinasoilandwatermixture.A verycommonprocedureistomixtwovolumesof waterwithonevolumeofsoil,allowthemixtureto equilibrateforabout30minutes,stir,anddetermine thepHofthesuspensionwithapHmeter.Thisisthe procedureusedbytheIFASExtensionSoilTesting Laboratory.pHMeterTheuseofaglasshydrogen-sensitiveelectrode andpotentiometer(pHmeter)isthemostcommon meansofdeterminingthepHofthesoil.ThepH valueobtainedforthesoilandwatermixtureisread directlyfromthedialorelectronicreadout.The metershouldbestandardizedusingtwostandard buffers,preferablypH7.0and4.0andcheckedwith apH10buffer.Itshouldbestandardizedeachtime themeterisusedandeveryhourwhenincontinuous operation.IftheinstrumentissettoreadpH7.0,the pH4.0buffershouldread4.0.IfthepH4.0buffer cannotbemadetoread4.0byadjustingthe temperaturecompensator,thenthebuffersshouldbe checkedwithanotherinstrumentornewonesshould bemadeup.Ifthebuffersstilldonotcheck,lookfor troubleintheelectrodes.Consulttheoperating manualforproceduresforcheckingtheoperationof theinstrumentitself.Theelectrodesshouldbekept moist,withthetipsindistilledwaterorpH7.0buffer atalltimeswhennotinuse.TheKClcrystalsinthe referenceelectrodealsoneedtobemaintainedatthe recommendedlevel.Diffusionofsaltthroughthesalt bridgetothelessconcentratedsamplescauses gradualdepletionofthesaturatedKClasindicatedin theoperatingmanual. TheExtensionSoilTestingLaboratorywillbe happytoassistcountylabsindiagnosingproblems withtheirpHmeters. CheckthepHofastandardsoilalongwithany unknowns.

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SoilAcidityandAlkalinity,LimeandLiming Page4IndicatorDyesIndicatordyeshavebeenusedextensivelyinsome laboratoriesandinkitsusedforrapidsoiltestingin thefield.Theyhavedefinitelimitations.Ifindicators areused,astandardsoilshouldbeusedtocheckthe indicatorseverytimeapHisdeterminedonan unknownsoil.Varioussaltsinthesoilsmayalterthe coloroftheindicatordye,thusgivingerroneouspH values. Amajorproblemwiththeuseofindicatorsfor determiningpHofFloridasoilsisthatorganicmatter tendstomaskthedyecolor.Indicatordyesfor determiningpHshouldbeusedwithcaution. Underthebestcircumstances,indicatordyes estimatesoilpHonlytothenearest0.5pHunit.This isadequatefordeterminingthegeneralrangeofsoil pH,butshouldnotbeusedforseriousmanagement decisions.LIMEANDLIMING Pre-RequisitesofSoilLimingMaterialsAmaterialmusthavethreefundamental characteristicsinordertobeconsideredsuitablefor neutralizingtheacidityofagriculturallands. Itmustremoveacidityfromthesoilsystem. Itmustnotaddharmfulionstothesoil. Itmustbeplentifulandrelativelyinexpensive. Thecarbonates,oxides,andhydroxidesofcalcium andmagnesiumarethemostcommonlyused agriculturallimingmaterialsbecausetheyfulfillthree prerequisites.Examplesofmaterialswhicharenotor cannotbeusedforlimingagriculturallandsbecause theyfailoneormoreoftheprerequisitesinclude: calciumsulfate(gypsum),producesnonet changeinacidityofthesoilsystemresults. sodiumcarbonatewouldaddlargequantities ofsodiumion;sodiumcauseslossofnutrient cationsandcanalsohavedetrimentaleffects onsoilphysicalpropertiesoffine-textured soils. potassiumcarbonatefillsthefirsttwo,butis tooexpensivetouseasanagriculturalliming material.LimingMaterialsUsedinFloridaCalciticanddolomiticlimestonearebyfarthe mostcommonlyusedagriculturallimingmaterialsin Florida,becausetheyarethecheapestandmost abundantmaterialsavailableforthispurpose.These materialsaretakenfromquarries,groundtoa powder,andshippedbyrail,barge,ortruck.Without anyfurtherprocessing,theymeetthefundamental criteriadiscussedabove.Transportationisamajor portionofthecostoftheselimingmaterials. Manyothermaterialsmaybeusedforliming agriculturalsoils,providedthattheymeetthe fundamentalcriteriadiscussedabove. Somethathavebeenused,andafewcomments abouteach,arelistedbelow: hydratedlime:fastactingcalciumhydroxide; considerablymoreexpensivethanagricultural lime burntlime:fastacting,mainlycalciumoxide, caustictohandle marl:variableincarbonateandmoisture contents shells:oystershellsorotherseashellsare composedmostlyofcalciumcarbonate,must befinelygroundtobegoodlimingmaterials industrialby-products:slagsandrefuselimes frompapermillsandwatertreatmentplants areexamples,frequentlymustbedriedbefore useable,mustverifythatharmfulimpurities arenotpresentImportanceofParticleSizeThefinertheagriculturallimeparticle,thehigher isitsacid-neutralizingefficiency.Amaterialthatis finelygroundhasmoresurfacearea,comesincontact withmoresoil,andthusraisesthesoilpHmore quicklythanthesamematerialcoarselyground.Data showninTable2illustratethiseffect.

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SoilAcidityandAlkalinity,LimeandLiming Page5 ByFloridalaw,agriculturallimestonesmustbe groundsothat: l.Notlessthan90%passesan8meshsieve. 2.Notlessthan80%passesa20meshsieve. 3.Notlessthan50%passesa50meshsieve. "Mesh"referstothenumberofopeningsper linearinchinthescreensusedforanalyzingparticle size.A60meshsievehas60openingsperlinear inch,or3600openingspersquareinch.Particles passingthrougha60meshsievearesmallerthan 0.0098inchindiameter.FactorsAffectingLimeRequirementSoilBufferingCapacitySoilswiththesamepHbutdifferentbuffering capacitiesrequiredifferentamountsoflimetoreach thedesiredpHlevel.Chemicaldeterminationof bufferingcapacityispartoftheAdams-EvansLime RequirementTestusedbytheIFASExtensionSoil TestingLaboratory.CroptobeProducedThepHleveltowhichasoilshouldbelimed dependsontherequirementofthespecificcroptobe produced.SeeCircular817fortargetpHlevelsof Floridacrops. Table2. IncreaseinsoilpHwiththreesizefractions ofdolomiticlimestone.(InitialsoilpHwas5.0.) TIMEAFTER APPLICATION (MONTHS) PARTICLESIZE(MESH) 8to2040to60 60to100 pH 1 5.0 5.4 5.4 12 5.66.0 6.2 24 5.9 6.3 6.4 36 6.3 6.5 6.6FertilizerApplicationsFertilizersaltsgenerallylowerthemeasuredsoil pHassoonastheyareaddedtothesoil.Assoonas thefertilizerdisipates,themeasuredpHreturnsto normal.Thenetacid-formingpotentialofvarious fertilizermaterialsisshowninthesection"Fertilizers &Fertilization".Inagoodlimingprogram,fertilizer applicationsshouldbetakenintoconsideration.LimingMaterialsAvailability,economy,magnesiumcontent, neutralizingvalue,andfinenessshouldallbe consideredinselectionofalimingmaterial. Thedecisionofwhethertousedolomiticor calcitic("hical")limeshouldbebasedprimarilyon costofthematerialtotheproducer.Whenbothlime andMgareneeded,dolomitecanserveastheliming materialandalsoasasourceofthenutrientMg. However,ifthecostofdolomiteissignificantlyhigher thanthatofcalcite,theproducershouldconsiderthe alternativeofapplyingcalciteasthelimingmaterial andMginthefertilizer.Applicationofdolomiteasa sourceofMgwithoutregardtothelimingeffectcan leadtoothernutritionalproblemsinsoilswithpH above6.3orso. Frequently,producersmayhaveaccessto by-productmaterialswhichcanserveverywellfor limingagriculturallandifthenatureofthematerial isunderstoodandproperprecautionsarefollowed. Limefrommunicipalwatertreatmentplantsisan example.Somesuggestionsaboutitshandlinganduse follow: Asreceivedfromthewatertreatmentplant, thelimeusuallyhastheconsistencyofathick paste.Pileandallowtodrybeforeattempting tospread. Turnwithafrontendloadertopromote drying.Spreadbeforecompletelydryandon acalmday,tominimizedrift. Useabout80%asmuchmaterialasyou wouldagriculturallimestone.Itwillreact quicklyduetoitsfinenessandthuscarries morepotentialforoverlimingifnotproperly used.

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SoilAcidityandAlkalinity,LimeandLiming Page6 Materialssoldasaglimearecoveredbythe FloridaCommercialFertilizerLawandmustmeet specificationsoffinenessofgrind,carbonate equivalence,andMgcontent(inthecaseof dolomite).Thisaffordssomeconsumerprotection. Limeby-productsarenotcoveredbythelawandthe consumermustrealizemorepersonalresponsibility whendealingwithsuchproducts. Limingisprobablythemostimportantsoil fertilitypracticeonstronglyacidmineralsoils. However,manyfieldcropsinFloridaproducejustas wellonmoderatelyacidasonslightlyacidsoil. Muchhasbeenwrittenaboutthe"optimumpH range"forcrops.Themostcommonlyquotedis5.5to 6.5.Thishasresultedinacommonly-heldbeliefthat "most"cropsproducebetterat6.5thanat5.5.Ifread carefully,thestatementsaysthatapHof5.6isjustas "optimum"foracropasisapHof6.4.Limingwhen nopositivecropresponseisobtainedisnotagood useofresources.FrequencyandPlacementThefrequencyoflimingcanbestbedetermined throughacombinationofsoiltestingeverytwoto fouryearsandgoodlimingandfertilizationrecords. Thelimerequirementiscalculatedonthebasisofa 6-inchplowlayerofsoil.Therefore,wherepractical, theappliedlimeshouldbemixedwiththesoilby cultivation.LimeRequirementDeterminationTheAdams-Evans(A-E)LimeRequirementTest usedbytheIFASExtensionSoilTestingLabinvolves shakingaknownamountofsoilwithagivenquantity ofbuffersolution.Thesolutioniscomposedof severalchemicalreagentsandisbufferedatpH8.00. Afteraperiodoftime,thepHofthesoil-buffer mixtureisdetermined.Theamountofsoilacidityis calculatedfromthepHdepressionoftheoriginal buffersolutionbythesoil.Thelimerequiredtoraise thesoilpHtoadesiredvalueisthenestimatedusing relationshipsassociatedwiththemethod.Theliming recommendation,roundedtothenearesthalfton,is reportedbytheIFASExtensionSoilTesting LaboratoryaspartoftheSoilTestReportand StandardFertilizerRecommendations.