Designation:D4972−19StandardTestMethodsforpHofSoils1ThisstandardisissuedunderthefixeddesignationD4972;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope*1.1ThesetestmethodscoverthemeasurementofthepHofsoilsthatwillpassthe2.00mm(No.10)sieve.Suchmeasurementsareusedintheagricultural,environmental,geotechnical,andnaturalresourcesfields.Thismeasurementdeterminesthedegreeofacidityoralkalinityinsoilmaterialssuspendedinwateranda0.01Mcalciumchloridesolution.Measurementsinbothliquidsarenecessarytofullydefinethesoil’spH.Thisvariableisusefulindeterminingthesolubilityofsoilmineralsandthemobilityofionsinthesoilandassessingtheviabilityofthesoil-plantenvironment.AmoredetaileddiscussionoftheusefulnessofthisparameterisgiveninRefs(1-6)2.1.2TwomethodsformeasuringthepHofsoilsarepro-vided.Themethodtobeusedshallbespecifiedbytherequestingauthority.Whennomethodisspecified,MethodAshallbeused.ThepHisdeterminedintestwaterandacalciumchloridesolutionforbothmethods.1.2.1MethodA—ThepHismeasuredusingapotentiometerhavingapHsensitiveelectrodesystem.Thismethodcanbeusedforanyapplicationandmustbeusedwhentheapplicationwarrantsahigherlevelofresolution.1.2.2MethodB—ThepHismeasuredusingpHsensitivepaper.Thismethodcanbeusedforanyapplication,however,becausepapertypicallyhasalowerresolution,itprovidesanapproximateestimateofthepHofthesoilandshouldnotbeusedwhentheapplicationrequiresahigherlevelofresolution(Note1).NOTE1—Forexample,paperwithasensitivitytothenearest1pHunitplacedintoabuffersolutionof4shouldindicateapHof4,however,itwouldnotindicateifthepHis4.449or3.449.1.3Units—ThevaluesstatedinSIunitsaretoberegardedasstandard.Nootherunitsofmeasurementareincludedinthisstandard.1.4AllmeasuredandcalculatedvaluesshallconformtotheguidelinesforsignificantdigitsandroundingestablishedinPracticeD6026.1.4.1Th...
