Soil Aggregate Stability(8)

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effectsareofthesefactorsonthehydraulicconductivityFrenkelwellestablishedQuirk,et(QuirkandSchofield,1955;McNealand/orandColeman,infiltration1966;rateer,Several1990;1986;al.,RengasamyAbu-Sharar1978;Alperovitchand1985;etal.,1981;Shainbergetal.,1981a,b;Olsson,Abu-Sharar1991;Amézketaetal.,1987;andShainbergAragüés,andSing-are1984;presentstudiesKaplanCurtinevenhavealsoshownthatoccurrenceofpoorphysicalconditions1995b).etal.,at1995;lowSARvalues(Osteretal.,1980;Rengasamyetal.,ticles,etal.,1996).SodiumCrescimannocausesswellingetal.,1995;and/orLevyandTorrento,1995;thresholdandslakingofunstableaggregates(Crescimannodispersionetal.,of1995).claypar-AusefulfrommustthosetodefineconcentrationunderchemicalcurvewhichconditionsdefinedfromSARandECvaluesisverystructureis(SAR,stable.EC)However,thatdestabilizesinglestabilitysoilstructureablesbealsodevelopedforeachsoil(PrattandSuarez,1990),sinceotherlinesvari-(1984),Guptaetaffectal.soil(1984),structuralArorastability.

andColeman(1979),ShainbergandLeteyChoromSuarezsoilthatpH.Theetal.etal.(1984),Chiangetal.(1987),Kerenetal.(1988)andimportance(1994)observedofthethatpHclaydispersionincreaseswithincreasingequivalentdifferencesinrelativehydrauliceffectconductivityisdemonstratedbetweenbypHthe6observationandAmézketapHandtodifferencesbetweenSAR20and40(Suarezetal.,91984).wereelectrolytevaluesontheAragüésenhancement(1995a)foundofthatthenegativeeffectofincreasingwithSomeauthorsconcentrationsclaydispersionwasonlyimportantforhavebelowtheflocculationvalue(FV).

al.a(1987),thepresenceHeilandofSpositoCafoundorMg.that,foragivenSAR,claydispersiondiffers(1993a),AbderrahmanandCurtinandetal.Rowell(1979),YousafetAllperovitchgivenSAR,CaismoreeffectivethanMginflocculating(1994b)foundthat,forgibleetal.(1986)observedthatthisdifferentialeffectsoilclaymayparticles.benegli-hancesindispersion.dissolutionsoilshighintheThus,AmézketaofcalciumCaCOcarbonate,becausetheexchangeableMgen-and3andAragüésthereleased(1995a)electrolytesfoundthatCapreventedandclayexchangeableOfsametheeffectfourmajoronthecationsdispersionfoundofinclaysoilsin(Ca,severalMg,calcareousNa,andK),soils.

Mghadtheeffectofleastand(1995)Schofieldclear.ReportedKonsoil(1955)resultsphysicalconsidervaryKorandhydraulicpropertiesisprobablytheasconflictdeleteriouswithrespectasNa.tothiseffect.Quirkmacro-aggregatefoundKasnotdeleterious,limitingclaydispersionLevyandandmaintainingTorrentoofandadsorbedK,whichstability.is72%TheythatattributedthistothelowerhydrationenergyandVanNa.Moreover,DerWatt(1990)theHofmeister’sobservedofanadsorbedlyotropicintermediateNa.Ontheotherhand,LevyserieeffectestablishesofKbetweenthatthede-

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