Soil Aggregate Stability(18)

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conditions,willtation,bedeterioratedwhereasbythefreezing,propertiesbecauseofuncompactedmicrofabricandchangeshighly(particlesaturatedorien-soilsthawdaetsettlementreductioncanineffectiveleadtoacompactionporespace)andbyicedecreasepressure,inpermeabilityconsolidation(Czur-andstabilityAiral.,and1995).

coolingtureofthroughsoiltemperaturealsohaveanindirecteffectonsoilaggregatethesoiltheireffectonwatercontentofthesoilsurface.Rapidetal.,tothesurfacesurfacefromdeeperinducessoil,gradientsincreasingwhichthecauseswatermigrationcontent(Bullockofmois-soilFinally,1988).

windvelocityaffectsalsosoilerodibility.InlossandlimitingWindagriculturalerosionisasustainabilityserioussoilsoilstructuraldegradationstability,andespeciallyinmanyplacesprocessofleadingtospeciallyagriculture,theriskofwinderosionisincreasedduringfallowtheperiods,world.erosionifresidueissparse(Larneyetal.,1994).TheseverityofwinderistheandfractionRosenau,dependsontheaggregatesizedistributionofthesoilsurface(Kemp-of1986).particlesIthassmallerbeenthanconsidered0.84mmthat(Campbellthewind-erodibleetal.,1993a,fractionb).Time(Aging)

bility.TimeparedIncreasesisanotherinrelativesoil-formingstabilityfactor,withwhichtimealsoinfluencesaggregatesta-addition,aggregatespactionincreasesheldinstrengthatconstantofwaterclaysovercontentweremonths(Blakefoundinartificiallypre-orandyearsGilman,1970).Inasorremoldinghavebeenobservedbycivilengineersfollowingandrecognizedcom-known‘‘thixotropicseemascuring,agehardening’’(Molopeetal.,1985a).Thiseffectisalsoreorientationtoberesponsibleorstrengthregain(Dexteretal.,1988).Physicalprocessesaofplatyclayforparticlesthesestabilizations.byexternallyMitchellapplied(1960)hypothesizedplateletsmoreuniformlyparallelarrangement.‘‘Inthismoreorderedshearingstructureforcesclayinto(leastrest,negative).canslippastoneanother,andmatricwaterpotentialismaximumticles.thermalWhentheshearingforceisremovedandthesystemcomestotime,Theresultingoscillationsdisordertendtorandomizetheorientationoftheclaypar-hydrationmatricsurroundingprocessespotentialanddecreasesimpartsbyredistributionastherigiditywatertothesystem,andatthesameofionsstructureinbecomesmodifiedbyassociatedtheclaysurfaces.’’Thus,orientationtheofelectricwatermoleculesdoublelayersandpositionsstabilityofcationloweredequilibrium,potentialandspontaneousshiftingofclayparticlestomentationduringthroughaging.thedryingDexterenergyeffectetal.could(1988)accountforthebuild-upinaggregatealsoaddedcontributethatparticle-particletoage-hardening.

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