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1、AggregationandSoilOrganicMatterAccumulationinCultivatedandNativeGrasslandSoilsJ.Six,*E.T.Elliott,K.Paustian,andJ.W.DoranABSTRACTDefiningSOMpoolsthatrelatetosoilstructureandTillageintensityaffectssoilstructureandthelossofsoilorganicdelineatingSOMfractionsthatare
2、functionallymean-CandN.Wehypothesizedthatno-tillage(NT)andconventionalingfulareimportantchallengesforresearchandaretillage(CT)differentiallyaffectthreephysicallydefinedparticulatenecessaryforabetterunderstandingofSOMdynamics.organicmatter(POM)fractions.Agrassla
3、nd-derivedHaplustollwasForexample,Elliottetal.(1996)andChristensen(1996)separatedintoaggregatesbywetsieving.Freelightfraction(LF)anddescribedtheimportanceofdifferentiatingthefreeandintra-aggregatePOM(iPOM)wereisolated.Naturalabundance"CintraaggregateSOMinconcep
4、tualmodelsofphysicallywasmeasuredforwholesoilC,freeLFC,andiPOMC.ThemeanbasedSOMpools.Intraaggregateorganicmatterisin-residencetimeofsoilCunderCT(44yr)was1.7timeslessthanincorporatedandphysicallystabilizedwithinmacroaggre-NT(73yr).TheamountoffreeLFCwas174,196,an
5、d474gCm~2gates(CambardellaandElliott,1992),whilefreeorganicforCT,NT,andNS,respectively.TotaliPOMCamountsinCT,NT,andNSwere193,337,and503gCnr2,respectively.Thelevelofmatterisfoundbetweenaggregates.ThisdifferenceinfineiPOMC(53-250jim)levelinmacroaggregates(250-200
6、0urn)positionwithinthesoilmatrixandtheresultantacces-obtainedafterslakingwasfivetimesgreaterinNTvs.CTandac-sibilityofSOMtosoilorganismsleadstopoolsthatcountedfor47.3%ofthedifferenceintotalPOMCbetweenNTanddifferinstabilityanddynamics(Golchinetal.,1994a,b).CT.The
7、amountofcoarseiPOMC(250-2000(Jim)wasonly2.4timesInaddition,mineralizationstudiesofcrushedvs.in-greaterandaccountedforonly21%ofthedifferenceintotalPOMtactaggregatesindicatethataggregate-protectedpoolsC.SequestrationofiPOMwasobservedinNTvs.CT,butfreeLFofCaremorel
8、abilethanunprotectedpools(Cambar-wasnotinfluencedbydifferentialtillage.WeconcludethatdifferencesdellaandElliott,1993)becauseprotectedpoolsarelessinaggregateturnoverlargelyco
