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2004 Aggregate-Size Stability Distribution and Stability C. O. Márquez Universidad de Los Andes - Venezuela

V. J. Garcia Universidad de los Andes

Cynthia A. Cambardella United States Department of Agriculture

Richard C. Schultz Iowa State University, [email protected]

Thomas M. Isenhart Iowa State University, [email protected] Follow this and additional works at: http://lib.dr.iastate.edu/nrem_pubs Part of the Hydrology Commons, Natural Resources Management and Policy Commons, and the Soil Science Commons The ompc lete bibliographic information for this item can be found at http://lib.dr.iastate.edu/ nrem_pubs/178. For information on how to cite this item, please visit http://lib.dr.iastate.edu/ howtocite.html.

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Abstract A new theoretical and experimental framework that permits an accurate determination of aggregate-size stability distribution is presented. The size-stability distribution in addition to estimating aggregate-size distribution distinguishes between amounts of stable and unstable macroaggregates (>250 μm). The determination of aggregate-size stability distribution involves the assumptions that soil aggregates can be categorized in terms of their size and water stability (slaking resistance). Experimentally this procedure involves the slaked and capillary-wetted pretreatments; and a subsequent slaking treatment of aggregates >250 μm in size. We also propose the stable aggregates index (SAI) and the stable macroaggregates index (SMaI) for studying soil stability based on aggregate resistance to slaking. These indices account for the total weighted average of stable aggregates and the total weighted average of stable macroaggregates, respectively. Both the SAI and the SMaI indices were shown to be sensitive to the effects of vegetation on soil stability under different riparian buffer communities. The SAI and the SMaI indices were higher in surface under cool- season grass than any of the other treatments. These soils samples are well aggregated with SAI = 74% and SMaI = 56% followed by SAI = 55% and SMaI = 37% under existing riparian forest, SAI = 40% and SMaI = 21% under 7-yr switchgrass and SAI = 36% and SMaI = 18% under cropped system.

Keywords size-stability, soil aggregates, slaking, riparian buffer

Disciplines Hydrology | Natural Resources Management and Policy | Soil Science

Comments This article is from Soil Science Society of America Journal 68 (2004): 725, doi:10.2136/sssaj2004.7250.

Rights Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The onc tent of this document is not copyrighted.

This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/nrem_pubs/178 Reproduced from Soil Science Society of America Journal. Published by Soil Science Society of America. All copyrights reserved. eoewtseigcnrl h eeiyo h disruption the of severity aggregates the soil controls soil sieving into the wet water before of content of moisture entry The the the aggregates. in emulates involved water in stresses soil natural sieving and cycli- submerging method, this cally In 1986). used Rosenau, and widely Kemper (Kemper, most 1966; method The wet-sieving de- the study. on methods based the are of approaches these purpose of the on suitability pends and The (Kemper 1986). stability Rosenau, and distribution aggregate-size 1993). Bruce, the and of (Beare magnitude and stress nature disruptive the bind of that and concept forces together the The particles both 1998). on al., depends stability et aggregate (Chen moisture) and ture tempera- fauna, (soil soil environmental roots, and plant microorganisms), and of activities matter, abiotic organic biotic (soil as cations), exchangeable grouped sesquioxides, be minerals, Factors can ( 1982). stability Oades, aggregate and (Tisdall affecting soil the in processes 7 .SgeR. aio,W 31 USA 53711 WI Madison, Rd., Segoe (2004). S. 68:725–735 677 J. Am. Soc.  Sci. author Soil in *Corresponding Published 2003. Mar. 27 of Dep. Received ([email protected]). Isenhart, University, 50011. State T.M. IA Iowa and Management, Ames, Schultz and R.C. Ecology 50011; Resource Natural IA Pam- 2150 Ames, Lab., Dr., Tilth mel Soil Me National Andes, USDA-ARS, los Cambardella, de C.A. Universidad Ciencias, de Facultad Me Andes, los de versidad Ma C.O. S SAI and SAI switchgrass forest, riparian existing other SAI the with aggregated of SMaI were well any and indices are than samples SMaI grass soils cool-season These the under treatments. be and soils different to surface SAI under in shown stability The higher were soil communities. on indices buffer vegetation SMaI of riparian effects the re- the and to macroaggregates, SAI sensitive stable the of average Both aggre- weighted slaking. stable spectively. total of to average the weighted resistance and total aggregate gates the on for account based indices stability These soil (SMaI) index studying macroaggregates for stable the and (SAI) index treat- aggregates stability slaking aggregates water subsequent of and a ment and size pretreatments; their capillary-wetted of and slaked the terms involves procedure in this Experimentally resistance). categorized (slaking be can aggre- soil gates that assumptions the and involves distribution stable stability gate-size of ( amounts macroaggregates between unstable aggre- distinguishes estimating distribution to addition gate-size in pre- distribution is size-stability distribution The sented. stability aggregate-size of determination accurate olSineSceyo America of Society Science Soil eea ehd aebe rpsdt eemn soil determine to proposed been have methods Several e hoeia n xeietlfaeokta emt an permits that framework experimental and theoretical new A i grgt stability aggregate oil eatosaogbooia,ceia,adphysical and chemical, biological, among teractions ´ qe,Fcla eCeca oetlsyAbetls Uni- Ambientales, y Forestales Ciencias de Facultad rquez, ϭ 6 olwdb SAI by followed 56% .O Ma O. C. ϭ Ͼ 250 6 n SMaI and 36% ´ ia eeul;VJ Garcı V.J. Venezuela; rida, ABSTRACT grgt-ieSaiiyDsrbto n olStability Soil and Distribution Stability Aggregate-Size ␮ Ͼ nsz.W lopooetestable the propose also We size. in m ´ 250 ϭ qe, .J aca .A abrel,R .Shlz n .M Isenhart M. T. and Schultz, C. R. Cambardella, A. C. Garcia, J. V. rquez,* 0 n SMaI and 40% ␮ stersl fcmlxin- complex of result the is ) h eemnto faggre- of determination The m). ϭ ϭ 5 n SMaI and 55% 8 ne rpe system. cropped under 18% ϭ ´ ´ ,Dp eFı de Dep. a, 1 ne 7-yr under 21% ia Venezuela; rida, ϭ 7 under 37% Published May,2004 ϭ ´ 74% sica, 725 eecsi grgt-iedsrbtosfrsiswith soils understand- for for also and histories distributions management different aggregate-size dif- contrasting in for used ferences been pressure has pretreatments 2000). air slaked al., internal et of Gale 1993a; buildup Elliott, Weak large and water. (Cambardella this inside with of sudden trapped the displaced of release is consequence rapidly a as that disrupted is are air aggregates pores the ; the in soil submerged air-dry pretreat- When is slaked disruption. minimal considerable the with causes contrast, escapes ment In air the disruption. and aggregate pores the in air buildup pressure not do aggregates misted because minimal disruption, produces pretreatment capillary-wetted This a sieving. The wet aggregates as before soil aggregates. the 1998) wetting slowly soil al., involves pretreatment et study Six to 1993a; means Elliott, and Cambardella tbemcogrgts hsi uncnb sdto used be This can distribution. turn stability un- aggregate-size and in the stable determine This of macroaggregates. amount the stable of ac- and more determination slaking a curate the yield should to pretreatments addition capillary-wetted in soil capillary-wetted the disruption. violent of lack the of a as un- from macroaggregates pretreatments stable differentiate comparison capillary-wetted to the means versus used (2000) slaked 1998). al. al., of et et Gale Six recently, 1993a; More Elliott, and (Elliott, Cambardella stability aggregate 1986; influence that factors the ing ailr-etdadsae rtetet Elot 1986; (Elliott, pretreatments slaked and used have capillary-wetted studies Several 1986). Rosenau, and (Kemper ae ae nterrssac osaig ntr,this turn, In slaking. to resistance their on based gates ne nsal n ntbemcogrgtsbecause macroaggregates unstable differ- and for stable account capil- in not ences the does contrast, pretreatment In biasing lary-wetted distribution. ac- fractions aggregate-size aggregate-size are smaller the that in aggregates for counted constituent smaller treatment slaking produces of the disruption during The aggregates macroaggregates aggregates. unstable soil with associated of C dynamics the and the the and by stability method soil wet-sieve assessing in errors significant causes aggre- unstable and stable between distinguish fully not stability and size their disruption. by unstable to and categorized stable aggregates of quantity soil the is sta- distribution aggregate-size bility The distributions. stability aggre- gate-size specify accurately the and from macroaggregates macroaggregates unstable stable the separate needed is clearly work to more contribution, important an resents n.Atog h ocpulzto fGl’ darep- idea Gale’s of conceptualization the Although slak- ing. to resistance their on based macroaggregates stable ae index. gates Abbreviations: h obndueo h ailr-etdadthe and capillary-wetted the of use combined The ehpteieta sn usqetsaigof slaking subsequent a using that hypothesize We xsigapoce o tdigsi grgtsdo aggregates soil studying for approaches Existing A,sal grgtsidx MI tbemacroaggre- stable SMaI, index; aggregates stable SAI, Reproduced from Soil Science Society of America Journal. Published by Soil Science Society of America. All copyrights reserved. i rigpu ailr eetn ofedcpct ls5% plus capacity field to rewetting capillary plus drying air ml arageae ewe 5 n 2000 and 250 between macroaggregates small macroaggregates large (i) fractions: ivn,altefatoswr vndida 70 at oven-dried were fractions the all fraction 250 sieving, mineral and the (iv) 53 and between microaggregates (iii) cplaywte)(i ta. 98.Bt usmlswere 4 at subsamples refrigerator Both a 1998). in overnight al., stored et (Six (capillary-wetted) ln h deo ahplot. each zone of buffer 0.50-m edge a the established along we effects edge eliminate To ln h it ftepo o ahcr a admylocated. randomly was core each for plot the of width the along rm7b 0mt 0b 0m olcrswr ae iha with taken were cm. cores 15 Soil of m. depth 20 a by to bit 10 steel-coring to were diam. m replicates 8-cm 20 three field by with within 7 block plots from complete Treatment experi- randomized replicates. The a field USA. was Iowa, design central mental north Keigley and in Branch, Dick watersheds Long and Branch Creek, Bear 1997) the (USDA-NRCS, in located filters are conservation practice dard rigfloe yrpdimrini ae sae)and (slaked) water in air immersion sieving: rapid wet by before applied followed are distribu- drying stability pretreatments air-dried aggregate-size Two of the analyze tion. subsamples to 100-g used Two were soil soil. sieved 8-mm air-dry ( ( brome grass smooth cool-season were the in sites species grass Dominant Iowa. ( Central switchgrass 7-yr a forest, virgatum riparian existing grass an cool-season filter, a were communities The communities. plant fterpra ln communities. plant riparian the of ( maize annual an under were fields crop The L.). umr ftemi hrceitc ftesisudreach under soils the of characteristics main the of summary a [ L.)–soybean ieTxnmccasfcto etr oa C Total Texture 21 21 33 25 loam loam classification Taxonomic loam sandy loam Endoaquolls Cumulic mesic superactive, mixed, fine-loamy, Endoaquolls Cumulic mesic superactive, mixed, fine-loamy, Haplaqudolls/ Cumulic mesic superactive, Endoaquolls mixed, Cumulic fine-loamy, mesic superactive, mixed, fine-loamy, system Cropped filter switchgrass 7-yr Dick Long forest Creek, riparian Bear Existing along filter grass properties Cool-season cm) (0–15 soil surface and sites field Site experimental the of characteristics General 1. Table different under stability detecting communities. new aggregate plant for the riparian and soil and stability in method soil new differences quantifying the for of (iii) suitability indices and the distribution, test stability to aggregate-size stability on soil for based indices simple distri- two develop stability to (ii) aggregate-size bution, determining for method for indices of development management. the to improving soil contribute and will associations dy- and the organomineral of of understanding namics our improve will information 726 hempratense Phleum grgtswr hsclysprtdi oraggregate-size four in separated physically were Aggregates ecletd1 oe e lt h xc oiotllocation horizontal exact the plot; per cores 10 collected We h betvso hssuywr:()t eeo a develop to (i) were: study this of objectives The grgt-iefatoswr sltdb e ivn using sieving wet by isolated were fractions Aggregate-size riparian different from 1997 September in soils collected We hs iainpatcmuiisaeeape ftestan- the of examples are communities plant riparian These rnhadKilyBac aesesi ot eta oa USA. Iowa, Central North in watersheds Branch Keigley and Branch . ufr n obfee o rpe rain area cropped row nonbuffered a and buffer, L.) AEIL N METHODS AND MATERIALS lcn max Glycine grgt Separations Aggregate .,adKnuk lers ( bluegrass Kentucky and L.), il Sampling Field L er]rtto.Tbe1shows 1 Table rotation. Merr.] (L) rmsinermis Bromus Ͻ 53 ␮ ielay ie,sprcie ei uui noqol loam Endoaquolls Cumulic mesic superactive, mixed, fine-loamy, Ͼ ndaee.Atrwet After diameter. in m 2000 Њ eoewtsieving. wet before C ␮ OLSI O.A.J,VL 8 A–UE2004 MAY–JUNE 68, VOL. J., AM. SOC. SCI. SOIL ndaee,(ii) diameter, in m ese) timothy Leysser), ␮ ␮ ndiameter, in m ndiameter, in m Њ ,ecp h arageae pnsaig( slaking upon macroaggregates the except C, o pratensis Poa e mays Zea Panicum u nsmlrfoigsi ape ihdfeetaonsof amounts different with samples soil footing similar on put ftesi seAppendix). (see soil the stability structural of and the distribution on aggregate effects of undesirable measurement introduces content sand. total L with g sieve (5 the on hexametaphosphate retained was total 53- that determined a The material was fraction. the fraction weighing size aggregate-size by the each each from of on fraction content retained size sand stable each sample small of of sub- content and amount sand by large total performed of the were tracting separation corrections the Sand for dried macroaggregates. used air capillary- later were the macroaggregates and by These obtained pretreatment. macroaggregates wetted small and large ramn r ersne yblclyi i.2. Fig. in symbolically represented are treatment below. given are determina- distribution stability the aggregate-size for the of needed aggregates tion considerations of Theoretical treatment size. slaking in pretreatments; proce- subsequent capillary-wetted This a and 1. and slaked Fig. the in involves shown dure is distribution stability gate-size ie ntrso hi ieadwtrsaiiy Therefore: stability. water and catego- size be their can of terms aggregates in soil rized that assumptions the involves .Tettlaon fageae olce nFato 2 Fraction in collected aggregates of amount total The 2. .Tettlaon fageae olce nFato 1 Fraction in collected aggregates of amount total The 1. pre- slaking the during pathways aggregate and Variables aggre- the determine to used procedure experimental The h eemnto fageaesz tblt distribution stability aggregate-size of determination The .Si grgtswt diameters with aggregates Soil 1. .Temnrlfato ( fraction mineral The 5. .Mcogrgtshv imtr agn ewe 3and 53 between ranging diameters have Microaggregates 4. .Mcogrgtsaeas aeoie ntrso their of terms in categorized also are Macroaggregates 3. macroaggre- large as categorized are Macroaggregates 2. ␮ eoesaig( slaking before ( tbesalmcogrgtsta eei rcin2 Fraction in the were origins, that different macroaggregates two small with but stable slaking survive that htrsle rmtefamnaino ntbelarge unstable of fragmentation the from resulted that r aee as labeled are Fato 4). (Fraction 250 n r aee ssal n hs htd o survive not do that those unstable. and as stable labeled are as labeled slak- are survive ing that Macroaggregates slaking. to resistance 2000 range and diameters 250 their between when macroaggregates small are and diameters their when gates r aee as labeled are aggregates. S cenuo ipra fteageae ihsodium with aggregates the of dispersal upon screen m lkdPeramn aibe Definition Variables Pretreatment Slaked 1 ); ␮ T Fato 3). (Fraction m 1S eemnto fteAggregate the of Determination ϭ ieSaiiyDistribution Size-Stability S 1 . T T S 1S 2 2S n h tbesalmacroaggregates small stable the and ) n r h ml macroaggregates small the are and , n r tbelremacroaggregates large stable are and Ϫ 1 ␮ .Sn orcini eddto needed is correction Sand ). Fato 2). (Fraction m ϩ ly a diameters has clay) Ͼ 250 G Ͼ 2 2000 ␮ ); r aee macro- labeled are m T 2S ␮ ϭ Fato 1) (Fraction m S 2 ϩ Ͼ Ͻ 250 G 53 gkg 2 . ␮ ␮ Ϫ m m 1 Reproduced from Soil Science Society of America Journal. Published by Soil Science Society of America. All copyrights reserved. e rtetetaerpeetdsmoial nFg 3. Fig. in symbolically represented are pretreatment ted i.1 xeietlpoeueue oass grgt-iesaiiydistribution. stability aggregate-size assess to used procedure Experimental 1. Fig. ailr-etdPeramn aibe Definition Variables Pretreatment Capillary-Wetted .Fnly h aeilcletdi rcin4i h mineral the is 4 Fraction in collected material the Finally, 4. .Tettlaon fageae olce nFato 1 Fraction in collected aggregates of amount total The 1. capillary-wet- the during pathways aggregate and Variables .Tettlaon fageae olce nFato 2 Fraction in collected aggregates of amount total The 2. .Tesmaino h muto grgtscollected aggregates of amount the of summation The 5. as labeled are 3 Fraction in collected aggregates The 3. three fraction in collected aggregates of amount total The 3. fraction arageae pnsaigfo l rvosfrac- previous ( all labeled are from tions, slaking upon macroaggregates pnsaigi ihrFatos1ado ,aelabeled are 2, and/or 1 Fractions either macroaggregates in unstable slaking of upon disruption the from sulted ( he eoesaig( fraction slaking in before were three that microaggregates origins; different ilb aee as labeled be will T rcinta eutdfo h rgetto funstable of fragmentation the from resulted that fraction grgts( aggregates r aee as labeled are ae ( gates ( htwsi rcin4bfr lkn ( slaking before 4 Fraction in was that rcin( fraction nec iefato fe lkn hudb qa othe to ( equal soil be of should amount slaking after total fraction size each in as labeled are G U 2S 1 3 ); ); ϩ T T T S 1CW 3S 2 3S T n h ntbesalmcogrgtsi this in macroaggregates small unstable the and ) ϭ U ϩ 4S ϭ 2 ihtodfeetoiis iea fraction mineral origins; different two with , ); S S T 3 S 1 T n h ntbelremacroaggregates large unstable the and ) T 4S T 1 ϩ . 2CW 3S 2CW ϩ G n hyaemcogrgtswt two with microaggregates are they and MA T U G n r h tbesalmacroaggre- small stable the are and ϭ 3 . 1CW ´ 1 4 . QE TA. GRGT IESAIIYDSRBTO N OLSTABILITY SOIL AND DISTRIBUTION SIZE-STABILITY AGGREGATE AL.: ET RQUEZ ); T S S 2 sdfrti study; this for used ) 3 n r h tbelremacro- large stable the are and T n irageae htre- that microaggregates and ) ϩ 4S U ϭ 2 un lkdteteti ersne yblclyi i.3. Fig. in symbolically represented is treatment slaked quent . S 4 ϩ G 4 . S 4 n mineral and ) T ϭ T 1S ϩ it hstetetfo h lkdtetet(i-r soil) (air-dry treatment slaked the from treatment this tiate ramn a efre ae ntepooo ugse by suggested protocol the on subsequent-slaked based The performed performed. was is treatment slaking drying second air this and wet-sieving, that capillary-wetting, empha- after to is and it subsamples that the size of set one to performed initially nFato n rmteusal arageae by macroaggregates unstable the from 2 and 1 Fraction in h SA(h lk et oass tblt ftesi when soil the of stability assess to test) slake (the USDA the muto grgtsta eandi h iv fe the after sieve the in remained that aggregates of amount diin ofloigteUD rtclw ege the weighed we protocol USDA the following to addition, usqetsaig h xetdotoefo h subse- the from outcome expected The slaking. subsequent efrigascn lkn ramn Fg ) ewl refer will differen- to We subsequent-slaked as 1). treatment (Fig. slaking second treatment this slaking second a performing xoe orpdwtig(SA 98 erc,19) In 1998). Herrick, 1998; (USDA, wetting rapid to exposed epyial eaae h muto tbemacroaggregates stable of amount the separated physically we .Tettlsmaino h mutcletdi each in collected amount the of summation total The 5. .Temnrlfato olce nFato slabeled is 4 Fraction in collected fraction mineral The 4. nadto otesae n ailr-etdpretreatment, capillary-wetted and slaked the to addition In as nti rcinbfr ao etraino Fractions of perturbation major before fraction this in eeult h hl muto ol( soil of amount whole study; the to equal be n 2; and 1 eoemjrprubto fFatos1ad2; and 1 Fractions of perturbation major before T iecasatrtecplaywte rtetetshould pretreatment capillary-wetted the after class size 3CW usqetSae aibe Definition Variables Subsequent-Slaked T 4CW n r h irageae htcudb found be could that microaggregates the are and T n stemnrlfato htcudb found be could that fraction mineral the is and T ϭ 3CW T 1CW ϭ S ϩ 3 . T 2CW ϩ T 3CW ϩ T 4CW . T sdfrthis for used ) T 4CW ϭ 727 S 4 . Reproduced from Soil Science Society of America Journal. Published by Soil Science Society of America. All copyrights reserved. i.3 eea ahasivle uigtecplaywte n h usqetsae treatments. subsequent-slaked the and capillary-wetted the during involved pathways General 3. Fig. pretreatment. slaking the during aggregates of Movement 2. Fig. 728 T te fractions, other aggregates, iSS ϭ oa muto grgtsi fraction in aggregates of amount total T i ϭ T oa muto grgtsi fraction in aggregates of amount total i ϭ oa muto grgtsi fraction in aggregates of amount total OLSI O.A.J,VL 8 A–UE2004 MAY–JUNE 68, VOL. J., AM. SOC. SCI. SOIL i fe usqetsae treatment. slaked subsequent after i , T iCW i and , ϭ S ϭ oa muto grgtsi fraction in aggregates of amount total T tbeaggregates, stable iS ϭ oa muto grgtsi fraction in aggregates of amount total U ϭ ntbeaggregates, unstable S i ϭ fe ailr-etdpretreatment capillary-wetted after tbeaggregates, stable i G fe slaking. after ϭ ani grgtsfrom aggregates in gain U ϭ unstable Reproduced from Soil Science Society of America Journal. Published by Soil Science Society of America. All copyrights reserved. r andi ieFato ,(q 1) ealthat Recall [1]). that (Eq. macroaggregates 2, Fraction small size stable in gained of are amount the and esavleta sascae ihtedfeec be- difference the with associated is that value a ders we h muto ntbesalmacroaggregates small unstable of amount the tween and pro- macroaggregates large treatment; capillary-wetted of treatment the by amount slaking duced total the the large by from stable of produced amount the macroaggregates subtracting by calculated be and eutfo h ailr-etdrsl nFato ren- 2 Fraction slaking in the result of capillary-wetted subtraction the The from two. result class size cannot for large- subtraction used unstable be this of slaking, disruption upon the macroaggregates of Because 2). (Table he unknowns three muto ntbesalmcogrgts hr are There macroaggregates. the small and unstable macroaggregates of small stable amount of calculation amount explicit the the impairs of information of lack The q 2 n 3.Tedlmao h unknowns the of dilemma The [3]. and [2] Eq. in2atrteiiilcplaywte rtetet e7y l wthrs,ad2 ne rpe system. cropped under 2% and switchgrass, old 7-yr We pretreatment. capillary-wetted initial Frac- the in after 2 collected tion aggregates the of subsequent-slaking q 2 n [3]. and [2] Eq. au fayo h he nnws n oeta can- potential One unknowns. is three didate the of any of value xeietltest Experimental iefato tbeageae ntbeageae Gains aggregates Unstable TS TS aggregates Stable checked be to Equations Totals Ͻ 53–250 250–2000 Ͼ ␮ fraction Size distribution; stability aggregate-size the determine to used equations the of Summary 2. Table of level significance sig- 1990). Institute, determine a SAS to (ANOVA-GLM, with test differences contrast used nificant We ANOVA. one-way m 53 2000 grgtsi fraction in aggregates h uniyo ntbelremcogrgtscan macroaggregates large unstable of quantity The treatment, h eemnto of determination The ifrne mn lnscmuiiswr etdby tested were communities plants among Differences 1 Fraction in collected aggregates of amount total The 1. aggregates, grgts n TG and aggregates, .Tettlaon fageae olce nFato 2 Fraction in collected aggregates of amount total The 2. T G h tbesalmcogrgts( macroaggregates as small stable labeled the are subsequent-slaked the after ( macroaggregates as large labeled stable be the will are subsequent-slaked the after 2S 2 ol eoecm fw ol eemn the determine could we if overcome be could eedfndaoeadte r erte in rewritten are they and above defined were S EUT N DISCUSSION AND RESULTS n ntbeMacroaggregates Unstable and 2 hc ol eetmtdb efriga performing by estimated be could which , T G ϭ eemnto fStable of Determination ϭ | T oa muto grgtsi fraction in aggregates of amount total ani grgtsfo te rcin,TS fractions, other from aggregates in gain S 2CW ttsia Analysis Statistical 2 , U ϭ Ϫ MA 2 i oa ani grgtsfo te fractions; other from aggregates in gain total and , T fe h lkdpretreatment, slaked the after ´ T S T QE TA. GRGT IESAIIYDSRBTO N OLSTABILITY SOIL AND DISTRIBUTION SIZE-STABILITY AGGREGATE AL.: ET RQUEZ 2CW 2S 2 2S and | ϭ ϭ ϭ G 2 | S S U U n nytoequations, two only and 2 2 2 2 ϩ ϩ sntstraightforward. not is T Ϫ 1SS S S S S G U 4 3 2 1 S G ϭ ϭ ϭ ϭ ϩ ϭ ϭ 2 2 2 ). 2 U T T T T TU S S | S 1 1 4 3 2SS 1S 1 1 CW CW ϩ ). ϩ ϭ S 2 T T T ϩ 2SS 1CW P S T n are and 3 Ͻ S 1SS Ϫ i ϩ 2 T fe h ailr-etdpretreatment. capillary-wetted the after T , S i 0.05 T SS and U 4 2CW [3] [2] [1] ϭ 1S ϭ 2 , , oa ecnaeo tbeageae,TU aggregates, stable of percentage total oa muto grgtsi fraction in aggregates of amount total h orfedsts(i.4.I umr,tedetermina- the summary, In 4). (Fig. sites field four the usqetsaigteteti h mlcthypothesis implicit the is treatment subsequent-slaking ae ( lated ae htsrie h lkn rtetet ( pretreatment, slaking the survived that gates etn n ifsv rcse rlntydispersion lengthy or ce- lengthy processes either diffusive is and particles menting air-dry between weaken- in and bonding slower strengthening the of is ing mechanism cohesion the in and found change soils They of content. rate water the and cohe- that time soil by studied affected who as (1984) sion supported Rosenau is and Kemper hypothesis by of This overnight. air-drying aggregates another the following capil- the treatment using separation does lary-wetted physical aggregates the unstable after and change stable not of amount the that calculate to of [3] determination the Upon with macroaggregates small stable treatment slaking the T of as result subsequent-slaking the from the this of differentiate result the label will ino h muto tbeadusal aggregates unstable and stable of amount the of tion after we aggregates Experimentally unstable pretreatment. and capillary-wetted stable changes major of the expect amount not the do we in result, a As processes. forest etdti yohssb efrigasubsequent-slak- a performing by hypothesis this tested on htteaon flremcogrgtsthat macroaggregates ( large subsequent-slaking of the amount survive the We pretreatment. that capillary-wetted found the Frac- following in collected 1 macroaggregates tion of samples 30 on ing ie ihdfeettpso eeain al presents 3 Table vegetation. of types different field with different sites four evaluated we distribution stability size rcin a infcnl nlecdb h vegetation ( macroaggregates the large of by amount The size influenced type. different significantly the was among fractions aggregates soil of distribution eut fe sn h prahotie bv.The above. outlined approach the using after results olwdteodr olsao grass cool-season order; the followed esngas 0 ne xsigrpra oet %under 3% forest, riparian existing under 10% grass, season novsteueo he ramnsa sotie in outlined is as treatments three of use the involves i.1adtesto qain umrzdi al 2. Table in summarized equations of set the and 1 Fig. al niaeta bu 7 ftesi r weight dry soil the of 17% about that indicate 3 Table a rsn ssal ag arageae ne cool- under macroaggregates large stable as present was T 2S n e on ntedtriainof determination the in point key One ots h ehdfrdtriigteaggregate- the determining for method the test To h euto hssbeun lkn hudb only be should slaking subsequent this of result The . ϭ oa ecnaeo olaggregates, soil of percentage total r Ͼ 2 TU TU ϭ U U switchgrass 2 1 .6 ihteaon flremacroaggre- large of amount the with 0.96) ϭ ϭ ϭ ϭ T T U TG 2CW 1CW 1 U ϩ ehdEvaluation Method Ϫ Ϫ 2 U and 2 T T 2SS 1S ϭ S G rpe ytm h eut in results The system. cropped ϭ 2 . tbeaggregates, stable S ϭ i 2 fe h usqetslaked subsequent the after ecnueE.[]and [2] Eq. use can we oa ecnaeo unstable of percentage total T 1SS T a ihycorre- highly was ) T 2SS Ͼ i S TG xsigriparian existing ϭ ϭ G G G 4 3 2 oa mutof amount total S ϭ ϭ ϭ ϭ S 2 U Tbe2). (Table , Ͼ G T T T 2 4S 3S 2S 2 ϭ sn the using 2000 ϩ Ϫ Ϫ Ϫ T unstable G T T T T 1S 4 3 2SS 3 2SS for ) CW CW ␮ ϩ 729 m) to G 4 Reproduced from Soil Science Society of America Journal. Published by Soil Science Society of America. All copyrights reserved. hr een infcn ifrne ntedsrbto of distribution the (53–250 in microaggregates differences significant no macroaggregates were There small of distribution (250–2000 the in ferences 3201. 3.)52(44 .a8.8 11.4 6.6 7.0b 9.3 3.6 5.2a TS 3.5a 11.6 11.0b 5.9 6.6a TS 4.1a 11.0b 5.0 11.0b 6.4a TS (99.5) 53.9 9.8b 3.4a (14.4) 5.2 (35.1) 18.0 ( correction. 11.0b (99.0) differences 7.0a sand 53.8 indicate without class soil size of same weight the dry within of TS letters grams (99.4) Different are (38.6) 48.3 ‡ parentheses 14.0 between Values † (10.1) (41.3) 6.6 22.4 14.6a Total Gains (38.3) 9.8b 14.5 Ͻ (99.4) 47.5 53–250 250–2000 (99.1) (28.6) 50.7 Ͼ 13.2 Unstable (16.8) (52.3) 6.4 20.3 Total (29.9) 14.0 14.6a‡ Ͻ (99.2) 50.4 53–250 250–2000 (99.5) (30.8) 53.5 Ͼ 10.0 Stable (14.4) (40.7) 7.0 21.5 Total (36.0) 18.1 Ͻ (99.0) 54.4 53–250 250–2000 (25.8) Subsequent-slaked Ͼ 12.9 (39.4) 19.6 Capillary-wetted Total Ͻ 53–250 250–2000 Slaked Ͼ ␮ fraction Size and 1997 from data pooled are Values sites. vegetation of types different four under distribution stability aggregate-size The 3. Table macroaggregates large of mass the between Relationship 4. Fig. 730 r egto olado adfe basis sand-free a on and soil of weight dry % m 31. 1.)72(.)72 8.1 6.4 21.3c 3.4 7.2b 19.6c 2.1c 2.1 4.8a 14.8b 2.8c 6.0b 9.5b 8.6a (7.2) 7.2 3.0a (42.8) 23.5 (15.3) 15.3 (5.5) 4.8 16.8a (3.8) 2.1 (45.5) 22.4 53 (11.2) 11.2 (6.0) 6.0 2000 (7.3) 2.8 (46.4) 24.3 53 (9.4) 9.4 (3.0) 3.0 2000 (18.3) 9.5 (46.1) 53 25.4 (5.1) 5.1 2000 (28.7)† 16.8 53 2000 nadto,co-esngassoe infcn dif- significant showed grass cool-season addition, In n nasn-rebasis. sand-free a on and ( treatment macroaggregates Ͼ h oa ecnaeo ntbeageae.T stettlgi nageae rmohrfractions. other from aggregates in gain total the is TG aggregates. unstable of percentage total the ifrne ( differences 98epesda ecnae fdywih fsi n nasn-rebasis sand-free a on and soil aggregates of weight dry of percentages as expressed 1998 2000 ␮ uniidb lkdperamn ( pretreatment slaked by quantified m ␮ T )cmae ihteohrvgtto types. vegetation other the with compared m) T 1ss P ϭ .Vle r xrse spretgso oldry soil of percentages as expressed are Values ). Ͻ TS Ͼ .5 ewe eeaintetet ihnsz lse.T stettlpretg fsal grgtsadT is TU and aggregates stable of percentage total the is TS classes. size within treatments vegetation between 0.05) 2000 ϩ TU. ␮ uniidb h subsequent-slaking the by quantified m ␮ )udrtevgtto types. vegetation the under m) ae rtetet grgt-iesaiiydistribution stability Aggregate-size pretreatments Water OLSI O.A.J,VL 8 A–UE2004 MAY–JUNE 68, VOL. J., AM. SOC. SCI. SOIL T 1s n tbelarge stable and ) xsigrpra forest riparian Existing P olsao grass Cool-season rpe system Cropped Ͻ -rswitchgrass 7-yr .5 codn otecnrs eaaintest. separation contrast the to according 0.05) olwdteodr rpe system cropped order; the followed ok ogtr rpigdcesdtelnt and length the this the by decreased under documented cropping clearly soils Long-term been in work. has macroaggregates system of small cropped reduction The and biomass. large microbial the supported of soil amount system 7-yr lowest cropped by the followed the and biomass, had switchgrass, Pickle microbial grass of addition, cool-season amount under In highest soil types. than that vegetation found biomass other (1999) root grass the fine cool-season of dead that any greater showed significantly paper being had study this the as in area research reported same Tufekcioglu the in by increased (1999) al. conducted and et Studies matter stability. organic soil aggregate more provide could the produce onstrated would grasses), (C3 highest grass such systems, cool-season root extensive as communities, with plant species that include existing which hypothesis the under These support grass. 19% cool-season results under switchgrass, 12% system, and old forest, cropped riparian 7-yr under under macroaggregates 23% present was unstable weight dry soil as the of 28% that indicate sults forest riparian existing ( macroaggregates unstable of amount The aso ieros n ologncmte eutn na 1980; in Oades, and resulting (Tisdall matter macroaggregates organic of soil reduction and roots, fine of mass abrel n lit,1992). Elliott, and Cambardella eeso arageain ans(93 dem- (1993) Haynes macroaggregation. of levels T T T T htasottr 5y)psue(3grasses) (C3 pasture (5-yr) short-term a that Ϯ ϭ ϭ ϭ ϭ ϭ ϭ ϭ ϭ . nec iefato.Dfeetltesindicate letters Different fraction. size each in 0.1 TS TS TS TS 55TU TU 25.5 TU 25.2 TU 31.7 41.4 ϩ ϩ ϩ ϩ TU TU TU TU ϭ ϭ ϭ ϭ 53.8 53.4 48.3 50.6 Ͼ olsao rs.Teere- These grass. cool-season T sttlpretg fsoil of percentage total is ϭ ϭ ϭ ϭ 31 TG 23.1b TG 18.9b 83 TG 28.3c TG 12.0a Ͼ switchgrass Ͼ 250 ϭ ϭ ϭ ϭ ␮ 22.3 18.6 28.3 13.9 m) ϭ Reproduced from Soil Science Society of America Journal. Published by Soil Science Society of America. All copyrights reserved. pnsaig ehv hw htmsedn results misleading material that of shown gains have as We slaking. slaking. interpreted upon upon fraction are same the values the from Negative in material as of interpreted mean loss are a values corresponding Positive capillary-wetted pretreatment. the the slaked in from value mean unstable pretreatment the the and on of clear based stable subtraction are a of indices of recent amount lack More macroaggregates. the the One is in stability. indices differentiation these soil quality. pro- in been assessing soil feature have common quantitatively that assessing indices for for the of posed factor some shows major 4 Table a is stability ae tbeAgeae:Kme 16)adUD (1998) USDA and (1966) Kemper (1950) Mazurak Aggregates: Stable Water Diameter: Mean Geometric enWih imtr MWD Diameter: Weight Mean tbeAgeae n tbeMcogrgtsIdx Ma Index: Macroaggregates Stable and Aggregates Stable irpinIdx DI Index: Disruption AI Index: Aggregation omlzdSaiiyIdx i ta.(2000) al. et Six Index: Stability Normalized stability. soil assessing for proposed Index indices of Summary 4. Table S( fsoil of WSA(% emnindi h nrdcinta olaggregate soil that introduction the in mentioned We DLS i (max) DL DLS NSI DL max DV i DVS ϭ ϭ ϭ ϭ ϭ max 1 Ͼ n {[( n egto r aggregates dry of weight [( 1 1 ne o olStability Soil for Index i P i Ϫ i GMD SMaI ͚ ͚ ϭ ϭ ϭ ϭ P 250 n n wih fdysoil dry of (weight i SAI 1 1 o i [( o ΂ [( Ϫ [(PW n 1 DL ϭ Ϫ ϭ n DL ␮ n i ͚ 2( ϭ P n ϩ ϭ m) DV ϭ S 100 max ϭ MA 1 ϩ p i DV P i ) o i 1) ) ΃ DVS j n i m j ͚ ´ exp ͚ 1) ϭ o ϩ ϭ Ϫ ϭ n n max j and QE TA. GRGT IESAIIYDSRBTO N OLSTABILITY SOIL AND DISTRIBUTION SIZE-STABILITY AGGREGATE AL.: ET RQUEZ Ϫ 2 ͚ Ϫ 1 j ϭ Ϫ 1 m ͚ ϭ Ϫ ΂ n [( 1 | Ϫ [( ϭ PW 100 1 ( ΄ ( IvnSenegne l (1991) al. et Steenbergen van DI [( S i P max n ͚ P [( n i ϭ n i ]DLS i i i o ͚ m 1 ϭ i ]DLS o n n ) ϩ ϩ w io Ϫ Ϫ 1 n DV and Ϫ ) x i ϩ ϩ i 1) 2( 1) log( ϩ w j S ϭ P ͚ Ϫ 1) i i 1) P n )] i i p Ϫ ؉ Ϫ | i ) i PW o 1 | sand) PW (max) x Ϫ Ϫ Ϫ ] ϩ Ϫ j j i ) ] ] ϭ Ͳ j T sand) i j S | S ( j ] ] Ϫ j o j P T i i ΃ S ͚ o n 1 ϭ and n ) j i j o 1 PW i w ͚ ϭ Ϫ n i 1 ϫ ΅ i i S o DVS | 100 i ] o ) Ϫ i ( P i Ϫ S i ) | } n a ae (1949) Bavel van stettlnme fageaesz classes. size aggregate of number total the is muto grgtsi fraction in aggregates of amount apewih nsz class size in weight sample a eutfo h rgetto fusal ag macroaggregates large unstable of slaking. fragmentation upon the from result can grgtssz ls fe opeedsuto ftewoesoil. whole the of disruption complete after class size aggregates lkn n ailr-etn,respectively. capillary-wetting, and slaking ayt aclt setegoercma imtridxfrvariables for index diameter mean geometric the definition). (see calculate to Easy adwt size with sand DVS possible. level disruption maximum the i to respect with Normalization G when Useful calculations. Extensive i. fraction size the in occurring weight sample total respectively. 250 o h ags iecas stettlnme fsz lse agrthan larger classes size of number total the is m class. size largest correction. the sand wetted for Total capillary subsequent-slake. and and Slaked pretreatments, distribution. size-stability on Based ee osbe ae nwih losses. weight on Based possible. level P lkdadcplaywte rtetet.Ol an r used. are gains Only pretreatments. capillary-wetted and Slaked ie adcnet omlzto ihrsett h aiu disruption maximum the to respect aggregate- with the Normalization for content. Correction sand sized pretreatments. capillary-wetted and Slaked ´ x grgtsadtettlwihe vrg fsi aggre- soil of average weighted stable total SAI of the the average and weighted define aggregates total We the between stability. ratio soil the as amount of quantifica- assessment the for metric and that a as tion is used be rationale can aggregates The stable of stability. soil al., assess to et Six 1991; al., 4). et (Table Steenbergen 2000) van 1966; Kemper, 1998; nor- 1949; the USDA, Bavel, and (van index index aggregation stability the malized as such diameter metrics elabo- weight and rate complex mean more to the aggregates water-stable as and such metrics simple from orsodn oFato 2. values Fraction these to between difference corresponding the using from emerge qe ta.(hspaper) (this al. et rquez i i ϭ and stema imtro ahsz fraction. size each of diameter mean the is h grgt-iesaiiydsrbto a eused be may distribution stability aggregate-size The evolved has index suitable a for search persistent The o h ags iecas PW class. size largest the for 1 ␮ max m. P steaslt aiu irpinvlefrsz class size for value disruption maximum absolute the is i0 S r h rprino oa apewih nsz class size in weight sample total of proportion the are j steaon fsal grgtsi fraction in aggregates stable of amount the is P p i 2 rmr adpril otn ihtesm iea the as size same the with content particle sand primary nageae fsize of aggregates in ϭ ;teeaentsal ml arageae that macroaggregates small stable not are there 0; Reference/Comments i pnsaigadcplaywtig respectively. capillary-wetting, and slaking upon j i pncapillary-wetting. upon n PW and i pnsaigadcplaywetting, capillary and slaking upon i ϭ S i and i0 o h mletsz class. size smallest the for 1 r h rprino total of proportion the are w S i i0 stepooto fthe of proportion the is r h rprin of proportions the are j . T j j ϭ stotal is i i . 1 upon 731 Reproduced from Soil Science Society of America Journal. Published by Soil Science Society of America. All copyrights reserved. etadw aesonta h muto stable of amount the that by shown overestimated is have macroaggregates pretreat- small we capillary-wetted and the the ment either or involves pretreatment aggregates water-stable slaked the determina- of the that tion is difference The (1998). (1966), USDA and Kemper by aggregates water-stable of definition grgtsidcsdfee nteodrcool-season order the macro- vegetation in stables four and grass differed the aggregates indices the across stable and aggregates trend the SAI Both clear The types. a vegetation. soils for of show indices types SMaI published four other with the [5] under and [4] Eq. in the of distribution the aggregates. about stable information partial only spretg tbeageae e nto r weight dry of soil. unit the per of aggregates stable percentage as Ͼ in n httecplaywte rtetetgives pretreatment capillary-wetted the frac- smaller that the and in for tions accounted are later that stituents ilrdsrbto fteusal arageaecon- macroaggregate unstable artifi- the an of produces redistribution pretreatment cial slaked the that shown olageae,E.[5]. Eq. aggregates, soil egtdaeaeo h muto tbemacroaggre- stable of ( amount gates the of average weighted fractions. size fraction of in and aggregates treatment) of capillary-wetted amount total the nteeequations these In S hsasrn esr fsi tblt.W lohave also We stability. soil and of distribution, measure aggregate strong a unstable thus of and assessment Three accurate stable an distribution. both get to stability needed are deter- aggregate-size treatments to enough the not shown are have mine pretreatments also two or We one pretreatment. that slaked the only ing rpe ytm3c1c4b7a07c2.57a 2.91a 2.79a 2.73a 0.71c 0.83c MWDcw 1.98a 1.46b 77a 83a MWDs 82a 76a WSAcw 46b 48b 67a 62a WSAs 18c 22c 56a 37b SMaI 36c 37c 74a† SAI 55b ( differences indicate column a within letters Different † system Cropped Switchgrass 7-yr forest riparian Existing grass Cool-season slaked of aggregates stable Treatments water (SMaI), index macroaggregates stable (SAI), index aggregates stable the for values Treatment 5. Table between aggregation in similarity The system. cropped of result the is system cropped the and switchgrass 7-yr [4]. Eq. aggregates, unstable and stable including gates 732 j 250 al oprstevle o h nie defined indices the for values the compares 5 Table qain[]cnb huh fa qiaett the to equivalent as of thought be can [5] Equation eas eieteSa stertobtenthe between ratio the as SMaI the define also We WA)adcplaywte WAw,ma egtdaee fsae MD)adcplaywte MDw ol ne four under soils (MWDcw) capillary-wetted and (MWDs) slaked sites. of vegetation diameter of weight types mean different (WSAcw), capillary-wetted and (WSAs) steaon fsal grgtsi fraction in aggregates stable of amount the is ␮ Ͼ Ͼ .Vle o oho hs nie r expressed are indices these of both for Values m. 250 xsigrpra forest riparian existing ␮ SMaI )adtettlwihe vrg fall of average weighted total the and m) SAI J ϭ m ϭ ϭ stettlnme fsz classes size of number total the is o h ags ieclass. size largest the for 1 m n j j ͚ ͚ ϭ ϭ n n j ͚ ϭ j 1 m 1 ͚ ϭ [( [( n 1 1 [( [( n n m n ϩ ϩ ϩ ϩ 1) 1) 1) 1) Ͼ n Ϫ Ϫ stettlnumber total the is Ϫ Ϫ -rswitchgrass 7-yr j j ] ] T j S j OLSI O.A.J,VL 8 A–UE2004 MAY–JUNE 68, VOL. J., AM. SOC. SCI. SOIL ] ] j j T S j j G P j Ͻ 2 fo the (from hnus- when .5 codn otecnrs test. contrast the to according 0.05) j . T [5] [4] j ϭ is %mm h auso ae-tbeageae sn h slaked the using aggregates biasing water-stable pretreatment. is of macroaggregates values unstable the and stable differentia- forest, of of lack riparian the tion that existing is point and key The grass respectively. cool-season for 19.4 ini osmercl(i ta. 00.Teequation The 2000). diameter al., weight et mean (Six distribu- nonsymmetrical aggregate-size is the tion when questionable is diameter weight index mean The vegetation. of types different respectively. system, cropped and switchgrass 7-yr for rtetetddntso n la rn costhe across trend clear any show not did pretreatment ini infcnl different; significantly is tion grgtsgvnb h grgt-iesaiiydistribu- stability macro- aggregate-size the stable by of given amount aggregates the While respectively. forest, Tbe3 o olsao rs n xsigriparian existing and grass cool-season for 3) (Table n o -rsicgasadcopdsse r not are system cropped and switchgrass different; significantly 7-yr for ing h muto grgts( aggregates of amount Similarly, the respectively. system, cropped and switchgrass ae tbeageae sn h ailr etdpre- wetted of capillary values the using the aggregates forest, stable riparian water for existing different and significantly cool-season are indices macroaggregates ytmwssal grgts ti ute neetn to interesting further is It aggregates. stable was system macroaggregates. ag- stable the of percentage higher a of much that note grgtswieol afo h egto stable of weight of the composed was of system cropped half the under only aggregates while macro- stable aggregates were grass cool-season the under gregates esngasadeitn iainfrs r o signifi- not are forest riparian existing and grass season amount the ( because aggregates is of This different. not are treatment cropped the under soil the of 36% stable only of while consisted aggregates grass cool-season weight the dry under the soil of the 75% of almost the that note to interesting atydifferent; cantly h mut fsal arageae ie ythe by given significantly different; not because macroaggregates are distribution is stable stability aggregate-size This of system. amounts cropped for the different and significantly switchgrass not 7-yr are pretreatment the using slaked aggregates water-stable and indices, aggregates etr h rata a rpe o ayyas tis It years. many to for used cropped was was of that that type area the grass) the and (C4 restore yr) grass (7 experiment warm-season the native of age young the h ae-tbeageae sn h capillary-wetted the using aggregates water-stable The lhuhtevle o tbeageae n stable and aggregates stable for values the Although h auso tbeageae n tbemacro- stable and aggregates stable of values The S 1 ϩ Ͼ S 250 S 2 1S seult 38ad1. o 7-yr for 13.1 and 13.8 to equal is MWD ␮ ϩ T )ta uvv lkn o cool- for slaking survive that m) 1S S ϩ 2S Ͼ ϭ T 250 seult 64ad31.0 and 36.4 to equal is S i ͚ 2S ϭ 1 n 1 ϩ seult 16ad24.6 and 21.6 to equal is x ␮ i w )ta uvvdslak- survived that m) S i 2 seult 14and 31.4 to equal is Reproduced from Soil Science Society of America Journal. Published by Soil Science Society of America. All copyrights reserved. inptwy o ntbemcogrgt constituents. macroaggregate unstable for pathways redistribu- tion different difference produce The can aggregates). composition structural bound in hyphae macroaggre- vs. (clay unstable gates of composition structural methods. but macroaggregates different sieving sam- unstable soil of wet amounts two by similar compare pretreat- with tem- we analysis ples slaked when room stability the down at gates break for air-drying would diameter suggested ment expect weight could (1984) mean We Rosenau the data. and that pretreatment slaked the diam- the using macro- weight eter and mean unstable the temperature of overestimating amount room thus, the con- aggregates, at by macroaggregate soils than unstable air-dry rather of stituents in redistribution slower the is determined mainly by is data pretreatment slaked storage. the macroaggre- diameter of using weight time unstable mean recog- with the increases Therefore, of (1984) constituents. not and gates drying redistribution Rosenau does upon favored and any pretreatment stable new capillary-wetted We Kemper to introduce due vegetation. effect the While, confounding of the that types of perature. extent different recall The the across using any trend show diameter clear not ag- weight did data mean stable pretreatment the capillary-wetted as sup- that the further fact remain is the will This by data. ported others aggregate-size pretreatment diameter could but slaked the weight the aggregates aggregates mean change using stable the stable turn, determines new that in distribution these that, con- of units macroaggregate unstable stituent Some aggre- of stable pro- stability. new redistribution hap- pretreatment yield a slaking this may the duces pores that did capillary Re- shown the Why have in 1990). We tained macroaggregates. pen? Kay, large and amount unstable the diam- (Pojasok to weight of sensitive mean is measurements pretreatment the slaked stability that the for observed eter From we 1986). 5 and Rosenau, 3 and Tables (Kemper size used broad, fairly are diameter five, fractions when weight pretreatment mean slaked the original for the overestimates also h grgts hrfr,smlstknfo h field the from taken samples Therefore, aggregates. the esne ElotadCmadla 91.Reproduc- 1991). Cambardella, and (Elliott personnel uin.I ape r ade aeul eoesieving before carefully handled are samples If butions. fsoae(epradRsnu 94.I a been has It 1984). time Rosenau, with and increases binding (Kemper and storage drying inorganic of upon of favored is precipitation agents However, mized. andi h ailr oe ardyn) lo reproduc- Also, drying). (air pores capillary the in tained ae otie ntecplayprs(i rig and drying) (air pores capillary the in contained water ugse hta nraei ufc cdt pndrying upon acidity surface in increase an that suggested ee a il nmlu e ivn eut.Differ- results. sieving wet anomalous yield common can a to level content moisture soil the adjusting without h e ivn edieotalo h rewtrcon- water free the of all out drive we before when sieving slaking wet upon the feasible more are results ible hnbfr h e ivn,w rv u l ftefree the wetting of all capillary out drive upon we sieving, feasible wet the more before when are results ible h il aaiypu %i ece Sxe l,1998). al., et (Six reached is 5% until plus water free capacity with field pores the capillary the fill slowly them otn nterpouiiiyo h eut smini- is results the of reproducibility the on content erdcbeee o aulmtosuigdifferent quite using are methods results manual normalized, for is even reproducible content water soil and nceia rpyia hrceitc,wihcnalter can which characteristics, physical changes or introduce particles may chemical and Air-drying in 1992). organic al., between et (Caron binding increases also ntm rsae a edt ifrne naggregate in differences to distri- aggregate-size lead in differences variations in can result that from space, stability resulting or contents, time water in soil in ences ivn svr estv oteiiilwtrcnetof content water initial the to sensitive very is sieving yardyn h ol h feto neeetwater antecedent of effect the soil, the air-drying By h iedsrbto fageae bandfo wet from obtained aggregates of distribution size The h fet fAtcdn ae Content Water Antecedent of Effects The MA ´ QE TA. GRGT IESAIIYDSRBTO N OLSTABILITY SOIL AND DISTRIBUTION SIZE-STABILITY AGGREGATE AL.: ET RQUEZ h ailr etddsrbto easmd i there from (i) amount slaked assumed: small a we the is distribution subtracting wetted of capillary effect the nullifying extent the the Studying of 2000). al., et (Six nullified onto is organic particles of adsorption inorganic increased and of agents precipitation binding the to distribution, due wetted aggregation increased slaked capillary the the of from subtraction the distribution is aggregates stable new of aggre- standardize to means a as samples soil perature Kemper Thus, process. lengthy diffusive or and processes cementing lengthy either is particles between bonding the weakening and strengthening of mechanism cohesion in change of rate the that is concluded also agents They binding inorganic of precipitation that nized tem- room at air-drying by minimized also is aggregates gregates. transient (hydration) aggregate rewetting soil upon unstable on become studies confound con- would water that free gates and water bound physically of moval fe h ailr-etdis capillary-wetted the after i-rigcudbcm ntbeand unstable upon become aggregates confounding could stable the air-drying new of transient minimization However, significant effect. a is there ifrn from different fsal n ntbeageae nfraction in aggregates respectively. unstable air-drying, and stable of fteaon fnwageae pnardyn and air-drying upon aggregates new of amount the If lkn ssmlrt h muto e grgtsupon aggregates new of amount the to similar is slaking i-rigadcplaywtigte ( then capillary-wetting and air-drying oetal ulf h feto i-rigdet the to due air-drying aggregates. of new of effect stabilization the can nullify distribution aggregate potentially rewetted the from slaked the aywte itiuinw obtain: we distribution capil- wetted the from lary slaked the subtracting By fractions. other i fageae nfraction in aggregates of i-rigaduo ailr-etd h oa amount total The capillary-wetted. upon and air-drying ml amount small pnardyn n pnsaigad(i hr sa is there (ii) and slaking upon and air-drying upon nefciewyt iiietecnonigeffect confounding the minimize to way effective An | | | | T T T T 4CW 3CW 2CW 1CW Ϫ Ϫ Ϫ Ϫ T T T T 4S 3S 2S 1S | | | | ␦ ␦ ϭ ϭ ϭ ϭ i * ϭ ϭ ϭ ϭ i fnwageae nfraction in aggregates new of ␦ ( | | | | | | | | i u u Ϫ Ϫ ␦ ( ( ( ( fnwsal grgtsi fraction in aggregates stable new of s s s s i * 2 1 4 3 2 1 g g Ϫ ϩ 4 3 ϩ␦ ϩ␦ ϩ␦ ϩ␦ ϶ ϩ ϩ g g ( ␦ i ␦ 2 stegi nageae from aggregates in gain the is 4 * ( ( 3 2 1 * * * i i .I ocuinsubtracting conclusion In ). 1 * ␦ ␦ ϩ ) ) fe h lkdis slaked the after T ϩ ϩ 4 * 3 * Ϫ␦ Ϫ Ϫ iCW ( Ϫ␦ Ϫ␦ ␦ u u ( ( 2 * 2 1 s s 1 and ) ) 4 ) 3 4 Ϫ␦ | 3 ) Ϫ Ϫ ϩ␦ ϩ␦ ) | | u ( ( ␦ 2 s s 4 i ) i * 3 2 1 ␦ | r h amount the are ϩ ϩ ϩ␦ ϩ␦ Ϫ␦ * i g ilbecome will g 4 3 ) 2 1 i ) ) ) | | ϩ | → i T i before g iS and 0 2 upon ) | and 733 Reproduced from Soil Science Society of America Journal. Published by Soil Science Society of America. All copyrights reserved. iesaiiydsrbto easmd i hr sasmall a is there amount (i) assumed: we distribution stability size pncplaywte n ii hr sasalamount small a aggregate stable is new there of (iii) and capillary-wetted upon → uniidb lkdperamn ( pretreatment macroaggregates slaked large by of quantified mass the between found 0.96) n ntbeageae osntcag fe h physi- stable the after of change amount not does C). the aggregates unstable that total and loam hypothesis (2.1–3.3% (sandy implicit content the texture matter Since solid organic of and repre- range study loam) narrow this very in a considered sent soils four the However, ␦ fsal n ntbeageae nfraction in aggregates unstable and stable of i-rig respectively. air-drying, arageae uniidb h subsequent-slaking ( the treatment by quantified macroaggregates un i rigadpirtesbeun slaking. subsequent the prior and drying air quent te rcin.Fo al ,w get: we 2, Table From fractions. other eedn nteetn ftesaiiaino new of stabilization of values the the estimated of on particularly over extent and or unstable aggregates the under aggregates, on are stable gains depending of the and amount aggregates the that Note yardyn h olsamples. soil stabilized the were air-drying that by aggregates new including fractions hsi h aei u td.Tehg orlto ( correlation high The study. our in case the is this i-rigaduo lkn,(i hr sasalamount small a is there ␦ (ii) slaking, upon and air-drying respectively. fraction in n ntbeageae ol edn when done be could aggregates unstable and i.5 estvt of Sensitivity 5. Fig. and 734 ″ i * i and 0 oee,ago siaino h muto stable of amount the of estimation good a However, . nlzn h feto i rigo h grgt-clseparation, cal aggregate- the on drying air of effect the Analyzing h oa muto sand. of amount total the fnwageae nfraction in aggregates new of U G G U i S S r h muto tbeadusal aggregates unstable and stable of amount the are 4 2 3 1 1 ␦ ␦ ϭ ϭ ϭ ϭ ϭ ″ i i i fnwsal grgtsi fraction in aggregates stable new of → g g s s T u pnpyia eaaino h aggregates, the of separation physical upon 3 1 4 2 1 1SS .Ide h eut nFg ugs that suggest 4 Fig. in results the Indeed 0. G ϩ ϩ ϩ ϩ ϩ ugs that suggest ) i ( ( ( ( stegi nageae rmother from aggregates in gain the is f ( ␦ ␦ ␦ ␦ ␦ ocagsi TS/(TS in changes to 1 3 * 4 2 * 1 * ); ); Ϫ␦ Ϫ␦ Ϫ␦ S S 2 4 g 4 * ␦ ϭ ϭ 2 ″ ) i 1 * i ); ); stegi nageae from aggregates in gain the is s nfraction in s 2 G U 4 ϩ ϩ ␦ 2 3 s i * ϭ ϭ ( i ( ␦ ␦ and and i 4 * u g 2 * pnardyn n ed ob oet ulf rt nwteetn fthe of extent the know to or nullify to done be to needs and air-drying upon ) T 3 2 ϩ␦ ϩ ϩ 1S ϩ u ␦ n tbelarge stable and ) i U safnto of function a as TU) i OLSI O.A.J,VL 8 A–UE2004 MAY–JUNE 68, VOL. J., AM. SOC. SCI. SOIL i ( pntesubse- the upon ( → r h amount the are 2 ″ ␦ Ϫ␦ ); 3 and 0 Ϫ␦ 2 ″ ␦ ) i , ␦ 3 * i ␦ i * ); i * ␦ i before and i and , ″ pnteasmto a oncsayb ai o other for valid be necessary no may assumption the upon r → 2 ϭ 0. S ␦ i i h rpsdmto,i hudb one u that out pointed be should it method, proposed the ais ngnrl adcudb ntredifferent three aggregates, in stable within be is that sand could (i) soil: sand the for in dy- forms essential general, and is In composition sand aggregate namics. of on amount results the interpreting for correction application the a that of recognized widely is it aggregates of erdsrbtd n ii adta sfree. is that sand (iii) and easily can redistributed, and aggregates be unstable within is that sand (ii) ( macroaggregates large stable of iainforest riparian hntreqatr ftewih fsal aggregates stable of weight the of quarters three than htteasmto a o eesrl evldfor valid management. be out type/soil necessarily soil pointed of not be combinations may should other assumption It the C). matter that organic total and soils (2.1–3.3% loam) range four loam, content narrow (sandy very the texture a solid correct, represent of study is this overnight in considered aggregates the the of air-drying using another separation following aggregates physical treatment unstable the capillary-wetted and after stable change not of does amount the that esis the communities. of vegetation aeration various the and under soils capacity surface potential for implications the strong has macro- information was This system aggregates. cropped the under aggregates stable s,4%udr7y wthrs n 36% and switchgrass 7-yr under 40% est, nie eehge nsraesisudrcool-season under soils surface in higher were indices fvgtto nsi tblt.TeSIadteSMaI the and SAI effects The the stability. to soil sensitive on highly vegetation and of suitable are indices tdwt h yaiso ologncmte n soil and matter organic soil of associ- dynamics closely the are with mechanisms ated two These aggregates. iedsrbto n h muto tbeadunstable and stable of amount the and distribution size arageae.Teaon n itiuino stable of distribution and amount The macroaggregates. arageae hl nyhl ftewih fthe of weight the of half only while macroaggregates ne h olsao rs osse fsal large stable of consisted grass cool-season the under ult.Tesal grgt n tbemacroaggregate stable and aggregate stable The quality. niao ftesaiiainaddsaiiaino soil of destabilization and stabilization the of indicator n ntbeageae ntesi a eue san as used be can soil the in aggregates unstable and rs hnayo h te ramns hs ol sam- soils These treatments. other the of any than grass ftesi olwdb 5 ne xsigrpra for- riparian existing under weight 55% by dry followed the of soil of average the of 74%, weighted representing the aggregates with stable aggregated well are ples en o nacrt eemnto fteaggregate- the of determination accurate an for means h tnadcplaywte rtetetpoie the provides pretreatment capillary-wetted standard the lydfee nteodrco-esngrass cool-season order the in differed ally obntoso oltp/olmngmn.Mr work More management. type/soil soil of combinations tae htteueo usqetsaigfollowing slaking subsequent a of use the that strated ofudn fetof effect confounding ytm h laetdfeec a ntettlamount total the in was difference clearest The system. lhuhsn ly asv oei h formation the in role passive a plays sand Although lhuhterslsi i.4idct httehypoth- the that indicate 4 Fig. in results the Although edvlpdatertclfaeokta demon- that framework theoretical a developed We Ͼ h adCorrection? Sand Why -rswitchgrass 7-yr ␦ i * CONCLUSIONS and APPENDIX ␦ ␦ i , i ␦ → i * and , and 0 ϭ Ͼ 2000 rpe ytm More system. cropped ␦ i ″ ␦ . i ″ → ␮ ) hc gener- which m), ,i rtclfor critical is 0, ne cropped under Ͼ existing Reproduced from Soil Science Society of America Journal. Published by Soil Science Society of America. All copyrights reserved. abrel,CA,adET lit.19.Priuaesi organic- soil Particulate 1992. Elliott. E.T. and for C.A., methods Cambardella, of comparison A 1993. Bruce. R.R. and M.H., Beare, ut nageaecmoiinaddynamics. and composition aggregate re- interpreting on sand correctly sults for for accounting essential becomes for content procedures of application SMaI. The the of values between would differences correction TS/(TS significant mask sand the ratio without stability the soil studying the in of could because sensitivity changes correction the results real limits sand sand the of the of amount using total interpretation not the that TS/(TS mislead 5 in ratio Fig. unit one the from of of change relative value a produce the in units ␺ Sand If of values the shows 5 Figure of amount total the on dependent Sand strongly sand is and [7] diameters with aggregates. sand the free to and similar aggregates stable Sand within that Note aggregates. Sand and aggre- aggregates. stable unstable of of Sand amount amount total the total is TU the and is gates, TS equation this In in shown losing as [6]. nomenclature without Eq. the and redefined simplicity we For generality, correction. and the sand correction on the sand soil whole the the used out We in SAI. sand the of sensitivity amount the fraction of impact microaggregate-size ( fractions the aggregate-sized in C ( produces of sand’ ‘loose of dispersion redistribution The El- 1986). 1993b; liott, Elliott, effect and sand’ Cambardella free ‘loose of 1996; so-called (Christensen, were redistribution the produces that aggregates The sieving) the of (e.g., sand aggregate. separation physical of any the following sand particles within and not that and sand) sand of fine (proba- macroaggregates particles bly of destruction origins: the two from result have can sand accumulated particles The diameters. similar of sand mulate Ͻ niomna fet nsi tutr.Goem 56:87–104. Geoderma structure. soil determining on for effects Implications environmental aggregates: water-stable measuring uigfatoain grgt-iecasswl accu- will classes aggregate-size fractionation, During h sensitivity The seult .5 hsmasta hneo four of change a that means This 0.25. to equal is 250 hl Soil Whole ␮ hl Soil Whole )adteercmn fca n iti macro- in silt and clay of enrichment the and m) tbeAggregates Stable hl Soil Whole x f stettlaon fsn ntewoesoil, whole the in sand of amount total the is ϭ ϭ ␺ϭ ϭ TS TS . TS .,te rmE.[]adfo i.5 Fig. from and [7] Eq. from then 0.5, ␺ ץ ץ TS ϩ ϩ x f REFERENCES of ϩ stesn soitdwt stable with associated sand the is ϭ MA TU TU f Sand ´ (1 QE TA. 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