Shrinkage properties of different managed Andisols as function of aggregate scale

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1 Dörner et l. / Agro Sur 41(1): 1-9, 2013 DOI:1206/grosur.2013.v41n1-01 Shrinkge properties of different mnged Andisols s function of ggregte scle Ls propieddes de contrcción de Andisoles jo distinto mnejo en función de l escl de los gregdos Dörner, J. *,, Dec, D.,, Sáez, C., Peng, X. c, Ivelic-Sáez, J., Zúñig, F.,d, Seguel, O. e Horn, R.,f Instituto de Ingenierí Agrri y Suelos, Universidd Austrl de Chile, Csill 567, Vldivi, Chile. Centro de Investigción en Suelos Volcánicos, Universidd Austrl de Chile. c Institute of Soil Science, Chinese Acdemy of Sciences, Nnjing, , P. R. Chin. d Doctordo en Ciencis Agrris, Universidd Austrl de Chile. e Deprtmento de Ingenierí y Suelos, Fcultd de Ciencis Agronómics, Universidd de Chile. f Institute of Plnt Nutrition nd Soil Science, Christin Alrechts University zu Kiel, Germny. Dedicdo en Memori del Profesor Roerto McDonld H. ( ), Instituto de Ingenierí Agrri y Suelos, Fcultd de Ciencis Agrris, Universidd Austrl de Chile. A R T I C L E I N F O A B S T R A C T Keywords: Volcnic soils Soil porosity Soil shrinkge Soil ggregtes Originl Reserch Article, Soil Science *Corresponding uthor: José Dörner F. E-mil ddress: josedorner@uch.cl Running tittle: Aggregte scle dependent shrinkge of volcnic sh soils Andisols cover pproximtely 50-60% of the rle lnd in The high porosity of volcnic soils chnges continuously due to mechnicl nd hydrulic stresses, which cn led to n increse of drought vulnerility in crops, even though precipittion exceeds 2,000 mm nnully. The im of this work ws to descrie the shrinkge ehviour of volcnic soils s function of lnd use nd ggregte scle. To descrie the effect of different lnd uses (Ntive Forest, 1 nd 50 yers old grsslnd) on the shrinkge ehviour of n Andisol t different scles, undistured soil smples (230 cm 3 ) nd ggregtes (etween 2 nd 20 cm 3 ) were collected t 5, 20 nd 40 cm depth. The weight nd deformtion of ggregtes nd undistured soil smples were registered t different wter contents. The ggregte shrinkge ws mesured using the Srn resin technique. The coefficients of liner extensiility (COLE) nd pore shrinkge index (PSI) were used to chrcterize the shrinkge ehviour. The intensifiction of the lnd use induced decrese in the totl porosity (TP) nd totl PSI mesured t 5 cm depth: TP y 7% nd PSI y 38% from NF to P50. This soil deformtion occurred not only due to soil compction ut lso s consequence of n intense drying. When lnd use chnges from ntive forest to psture, soils dry out more intensively, leding to smller shrinkge properties, e.g. COLE decresed s result of the incresing ulk density, which is lso relted to the mount of llophne. The smller ggregtes presented higher ulk densities thn soil cores. Finlly, significnt scling reltionships were not oserved for initil soil volume nd COLE, therefore, further conceptul nd experimentl development re required to understnd these scling effects. RESUMEN Los Andisoles curen proximdmente el 50-60% de los suelos rles en Chile. L lt porosidd de los suelos volcánicos cmi continumente, deido estreses mecánicos e hidráulicos, que pueden conducir un umento de l vulnerilidd l sequí en cultivos, pesr de que l precipitción excede mm nules. El ojetivo de este trjo fue descriir el comportmiento de contrcción de los suelos volcánicos en función del uso del suelo y de l escl de muestreo. Pr descriir el efecto de los diferentes usos de suelo (osque ntivo, prders de 1 y 50 ños) sore el comportmiento de contrcción de un Andisol diferentes escls, se recolectron muestrs de suelo no disturds (230 cm 3 ) y gregdos (entre 2 y 20 cm 3 ) profundiddes de 5, 20 y 40 cm. L ms y l deformción de los gregdos y ls muestrs de suelo se registrron diferentes contenidos de gu. L contrcción de los gregdos se midió usndo l técnic de resin Srn. Pr crcterizr l contrcción se determinó el coeficiente de extensiilidd linel (COLE) y el índice de contrcción de los poros (PSI). L intensificción del uso del suelo induce un disminución de l porosidd totl (TP) y del PSI registrdo 5 cm de profundidd: TP en un 7% y PSI en un 38% de NF P50. Est deformción del suelo se produjo no sólo deido l compctción del suelo sino tmién como consecuenci de un secdo intenso. Con el cmio de uso de suelo de osque ntivo prders, los suelos se secn más intensmente, lo que redujo l cpcidd de contrcción, p.ej. COLE disminuyó con el umento de l densidd prente, lo que está tmién relciondo con l cntidd de rcills lófns. Los gregdos más pequeños presentn densidd prente más lt que l mtriz de suelo. Finlmente, no se oservron relciones de escl significtivs pr el volumen inicil de suelo y COLE, por lo tnto, se requiere un myor desrrollo conceptul y experimentl pr entender el efecto de escl. Ciencis del Suelo 1

2 Dörner et l. / Agro Sur 41(1): 1-9, 2013 INTRODUCTION Volcnic sh soils re of gret importnce in southern Chile, since they cover etween 50-60% of the rle lnd in this country (5.4 million h, Besoin, 1985) n owing to their prticulr properties, re very productive (Soil Survey Stff, 2010). The development of griculture leds to n intensifiction of lnd use, which cn induce degrdtion of soil structure in volcnic soils due to excessive trffic nd lost of soil orgnic mtter (Ellies et l., 2000; Toón et l., 2010). The sme is lso true if these soils dry out intensely ecuse, due to its shrinkge properties (Dörner et l., 2010), the soil contrction lso results in soil deformtion (Dorel et l., 2000; Gry nd Allrock, 2002; Brtoli et l., 2007). These volumetric chnges in the soil due to externl (e.g. tillge trctor) nd internl (e.g. wter menisci force) stresses modify pore size distriution, chnge wter holding cpcity, nd increse the mount of corse pores s consequence of crck formtion (Horn nd Bumgrtl, 2002). Thus, the mgnitude of soil deformtion depends on oth the soil mechnicl strength (precompression stress) nd the hydrulic stress (preshrinkge stress) (Bumgrtl nd Köck, 2004), showing tht the stress level cn e loded or drined without further irreversile deformtion (Horn nd Bumgrtl, 2002). When soil is continuously exposed to dryness, four shrinkge stges cn e defined from the shrinkge curve. The stges of the curve, which compre the void rtio (e) responses to moisture rtios (ϑ), re defined s structurl, proportionl, residul nd zero shrinkge phses from sturtion to complete dry condition (Brudeu et l., 1999; Peng nd Horn, 2005). In the first phse, the structure-dependent pores nd iopores re emptied without significnt reduction in soil volume, llowing ir to enter lrge pores (Cornelis et l., 2006). In the second phse, the proportionl shrinkge is defined s the decrese in wter volume equlling the decrese in ulk soil volume (McGrry nd Mlfnt, 1987). In the third phse, ir enters into the previous wter sturted intr-ggregte pores nd further decrese in wter upon drying exceeds the volume chnge of the ggregtes (Cornelis et l., 2006). In the fourth stge, soil prticles hve reched their densest configurtion nd the volume of the ggregtes remins unltered s the wter volume further decreses (Bronswijk, 1991). The shrinkge of soils s function of ggregte scle ws previously investigted in different Europen Andisols (Brtoli et l., 2007). They found scling reltionships etween finl shrinkge nd initil totl soil volume, i.e. the smller the smpling size, the greter ws the shrinkge, scriing this reltionship to greter men rte of wter loss of soil clods thn soil volumes. Exceptions were the most porous Andisols horizons rich in Al-humus, i.e. the clods shrunk less thn the soil core counterprts. These results showed tht further investigtions re needed to understnd the scling reltionships, which cn e relevnt in Chilen volcnic sh soils, since it is well known tht Andisols exhiit very specil nturl properties such s vrile chrge, low ulk density, lrge volume of pores t different wter tensions, high hydrulic conductivity, the formtion of stle soil ggregtes nd gret shrinkge cpcity (Ellies, 1988; Shoji et l., 1993; Ellies et l., 1997; Dorel et l., 2000; Brtoli et l., 2007). The soil deformtion of Chilen Andisols s function of mechnicl stresses hs een documented (e.g. Ellies, 1988; Ellies et l., 2000; Dörner et l., 2009; Dörner et l., 2011). On the other hnd, results relted to the pore dynmics in ggregted eds due to wetting-drying cycles of low intensity hve een reported (Seguel nd Horn, 2006). However, there is lck of informtion out the mgnitude of the deformtion of different mnged Andisols s consequence of hydrulic stresses, oth t soil core nd ggregte scle. Therefore, the im of this work ws to descrie the shrinkge ehviour of volcnic soils s function of lnd use nd the scle. MATERIAL AND METHODS Smpling collection The smpling took plce t the end of Octoer 2007 when the soil reched field cpcity. Distured nd undistured soil smples (ggregtes nd cores) were collected t 5, 20, nd 40 cm depth t the three lnd uses of Ntive Forest (NF), pririe used for permnent psture during the lst 50 yers (P50) nd nother seeded in Mrch 2007 (P1) fter previous permnent psture. The soil cores (7 replictes for ech soils nd depth) were smpled in metl cylinders (230 cm 3 ; h: 5.6 nd d: 7.2cm). The smples were covered with plstic cps to protect the soil from mechnicl disturnces nd evportion. The soil ggregtes were crefully collected from NF nd P1 in plstic oxes to void wter evportion nd mechnicl disturnce (lthough ggregtes from P50 were collected, they were not mesured due to mechnicl disturnces nd soil shrinkge). Lortory determintions The wter retention curve (WRC), pore-size distriution nd soil shrinkge were mesured from undistured smples (7 replictes per horizon). For the determintion of WRC, the sturted smples were drined t decresing wter potentil vlues ( 10, -20, -30, -60, -150, -330, -500 nd -15,000 hp). In order to descrie the shrinkge ehviour t wter potentils lower thn -500 hp, smples were shifted to ir-dry conditions (20 ± 2 C) for 14 dys. During this period, the wter content nd verticl deformtion (mesu- 2 Ciencis del Suelo

3 Aggregte scle dependent shrinkge of volcnic sh soils red in 7 points t ech soil smple) were recorded 1, 7 nd 14 dys fter the eginning of dehydrtion with n electronic lnce nd cliper guge (0.05mm ccurcy), respectively. The undistured smples were then stepwise oven dried t 30, 60, nd 105 C. Aggregte shrinkge (8 replictes per horizon) ws mesured using the Srn resin technique. Soil ggregtes (etween 2 nd 20 cm 3 volume) were pending in cotton slings, then put on moist filter pper nd sturted y cpillrity. After sturtion ws reched, soil ggregtes were coted with Srn resin. After the Srn ws ir dried, the coted ggregtes were weighted nd their volumes were mesured following Archimedes principle (Gry nd Allrock, 2002). The determintion of weight nd volume were repeted t intervls of 6h, 12h, 24h nd 48h until constnt weight ws reched when they were dried t 30 C. To determine the ulk density of soil ggregtes, they were dried in the oven t 105 C for 24 hours. Clcultions Soil shrinkge curves To chrcterize the shrinkge ehviour the void (e) nd moisture (ϑ) rtios were used, which re defined s: (1) (2) where V f, V w nd V s re the volumes of pores, wter nd soil, respectively. Since only the verticl deformtion ws mesured, we ssumed tht n isotropic shrinkge occurred. We used modified vn Genuchten eqution (Peng nd Horn, 2005) to fit the shrinkge curve: (3) where χ, p nd q re dimensionless fitting prmeters. Prmeter p in Eqution (3) is lwys positive vlue. e s nd e r re the sturted nd residul void rtios, respectively, which cn e otined either y mesurements or y fitting. In this work, we used the mesured dt. ϑ s is the sturted moisture rtio. The chrcteristic shrinkge phses cn e determined mthemticlly fter following the method proposed y Peng nd Horn (2005). Soil shrinkge indexes ee = VV ff VV ss [mm 3 /mm 3 ] θθ = VV ww VV ss [mm 3 /mm 3 ] ee ss ee rr ee(θθ) = ee rr + [1 + (χχχχ) pp ] qq 0 θθ θθ ss The shrinkge cpcity ws defined y the pore shrinkge index (PSI), which reltes the shrinkge volume of the soil (ΔV t ) to the drined wter-filled pore volume (ΔV p ) s follows: (4) The PSI ws defined for wcp (wide corse pores, >50µm), ncp (nrrow corse pores, 50-10µm) nd MP+FP (medium plus fine pores, <10µm) of the soil cores. The coefficient of liner extensiility, which defines the one-dimensionl vrition of soils from wet until dry conditions (Grossmn et l., 1968), ws used y mny uthors (Gry nd Allrock, 2002; Peng et l., 2007) to quntify the shrinkge mgnitude. We define the coefficient of liner extensiility for soil cores (CO- LE SC ) s follows: (5) where, L 0 nd L 105 C re the length of the smple t sturtion nd fter oven drying t 105 C, respectively. To define the COLE of soil ggregtes we clculte the equivlent dimeter of n irregulr ggregte (d) defined y: (6) where m is the mss [g] of the ggregte nd d B the ulk density [g/cm 3 ]. The eqution gives the equivlent dimeter of sphere hving the sme mss nd density s the tested ggregte. Therefore, we define the coefficient of liner extensiility for ggregtes (COLE SA ) s follows: Sttisticl nlysis (7) In order to test the effect of the lnd use on structure dependent properties, sttisticl nlysis ws performed y nlysis of vrince. The differences of mens were ssessed y the Tukey-test (P 0.01). RESULTS PPPPPP = VV tt VV pp [mm 3 /mm 3 ] CCCCCCCC SSSS = LL 0 LL 105 CC LL 105 CC dd = [ 6mm 1 3 ] [cccc] ππ dd BB CCCCCCCC SSSS = dd 0 dd 105 CC dd 105 CC Generl properties of the soil [ ] [ ] The high orgnic cron concentrtion, high cly nd llophne contents, nd lrge pore volume re typicl chrcteristics of volcnic soils nd re defined s the ndic properties (Tle 1 nd 2). The orgnic cron concentrtion nd pore volume decresed with the lnd use from NF to P1 nd then to P50, especilly in the top 5cm lyers. The mount of llophne incresed Ciencis del Suelo 3

4 Dörner et l. / Agro Sur 41(1): 1-9, 2013 Tle 1. Generl properties of studied soils. Cudro 1. Propieddes generles del suelo. Site Depth Corg. Snd Silt Cly Alloph. d dp VR [cm] [%] [Mg/m 3 ]---- [m 3 /m 3 ] NF P P Different lowercse letters etween smples collected on the sme depth ut different lnd use indicte significnt differences (P 0.01). (Corg.= Orgnic cron, Alloph.= Allophne, d= ulk density, dp= prticle density, VR= void rtio). Tle 2. Totl porosity (TP) nd pore size distriution s function of lnd use nd soil depth. Cudro 2. Poros totles (PT) y distriución del tmño de poros en función del uso del suelo y profundidd. Site Depth [cm] wcp (>50µm) [%] ncp (50-10µm) [%] MP+FP (<10µm) [%] TP [%] NF P c P c Different lowercse letters etween smples collected on the sme depth ut different lnd use indicte significnt differences (P 0.01). with depth ffecting the ulk density, especilly in P50 nd P1. The decrese in pore volume (TP) due to lnd use chnge ws lso oserved for corse pores. On the other hnd, the mount of medium plus fine pores remins constnt etween NF nd P1 nd slightly incresed from NF to P50 (Tle 2). A detiled description of mechnicl properties nd pore functions of these soils cn e found in Dörner et l. (2009). Effect of lnd use on shrinkge ehviour The soils, independent of the lnd use, shrunk. Two shrinkge phses cn e well identified in Figure 1: structurl nd norml shrinkge. The residul nd zero shrinkge were not clerly oserved. NF presented wider rnge of shrinkge thn the other two lnd uses in which the soil t P50 presented the shortest rnge of shrinkge. The shrinkge dt ws fitted with Peng nd Horn s model (2005) well with high coefficient reltion (r >0.99). With this model, we defined the trnsition point from structurl shrinkge to proportionl shrinkge y the wet-side mximum curvture point (ϑ shw, e shw ). The volume chnge (e s e shw ) during the structure dependent shrinkge ws lso clculted. The shrinkge prmeters were listed in Tle 3. Of the entire shrinkge, the structure shrinkge phse ecme nrrower nd the slope t the inflection point decresed grdully with the incresing intensity of lnd use from NF, P1 to P50. Such lnd use-dependent shrinkge ws clerly oserved in the top 20 cm, ut t 40 cm these oserved difference disppered. Especilly for the top 5 cm in P50, the structurl pores were completed compcted due to the long-term cttle treding. From the fitted model, we could not find the 4 Ciencis del Suelo

5 Aggregte scle dependent shrinkge of volcnic sh soils structurl phse due to its liner shrinkge ehviour. If we compred the three depths, the 40 cm depth soil showed lrgest void rtio due to the higher mount of llophne (Tle 1) ut lso s consequence of the light mechnicl nd hydrulic stresses in the pst. The rnge of structurl shrinkge incresed with incresing soil depth for ech lnd use. The trend is more pronounced in pstures thn in ntive forests. At the 40 cm depth, the soil deformtion presented well-defined chnge etween the structurl nd proportionl shrinkge, which strted with lower moisture rtios (lso pf vlues) in NF thn P1 nd P50. Effect of lnd use on shrinkge cpcity of soil pores The pore shrinkge index (PSI) vried from 0.19 to 0.39 for the totl pores (TP) in the three lnd uses (Figure 2). PSI of the totl pores ws greter in NF thn P1 nd P50 t 5 nd 20 cm depths (P <0.01), ut such difference ws opposite t 40 cm depth. In some cses, the PSI of wcp nd MP+FP were greter thn those of the totl pores. The shrinkge index vlues of corse pores (wcp nd ncp) did not differ s function of the lnd use with the exception of the gret vlues found in P50 nd P1 t 20 nd 40 cm depth, respectively Void rtio [m 3 /m 3 ] NF-5cm 1.5 P50-5cm P1-5cm NF-20cm 1.0 P50-20cm P1-20cm 0.5 NF-40cm P50-40cm P1-40cm Moisture rtio [m 3 /m 3 ] Figure 1. Shrinkge curves s function of lnd use nd soil depth. The prmeters re listed in Tle 3. Figur 1. Curvs de contrcción en función del uso del suelo y profundidd. Los prámetros derivdos de ls curvs están indicdos en el Cudro 3. Tle 3. Prmeters derived from the shrinkge curve ccording to the eqution proposed y Peng nd Horn (2005). Cudro 3. Prámetros derivdos de l curv de contrcción de cuerdo l ecución propuest por Peng y Horn (2005). Site Depth e r e s ϑ shw e shw e s - e shw χ p q r Slope [cm] [m 3 /m 3 ] [-] NF P P Ciencis del Suelo 5

6 Dörner et l. / Agro Sur 41(1): 1-9, 2013 NF P1 P50 5cm y=9 e -3.5x R 2 : 2 COLE [-] PSI [m 3 /m 3 ] 0.0 NF P1 P50 20cm Bulk density [Mg/m 3 ] Figure 3. Coefficient of liner extensiility s function of initil ulk density of the soil. Figur 3. Coeficiente de extensiilidd linel en función de l densidd prente inicil del suelo. 0.0 NF P1 P50 40cm d [Mg/m 3 ] nd COLE [-] Bulk Density COLE y= x R 2 : 0.76 P<0.05 y= x R 2 : 0.59 P< wcp ncp MP+FP TP Pores [-] Figure 2. PSI of wide (wcp, >50µm) nd nrrow corse pores (ncp, 50-10µm) nd medium plus fine pores (MP+FP, <10µm) depending on lnd use nd soil depth. Different lowercse letters on the rs indicte significnt differences of ech pore clss s function of lnd use (P <0.01). Figur 2. PSI de los mcroporos (wcp, >50µm), mesoporos (ncp, 50-10µm) y de los poros medios y finos (MP+FP, <10µm) en función del uso del suelo y profundidd. Diferentes letrs minúsculs indicn diferencis significtivs pr cd tmño de poro en función del uso del suelo (P <0.01). The coefficient of liner extensiility (COLE) of soil cores decresed exponentilly s the ulk density incresed (Figure 3) which is strongly relted to the lnd use (e.g. cttle treding incresed the ulk density s shown in Tle 1) ut lso to the mount of llophne (Figure 4). The ulk density decresed s function of the initil soil volume, i.e. the smller soil ggregtes re denser Allophne [%] Figure 4. Bulk density (d) nd COLE s function of llophne mount. Figur 4. Densidd prente (d) y COLE en relción l contenido de lofán. thn soil cores for ech smpling site nd soil depth (Figure 5). The coefficient of liner extensiility nd the initil soil volume mesured from ggregtes nd soil cores collected in NF nd P1 ws used to chrcterize the scling reltionship (Figure 6). While COLE t 5 cm depth in NF incresed y lrger initil soil volumes the opposite ws oserved t 5cm depth in P1. On the other hnd, the COLE t 20 nd 40cm depth, in oth smpled sites, presented the sme tendencies, i.e. t 20 cm it tends to decrese nd t 40 cm to increse with lrger soil volumes. 6 Ciencis del Suelo

7 Aggregte scle dependent shrinkge of volcnic sh soils Bulk density [Mg/m 3 ] Bulk density [Mg/m 3 ] NF 5cm 20cm 40cm y = x R 2 : 0.99, P<0.01 y = x R 2 : 0.97, P<0.01 y = x R 2 : 0.99, P< P1 Initil soil volume [cm 3 ] 5cm 20cm 40cm y = x R 2 : 0.99, P<0.01 y = x R 2 : 8, P<0.01 y = x R 2 : 0.75, P< Initil soil volume [cm 3 ] Figure 5. Initil ulk density s function of initil soil volume (NF: Ntive Forest, P1: one yer old psture). Figur 5. Densidd prente inicil en relción l volumen inicil del suelo (NF: Bosque Ntivo, P1: Prder de un ño). COLE [-] COLE [-] cm cm 40cm Initil volume [log cm 3 ] cm cm 40cm Initil volume [log cm 3 ] Figure 6. Coefficient of liner extensiility s function of initil soil volume (NF: Ntive Forest, P1: one yer old psture). Figur 6. Coeficiente de extensiilidd linel en función del volumen inicil del suelo (NF: Bosque Ntivo, P1: Prder de un ño). NF P1 DISCUSSION The shrinkge ehviour of volcnic soils showed wide structurl shrinkge nd pronounced proportionl phse ut lcked the residul nd zero shrinkge. The coefficient of liner extensiility (COLE) of the three soils ws chrcteristic for high shrinking orgnic soils (COLE >0.06; Peng et l., 2007). In these terms, the high shrinkge cpcity is lso relted not only to the mount of orgnic cron, ut lso to the presence of llophne nd the low ulk density (Figure 4). The ltter ws lso supported y Brtoli et l. (2007), which reported n incresing shrinkge y lower ulk density s result of the incresing mount of llophne. This type of cly minerl, composed of porous spheres, does not ecome ggregted s plty cly prticles derived from phylosilictes do, leding to porous structures with low cohesion etween soil prticles (Allrook, 1985; Gry nd Allrook, 2002). Woignier et l. (2007) descried tht llophne ggregtes s nturl gels present the spongy structure tht they uild with llophne prticles smller thn 5 nm. The void rtio (VR) decresed from NF to P1 nd then to P50, especilly for the top 20 cm. The dense soil structure with incresing intensity of soil mngement is certinly owe to soil compction, which, in turn, leds to smll mount of wide corse pores (wcp, >50µm) s presented in Tle 2. However, the medium plus fine pores (MP+FP, <10µm) re independent of soil mngement (e.g. no differences were ssessed t 5 cm depth etween NF nd P1). Pore dependency of soil mngement grees with former reporter (Richrd et l., 2001; Kutílek et l., 2006; Peng et l., 2012) who ddressed tht structurl pores cn e compcted while the texturl pores re not. As result, the rnge of structurl shrinkge phse decresed with the incresing intensity on soil mngement (Figure 1 nd Tle 3). Ciencis del Suelo 7

8 Dörner et l. / Agro Sur 41(1): 1-9, 2013 Smll shrinkge cpcity for the wide corse pores s indicted y PSI is in ccordnce with findings of other reserchers (Brudeu et l., 2004, Peng et l., 2007, 2012) reporting lrge pores in generl hve less shrinkge thn the medium nd fine pores. Theoreticlly, soil mngement (e.g., lnd use) cnnot chnge soil shrinkge cpcity of MP+FP. In this study, however, the COLE (dt not shown) nd PSI vlues of MP+FP show tht lnd use intensity reduced soil shrinkge in the top 20 cm, lthough the lnd use could not modify the volume of medium nd fine pores (Tle 3). We ssume tht this chnge is not due to the intensity of lnd use, it is owing to the different intensity of wetting nd drying cycles s ffected y the three lnd uses. This grees with studies conducted y Mordhorst et l. (2012), they indicted tht not only the comintion of hydrulic nd mechnicl stresses ut lso the ggregtion level influenced the soil deformtion y drying (s ssessed y COLE). The ltter lso grees with the findings of Dörner et l. (2012), which ssessed tht fter tillge nd due to ggregte destruction the COLE incresed, which is lso relted to decrese in the soil mechnicl stility. Soil ggregtes presented higher ulk density thn the soil mtrix, showing the effect of mcro structure formtion uild up y denser soil ggregtes. Similr reltionships were oserved y Seguel nd Horn (2006) in southern Chile. The sme uthors found out s well tht the ggregte strength generlly incresed with decresing ggregte dimeter. Some discrepncies, however, were oserved in deeper soil horizons when ggregtes were ir-dried scriing these phenomen to the presence of chemicl structurl gents s Fe nd Al. Since the ulk density decresed with incresing initil soil volume, we expected n incresing shrinkge s Figure 2 showed for the sme smpling sizes ut different lnd uses. The ltter, however, ws not lwys ssessed s lso presented y Brtoli et l. (2007) i.e. they presented decresing nd incresing scling reltionships s function of initil soil volume. They found tht the smller the smpling size, the greter ws the shrinkge, scriing this reltionship to greter men rte of wter loss of soil clods thn soil volumes; however, exceptions were found for the most porous Andisols horizons rich in Al-humus, i.e. the clods shrunk less thn the soil core counterprts. Hllet et l. (2000) mentioned tht ggregte strength incresed with decresing ggregte size (s lso oserved y Seguel nd Horn, 2006 in similr smpled sites), which cn e relted to the reduction of crck sizes ville for frcture, therefore, we cn expect decresing shrinkge s well. However, if we considered tht llophne is composed y porous spheres, which leds to porous structures with low cohesion etween prticles, it is possile to conclude tht no significnt scling reltionships hs to e found. In order to understnd this scling reltionship further experimentl development hs to e done s proposed y Brtoli et l. (2007). CONCLUSIONS The three volcnic soils (Andisol) showed very high shrinkge eing strongly relted to the presence of llophne. Their generl shrinkge curves include wide structurl shrinkge phse nd cler proportionl shrinkge, ut the residul nd zero shrinkge phses re not oviously oserved. The intensity of lnd use ffects the mount of lrge pores nd the structurl shrinkge rnge. At the sme time, the intensity of previous wetting/drying cycles depending on the lnd use influences pore shrinkge cpcity significntly nd finlly presents soil shrinkge ehviour differently. Scling reltionships were oserved for initil soil volume nd ulk density, i.e. smller ggregtes presented higher ulk density thn soil cores. However, the sme ws not oserved for initil soil volume nd COLE. Further conceptul nd experimentl developments re required to understnd these scling results. ACKNOWLEDGEMENTS This study ws sponsored y FONDECYT nd The first uthor lso thnks Clus Prehn for llowing us ccess to smpling sites on his frm. REFERENCES ALLBROOK, R.F The effect of llophone on soil properties. Applied Cly Science 1: BARTOLI, F., BEGIB, J., BURTIN, G., SCHOULLER, E Shrinkge of initilly very wet soil locks, cores nd clods from rnge of Europen Andosol horizons. Europen Journl of Soil Science 58: BAUMGARTL, Th., KÖCK, B Modeling volume chnge nd mechnicl properties with hydrulic models. Soil Science Society of Americ Journl 68: BESOAIN, E Minerles secundrios. In: Tosso, J. (Ed.), Suelos Volcánicos de Chile, INIA, Sntigo, pp BRAUDEAU, E., COSTANTINI, J.M., BELLIER, G., COLLEUILLE, H New device nd method for soil shrinkge curve mesurement nd chrcteriztion. Soil Science Society of Americ Journl 63: BRAUDEAU, E., FRANGI, J.P., MOHTAR, R.H Chrcterizing nonrigid ggregted soil wter medium using its shrinkge curve. Soil Science Society of Americ Journl 68: BRONSWIJK, J.J.B Reltion etween verticl soil movements nd wter- content chnges in crcking clys. Soil Science Society of Americ Journl 55: Ciencis del Suelo

9 Aggregte scle dependent shrinkge of volcnic sh soils CORNELIS, W.M., CORLUY, J., MEDINA, H., DÍAZ, J., HART- MANN, R., VAN MEIRVENNE, M., RUIZ, M Mesuring nd modelling the soil shrinkge chrcteristic curve. Geoderm 137: DOREL, M., ROGER-ESTRADE, J., MANICHON, H., DELVAUX, B Porosity nd soil wter properties of Crien volcnic sh soils. Soil Use nd Mngement 16: DÖRNER, J., SCHROEREN, V., DEC, D., HORN, R Effect of lnd use on physicl properties of volcnic soil in South Chile. ISTRO 18 th Triennil Conference Proceedings, June 15-19, 2009 Izmir-TURKEY. DÖRNER, J, DEC, D, PENG, X, HORN, R Effect of lnd use chnge on the dynmic ehviour of structurl properties of n Andisol in southern Chile under sturted nd unsturted hydrulic conditions. Geoderm. 159: DÖRNER, J., DEC, D., ZÚÑIGA, F., SANDOVAL, P., HORN, R Effect of the lnd use chnge on Andosol s pore functions nd their functionl resilience fter mechnicl nd hydrulic stresses. Soil & Tillge Reserch : DÖRNER, J., DEC, D., FEEST, E., DÍAZ, M., VÁSQUEZ, N Dynmics of soil structure nd pore functions of volcnic sh soil under tillge. Soil & Tillge Reserch 125: ELLIES, A., Mechnicl consolidtion in volcnic sh soils. In: Drescher, J., Horn, R., De Boodt, M. (Eds.), Impct of Wter nd Externl Forces on Soil Structure, CA- TENA, Suppl. 11, pp ELLIES, A., GREZ, R., RAMÍREZ, C L conductividd hidráulic en fse sturd como herrmient pr el dignóstico de l estructur del suelo. Agro Sur 25(1): ELLIES, A., HORN, R., SMITH, R Effect of mngement of volcnic sh soil on structurl properties. Interntionl Agrophysics 14: GRAY, C.W., ALLBROOK, R Reltionships etween shrinkge indices nd soil properties in some New Zelnd soils. Geoderm 108: GROSSMAN, R.H., BRASHER, B.R., FRANZMEIER, D.P., WALKER, J.L Liner extensiility s clculted from nturl-clod ulk density mesurements. Soil Science Society of Americ Procedures 32: HALLET, P. D., DEXTER, A. R., BIRD, N. R., SEVILLE, J. P Scling of the structure nd strength of soil ggregtes. In: Horn, R., vn den Akker, J., Arvidsson, J. (Eds.), Susoil compction. Distriution, processes nd consequences. Advnces in Geoecology 32, Cten Verlg, Reiskirchen, pp HORN, R., BAUMGARTL, Th Dynmic properties of soils. In: Wrrick, A.W. (Ed.) Soil Physics Compnion, CRC Press, Boc Rton. KUTÍLEK, M., JENELE, L., PANAYIOTOPOULOS, K.P The influence of unixil compression upon pore size distriution in i-model soils. Soil & Tillge Reserch 86: McGARRY, D., MALAFANT, K.W The nlysis of volume chnge in unconfined units of soils. Soil Science Society of Americ Journl 51: MORDHORST, A., ZIMMERMANN, I., PETH, S., HORN, R Effect of hydrulic nd mechnicl stresses on cyclic deformtion processes of structured nd homogenized silty Luvic Chernozem. Soil & Tillge Reserch 125: PENG, X., HORN, R Modelling soil shrinkge curve cross wide rnge of soil types. Soil Science Society of Americ Journl 69: PENG, X., HORN, R., SMUCKER, A Pore shrinkge dependency of inorgnic nd orgnic soils on wetting nd drying cycles. Soil Science Society of Americ Journl 71: PENG, X., ZHANG, Z.B., WANG, L.L., GAN, L Does soil compction chnge soil shrinkge ehviour?. Soil & Tillge Reserch 125: RICHARD, G., COUSIN, I., SILLON, J. F., BRUAND, A., GUÉRIF, J Effect of compction on the porosity of silty soil: influence on unsturted hydrulic properties. Europen Journl of Soil Science 52: SEGUEL, O., HORN, R Structure properties nd pore dynmics in ggregte eds due to wetting-drying cycles. Journl of Plnt Nutrition Soil Science 169: SHOJI, S., NANZYO, M., DAHLGREN, R. A Volcnic Ash Soils Genesis, Properties nd Utiliztion. Elsevier, Amsterdm. TOBÓN, C., BRUIJNZEEL, J., FRUMAU, K., CALVO-ALVARADO, J Chnges in soil physicl properties fter conversion of tropicl montne cloud forest to psture in northern Cost Ric. In: Bruijnzeel, L.A., Scten, F.N., Hmilton, L.S. (Eds.), Tropicl Montne Cloud Forests: Science for Conservtion nd Mngement, Pulished y Cmridge University Press. SOIL SURVEY STAFF Keys to Soil Txonomy. Eleventh Edition. USDA-NRCS, Wshington DC. WOIGNIER, Th., POCHET, G., DOUMENC, H., DIEUDONNE, P., DUFFOURS, L Allophne: nturl gel in volcnic soils with interesting environmentl properties. Journl of Sol-Gel Science nd Technology 41: Ciencis del Suelo 9

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