(1994) Chronosequence in Almar River Fluvial-Terrace Soiledafologia.ugr.es/introeda/tema01/imagenes/AlmarUSA.pdf · 912 SOIL SCI. SOC. AM. J., VOL. 58, MAY-JUNE 1994 on river terraces

Chronosequence in Almar River Fluvial-Terrace SoilC. Dorronsoro* and P. Alonso

ABSTRACTThe aim of this work was to analyze how soils formed fundamentally

from the erosion of granites evolve under a subhumid Mediterraneanclimate as a function of age. Their evolution was evaluated by meansof the changes in components and properties, as well as the use ofdevelopmental indices. The soils are Xerorthents (Holocene), Haploxer-alfs (Upper Pleistocene), and Palexeralfs (Middle Pleistocene). Theproperties have been subject to several trends: (i) some propertiesincrease with regularity throughout the chronosequence (availablewater and coefficient of linear extensibility [COLE] of the Bt horizons)(ii) other properties increase strongly only during the first phases,while some continue to increase with age but only moderately (Aphorizon water retention and cation-exchange capacity, Bt horizondithionite-citrate-extractable Fe, soluni thickness, clay accumulation,quartz content, and quartz/feldspar ratio), whereas other MiddlePleistocene age soil properties cease to increase (the Ap horizon silt andavailable water, and Bt horizon water retention and cation-exchangecapacity; (iii) others decrease with age, with pronounced decreasesduring the first phases (Ap and Bt horizon feldspar content and sandcontent and Bt horizon bulk density); and (iv) some properties arenot age related (the Ap horizon base saturation and N content andthe Bt horizon silt content). The horizon development indices and thesoil development indices indicate good relationships with age. In mostcases the rate of increase declines strongly for the oldest soils. Inthe great majority of cases, the properties and development indicescontinue to evolve through the chronosequence without reaching asteady state.

Departamento de Edafologi'a, Avda Campo Charro s/n°, Facultad deFarmacia, Universidad de Salamanca, E-37007 Salamanca Espana (Spain).Contribution from the Dep. of Edafologia, Universidad de Salamanca.Supported by a grant from the Spanish DGICYT (PB90-0542). Received14 Aug. 1992. ""Corresponding author.

Published in Soil Sci. Soc. Am. J. 58:910-925 (1994).

MOST SOIL PROPERTIES are time-dependent variables(Jenny, 1941). Therefore it is likely that soils of

different ages will display their properties in differentways, especially under conditions in which the actionsof other soil formation factors remain constant. Thus,the study of how the properties of soils vary with ageis of great interest and may offer useful information inregard to their genesis.

Studies of soil chronosequences have focused onwidely differing materials such as fluvial, eolian, lacus-trine, marine, dune, morainal, volcanic ash, and evenanthropogenic deposits such as the slag heaps of aban-doned mines. Of all these types of chronosequences,river terraces have undoubtedly been the focus of mostattention since they are very good examples of naturalsoil sequences whose evolution has been shaped by time.Although river terraces do cover an extended period oftime, the changes occurring in their soils should not beattributed exclusively to the action of this parameter;rather, climatic changes and those due to the developmentof biological organisms should also be taken into account,insofar as these will also have affected soil development.

The aims of our study were several: (i) to evaluatehow the properties and development of soils change withthe progression of time; (ii) to define soil developmentage trends; and (iii) to analyze whether the development

Abbreviations: Fe<i, dithionite-citrate-extractable Fe; COLE, coefficientof linear extensibility; MI, morphological index; AI, analytical index;Minel, mineralogical index.

DORRONSORO & ALONSO: ALMAR RIVER CHRONOSEQUENCE 911

of the soils under study becomes fixed at a steady stateor not.

MATERIALSThe soils examined in this study are from a sequence of

river terraces formed by the Almar River in the province ofSalamanca (central western Spain).

Over geological time this river has left a typical scaledrelief, with abundant horizontal surfaces placed between sharpscarps. According to Vreeken (1975), these are post-incisedsequences. The river terraces analyzed are located in the neigh-borhood of Macotera village (UTM coordinates: 466694 and471698 of National Grid Map 479).

A representative profile was chosen from each of the sevengeomorphological surfaces distinguished, although in somecases, due to lateral changes, two profiles were sampled (Table1). The sequence comprised all soils from the riverbank to aterrace 64 m above the riverbed.

The soil surfaces have been dated by Santonja et al. (1976,1982, 1984) and the IGME (1982), mainly by archaeologicaland stratigraphic methods.

The fluvial deposits have thicknesses ranging between 1.5and 5 m and are composed mainly of gravel and sand thatoriginated from the erosion of granitic rock, slate, quartzite,and siliceous sediment.

The present-day climate can be classified as subhumid (meanannual rainfall 412 mm), mesic (mean annual temperature,11°C), of the continental Mediterranean type.

The climax vegetation is composed of holm oak (Quercusrotundifoliae Lam.) with Genistra histrix Lange. In certainareas this vegetation has been altered by human activity forcrop cultivation and in others it is characterized by more orless open holm oak populations with abundant undergrowth.

METHODSField and Laboratory Methods

The descriptions of the morphological properties and thephysical and chemical analyses of the soils were conductedaccording to traditional methods (Soil Survey Staff, 1951,1984). The mineralogy of the sand and silt fractions wasdetermined by x-ray diffraction.

In order to analyze the soil development trend with age,representative samples were chosen. The properties of the Aphorizon always refer to those of the horizon closest to thesurface. When two or more Bt horizons within one soil arereferred to, the following have been selected: (i) the maximum

value of all the Bt horizons for clay content, water retentionat 0.03 and 1.5 MPa, available water contents and cation-exchange capacity; (ii) for the sand and silt, those correspond-ing to the horizon with the maximum enrichment in clayswere selected; (iii) in the case of clay, we also calculated theaccumulation indices at the preset depths of 15, 50, 100, 150,200, and 250 cm in the profile (cumulative values of thepercentage of clay particles by horizon thickness in meters);(iv) the mineralogy of the sand and silt fractions was alwayscalculated by taking the values corresponding to the second-most superficial horizon of each profile; (v) solum thicknesswas calculated as the sum of the thicknesses corresponding toAp and Bt horizons (measured in centimeters) plus one-halfthe thickness of the BC and CB transition horizons; (vi) thethickness of the Bt horizon was also considered in this way,logically without taking the Ap horizons into account.

Soil Development IndicesSeveral studies have stressed the considerable difficulty in

evaluating the degree of development shown by soils due tothe enormous amount of data about different soil propertiesthat such studies usually generate. To overcome this problem,quantitative indices have been developed; using a single value,these quantitative indices evaluate the degree of evolutionamong different soils. They can also be applied to the differenthorizons of a single soil (Buntly and Westin, 1965; Walkerand Green, 1976; Bilzi and Ciolkosz, 1977; Harden, 1982;Birkeland, 1984a,b). These indices were calculated by de-termining the intensity of the change occurring between theproperties of the horizons and those of the original material.

Morphological IndicesTo calculate the MI we followed the guidelines of Harden

(1982), using seven properties chosen by this author, namely:(i) structure (type and degree of development); (ii) total texture(textural class plus type of stickiness and plasticity of the wetconsistence); (iii) dry consistence (class); (iv) moist consistence(class); (v) clay films (abundance, thickness, and location);(vi) melanization (color value); and (vii) nitrification (colorhue and chroma).

A detailed morphological description of the soil profile wasthe starting point for the calculations. Quantification of thefield properties was modeled after Bilzi and Ciolkosz (1977).They assigned points on the basis of the difference betweenthe properties observed in the soil horizons and the originalmaterial. The Bilzi-Ciolkosz index yields very good resultsfor comparing soils developed from different original materials,although in the particular case of chronosequences developed

Table 1. Soils, geomorphic surfaces, and ages.Profilecode

AM4AM7AM14AMISaAMISbAM36AM47AM64

Stratigraphicposition

FloodplainFloodplain5th terrace4th terrace4th terrace3rd terrace2nd terrace1st terrace

Elevation

m47

141818364764

Geologic age

HoloceneHoloceneLate PleistoceneLate PleistoceneLate PleistoceneMiddle PleistoceneMiddle PleistoceneMiddle Pleistocene

Approximateage

yr500

1000050000

100000100000300000500000600000

Classificationt

Typic XerorthentTypic HaploxeralfTypic HaploxeralfTypic HaploxeralfTypic HaploxeralfTypic PalexeralfTypic PalexeralfTypic Palexeralf

t Soil Survey Staff (1975).

912 SOIL SCI. SOC. AM. J., VOL. 58, MAY-JUNE 1994

on river terraces it is not completely satisfactory, as demon-strated by Meixner and Singer (1981). For comparative pur-poses, better results are obtained using the indices of Harden(1982), in large part because of the introduction of thicknessand the ability to combine several properties.

To calculate the MI, the following steps were observed(Harden, 1982; Busacca, 1987): (i) description of the soilprofile; (ii) assessment of parent materials (measurement offresh deposits or deep C horizons); (iii) quantification of eachfield property for each horizon (assessing 10 points to stepincreases); (iv) normalization of quantified properties (divisionby maximum quantified property) to obtain the Ml for eachproperty and horizon; (v) multiplication of the value obtainedin the previous step by the thickness (in centimeters) of thehorizon and adding all of the values corresponding to all ofthe horizons of a given soil which yields the MI for a singleproperty for each profile; (vi) adding together all the normalizedvalues from step iv and dividing by the number of propertiesconsidered, which gives MI (general properties) per horizon;(vii) multiplying the latter values by the thickness correspond-ing to each horizon and then adding these products, whichgives the general MI for each profile.

So that the thickness of the soil will not be overvalued inthese indices, Harden and Taylor (1983), Birkeland (1984a,b),and Busacca (1987) proposed that the values could be dividedby the true thickness of each soil. In this same sense, Birkeland(l984b) suggested the use of a constant thickness for each ofthe soils, choosing the thickness of the deepest soil in thechronosequence as a homogenization factor, artificially thick-ening the thinnest soils until the thickness of the deepest soilis reached. We obtained good results by dividing the value ofthe index by the true thickness of each soil (data not shown)and also for a standard thickness of 2 m.

Analytical IndicesFor the results of the physical and chemical analyses, we

calculated the indices of Birkeland (1984a). These indices area modification of the index of profile anisotropy (IPA) ofWalker and Green (1976) and are calculated thus:

mlPA = D/PM

where D represents the numerical difference between the valueof the horizon property considered and its value in the originalmaterial, and PM refers precisely to this latter value.

To calculate the AI, we followed the steps described abovefor the MI (Step iv, AI for each property and horizon; Stepv, AI for each property and profile; Step vi, general AI forall properties and horizon; Step vii, general AI for all propertiesand profile). As was done for the MI, calculations were madefor normalized thicknesses (AI divided by the thickness ofeach soil) and for standard thicknesses of 2 m.

In this study, we calculated the AI for a single propertyand profile for nine properties: sand content, clay content,water retention at 0.03 and 1.5 MPa, available water, organicmatter content, CaCOs content, pH, and cation-exchange ca-pacity. We also calculated the general AI (all properties) forhorizon and the general AI for profile.

Mineralogical IndicesLikewise we calculated Minel as a function of the contents

of quartz and feldspars of the total sand and total silt fractionsof the soil.

To calculate these Minel, we followed the same steps asfor the AI, calculating the general Minel as a function of thevalues of the quartz/feldspar ratio.

RESULTS AND DISCUSSIONThe calculated ages for these Spanish soils have been

contrasted (Fig. 1) with the values obtained by others(Meixner and Singer, 1981; Harden, 1982; Busacca,1987) for California soils that were formed under condi-tions similar to ours: fluvial terraces formed by materialsoriginating from the erosion of granitic rock, Mediterra-nean climate, and average annual precipitation of 310to 640 mm. We illustrate the results for the rate of soilformation in Fig. 1. We have simply calculated thesevalues on the basis of the proportion between the soildepths in millimeters (A horizon + B horizon + 1/2AC horizon + 1/2 BC horizon, excluding CA, CB, and Chorizons) and the soil age in years (soils with anomalousperformances have not been represented). A strongagreement was found between the respective values ofSpanish and California soils.

The formation rate of the soils drastically decreaseswith age. The soils deepen at a rate of 0.2 to 0.6 mm/yr for those that are < 1000 yr old in these soil conditions.The soil that is 10000 yr old has formed at 0.1 mm/yr. The soil that is 100000 yr old has formed at 0.01mm/yr. The rate decreased to 0.005 mm/yr at 500000years old, and finally decreased to 0.001 mm/yr at about1 million yr.

A selection of the results of the morphological, physi-cal, chemical, and mineralogical analyses of these soilsis offered in Tables 2 and 3.

In this chronosequence, it is possible to observe aprogressive and pronounced development of the soil withage. In the current flood plain there are Xerorthents.The soils of the Upper Pleistocene surfaces have becomeHaploxeralfs. Finally, in the Middle Pleistocene thereare Palexeralfs.

Soil Development Indices vs. Horizon Depthwith Age

Figures 2, 3, and 4 summarize the values of the threegeneral indices: MI, AI, and Minel. It can be seen howthe distributions of these indices follow a progressiveevolution with age, and form two general developmentaltrends. One corresponds to the global values of the

0)C"c0)Q.o>

El|itoM—O03

10° i

10-1:

10^1

m-3-

n O^

n }t

8 o-aD

° * nO SJC3< B

a HARDEN O O» xx BUSACCA T°• MEIXNER U

O Almar (D x an

Fig. 1.and

.1 1 10 100 1000 10,000AGE, 103 years

Profile deepening rate vs. age of some soils from CaliforniaSpain.


Table 2. Major macromorphological characteristics of the soils studied.

Waterretention

Profilecode

AM4

AM7

AM14

AMISa

AM18b

AM36

AM47

AM64

Parentmaterials

Horizon

AplAp22C12C22C3ApBt

BCt

CBtApBtBtg

2Btk

2CBtkl2CBtk2

Ap2Btl

2Bt23BCt3Ckl4Ck25Ck3ApBt

2Btg

2BCtk2CBtApBtl

Bt2

CBtkl

CBtk2

CBtk3

2CkApBtl

Bt2

CBtkl2CBtk23CBtk3

4CBtk4Ap

2BI1

2Bt22Btk

2BCtkl

2BCtk2

Depth

cm0-2525-38 •38-7070-90

90-M200-40

40-115115-170

170->2000-3030-5555-83

83-105/140$

105/140-200200->2250-22/55

22/55-60/70

60/70-9292-114114-150150-200

200->2500-3737-70

70-103

103-190190->230

0-3030-55/65

55/65-110/120

110/120-170

170-205

205-225

225->2800-3232-50

50-106

106-180180-215215-240

240->2800-2525-45

45-100100-110110-140

140->200

Moist color StructuretGravel

(>2 mm)Sand Silt

(2-0.05 mm) (0.05-0.002 mm)Clay

(<0.002 mm)0.03MPa

1.5MPa

a- ~ i,_-l

7.5 YR 5/47.5 YR 5/410 YR 6/410 YR 7/410 YR 6/67.5 YR 4/32.5 Y 5/32.5 Y 6/3

7.5 YR 5/65 Y6/3

7.5 YR 5/4SYR 4/62.5 Y 5/32.5 Y 6/410 YR 6/610 YR 4/210 YR 4/3

5 Y7/35 Y6/3

7.5 YR 5/410 YR 5/32.5 YR 3/610 YR 6/32.5 Y 5/45 Y5/35 Y5/35 Y5/3

10 YR 4/42.5 YR 4/8SYR 5/8

7.S YR 5/4SYR 5/82.5 Y 6/32.5 Y 5/32.5 Y 5/310 YR 4/4SYR 5/8

7.5 YR 6/4, 10 YR 6/42.5 YR 5/8, 5 YR 5/8

10 YR 5/32.5 Y 6/4

5 Y 7/4, 7.5 YR 6/47.5 YR 6/4, 2.5 Y 6/4

5 Y7/47.5 YR 6/42.5 Y 6/45 Y7/4

7.5 YR 5/610 YR 4/32.5 YR 4/8SYR 4/5

2.5 YR 3/67.5 YR 4.5/3

10 YR 6/8, 2.5 Y 7/4yellowish white

7.5 YR 6/810 YR 6/810 YR 6/67.5 YR 5/42.5 YR 4/6SYR 5/6SYR 3/4

7.5 YR 5/410 YR 5/42.5 Y 6/42.5 Y 6/410 YR 5/410 YR 5/610 YR 6/5

vflcr0000

vflcrm3abk

ml,2abk

mlsbkm2crc2sbkc3pr

m

mm

m2crCsbk

c3prm3pr

mmm

m2crc3sbk

c2pr

mm

f2sbkc3abk

c3pr

m

m

mm2crc3abk

c3pr

m

m

mm2crc2abk

c3prm3pr

m

m

m

48.3S3.542.561.423.331.143.075.0

45.643.943.424.9

63.2

21.316.935.151.3

2.91.18.22.21.0

29.053.9

21.8

52.946.419.424.8

47.5

41.4

77.3

43.5

0.016.812.1

33.1

62.574.854.3

19.827.04.8

5.48.0

16.0

4.9

42.0

81.482.096.795.893.863.553.869.1

61.056.042.140.3

46.3

58.061.968.938.4

23.523.546.420.031.452.437.6

47.9

44.267.152.833.4

22.1

55.4

51.9

73.2

15.057.030.0

21.1

58.250.766.9

50.052.231.4

22.329.144.8

32.0

%

13.711.21.22.21.8

26.613.95.8

16.732.315.87.9

12.8

22.417.623.912.5

18.333.333.947.036.334.610.8

5.9

15.99.3

33.423.6

7.2

11.2

7.6

1.4

29.931.213.4

6.7

12.917.53.8

20.121.618.9

11.516.519.0

14.1

2.2

4.96.82.12.04.49.9

32.325.1

22.311.742.151.8

40.9

19.620.57.2

49.1

58.243.219.733.032.313.051.6

46.2

39.823.613.843.0

70.7

33.4

40.5

25.4

55.111.856.6

72.2

28.931.829.3

29.926.256.3

70.654.442.2

53.9

2.8

6 "667 2555121032

13.823.717.1

21.515.924.728.5

28.2

21.720.112.130.4

45.543.625.932.030.117.727.4

27.0

29.214.317.427.8

42.1

26.3

28.4

18.0

43.316.239.9

43.2

21.826.421.9

24.221.538.5

44.237.932.4

40.5

4.0

291009215.1

13.511.3

11.95.5

16.320.0

17.3

12.111.54.1

20.9

29.428.716.920.717.76.1

19.7

20.7

17.510.46.2

17.4

29.5

16.8

17.4

11.6

29.75.5

24.3

29.9

12.315.213.8

12.310.721.8

29.023.619.5

22.1

2.0

t vf = very fine, f = fine, m = medium, c = coarse, 0 = structureless, 1 = weak, 2 = moderate, 3 = strong, cr = crumb, sbk = subangular blocky, abk =angular blocky, pr = prismatic. Abbreviations from Soil Survey Staff (1951, p. 139-140).

$ Variations of horizon boundaries.


Table 3. Selected chemical and mineralogical properties of the soils studied.

Profilecode

AM4

AM7

AM14

AMISa

AM18b

AM36

AM47

AM64

Parentmaterials

Horizon

AplAp22C12C22C3ApBt

BCtCBtApBtBtg

2Btk2CBtkl2CBtk2

Ap2Btl2B123BCt3Ckl4Ck25Ck3ApBt

2Btg2BCtk2CBtApBtlBt2

CBtklCBtk2CBtk32CkApBtlBt2

CBtkl2CBtk23CBtk34CBtk4

Ap2Btl2Bt22Btk

2BCtkl2BCtk2

OrganicC

—— gkg- 1-4.12.70.90.70.97.84.92.32.08.57.44.33.62.01.57.18.56.24.52.82.62.25.84.12.31.80.76.55.03.50.80.60.41.14.85.53.51.11.50.20.6

11.06.55.94.52.23.3

1.0

N

0.50.30.20.10.50.60.40.20.20.20.40.60.30.20.20.20.20.50.40.30.20.10.60.50.40.20.20.10.20.40.50.40.20.20.20.10.80.60.50.40.30.4

0.0

PH(paste)

4.75.46.97.88.06.06.26.16.85.15.37.17.67.67.54.75.06.77.47.47.67.55.65.76.37.66.65.35.56.97.47.67.67.55.16.06.77.67.77.67.56.36.96.87.57.67.7

7.6

Cation-exchangecapacity (NH,OAc)

cmolc kg"1

2.83.62.52.24.55.3

23.120.225.04.2

17.832.639.632.828.82.9

22.042.143.545.548.746.55.3

21.024.634.116.24.4

18.733.933.135.418.149.14.4

25.531.127.626.820.727.814.623.540.049.944.045.5

1.4

Basesaturation

%10010010010010010010010010095

10010010010010082

10010010010010010010010010010010087

10010010010010010091

100100100100100100100100100100100100

100

MineralsCaCO3

gkg-1

0.00.00.00.00.00.00.00.00.00.00.00.0713824

0.00.00.00.056

1881150.00.00.01870.00.00.00.015471414

0.00.00.0175672419

0.00.00.06191

251

0.0

Quartz

350190270300220370310380340460500510300260470390430360300240260330590430360240330370480550480510280300450660550470330470240810730600470310220

270

Feldspar

eke-'e &600810600560720580640650310540490480600440300510500630630750690490410560630750490600470430440420600610540340460410670530660190270400530690780

720

indices and the other refers to the degree of differentiationamong the horizons of each soil.

A marked increase with age is observed in regard tothe global values of these indices. The floodplain soilsare outstanding due to their very low values. In the soilsof Upper Pleistocene age, the indices corresponding tothe mineral alterations continue to be spectacularly low,while those corresponding to MI and AI have moderatevalues. In the soils of the Middle Pleistocene age, allthe indices increase as the age of the soils advances.

In regard to the degree of differentiation of the horizonsof each soil, the following trend was observed: the soilsof the present floodplains show very underdevelopedprofiles. The soils of the Upper Pleistocene surfaceshave a pronounced horizoning; these soils show a horizonof maximum differentiation situated at about 100-cm

depth. In the soils of the Middle Pleistocene age, themost developed horizons increase in their absolute valuesand become broader towards horizons above and below.Very similar distributions have been reported for the MIof California soils by Harden (1982, Fig. 7) and Busacca(1987, Fig. 3).

The Minel disclose the very low degree of alterationshown by soils of the Holocene and Upper Pleistoceneages (AM7, AM14, and AMIS) whereas for the otherindices—MI and AI—these soils are already clearly de-veloped. The main process responsible for the develop-ment of these soils is clay illuviation; this process beginsin the initial phase of soil development, long beforemineral alteration is developed. We believe that this isdue to the special characteristics of the fluvial depositsover which the soils have been formed.


MORPHOLOGICAL HORIZON INDEX

0.0 0.4 0.8U

E0-,-- 100 -tLUO

0 200-NCCo

5{6

o? n fi 1

+64 m.600,000 yr

/ +47 m.

0.2 0.6 1.0AM14 AM18

+36 m.300,000 yr

500,000 yr

AlmarRiver

AM4AM7

+4 meters500 years

+7m.10,000 yr

/ +14 m.50,000 yr

+18 m.100,000 yr

HOLOCENE UPPERPLEISTOCENE

MIDDLEPLEISTOCENE

Fig. 2. Distribution of general morphological horizon indices by depth and soil age.

First, the deposits of fluvial sands display a certainmineral stability since, on the one hand, due to theirsize the mineral fragments are fairly well protected fromweathering and, on the other, these fluvial deposits con-tain reasonably stable minerals, since the unstable ones

would have decomposed during previous phases of ero-sion and river transport.

Secondly, the fluvial deposits are mostly formed ofloose grains of sand and are therefore very porous,thereby enormously facilitating the infiltration of rain-

0.0 04 0.8

ANALYTICAL HORIZON INDEX

0.0 0.4 0.8

E (

ox 100-tLUO

0 200-NtrOi

AI

no n c ^

0.2 0.6 1.0

0.2 0.6 1.0 AM64

/+64m.

600,000 yr

0.2 06 10 AM36 / +47m-0.2 0.6 1.0 I—————' 500,000 yr

AlmarRiver AM4

+4 meters500 years

0.2 0.6 1.0

AM7 /

+7 m.10,000 yr

AM14AM18

+36 m.300,000 yr

+14m

50,000 yr

+18m.100,000 yr


MIDDLEPLEISTOCENE

Fig. 3. Distribution of general analytical horizon indices by depth and soil age.


0.0 0.4 0.8

MINERALOGICAL HORIZON INDEX

0.2 0.6 1.0I ^ i i i

0.2 0.6 1.0 AM64/i +64 m.

b (, ___ AM47 / 600,000 yr

————U-^ 02 06 10 AM36 / +47 m., 0.2 0.6 1.0 I——"———' 500,000 yrI I • • • ' • • • ' / +36m.

0.2 0.6 1.0 ' °'6 1'° „.„,„ AM18 / 300,000 yrAM14 s——~———'

AlmarRiver

AM7 /——77—— +18 m.AM4 .—————f +14m. 100,000 yr

———;——' +7 m. 50,000 yr+4 meters 10,000yr500 years____ '_________________


Fig. 4. Distribution of general mineralogical horizon indices by depth and soil age

MIDDLEPLEISTOCENE

water and hence the vertical transport of clay suspen-sions. Since they are present in small amounts, the claysare weakly retained in the soils and migrate with ease.Indeed, micromorphological study clearly shows that,at the present time, clay illuviation has already developedon the floodplain. Rapid clay translocation at an earlystage seems to explain the absence of Inceptisols in thisdevelopmental sequence.

Soil Development Age TrendsSoil Properties

Particular types of behavior of different soil propertiescan be grouped in three broad categories, according towhether the value of the property tends to increase withage, decrease, or whether there is no relationship withage at all. For the first two groups, a series of subgroupscan be established as a function of the intensity andconstancy of the change.

Properties that increase with age. Many propertiesshow a direct dependence with age. According to theevolution of the property with age, the following groupscan be differentiated:

1. Constant and regular increase throughout the chro-nosequence depending strongly on age: the availablewater and COLE of the Bt horizon (Fig. 5).

2. Strong increase only during the first phases. Anothergroup of properties shows strong increase with age forthe Holocene and Upper Pleistocene soils, thereafterundergoing a change in their development in the finalstages, corresponding to the Middle Pleistocene. Thischange may follow different trends: (i) some propertiescontinue to increase with age but more moderately (Fig.

6): water retention at 0.03 and l.SMPa and cation-exchange capacity of the Ap horizon (also in Dicksonand Crocker, 1953; Torrent, 1976; Ahmad et al., 1977;Jongmans et al., 1991), Fed of the Bt horizon (Hendershotet al., 1979; Torrent et al., 1980; Alexander and Holo-

2.0

5 1.51

oO 0.5 H

0.0

250

1 2 3 4 5 6 7AGE, 105 years

Fig. 5. Profile properties vs. soil age for properties that increaseconstantly and regularly throughout the chronosequence. For curvefittings, see Table 5.


300

es 10 8 i

Sol

I— 8 '

0 1 2 3AGE, 10s years

E2?

E

1 2 3 4 5 6AGE, 105 years

o

0 1 2 3 4 5 6 7AGE, 10s years

80

60"

40-

20-

0 1 2 3 4 5 6 7AGE, 10s years

100

80-

60-

40"

20-

01 2 3 4 5 6

AGE, 10s years1 2 3 4 5 6 7

AGE, 10s years

iso-

ioo-

50'

1 2 3 4 5 6 7AGE, 10s years

3 juur:Q.^rf^ 200-0. I5°>

l r o .oo-j_CD"(5

5 0-

_^^ _________ _

D ^_^- —— T] — ' ~~

x"1"*"" °<°

150'o.co

< 100-CO T~Q- 's S1

"> o> 50-^~S '"55 oJ

n

f*- ="

1 15

0.<^- 10-I

D)^

~o 5Eo

a

xTf" —— ' ——— ~v a

0 ?LUO 0" , , , , , , , , , , — ,__-

0 1 2 3 4 5 6 7AGE, 10s years

0 1 2 3 4 5 6 7AGE, 10s years

0 1 2 3 4 5 6 7AGE, 10s years

O

900-

600-

300- 5

00 1 2 3 4 5 6 7

AGE, 10s years

StoQ.CO2£a1

2-

0*1 2 3 4 5 6 7

AGE, 10s years

30

10

1 2 3 4 5 6 7AGE, 10s years

Fig. 6. Profile properties vs. soil age for properties that increase with age with strong increase only during the first phases. Clay at 15, 50, 100,150,200, and 250 cm are cumulative values of the percentage of clay particles by horizon thickness in meters; Fed is dithionite-citrate-extractableFe; CEC is cation-exchange capacity. For curve fittings, see Table 5.


waychuck, 1983; Pena and Torrent, 1984; Arduino et al.,1984, 1986; Aniku and Singer, 1990), solum thickness(Ahmad et al., 1977; Meixner and Singer, 1981; Littleand Ward, 1981; Harden, 1982; Muhs, 1982; Alexanderand Holowaychuck, 1983; Arduino et al., 1984, 1986;Chittleborough et al., 1984; Busacca, 1987; Ajmone etal., 1988; Reheis et al., 1989), clay accumulations atdepths of 15, 50, 100, 150, 200, and 250 cm, quartzcontent, and quartz/feldspar ratio (also in Ruhe, 1956;Barshad, 1955; Muhs, 1982); (ii) other properties ceaseto increase for the soils from the Middle Pleistocene:silt and clay contents, and available water of the Aphorizon, and available water at 0.03 and l.SMPa andcation-exchange capacity of the Bt horizons (Fig. 7). Ahighly representative property of this type of study isthe concentration of clay accumulated in the B horizonof the soils. Logically, as age increases, a progressiveincrease in the amount of clay present would also beexpected to occur. This kind of behavior has been ob-served both in our soils and in many others studied(Ruhe, 1956; Franzmeier and Whiteside, 1963; Jandaand Croft, 1967; Torrent, 1976; Ahmad et al., 1977;Pastor and Bockheim, 1980; Meixner and Singer, 1981;Dorronsoro et al., 1988; Fine et al., 1989; Reheis etal., 1989; Aniku and Singer, 1990). All of these chrono-functions can be adapted to power and logarithmic modelswithout a value of maximum enrichment being reachedafter which the values remain constant, although thisdoes occur in some cases (Pena and Torrent, 1984) andalso in this study for the total enrichments in clay atdefined depths (clay [%] x thickness) of 50, 100, 150,and 200 cm.

3. Strong increase only during the last phases. Anothergroup of properties shows strong increases with age forthe Middle Pleistocene soils. In this situation are the

clay and N content of the Ap horizon, the thickness ofthe Bt horizons, and carbonate accumulations (Fig. 8).Some of these properties are not strongly age dependentand could be included with the group of properties thatare not age related.

Properties that decrease with age. These show theopposite behavior to that of the previous group; that is,the increase in these properties diminishes as the soilages.

The properties belonging to this group are minor. Allof these properties (Fig. 9) show strong decreases up tothe Upper Pleistocene soils, thereafter decreasing verymoderately (feldspar content), or else they cease to in-crease for the soils from the Middle Pleistocene (sandcontent of the Ap and Bt horizons) or show increaseduring the last phases (bulk density of the Bt horizon).

Properties that are not age related. Finally, for onegroup of properties it is not possible to establish anylogical relationships between their degree of manifesta-tion and the age of the soil (pH and base saturation ofthe Ap horizon, and silt content of the Bt horizon)(Fig. 10).

The organic matter contents were expected to increasewith age (Dickson and Crocker, 1953; Ruhe, 1956;Viereck, 1966; Leisman, 1957; Olson, 1958; Syers etal., 1970) although, in our soils, an increase was observedonly for the very young soils; after the Upper Pleistocene,the soils display a chaotic behavior, possibly due to theintense anthropogenic activity to which they have beensubjected.

The absence of a dependence between base saturationand age could also be the result of land practices.

In other chronosequences, the pH of the soils clearlyreflects the progressive acidification that atmosphericprecipitation tends to produce on the surface horizon

oc.o.

<D TM D>3 *

to'5<r

1JHJ-

100-

50-

Dn n a

3a

Oc.s£T0,T—

V-

"co2

JXJU"

400-

300-

200-

100-r\-

a a DD

0 D

3

0 1 2 3 4 5 6AGE, 105 years

1 2 3 4 5 6AGE, 105 years

O.c

m

750

500-5 S>

250- =<Dra

0 1 2 3 4 5 6AGE, 105 years

Q.<

50

40-

30-

20-

js 10

6£vo"

(0o

1UU

80-

60

40-

20-

D D

D

DD D

D

0- • . • . • . • . • ! • . ————— 1

1 2 3 4 5 6 7AGE, 105 years

0 1 2 3 4 5 6AGE, 105 years

o 50

ao 40-

'o> 30-

o 20-eoOLUO

10-

0 1 2 3 4 5 6AGE, 105 years

Fig. 7. Profile properties vs. soil age for properties that cease to increase for the soils from the Middle Pleistocene.


COO

400

300-

200-

100-

00 1 2 3 4 5 6 7

AGE, 105 years

Q.<

O

30

20-

1 2 3 4 5 6AGE, 105 years

Q.<

<DO)O

2 3 4 5 6AGE, 10s years

Eoo.cffl'o

250

200-

150-

100

50"

00 1 2 3 4 5 6

AGE, 10s years

Fig. 8. Profile properties vs. soil age for properties that show a strong increase only during the last phase. For curve fittings, see Table 5.

(Dickson and Crocket, 1954; Crocker and Dickson,1957; Wilson, 1960; Cowie, 1968; Ugolini, 1968; Vier-eck, 1970; Bockheim, 1979; Alexander and Holoway-chuck, 1983; Arduino et al., 1984; Chittleborough etal., 1984; Pena and Torrent, 1984; Aniku and Singer,1990).

Soil IndicesMorphological Indices. As shown in Fig. 11, all of

the MI show strong increases during the initial phasesof soil formation; as for the Upper Pleistocene soils,

these increases are reduced to the minimum (MI oftexture, dry consistency, and the general one for all theproperties together) or may even remain constant (moistconsistency and rubification MI). A similar kind of be-havior, with continuous increases and mostly in the earlyphases of the development of the soils, has been reportedfor these MI by Harden (1982), Birkeland (1984b), Bu-sacca (1987), and Reheis et al. (1989).

Analytical Indices. As occurs with the MI, the Alshow a very dominant type of behavior. The values ofmost of the Al increase throughout the chronosequencebut only do so very intensively in the case of the soils

1 2 3 4 5 6 7AGE, 10s years

60"

40-

I 20

1 2 3 4 5 6AGE, 105 years

-C£7"EoCT

"35c-o

CO

z,u

1,5-.

1,0-0,5-

S^^ D

n^ — — a _-n — **~~—————— g —————————————————————————— . ————————————

0,0- — , • . • , • i • i • . — ,0 1 2 3 4 5 6 7

AGE, 105 years

0

Q.

^~

-o

S

1UU 1

80JI

•60-

40-

20-

v D

1 2 3 4 5 6 7AGE, 105 years

Fig. 9. Profile properties vs. soil age for properties that decrease with age. For curve fittings, see Table 5.


20-

i 0enO 0 1 2 3 4 5 6 7

AGE, 105 years

20-|S 15DO

* 10:« 5-

0 1 2 3 4 5 6 7AGE, 105 years

1 «•Q.

120

* ""

• 30-

0 1 2 3 4 5 6 7AGE, 105 years

Fig. 10. Profile properties vs. soil age for properties that are not age related.

00 1 2 3 4 5 6 7

AGE, 105 years

200"

I 150

x -•= 1001CD ^*- 13

21 50-

0 1 2 3 4 5 6 7AGE, 105 years

100

E 80-ox 60-

W 20-w

100

1 2 3 4 5 6 7AGE, 105 years

o> | 80-

CD x 60-1OT :!±

'<2 § 40-|

£ 20£" wQ 0*

0 1 2 3 4 5 6 7AGE, 10s years-

^ 100-

S E 80-1

!2 —"to -p5 i 401

1 2 3 4 5 6 7AGE, 105 years

100

i § solc•3 X 60-

|-201

00 1 2 3 4 5 6 7

AGE, 105 years0 1 2 3 4 5 6 7

AGE, 10s years

200

150-

O

0*0 1 2 3 4 5 6 7

AGE, 10s yearsFig. 11. Morphological indices vs. soil age.

100

- § 80

20

0^0 1 2 3 4 5 6 7

AGE, 105 years


5000

o 4000-< X^>, 3000-to 'cO f 2000-

w 1000-

1 2 3 4 5 6 7AGE, IQS years

200

_<w

50-

0+1 2 3 4 5 6

AGE, 105 years

1500

1000-E .t:

5 6AGE, 10s years

5 3000(5 o5 x 2000-« "EQ- 3

1000-c>ci

1 2 3 4 5 6AGE, 10s years

4000

« x-

1 3000-

2000-

1000-

0 1 2 3 4 5 6AGE, 10s years

2500

^ £20000) O

I x 1500-

-| § 1000to —•5 < 500"> w

1 2 3 4 5 6AGE, 10s years

2500

< ° 20001® X

1 .1= 15001o =•§ - looo-

500-

o-

50

0 1 2 3 4 5 6AGE, 10s years

E 40-

20-

10

0

X cCL D

<w

0 1 2 3 4 5 6AGE, 10s years

_ 4000

Si o 3000'ra xo .•= 2000

o < 1000-

0 0*0 1 2 3 4 5 6

AGE, 10s years

Fig. 12. Analytical indices vs. soil age.

150-E

— ox 100-

ra ^

- 50-w

0*0 1 2 3 4 5 6 7

AGE, 10s years

of the Holocene and Upper Pleistocene age (Fig. 12).Similar increases as for these AI have been describedby Birkeland (1984b) for soils of the Holocene age inNew Zealand. Some of these AI are not strongly agedependent, such as organic C and carbonate.

Mineralogical Indices. The Minel are also well relatedwith age. These Minel point to a constant and intenseincrease with age (Fig. 13).

ChronofunctionsFive models of regression equations were assayed for

the chronofunctions of these soils: linear (Y = a + bX),second-degree polynomial (Y = a + bX + cX2), power

(Y = aXb), logarithmic (Y = a + blogX), and exponential(Y = abx). In each equation Y is a soil property and Xis the geomorphic age of the soil surface. Of all thesemodels, the power, second-degree polynomial, and loga-rithmic equations proved to be the ones best represented:almost all the regressions defined for the MI and AI andalso for many of the properties corresponded to theseequations (Tables 4 and 5). The linear model was thebest fit hi very few cases; the exponential equations hadno representativity at all for these soils. In previousstudies (Birkeland, 1984a,b; Yaalon, 1975; Bockheim,1980,1990; Little and Ward, 1981; Harden, 1982; Muhs,1982), the equations most frequently found have beenthe logarithmic and power models.

922 SOIL SCI. SOC. AM. }., VOL. 58, MAY-JUNE 1994

300

- 800LUz ES ° 600">_ xCO ^

§•'1 400-

O o-i0 1 2 3 4 5 6 7

AGE, 105 years

Fig. 13. Mineralogical indices vs. soil age.

In general, the correlation coefficients obtained hadhigh values. The regression equations with the best fitsfor each chronofunction are shown hi Table 5.

Steady State?It is interesting to note that very few properties of the

soils studied here seem to reach steady state duringtheir development. All of them, except for sand content,continue to undergo changes even in the oldest soils ofthe chronosequence. For a large number of properties,however, development manifests only during the firstperiod, corresponding to the Holocene and Upper Pleisto-cene soils (up to about 100000 yr), with the rate ofdevelopment slowing thereafter.

The paucity of results confirming the steady-state the-ory seems to be quite patent in most chronosequencesinvestigated hi different studies. Bockheim (1980) indi-cates that "the trends shown in this study cast somedoubt as to whether soils reach a steady state (dynamicequilibrium) with their environment. Most of the proper-ties investigated continue to change despite the passageof as many as 106 yr." Similar conclusions were reachedby Muhs (1982) for the soils of marine terraces in Califor-nia of up to 106 yr old. Also, Busacca (1987), studyinga chronosequence of river terraces of the SacramentoValley (California) of up to 106 yr, concluded, "Appar-ently none of the soils hi the sequence has reached asteady state of development."

In light of this, it seems clear that most soil propertiescontinue to develop with tune and that no final stage ofdevelopment is reached. Despite this, it is necessary totake into account that, during the development of achronosequence, not only are there changes with tunebut also modifications due to climatic factors and thesubordinate factor of organisms; these may have led toimportant variations hi the final behavior of the soils ofthe chronosequence (hi fact in most studies investigatorsshould be using the term climobiochronosequences).

CONCLUSIONSThe following conclusions can be drawn from the

results. First, the soil properties show several types ofbehavior.

1. As age progresses, some properties increase regu-larly throughout the chronosequence. This is stronglydependent on the age, COLE, and the available waterof the Bt horizon.

2. Some properties continue to increase with age butmore moderately during the last phases: for example,water retention at 0.03 and l.SMPa and cation-exchangecapacity of the Ap horizon, Fed of the Bt horizon, solumthickness, clay accumulations at depths of 15, 50, 100,150, 200, and 250 cm, quartz content, and quartz/feld-spar ratio.

3. Other properties cease to change hi the soils fromthe Middle Pleistocene. In this situation are the silt andavailable water of the Ap horizon and the clay content,water retention at 0.03 and 1.5MPa, and cation-exchangecapacity of the Bt horizons.

4. Still other properties show a strong increase onlyduring the last phases (Middle Pleistocene and oldersoils). In this situation are the clay and N contents ofthe Ap horizon, the thickness of the Bt horizons, andcarbonate accumulation.

5. Other properties decrease with age, with strongdecreases up to the Upper Pleistocene soils, thereafterdecreasing very moderately (feldspar contents), or theycease to increase for the soils from the Middle Pleistocene(the Ap and Bt horizon sand contents) or show an increaseduring the last phases (Bt horizon bulk density).

6. Other properties are not age related. Within thisgroup there are two subgroups. One includes those prop-erties that remain constant (Ap horizon base saturation)and the other those that vary chaotically (Ap horizonorganic matter and pH and Bt horizon silt).

The second conclusion is that the horizon developmentindices show marked increases hi their values with theadvancing age of the soils and also show a progressivedifferentiation with tune for the horizons of the soilprofile.

Third, the soil development indices show very goodcorrelations with age. In the vast majority of cases, thetendency to increase falls off strongly for the oldest soilsof the Middle Pleistocene age.

Finally, in most cases, the properties and developmentindices continue to evolve constantly throughout the chro-nosequence without steady state being reached; however,


Table 4. Correlation coefficients for regression equationst relating to properties and indices with soil age.

Solum thicknessBt horizon thicknessSand, Ap horizonSand, Bt horizonSilt, Ap horizonSilt, Bt horizonClay, Ap horizonClay, Bt horizonClay accumulation to IS cmClay accumulation to 50 cmClay accumulation to 100 cmClay accumulation to ISO cmClay accumulation to 200 cmClay accumulation to 2SO cmWater retention at 0.03 MPa, Ap horizonWater retention at 0.03 MPa, Bt horizonWater retention at l.S MPa, Ap horizonWater retention at 1.5 MPa, Bt horizonAvailable water, Ap horizonAvailable water, Bt horizonOrganic matter, Ap horizonN, Ap horizonpH, Ap horizonCation-exchange capacity, Ap horizonCation-exchange capacity, Bt horizonDithionite-citrate-extractable Fe, Bt horizonCaCO3QuartzFeldsparQuartz/feldspar ratio

Structure, morphological indexTexture, morphological indexDry consistence, morphological indexMoist consistence, morphological indexClay films, morphological indexMelanization, morphological indexRubification, morphological indexGeneral morphological indexSand, analytical indexClay, analytical indexWater retention at 0.03 MPa, analytical indexWater retention at 1.5 MPa, analytical indexAvailable water, analytical indexOrganic matter, analytical indexCaCOj analytical indexpH, analytical indexCation-exchange capacity (sum of bases),

analytical indexGeneral analytical indexQuartz mineralogical indexFeldspar mineralogical indexGeneral mineralogical index

Linear

0.350.330.340.590.030.160.590.670.600.730.700.630.640.670.500.460.470.430.280.300.120.370.120.640.200.570.420.470.450.55

0.150.410.340.340.290.460.660.490.420.620.490.450.530.070.420.63

0.270.460.500.910.73

Polynomial

Properties0.360.440.450.820.500.230.670.920.660.730.800.770.750.760.520.630.620.740.470.310.210.560.370.720.770.670.420.470.450.50

Indices0.180.480.480.480.480.530.750.650.570.750.620.650.570.090.420.68

0.370.570.520.940.76

Power

0.67J0.280.710.850.500.180.550.940.610.900.920.900.900.900.810.670.640.790.770.250.310.140.040.710.590.860.790.790.580.71

0.660.770.810.760.790.860.410.830.830.860.810.830.810.450.770.35

0.770.860.320.08

. 0.05

Exponential

0.270.240.350.640.040.160.580.590.560.510.380.350.360.380.400.480.530.430.250.330.100.320.120.640.230.480.360.420.500.46

0.180.220.240.220.220.440.690.280.240.300.250.250.260.100.360.65

0.210.300.490.510.40

Logarithmic

0.610.140.490.870.420.160.400.930.430.780.970.970.950.920.760.620.570.740.770.250.230.180.040.430.500.900.530.670.670.59

0.340.820.830.730.690.730.400.920.920.970.930.930.890.250.490.39

0.750.920.320.300.24

t Linear, y = a + bx; polynomial, y = a + bx + ex1', power, y = ox*; logarithmic, y = a + b log*; exponential, y = ab*.j Maximum correlation coefficients are in italics.

the soils of the Middle Pleistocene age do reach a stateof evident maturity from which development progressesvery slowly.


Table 5. Parameters included in each regression equation, and best fits for each correlation.

Solum thickness, cmBt horizon thickness, cmSand, Ap horizon, %Sand, Bt horizon, %Silt, Ap horizon, %Silt, Bt horizon, %Clay, Ap horizon, %Clay, Bt horizon, %Clay accumulation to IS cm, % mClay accumulation to 50 cm, % mClay accumulation to 100 cm, % mClay accumulation to 150 cm, % mClay accumulation to 200 cm, % mClay accumulation to 250 cm, % mWater retention at 0.03 MPa, Ap horiz., g kg"1

Water retention at 0.03 MPa, Bt horiz., g kg-'Water retention at 1.5 MPa, Ap horiz., g kg"'Water retention at 1.5 MPa, Bt horiz., g kg"1

Available water, Ap horiz., g kg"1

Available water, Bt horiz., g kg"1

Organic matter, Ap horiz., g kg"1

N, Ap horiz., g kg"1

pH, Ap horizonCation-exchange capacity, Ap horizon, cmolc kg"1

Cation-exchange capacity, Bt horizon, cmolc kg"1

Extractable Fed, Bt horizon, g kg"1

CaC03, g kg"1

Quartz, g kg"1

Feldspar, g kg"1

Quartz/feldspar ratio

Structure, morphological index (MI) (EMIunit x cm)Texture, MI (EMI unit x cm)Dry consistence, MI (EMIunit x cm)Moist consistence, MI (EMIunit x cm)Clay films, MI (EMIunit x cm)Melanization, MI (EMIunit X cm)Rubification, MI (EMIunit x cm)General MI (EMIunit x cm)Sand, analytical index (AI) (EAIunit x cm)Clay, AI (EAIunit x cm)Water retention at 0.03 MPa, AI (EAIunit x cm)Water retention at 1.5 MPa, AI (EAIunit x cm)Available water, AI (EAIunit x cm)Organic matter, AI (EAIunit x cm)CaCO3, AI (EAIunit x cm)pH, AI (EAIunit x cm)Cation-exchange capacity (sum of bases) AI (EAIunit x cm)General AI (EAIunit x cm)Quartz mineralogical index (Minel) (EMinelunit x cm)Feldspar Minel (EMinelunit x cm)General Minel (EMinelunit X cm)

Model

Dependent variablePowerpolynomialPowerLogarithmicpolynomialpolynomialpolynomialPowerpolynomialPowerLogarithmicLogarithmicLogarithmicLogarithmicPowerPowerPowerPowerPowerExponentialPowerpolynomialpolynomialpolynomialpolynomialLogarithmicPowerPowerLogarithmicPower

IndicesPowerLogarithmicLogarithmicPowerPowerPowerpolynomialLogarithmicLogarithmicLogarithmicLogarithmiclogarithmicLogarithmicPowerPowerpolynomialPowerLogarithmicpolynomialpolynomialpolynomial

a

154.210136.46958.57934.11820.68114.2059.556

52.6641.377

10.50337.68354.13969.21283.22215.03333.2585.656

22.0329.3299.6731.5330.0505.4853.579

14.6211.6372.317

49.13746.798

1.109

36.749102.87048.66330.28050.25048.10812.64556.85497.523

2445.4001611.5001951.6001257.000478.86197.99425.673

1581.71381.19346.0032.598

46.532

b

0.199- 15.865- 0.055- 18.929

9.932-2.845-0.964

0.187-0.103

0.25615.16620.74626.32131.8120.1450.1520.1300.1820.1510.0290.084

-0.008-0.417-0.56811.9770.6441.6430.170

-14.6040.295

0.57037.75717.5360.3910.6710.211

15.04420.55536.611

999.380628.230770.220472.500

0.1922.0870.3630.404

27.9514.6902.473

26.271

c

4.260

- 1.6230.3510.521

0.072

0.0020.0850.269

-1.175

- 1.550

-0.357

4.1651.481

11.550

R2

0.670.440.710.870.500.230.670.940.660.900.970.970.950.920.810.670.640.790.770.330.310.560.370.720.770.900.790.790.670.71

0.660.820.830.760.790.860.750.920.920.970.930.930.890.450.770.680.770.920.520.940.76

P

0.050

0.0100.0050.050

0.0500.0010.0500.0010.0010.0010.0010.0010.0050.0500.0500.0100.005

0.050

0.0100.0100.0050.0050.0050.0500.010

0.0500.0050.0050.0050.0050.0010.0100.0010.0010.0010.0010.0010.001

0.0050.0500.0050.0010.0500.0010.005


Documents

(1994) Chronosequence in Almar River Fluvial-Terrace Soiledafologia.ugr.es/introeda/tema01/imagenes/AlmarUSA.pdf · 912 SOIL SCI. SOC. AM. J., VOL. 58, MAY-JUNE 1994 on river terraces