Evolution and significance of soil magnetism of basalt-derived chronosequence soils in tropical southern China

doi:10.4236/as.2011.24070

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Vol.2, No.4, 536-543 (2011)

doi:10.4236/as.2011.24070

Agricultural Scienc es

Evolution and significance of soil magnetism of

basalt-derived chronosequence soils in tropical

southern China

Decheng Li1*, Yanfang Yang1,2, Jinping Guo3, Bruce Velde4, Ganlin Zhang1, Feng Hu2,

Mingsong Zhao1

1State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China;

*Corresponding Author: dcli@issas.ac.cn

2College of Resources and Environmental Science, Nanjing Agricultural University, Nanjing, China;

3Fujian Province Tobacco Company, Fuzhou, China;

4Laboratoire de Géologie, Ecole Normal Supérieure, Paris, France.

Received 25 August 2011; revised 10 October 2011; accepted 26 October 2011.

ABSTRACT

Soil samples were collected from eight basalt-

derived chronosequence soils with the ages of

0.01, 0.58, 0.92, 1.33, 2.04, 3.04, 3.76 and 6.12 Ma

respectively from Leizhou Peninsula and north-

ern Hainan Island of tropical southern China.

Magnetic parameters of magnetic susceptibility

(MS), percentage of frequency-dependent mag-

netic susceptibility (FDS%), anhysteretic rema-

nent magnetization (ARM), saturation isother-

mal remanent magnetization (SIRM), soft and

hard isothermal remanent magnetization (IRMs

and IRMh) of the collected samples were meas-

ured to study the evolution and the significance

of the magnetism with soil age. The results

show that the magnetic parameters changed

fast from Primosols to Ferrosols (0.01 - 0.92 Ma)

but slowly at Ferralosols stage (1.33 Ma~), it

suggests a stable phase occurred for soil mag-

netism at Ferralosols, the existence of this

phase could be supported by the little changes

in the contents of clay, Fet and Fed. Obvious

differences existed in the values of magnetic

parameters between Ferralosols and other soil

types (Primosols and Ferrosols), FDS%: Fer-

ralosols > 10%, Primosols and Ferrosols < 10%;

ARM, Ferralosols < 7000 × 10–8 SIm3·kg–1, Pri-

mosols and Ferrosols > 8000 × 10–8 SIm3·kg–1,

thus, it is possible to differentiate Ferralosols

from other soil types in tropical region by using

magnetic indices.

Keywords: Magnetic Parameters; Basalt-Derived

Chronosequence Soil; Iron Oxides; Tropical

Southern China

1. INTRODUCTION

Soil chronosequences, given that the other soil-form-

ing factors are similar, are often used to demonstrate the

relative degree of soil development under varying dura-

tion of soil formation [1]. Studies have proved that dif-

ferent soil types may be formed from the same parent

material in a region with the continuation of the weath-

ering process, for examples, the systematical studies of

soil development in Hawaii by Kennedy et al. [2], Chad-

wick et al. [3,4], Kurtz et al. [5] and Derry et al. [6] and

in northern Hainan Island by Huang and Gong [7],

Huang et al. [8,9] and Zhang et al. [10].

Magnetic measurement is a simple, quick and non-

destructive technique for characterizing soils and sedi-

ments. Soil taxonomy has got remarkable achievements

in the world, for examples, USDA-NRCS, 2010; IUSS-

ISRIC-FAO, 2007; CRGCST, 2001. Although some re-

searchers attempted to use magnetic susceptibility as a

tool for soil classification to separate Oxisols, Ultisols

and Entisols at a low taxonomic level [11-14], no quan-

titative diagnostic information of magnetism available in

current soil taxonomy.

As Huang et al. [9] disclosed that basalt-derived soils

in the tropical Leizhou Peninsula and Hainan Island of

south China can develop gradually from Primosols into

ferralic-horizon characterized Ferralosols [15], so here

we collected chronosequence samples of basalt-derived

soils in this region in 2007 to explore the possible sig-

nificance of magnetic parameters in identifying soil types

by studying the evolution of soil magnetism.

D. C. Li et al. / Agricultural Sciences 2 (2011) 536-543

537537

2. MATERIALS AND METHODS

2.1. Chronosequence Red Soil Samples

The studied soils are from located in the tropical Le-

izhou Peninsula and northern Hainan island of southern

China, where with a present tropical monsoon climate of

a mean annual rainfall of 1400 - 1800 mm and a mean

temperature of 23˚C - 24˚C. The change of climate dur-

ing the Quaternary is negligible, which remains in a

warm subtropical climate and no more than 2.5˚C change

of temperature [16]. The studied eight basalt-derived

chronosequence soils (see Ta ble 1) were located at up-

lands Soils, all sampled sites have udic soil moisture

regimes and hyperthermic soil temperature regimes and

under secondary shrub or forest vegetation. The ages of

the parent basalt-rocks of the eight soil profiles were

dated by using K-Ar methods [17-19], which could be

taken roughly as the proxies of the time-spans of soil

formation due to the general lack of well-dated soil real

age [20].

Fed/Fet usually can be used to validate the chronose-

quence reliability because it is a good indicator of the

wearthering degree of soils [10,21-25], The increase of

Fed/Fet in B horizons with soil age proved the reliability

of the studied chronosequence soils (Figure 1).

2.2. Measurements of Soil Samples

Soil magnetic parameters of all horizons of the sam-

pled profiles were measured in the State Key Lab of Es-

tuary and Coast of East China Normal University. Mag-

netic susceptibility (MS) was measured at low frequency

(0.47 kHz, MSlf) and high frequency (4.7 kHz, MShf)

using a Bartington MS2 meter with dual frequency sen-

sor. Frequency-dependent magnetic susceptibility (FDS%)

was calculated as: FDS (%) = 100 × [(MSlf − MShf)/

MSlf]. Anhysteretic remanent magnetization (ARM) was

measured in the Molspin magnetometer after magnetiza-

tion with a Molspin AF demagnetizer. The peak AF field

used was 100 mT and the DC bias was 0.04 mT. Iso-

thermal remanent magnetization (IRM) was produced in

progressively increasing magnetic fields up to 1000 mT

with a Molspin pulse magnetizer. IRM1000 mT was defined

as the saturation isothermal remanent magnetization

(SIRM). IRM20 mT was defined as soft IRM (IRMs), and

(SIRM-IRM300 mT) was defined as hard IRM (IRMh).

DC−100 mT was defined as demagnetizing factor in 100 mT.

Figure 1. The temporal change of Fed/Fet in B horizons of

basalt-derived chronosequence soils.

Table 1. Basic information of basalt-derived chronosequence soils.

Profile Sampling site Location Soil age (Ma) Soil type(CRGCST, 2001) Vegetation Horizon (cm)

HN01 Shizilu town,

Northern Hainan

19˚51.488'N

11 0 ˚21.327'E 0.01 Primosols Pineapple, loquat, azedarach

A 0 - 16

B 16 - 40

BC 40 - 100

C > 100

LZ01 Yinli town

Leizhou Peninsula

20˚36.361'N

11 0 ˚10.147'E 0.58 Ferrosols Sparse grass, shrub

A 0 - 20

B 20 - 90

BC 90 - 150

C > 150

LZ04 Chenbei town

Leizhou Peninsula

20˚20.367'N

11 0 ˚07.051'E 0.92 Ferrosols Eucalyptus, sparse grass

A 0 - 23

B 23 - 105

BC > 105

HN03 Yongfa town

Northern Hainan

19˚46.346'N

11 0 ˚12.887'E 1.33 Ferralosols Azedarach, eucalyptus,

A 0 - 15

B 15 - 118

BC > 118

LZ07 Nanshan town

Leizhou Peninsula

20˚15.947'N

11 0 ˚09.583'E 2.04 Ferralosols Eucalyptus, sparse grass

A 0 - 20

B 20 - 120

BC > 120

LZ05 Haian town

Leizhou Peninsula

20˚16.609'N

11 0 ˚15.218'E 3.04 Ferralosols Eucalyptus, sparse grass

A 0 - 18

B 18 - 120

BC > 120

HN04 Bailian town,

Northern Hainan

19˚53.998'N

11 0 ˚07.438'E 3.76 Ferralosols Eucalyptus, sparse grass

A 0 - 30

B 30 - 120

BC > 120

LZ08 Hainan town

Leizhou Peninsula

20˚17.662'N

11 0 ˚11.441'E 6.12 Ferralosols Eucalyptus, sparse grass

A 0 - 20

B 20 - 150

BC > 150

D. C. Li et al. / Agricultural Sciences 2 (2011) 536-543

538

Soil other properties were measured in the Soil and

Environmental Analysis Center of the Institute of Soil

Science, Chinese Academy of Sciences (ISSCAS) ac-

cording to the standard methods outlined by the Chinese

Society of Soil Science [26] (CSSS, 1984). The sand, silt

and clay fractions were extracted by the pipette method.

For the fine earths (<2 mm), the content of total iron (Fet)

was measured by ICP-AES method after hydrofluoric

acid digestion and the content of free iron oxide (Fed)

was determined by the phenanthroline-colorimetry method

after being extracted by the dithionitecitrate-bicarbonate

solution (DCB) [27].

Particle size distribution (PSD) of clay fraction ob-

tained by the pipette method was measured by laser dif-

fraction (LD) method: soil samples were sieved by 2 mm

mesh size after air-dried at room temperature, the or-

ganic matter was removed with 6% H2O2, carbonate

removed with 0.2 mol·L–1 HCl, Ca2+ and chlorides re-

moved with 0.05 mol·L–1 dilute HCl and distilled H2O.

Then soil samples were put into 0.5 mol·L–1 NaOH for a

night after being shaken for several minutes and were

dispersed with the supersonic method (160 w, 10 - 15

min), then PSD data were obtained by using Beckman

Coulter LS230 (He-Ne laser, 5 mw power, 750 nm wave-

length, 0.04 - 2000 μm measuring range, about 0.1 g soil

for each sample).

3. RESULTS AND DIS CUSSION

3.1. Temporal Changes of Magnetic

Parameters

The data of mesured magnetic parameters of 0.01 Ma

(Primosols), 0.58 Ma (Ferrosols), 1.33 Ma (young Ferro-

sols) and 6.12 Ma (old Ferralosols) were compared here

to disclose the evolution of magntism with time (see

Figure 2).

MS gives an approximate indicator of concentration

of the ferrimagnetic minerals in the soil. From the ir-

regular change of MS with soil age, we fails to find the

decline tendency of magnetic susceptibility of basalt-

derived soils with pedogenic development or soil age as

proposed by Lu et al. [25]. Most studies found that MS

hardly can be used solely to indicate the pedogenic de-

velopment becauese that fatcors which can affect MS are

complicated [7].

Figure 2. The temporal change of magentic parameters of basalt-derived chronosequence soils.

D. C. Li et al. / Agricultural Sciences 2 (2011) 536-543

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From MS change from C to BC to B to A horizons it

can be found that pedogenic process can enhance MS of

basalt-derived soils as others have found it (for example,

[7]). No significant correlation exitsed between MS and

Fet, Fed, Feo, Fed/Fet and Feo/Fet,which prove that MS is

determined by the concentration of ferrimagentic miner-

als but not of iron iorn oxdies.

FDS indicates the presence of grains lying at the sta-

ble single domain (SSD)-superparamagnetic (SP) bound-

ary, around 0.02 μm for isodiametric grains [28,29],

while ARM is generally more sensitively proportional to

the concentration of SSD grains of ferrimagnetic miner-

als. According to Dearing’s model [29], FDS of 0.01 Ma

profile is lower than 5%, indicating little SP grains in the

soil. FDS% of 0.58 Ma profile ranges from 5% to 10%,

indicating significant amount of SP grains existed in the

soil [11,28]. FDS of 1.33 Ma profile and 6.12 Ma profile

both are higher than 10%, suggesting more than 75%

frequency-dependent ultra-fine SP grains appeared in the

soils. The origin of the magnetic susceptibility in 0.01

Ma is believed to be inherited coarsed MD grains, while

SP particles are assumed to be autogenic and suggest

enhanced pedogenic development [30,31], thus, from the

decrease of ARM and the increase of FDS with soil age,

it may be concluded that SSD grains were weathered

further into SP grains.

SIRM is a concentration-dependent magnetic parame-

ter, while IRMs is more sensitively proportional to the

concentration of coarsegrained (MD or PSD grains)

ferrimagnetic minerals. The significantly positive liner

correlation between SIRM and IRMs (R = 0.991**, n =

24) proves that SIRM is dominantly contributed by IRMs.

SIRM and IRMs decreased with soil age means MD and

PSD grains decrased grudally. SIRM and IRMs of 0.01

Ma profile is higher than those of other three profiles,

which means higher concentrations of coarsed-ferrimag-

netic phases (e.g. magnetite and maghemite) in young

profile due to the input of parent material. The rapid

decrease of SIRM and IRMs after 0.01 Ma shows the

quick reduce of ferrimagnetic phases with soil age in

soils, howere, the reduce becomes slowly from 0.58 Ma

to 6.12 Ma, which means a slow decrease of MD or PSD

grains of ferrimagnetic phases in the older soils.

IRMh can reflect the concentrations of antiferromag-

netic minarals (e.g., hematite and goethite). DC−100 mT

reflect the ratio of antiferromagnetic minerals to ferri-

magentic minerals (e.g., magnetite and maghemite). The

increase of IRMh and the decrease of DC−100 mT with soil

age means the more and more antiferromagnetic miner-

als appeared in the soils due to the transformatiuon of

ferrimagentic minerals to antiferromagentic minerals.

From the values of IRMh, it may be concluded that the

magnetic minerals in 0.01Ma proflie is dominated by the

little amount of ferrimagnetic minerals, but 0.58 Ma and

1.33 Ma profiles contain ferrimagnetic minerals and an-

tiferromagentic minerals, while in the 6.12 Ma the mag-

netic minerals are dominated by antiferromagentic min-

erals.

3.2. Evolution Mechanism of Magnetic

Parameters

Soil magnetism is dominated by magnetic minerals,

particularly by ferrimagentic minerals. It has been

proved well that the evolution mechanism of soil mag-

netism are mainly on the following two underlying hy-

potheses: with pedogenic development, firstly, the litho-

genic ferromagnetic minerals, in subtropical and tropical

basalts mainly magnetite and titanomagnetite, were weath-

ered gradually and partly transformed into maghemite,

hematite; secondly, at the same time nano-sized pe-

dogenic grains (mainly SP grains) of ferromagnetic min-

erals were being progressively formed [9,14,25,32-34,].

X-ray diffraction results of iron oxides from Huang et

al. [9] (see Tab le 2) in the similar basalt-derived chro-

nosequence soils in northern Hainan Island were cited

here to show the transform of ferromagnetic minerals,

from Table 2 it can be found with the increase in soil

forming age magnetite descended while hematite and

maghemite ascended in fine earth fraction and clay frac-

tion. Although now it is impossible to differentiate be-

tween magnetite and maghemite using X-ray diffraction

Table 2. Iron oxides in soils at different developing and weathering age (cited from [9]).

Age Iron oxides in clay fraction (<2 μm) Iron oxides in fine earth (<2 mm)

0.01 Ma He (+) He (+), magnetite (+)

0.58 Ma He (+), Tm (+) Tm (+)

1.33 Ma He (+++), Go (+++), Mh (+) He (+++), Go (+++)

6.12 Ma He (+++), Mh (++) He (+++), Mh (++), Go (++)

He, hematite; Mn, magnetite; Tm, Titanomagnetite; Go, gothite; Mh, maghemite; +, small amount; ++, certain amount; +++, larger amount.

D. C. Li et al. / Agricultural Sciences 2 (2011) 536-543

540

because their peaks are very close and practically indis-

tinguishable, studies found that the corresponding mag-

netic phase in the superparamagnetic (SP) and single

domain (SD) particles is maghemite rather than magnet-

ite because pedogenic ferrimagnetic mineral particles

with high surface to volume ratios are eventually oxi-

dized into maghemite regardless of their initial states

(magnetite or maghemite). To prove the maghemite is

the main controbutor to the mangetism of studied soil

profiles, DCB solution is used to treated the soil samples,

it found that FDS after DCB solution treatment de-

creased by 58.0% ~ 95.7% with a mean of 81.6%, which

indicates the high content and the significant contribu-

tion of maghemite to soil magnetism in the studied soils

because DCB solution can dissolve nanosized (<100 nm)

magnetite but not maghemite [7,35-37].

The grain sizes of magentic minerals in soils are usu-

ally less than 2 μm (clay fractions), LD techniques can

provide the information of PSD distributions of clays

[38,39]. Figure 3 showed that Primosls is domintaed by

the particles of 0.4 - 2 μm (PSD grains, 0.05 - 1 μm; MD

grains, 1 - 2 μm), and then from Ferrosols to Ferralosols

the particles of ≤ 0.4 μm increased obvisouly, means

more finer particles formed. Due to the detect limit (usu-

ally is 0.04 or 0.05 μm) of LD instrument, it can’t give

PSD informatoion of particle fractions of ≤ 0.04 or 0.05

μm, however, the uniform PSD distribution patterns in

clay fractions in Ferrosols and Ferralosols may indicate

that PSD similarity of magnetic iorn oxides in Ferrosols

and Ferralosols.

3.3. Potential Significance of Magnetic

Parameters in Identifying Soil Types?

The data of the less disturbed B horizons of the stud-

ied soils were used here to explore the potential signifi-

cance of magnetic parameters in identifying soil types

(Figure 4). Significant correlations existed between FDS,

ARM, SIRM, IRMs and soil age, among of which, a

positive exponential correlation for FDS, while negative

logarithmic correlations for ARM, SIRM and IRMs,

which proved that these magnetic parameters of B can

indicate the soil age or soil development degree, which

were already disclosed well by other studies (for exam-

ples, [7,25]).

It could be also found from Figure 4 that in the period

of Ferrolosols (1.33 Ma~), FDS, ARM, SIRM and IRMs

changed slowly, suggesting a relative stable phase oc-

curred at 1.33 Ma for soil magnetic parameters, which

may be regarded as a stable phase to be added into Lu et

al.’s new conceptal model of soil magentism evolution

[25], the lack of this new stable phase in Lu et al.’s

model is attributed to no Ferrolosols in subtropical

Zhejiang province.

The existence of the stable phase may be proved from

one aspect by the temporal changes of clay content and

Fet and Fed. Soil magnetism is mainly dominated by the

contents, components and grain sizes of magnetic iron

oxides. Iron oxides are concentrated mainly in the fine

fractions of soils in subtropical and tropical regions, par-

ticularly in clay fractions. Figure 5 shows Ferralosols

was dominated by clay fractions and Fet and Fed changed

little in Ferralosols stage.

Figure 3. The temporal changes of clay fractions of basalt-

derived chronosequence soils.

D. C. Li et al. / Agricultural Sciences 2 (2011) 536-543

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Figure 4. The temporal changes of magnetic parameters of B horizons of basalt-derived chronosequence soils. R2* significant at P <

0.05 level, R2** significant at P < 0.01 level.

Figure 5. The temporal changes of clay content, Fet and Fed of B horizons of basalt-derived soils.

The above stable phase is significant in Ferraloslos

identification with soil magnetism. From Figure 4 it can

be found that obvious differences in the values of FD

and ARM between Ferralosols and other soils, i.e., Pri-

mosols or Ferrosols: FDS, Ferralosols > 10%, Primosols

and Ferrosols < 10%; ARM, Ferralosols < 7000 × 10–8

SIm3·kg–1, Primosols and Ferrosols > 8000 × 10–8

SIm3·kg–1.

With the consideration of the measured values of

magnetic parameters in other studies on basalt-derived

soils [7,25,40], for examples, FDS of Ferralosols B ho-

rizons in Huang and Gong [7] were also > 10%, while <

10% in other soil types; in the five soil profiles of Lu et

al. [25], B horizons FDS% of four profiles were < 10%,

therefore, it is possible to use magnetic indices to iden-

tify Ferralosols in tropical region. To establish the mag-

D. C. Li et al. / Agricultural Sciences 2 (2011) 536-543

542

netic diagnostic indices of soils, one way more reliable is

by the systematical collection and analysis of enough

soil samples, but it is costly in time and fund; the other

way more conveniently may be by studying the chro-

nosequence soils as we did here. However, we advise

here that more studies need to validate the above-men-

tioned magnetic indices and they should be used simul-

taneously with the existing other indices of profile mor-

phological, physical and chemical properties.

4. CONCLUSIONS

Our study disclosed further that evolution of soil

magnetic parameters with soil age, and they changed fast

from Primosols to Ferrosols but slowly during Fer-

ralosols, which suggested a relative stable phase oc-

curred in Ferrolosols phase, it proves the possibility to

use establish magnetic diagnostic indices for Ferralosols

identification in the tropical regions.

5. ACKNOWLEDGEMENTS

This study was jointly supported by the Knowledge Innovation Pro-

gram of the Chinese Academy of Sciences (KZCX2-YW-409) and the

National Natural Science Foundation of China (Nos. 40771091 and

40625001). We thank Dr. Yaoguo Hu of Guangdong Institute of

Eco-Environment and Soil Sciences) and Prof. Zhiping Qi of Hainan

University for their helps in soil sampling.

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