The Characteristics of Iron Concentration in Tropical Paddy Soils with Different Organic Matter Content

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J. l'anah 1!-0fJ. ""it,', J6, 1003

The Characteristics of Iron Concentration in Tropical

Paddy Soils with Different Organic Matter Content

A rief Hartono I , W idiatmaka I , P. Cunni,2 J. Berrier2, A Jaffrezic

ABSTRACT

The Characteristics of fron Concentration in Tropical Paddy Soils " 'ith Different Organic Matter Content (A. Hartono, Widiatmaka, P. Curmi,

J.

Berrier, and A JaffreJ:ic): To characterize iron (Fe) concentration in tropical paddy soils with ditTerent organic matter content, selected Fe pedological features were collected from two paddy soil profiles in Damlaga, Bogor and tv.·o paddy soil profiles from Karawang. Bulk samples and Wlcovercd thin section were subjected to selective dissolution by bicarbonate (CB) or dithionite citrate-bicarbonate (DeB). Bulk Sal1lples analyses showed that Fe-CB increased with increasing organic matter content. On the contmry in samples with less organic matter content , Fe-OCB tended to increase. 336 hours dissolution tinle was not enough to dissolve all Fe-CB as indicated by the tendency of the curve to increase with tinle but it was optinlum for F e-DCB Compared to Fe-total, all samples showed relatively low Fe complexed or adsorbed by organic matter (Fe-CB) (u .S %-5:53 %) and high Fe oxide amorphous and crystalline (Fe-OCB - Fe-CB ) (6057 %-69.07 %) The wlcovered thin section observation showed that there was no Fe dis:;olution observed in selected coatings and mottles after 150 hours immersion in OCB solution. The XRD analyses showed the presence of goethite and ferryhydrite in the bulk samples. TIlese facts suggested that organic matter will enhance complexation and adsorption of Fe in the formation of Fe pedological features and atTected Fe oxide ratio in Fe concentration. These coating and mottle \\ere stable and dominated by Fe oxides partly cl)'stalline as shovm by the presence of goethite and ferrvhidrite minerals.

Key words: Fe Concentration, Fe Form, Paddy Soil, Pedological Feature

INTRODUCTION

Paddy soils undergo submersion and and organic acids or as solid in the fonn of drying periodically in a year. It enhances amorphous or crystalline minerals (Wang el

reduction and oxidation processes in the soil aI. , 1993 ; Jokoya I:!I 01., 1999). The and changes some chemical, biological and precipitation of iron and manganese as oxides physical properties . of the soils (Murase and are typical pedological features existing . in Kimura, 1997; Tae et 01. , 1998; Mozammel hydromorphic soils. Coatings in void, or

et 01.,2001; Kimura et 01., 2002) . Reduction concretion and diffuse mottles in matrix are and oxidation processes occurring in paddy the common formation . These pedological soils profoundly influence the dynamics of features are also can be observed in paddy iron in solution as free ion or complexed by soils. But so far the mechanism engaged in ligand existing in the soil such as hydroxides

lDepartment of Soil Sciences, Faculty of Agriculture, Bogor Agricultural University, Jalan Meranti, Kampus IPB Dannaga Bogor 16680, Indonesia

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Hartono, A., dick. : The Charaderistics of Iron Concentration in Tropical Paddy Soils

the formation of Mn or Fe concentration in hydromorphic environment are still not well understood.

Selective dissolution technique is one of the ways to study about formation of iron concentration. Citrate-bicarbonate (CB) and dithionite-citrate-bicarbonate (DCB) were introduced by Mehra and Jackson (1960) to selectively dissolve iron concentration. Pagliai and Sequi. (1982) proposed amonium oxalate to remove iron as amorphous form . Identification of iron concentration using Differential X-ray Diffraction (DXRD) was introduced by Schulze (1981) .

By using selective dissolution techniques citrate-bicarbonate (CB) and dithionite-citrate-bicarbonate (DCB) and X-ray Diffraction (XRD), Soulier (1991) and Acebal et al. (2000) identified and characterize Fe concentration. By using this dissolution techniques iron concentration can bc fractionated into I) iron complexed bv citrate without reduction, 2) amorphous

ｩｲｯｾ＠

forms. and 3) more or less crystallized iron

oxide. .

Iron concentration in the form of coating. mottle, nodule and concretion can develope in each horizon in soil profile with different environtment · such as different in organic matter content. The effect of organic matter to the formation Fe concentration is not well evaluated. By evaluating Fe concentration with different organic matter content will give insight into how organic matter . affect the formation of Fe concentration. Further, how Fe was immobilized in the form of coating,

ｭｾｴｴｬ･＠

or concretion in paddy soil. By using CB and DBC selective dissolution techniques the Fe form in the Fe concentration can be determined .

The objectives of this study were to evaluate how organic matter content effect the Fe form in Fe pedological features and its effect to ｾｨ･＠ formation of crystalline Fe oxide

by using selective dissolution citrate-bicarbonate (CB) and dithionite-citrate-bicarbonate (DCB) in bulk samples and in thin section. XRD analyses was used to identify the of Fe o.,ide crystalline in Fe concentration.

MATERALS A'iD METHODS

Samples

Selected samples were collected from two soils profiles of tropical paddy soils developed under volcanic ash parent materials in Darmaga, Bogor and two soils profiles developed under alluvium parent materiaJs in Karawang. Sampling was conducted where the paddy fields were dried and bared. The soil proflles in Darmaga were taken toposequencely. Upslope profile was symbolized as PID and downslope profile was symbolized with P2D. Two soil profiles from Karawang were taken in flat area and symbolized with PIK and P2K respectively. Soil profiles and selected horizon for bulk samples analyses and thin section observation are presented in Figure 1.

Bulk sample analyses which is ' to evaluate the kinetic of Fe dissolution of pedological feature of Fe to CB and DCB . solution were performed by selecting samples from horizons with different organic matter content from both locations. Kinds of samples evaluated were coating around root in Ap honzons from both locations and mottles in B horizon from Karawang. Besides, matrix from both locations were also sclected. Table I presents the selected samples and their . content of organic matter.

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ｾ｡ｬ＠ Paddy Soils

dissol utio n ci trate-and dil io nnecitrate-n bulk sam ples and iio nnecitrate-n

anal \ ses \1 S used to )xide cr. 5>wlll ne in Fe

\:\D '\lETHODS

es II 'fC II - ed from

f l ro lcal paddv soils \ ｯｬ｣｡ｮｾＮ＠ h parent

a.

80£ ｾ＠ two soils

:uI

·'lu m parent h og was - :' ｾ＠ I I ere dried

)il ｰＺｾＺＧＮ＠ 1 Darrnaga

cr: . l ;"'I- -" pe profile P! D a.: \yns]ope ::d \\: ' h P:: :> Two soil an .... ｾ＠ lai n in flat

i ｜ｾ＠ＬＺＺ＠ ? , and P2K and selected

,scs and thin in Figure I

\1 hich is to . F di ssolution of f F 0 CB and DCB

ｾ＠ selecting samples

·ff l'n organic matter n· Kinds of samples g a ound root in Ap

Ions and mottles in B

ｾ｡ｮ｟＠ Besides, matrix al so selected. Table samples and their ne r

l pedological features

10 i hei r stability same lechn ique were used on

)fl wilh size 110 x 70

I Ihe sile of samples for

J. Tanah Trop. No. 16, 2003

Apg21920 em

Bg3/53-69 em

P1D

P2D

Apg213060 em

Bg1l3760 em

Bgl/60-81 em

P1K P2K

[image:3.612.27.419.58.548.2]

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Hartono, A., dkk : The ｃｨＮＨｊｊｲ｡｣ｴ･ｲ［ＡｊＱｩ｣Ｎｾ＠ ofJron Concentration in J'ropicaJ Paddy .""oils

l abd ] . Sampl e used for I-mlk ｡ｮｾＬ＼［＠

r- ]'rOlil /hori/Oll/dcptil represt:llwtif

!

ｦＧ｣､ＨＩｾｩ｣｡Ｑ＠ fe8tures --- - l -( lrgil il ic ｃＨｊｾｉｾＭ［［ｬＨｾｬｬｧＯｧＩＭＭＭＧ＠

.

_P2D/Apg2N-20_C111 ＭＭｾｩＭＭ_I ＭＭＭＭ _{coating around rO(;I--}ｾＭＭＭＭ _{--- - - 2 ｾＭｉＭＭ} _ＭＭ _ＭＭ _ＭＭＭ _ｬ＠

P2KJApg2/30-60 cm ｾＮ coating around root i

'-- - 'T7- - '- - - 1

:-- P2KJBg l/60-S! cm

-t--

mottle

·- - r---zA- -- ---l

r-- ---:-:p-.]-:-;K-::/I::-'lg=-c_IC':/-::-:37=-_--::6(··-c)- mc- - - - t -· Crrey matrix

-l

7.8--- -1

PI K/Bgl/37-60cm Bnw,11lllatrix I 6.7

1

Tabk 2. Sampks used for thin section observation

I Proii lIhonzonJdepth n.:prest:nUltif ｾＭＭＭＭＭｬ］ＭＩ｣ＭＧ､ＢＧＭｯＭＧＭＭｉｯｧＭＭｃｩ｣｡ＭＧ＠ -"-I--:Cft:-atu-r-e-' - s

----=jl

l - -

-I P2D/Apg2/9-2 0 cm coating around root

r---·- ---P2=-=-:KJ:-:--:-A,.--P-g2-:-:"/3c-:_O--₆.,.-O,....·-crn- coating around root

ｾ＠

i

f _{PIKJBg1l37-60 cm} _mottle

ｲＭＭＭＭＭＭＭ］ｾｾｾｾｾＭ _P2KJBg ＭＭＭＭｾＭＭＭＭＭＭＭＭＭＭＭＭＭＭｾＭＭＭＭ

1I60-S I Clll mottle I

Table 3. I'c::arson correlation (r) between orgulll( i11a tlc::r cont enl il nd Fe,CH and Fe,(OCI3·CB )

ｾ＠

L - ..-:--:-(_)r_g..,.a_lU--::·cc-:1,.,..l1ft1_tc_r-::c::-on_t,....en.,..tc--___

_:=

-... signiticantly different (P<O .O] )

Bulk samples anal)'ses

Pedological features of related horizons were extracted in situ to have more concentrated samples. After collecting the sample, modified selective dissolution technique of Mehra and Jackson (1960) according to Jeanroy and Pill on (1989) was performed. Two series of experiment were conducted. One serie was DCB and the other was CB. Two hundred mg of six pedological feature samples were treated by DCB and the other by CB. Each sample of one serie (DCB or CB) were shaken for 1 hour or 2 hours or 6 hours or 48 hours or 336 hours. The solutions obtained after e:\,1raction were filtered through micropores filter papers and senl to analyses laboratorium in ARRAS. TOlal Fe of each pedological feature samples were also analysed .

Fe-GJ Fe-(IX..'I3-C B J !

- -U-::9--::)-=-·.:-c

- - - ---;---- - ---0.04 I ｾ＠

Unco\'ered thin section obsen'ation

[image:4.611.35.415.67.356.2]

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PCl ddy ,\'oils

c ｾｾＩｉｾＧｮｴｩＷＱＱｧＯｧＩＭＭＺ＠

- 2-J-J - --

- ---1

- - - '- - -'-- - 1

R.7 !

- - --

--_.---_.

.,

(,'l !

- - -78---- -

'

6.7

I

aI ' features I

: around root

=j

: around root I

｟Ｎｏ｟ｉｾｬｬ｟･

___

ＭＭＭＭＭｾＮ＠

n Ollle

=-=====:J

,and l:-dDCB-CB)

Fe-(IX.'B-CB)

!

-0 .04 J

I

ｾｴｩｯｮ＠ obsen'ation

1 sections were treated only Inunersion in CB solution because no Fe dissolution ulier (199 1) 's ex-periment. inunersed in DCB in series

re

immersed in I minute or ninutes Qr 45 minutes or 1 r I 50,hours. Dissolution by

xl in a hot water bath (70 10 Fe dissolution after 130 DeB solution were applied 'as enough to immerse the ock et al., 1975 ; soulier, :nd of inunersion, the th.in rinsed by ultra pure :e destillation) water and nder optical microscope.

XRD ａｮ｡ｬｾＧｳ･ｳ＠

XRD. ana.lyses was conducted to determine qualitatively Fe oxide crystalline. Samples were deriyed from bulk samples

RESULTS AND DISCUSSIONS

Bulk Sample Analysis

The Fe dissolution of the samples are described in kinetic dissolution in time course (Figure 2). Fe-CB showed the amount of Fe complexed or adsorbed by organic matter and Fe-DCB showed the amount of Fe in the form of oxides in crystalline or amorphous, Fe complexed or adsorbed but not Fe in crystalline silicate structure (Jeanroy, 1983) The subtraction between Fe-DCB and Fe-CB ( (DCB-CB) ) showed the amount of Fe-oxide amorphous and crystalline.

Figure 2a shows that coating around root in P2DI Apg2/9-20 cm resulted in Fe-CB profoundly higher than the others in each dissolution series (I hour, 2 hours, 6 hours, 48 hours and 336 hours) (Fig. 2a). It was followed by brown matrix in PIDlBg3/53-69

cm. Fe-CB of coating around root in

P2K/Apg2/30-60 cm, mottles in P2KJBgl/60-8] cm and grey matrix in PIKfBg137-60 cm were comparable and the values far below coating around root . in P2DIApg2/9-20 cm. On the contrary Fe-DCB. where coating around root in P2KfApg2/30-60 cm and mottles in P2KlBgl/60-81 cm resulted in higher values of Fe-DCB compared with coating around root in P2D/Apg2/9-20 em and brown matrix in PIDlBg3/ 53-69 cm (figure 2b) . Grey matrix in P1KlBg]/37-60 cm resulted in little amount of CB and Fe-DCB as well After 336 hours of dissolution, Fc-CB dissolved ranging from 0.42 to 5.07 mglg while Fe-DCB dissolved ranging from 12.14 to 65.65 mg/g.

These results showed that organic Inaller content of the samples affected

Fe-complexcd or adsorbed and Fc-oxide

J. l'anah Trop, No. 16, 20()3

amorphous Clnd crystaWne distribution of Fe

concenlration Fe-CB clearly had

relationship \Iith the organic matter content of the sample Coating around root in

P2DIApg2/9-2 0 em with 2 I. I mg/g C-organic content resulted in fe-CB profoundly higher than the others \Iith lower organic matter content. Simple pearson correlation (r) between C-organic content and Fe-CB after 360 hours e'.1raclion shows that C-organic content significantl\ correlated with Fe-CB (r = 0.95) and did nol correlated with

Fe-(DCB-CB) (r=-O.041) (Table 3)

Organic matter will complex and adsorbe Fe 2- and Fe Ｓｾ＠ (soulier, 1991:

Xingkai el aI, lY 9 : 10kova el 01 , 1999; Yang el aI, 200 1 : Rose et aI, 2002) so its present in Fe concentration process will tend to increase Fe-complexed or adsorbed pool

and will prcyent c formation of Fe oxides

pool as amorp holls and crystaJline. It was indicated by the inc rease of Fe-CB in this experiment .

This expefl me nl also showed that 336 hours dissolution was not enough to dissolvc all Fe-CB. All sam ples had tendcncy to have more Fe-CB if dissolution time was increased especiaJly In wating around root in P2D/Apg2/9 -20 cm (fig. 2a). Meanwhile 336 hours dissolution was optimum for dissol\'ing Fe-DCB '''ith indicated by . the levelling CUf\e after 336 hours dissolution in all samples (Fig. 2b) . It means tha1 Fe dissolution ｢ｾ＠ complexing Fe2• and Fe ｾＬ＠ needs more time than reduction processes because citrate in CB must compete with acid organic matter as the other ligand in the soil solution or because Fe complexed in the samples in the form of Fe 3" so it was difficult

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•

Hartono, A., dkk. : 1'Iu ChtU·ad'!ri.ftil:.'i: of Iron Concentration

in.

Tropical Paddy Soils

6

. • coating around root in P2DtAp2g19-20 em

5

•

• coating around root in

P2K1Apg2l30-60 em

:. rrottle in P2K1Bg1160-81 em

4

ｾ＠_Q : & grey rretrix in P1K1Bg1137-60

§. em

3 II)

1 -brow n rreatrix in 0

do P1 DtBg3/53-69 em

u..

•

._ .. _ - -- -._ ---

--2

•

2()() 300 4·()() 100

tim e (hour)

a

70

...

60 fI

•

SO l

• eoatfig around root in . P2OIAp2g1920 em 40

f

I • eOlltfig around root in

P2K1Apg2l3O-60 em

• rro(tle in P2KIBg 1 /60-81 em

ｾＨ＠

•

ｾ＠

• grey rmtrix in P1K1Bg1137-60 em :

20. I

• bmw n rrntrix n P1G'Bg315l-69 I

1

em 10

t

I

o .

-o 100 200 300

time (hourI

[image:6.611.42.385.79.561.2]

b

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400

·u u Paddy Soils

9 around root in 1;129/9-20 em

9 around root in Ipg2f30-60 em

i1 P2K1Bg1/60-81 em

ratrix in PtKlBg1l37-60

1 rraatrix in g3/53-69 em

root In

em root In Oem

I

11160-81 em

I

1K/Bg1137-60 em'

I P1D1Bg3/S3-69

The distribution of Fe oxides as amorphous and C0 slalline pool was shown in Fig. 3. After 336 hours dissolution, Fe oxide as amorphous

or

｣Ｐｳｴｾｬｉｩｮ･＠ in the samples ranged between 31. 72 mglg to 65.1 ｾ＠ mg/g.

Fe-lotal of the samples arc presented in Table 4. Fe-lotal of all samples \\ere relatively comparable except grey matrix in PIKlBgl137-60 cm. The highest Fe-total was brown matrix in PlD/Bg3/53-69 cm (99.70 mg/g) and lhe least was grey matrix in P1KfBgJ/37-60 cm (5360 mg/g). It is clearly explained why PKlBlmatrix resulted in little amount of Fe-CB and Fe-DCB. Kinetics Fe dissolution curve by CB and DeB compared to Fe-total are shown in Fig. 4. It

is shown that Fe-CB dissolved after 336 11 compared to Fe-total ranged between 0.53 % (grey matrix in PIKfBgl/37-60 cm) to 5.53 % (coating around root in

P2D/Apg2/9-ｆｾ＠＼ﾷＰｭｰｬｾｸｾ､＠ or Jdsorbcd

Fe2_+;_Fe3 ₊ in solution

t

SOM (soil organic matter)

Tabel4. Fe-total of the samples ..

.1_ Tanah _{Trop_ No.}_16,_Z003

20 em) (Fig 4a) while Fe-DCB dissolved after 336 h ranged between 61.1 0 % (grey matrix in PIK/Bg1/37-60 cm) to 74.60 % (mottles in P2K!Bg J160-8 J cm) (Fig. 4b) From these Figures it is shown that not all Fe dissolved by tilese solutions. This was because that DeB could not extracl Fe in crystalline silicate structure (]eamoy, ＱＹｾＳＩＮ＠ This experimenl showed that Fe complexed by organic matter pool occupied small portion of tile Fe concentration in the samples and It was shown that all samples were dOlninated by Fe oxides as amorphous and crystalline which occupied 60.57 % to

69J)7 %.

The formation mechanism of Fe

concentration involving Fe in solution and soil organic matter in these selected samples could be proposed as scheme below.

Fe-comple.xed or adsorbed

... !O53 %-5.53 %)

Fe concentration (coating, mottle)

Fe-oxide amorphous and

crystalline (60.57 %- 69.07 %)

i

ProtillhorizonJdepth representatif Pedological features Fe-total (mg/g)

PlD/Apg2/9-20 cm coating around root in Ap horizon 21.1

PlKJApg2/30-60 em coating around root in Ap horizon 8.7

PlKfBgl/60-81 em mottle 6.4

PIKfBgl/37-60 ern Grey matIi'{ 7.8

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••

Brown I1>akll in PI O/Bg3/53·69 em

ｾ＠ "TJ to,tin, .round roo I In P20JApV2J'9·20 em

ｾ＠

ｾＮ＠

ｾ＠

70 ｾ＠

(; 60 _$'

60

w

50 ｾ＠

ｾｳｯ

A ｾ＠

.

::J

r

40 • .§. 40 ;.

ｾ＠ CD ｾ＠

ｾ＠

;:; . til

<? 30 ｾ＠ 30 ｾ＠

n

"TJ

.,

e.

u

.,

₂₀. _ｾ＠

I g _..,-20 _«>

LL

0 _{10 :}

I"') :. 10

Q

CO _{o '}

o 100 200 300 ' 400

"TJ

fl

ｾ＠

(1) 100 200 300 400 _{linie (hour)}

ｾ

h

lime (hour)

b

CO a

ｾＺ＠

() _mot1le_in_{P2K1Bg 1/60-81}_em ｾ＠

c: eo_ting at'o __ ncf rool in P2K/Apf2l3G-SO em

='

ｾ＠

('l

70 _ｾ＠

70

1

<:)

60 ;.

ｾ＠ .

60

1-

:t ("\

r

50

r

ｾＮ＠

0; 50 ｾ＠

5" '0" Q, , ｾ＠

.§. 40

ｾＮ＠ 30 _co

ｾ＠

0

::t

ｾ＠ 30

; 20

<..)

ｾＮ＠

10 ｾＲＰ＠ _ｾ＠

u. '" 10 I

S·

100 200 300 _00

lime (hour) o ----:..-- ｾ＠

c ｾ＠

o tOO 200 300 400 ｾ＠

Grey matrix in Plt<.!Bg1137..fO em _(").

time (hour) _ｾ＠

'0 _d

ｾ＠

ｾ＠ 30

ｾ＠

35

!.

25

;;; ｾ＠

'! 20

ID

e.

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ｾ＠

(9)

:-01 Paddy Soils J. !anahhNJ. . to. /6, 2003

a

o

ｾ＠

..

....,...

-ｾ＠ g ｾ＠ｾ＠ｾ＠ｾ＠ｾ＠

(B/Bw) (8:1-8:10) ' Ｎｾ＠

0

6

•

5

• coaling around rool in P2Q1Apg2/9-20 em

• coating around root in

l

4

P2KJApg2l30-60 em 'iii

0 _{• rrottle in P2KJBgl/6O-81 em}

1

3 u.

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C) • grey rralnx In P1 K/Bgl/37-60

cI> em

u. 2

- brow n rratrix in P1

CVBg3/53-ｾ＠ i 69cm

+

r

I

•

of

. ... _..'

-0 100 200 300 400 time (hour)

a

100 90

80 : Ｎｾｯｾﾷｬ［ｮｾｾｾ､＠ｲｯｯ［Ｍｾ

•

_, P2D/Apg2/9 20 em 70

ｾ＠

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_{: . coating around root in}

ｾ＠

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6- , P2KJApg2/30·60 em

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ｾ＠ I .

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ｾ＠

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0

..

ｾ＠

" 30 ｾ＠

brow n matrix in PIO/B93/53·

20 69 em

10 0

0 100 200 300 400 tim e (hour)

b

[image:9.611.45.406.55.559.2]

(10)

Harlono, A., dkk. : The Characteristics of Iron Concentration in Tropkal Paddy Soils

That proposed mechanism pointed out that soil organic matter is determining factor for Fe concentration like coating or mottle to contain amorphous or cI)'staliine form.

The small amount of Fe complcxed or adsorbed by organic matter in the samples indicated that reduction and oxidation process occuring in these paddy field have been· lasting for long periode which enhanced the formation of Fe oxide amorphous and crystalline.

The U nco\'ered thin section observation

Thin section observation was used to evaluate the stability of Fe concentration. Fe dissolution to DeB of selected pedological . features were obsented. The results showed that there was no Fe dissolution observed in selected pedological features when they were immersed in DeB solution. It was sho\\TI that there was no Fe dissolution in all samples after 150 h immersion. There was no changes observed for examples at coating around root in P2D/Apg/9-20 em (Fig. 5a,b) ;Jnd at mottle in PIK1Bg1/37-60 cm (Figure 5e and d) Probably Fe dissolution occured but it was too small amount to be observed through the picture.

Different results were obtained where dissolution by DeB was conducted in a hot water bath (

70 ()

C) for 15 minutes . By this method some dissolutions of Fe were observed in some pedological features. Representatives figure is mottle in PI KJBgJ 137-60 em (Figure 6). But Fe dis.solution ｢ｾＧ＠ DeB in a hot water bath ( 70° C ) for 15 minutes did not occur in coating around root. for intances in P2DIApg/9-20 em (Fig . is not shown). This result showed that the selected Fe concentration were stable and confirmed the bulk analyses results that the Fe pedological features in these paddy

soils were dominated Fe oxide amorphous and CI),stalline.

XRD analyses

Bulk samples analyses and thin section observation showed that Fe concentration in selected pedological features were dominated by Fe oxides amorphous

or

crystalline. XRD . analyses was perfonned to evaluate qualitatively the kinds of Fe oxide minerals in the samples.

By using characterisation of goethite and ferribydrite proposed by Brindley and Brown (1980), XRD analyses showed clearly that Fe concentration in some pedological features was goethite and . probably ferrihydrite. Mottles from P2K1Bgl/60-81 cm before treated by CB and DCB showed the presence of goethite and probably ferrihydrite and collapsed after ex1racted by DeB for 336 h (Fig. 7). The presence of goethite and ferrihydrite were also found in coating around root in Ap horizon from P2DIAPG2/9-20 em before treatments and also collapsed after ex1racted by DCB for 336 h (Fig. 8).

The presence of goethite and ferrihydrite in coatings arround root and mottles showed that some Fe concentration in these pedological features have already developed to crystalline mineral.

CONCLUSIONS

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pical Paddy Soils

ｾ＠ Fe oxide amorphous

, analyses and thin section I that Fe concentration in I features were dominated hOllS

or

crystalline.

XRD

lerfonned to evaluate ds of Fe oxide minerals in

lracterisation of goethite oposed by Brindlev and ) analyses showed ｾｬ･｡ｲｬｹ＠ on in some pedological :>ethite and probably es from P2K1Bgl/60-81

CB and DCBsbowed the and probably ferrihydrite :x1racted by DCB for 336

·esence of goethite and Iso found in coating Ap horizon from before treatments and :-.1racted by DCB for 336

e

of goethite and ings arround root and ;orne Fe concentration in features have already ne mineral.

LUSJONS

content · affected the Fe ie fonnation of Fe coating and mottles. Fe >cd pool will increase nic matter content. The

ｾｸ･､＠ or adsorbed pool

e

pool ratio in Fe

e

=

Figure 5. Coaling around root in thin section located in P2DIApgN-20 cm before DCB treatment (a): after J50 h immersion in DCB Solulion (b) and mottle in PIK /BG1I37-60 em before treatment (c) : after 150 h immersion in DCB solution

[image:11.611.40.391.57.538.2]

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HiJriono, A., dkk. : The Churaderi!>1ics of Iron Concentration in Tropical Paddy Soi/.\

a

lmm

[image:12.611.52.418.69.563.2]

b

Figure 6. Mottle in PIKIBGl/37-60 em before treattnent (a) ; immersed in DeB solution in

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Imm

1

Goethite Goethite

I

i

4.94

A

4.17

A

I

1

i

J

i

1

j

1

·

IlJ)m

Figllre 7 XRD analyses of mottles from

rnersed in DeB solution in c.,\(rrteted bv DCB for 336 It

after extracted

by

DCB for 336 h

Ferryhidrite

o 2.56

A .

oethlte Goethite

rg

A

! j

.0 j I f . 2. 18

A

ｾ＠

I

1

, I

I

: ,; f

ｾｾ

_• _I

ｉＯ

i

I

I·

; :

I

f

; :

1 I

,

· iT' ｾｾＮ＠ I

before treatment

[image:13.613.67.400.111.522.2]

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Hartono. A. , dkk. : The Charcu1eri.\1ic.<; of Iron Concentration in Tr opiclil Pllddy S(J il.\

ｾｦｴ･ｲ＠

extracted by DeB for 336 h

Go thite

1

I

J

lBefore treatment

i

_i I

ｾ＠

\JU·I

F errih ydri te

1.71

A

. I

\

f ig ure 8. XRD analyses of coating around root from P2D/Apg2/9-20 cm before treatment and

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,I! Paddy Soils

ｾｲｲｩｨ ydrite

PIA

20 cin before treatment all..

336 h dissolution time was not enough o dissolve all Fe-CB as indicated by the lendency of the curve to increase but it was )ptimilm for Fe-DCB. Compared to Fe-total,

1>1 all samples Fe complexed or adsorbed was

\ery small amount (0.5 % 5.53 %) while Fe oxide amorphous and crystalline was ｾ･ｬ｡ｴｩｶ･ｬｹ＠ high amount (60.57 %69.07 %).

The stability of Fe concentration in selected pedological features were very high and containing goethite and ferrihydrite. The presence of goethite and ferryhidrite in selected pedological features indicated that some Fe concentration has developed to cr:vstalline Fe oxides.

ACKNOWLEDGEMENTS

The authors thank Directorate General of Higher Education (Dikti), Department of 'iational Education, for the financial support through URGE project, so this research could be conducted and thank Center for Wetland Studies (CWS) Department of Soil Science Bogor Agricultural University and Unite Sol et Agronomie Rennes Quimper (INRA). Rennes France for their cooperation and fully supports so this research run well.

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