Pertanika 1(2), 136-142 (1978)

Mineralogy and Related Properties of Acid Sulphate Soilfrom Melaka, Peninsular Malaysia

SHAMSUDDIN JUSOP and TUAN OMAR RAJA SENIK1

Department of Soil Science, Faculty of Agriculture, Universiti Pertanian Malaysia

Key words: Acid Sulphate, Montmorillonite, Pyrite

RINGKASAN

Sifat mineralogi, kimia dan fizik tanah asid sulfat dari Kuala Linggi, Melaka telah dikaji. Tanahini didapati mengandungi mineral montmorillonit, kaolinit, illit, klorit dan pirit. Tidak ada perbezaan darisegi mineralogi diantara lapisan atas dengan lapisan bawah, tetapi kuantiti montmorillonit dan pirit mungkinbertambah ke bawah. Tanah asid sulfat ini mungkin berkeupayaan untuk menghasilkan pengeluaran pertanianyang tinggi; kehadiran montmorillonit meninggikan keupayaan pertukaran kation (melebehi 16 m.e./lOOgtanah). Walau bagaimana pun, kehadiran pirit yang senang teroksid kepada asid sulfat apabila air disalirkan,menyebabkan potensil pertanian tanah ini rendah. jfumlah sulfat bertambah ke bawah, begitu dengan sulfatlarut-air. Sekiranya pirit itu dapat dimusnahkan dengan tidak menjejaskan sifat-sifat fizik dan kimiamineral lain, mungkin tanah ini mempunyai potensil pertanian yang tinggi.

SUMMARY

Miner a logical, chemical and physical properties of acid sulphate soil from Kuala Linggi, Melaka, werestudied. The study shows that the soil contains kaolinite, montmorillonite, illite, chlorite and pyrite. Thereare no mineralogical differences between the top and the lower horizons. Both total sulphate and water-solublesulphate increase with depth. The CEC of the soil is above idme/lOOg soil, probably due to the presence ofmontmorillonite. However, the presence of pyrite, which is easily oxidizable to acid sulphate on exposure,makes the soil less suitable for agricultural purposes.

INTRODUCTION

Acid sulphate soils are those with a pH < 3.5(1:2.5) and with a water soluble sulphate contentof > 0 . 1 % within 50 cm of the soil surface2. Thesoil contains a high amount of FeS2 and is normallylow in bases. In Peninsular Malaysia alone, acidsulphate soils probably cover an area of about141,700 ha, found mainly in the coastal region(Fig. 1) of Melaka, Kedah, Perlis, Kelantan,Selangor, Trengganu, Johor and Pahang (Lawand Seivadurai, 1968; Chow, 1968; Kanapathy,1966; Paramanatham and Law, 1974; Law andTan, 1975; Kanapathy, 1976) and are largelygrown with padi, coconut, oil palm and rubber.

Five soil series namely Telok, Linau, Guar,Sedu and Parit Botak are known to be acidsulphate soils; and are classified at the subgrouplevel as either sulfic Tropaquept or Typic Sul-faquept (Law and Tan, 1975; Gopinathan et aL,1977). Acid sulphate soils are derived frommarine alluvium. Pvrite in the soils is formed

under reducing conditions in the areas inter-mittently flooded with sea water.

Periodic flooding of recent coastal plain soilscauses either acidification or deacidification(Breemen, 1975). Acidification results in theformation of FeS2 and partial loss of alkalinityin flood water during the wet season, followedby oxidation of pyrite during the dry season.Upon flooding Fe++ increases at all depths;most strongly in the A horizon. This suggeststhe occurrence of SO4 reduction with accom-panying FeS2 prepitation (Breemen and Harmsen,1975).

Oxidation of FeS2 results in the productionof acid sulphate and ferric sulphate :-

FeS2

oxidationFe2(SO4)3

Fe2(SO4)3 + 2H2O H2SO4+Fe2(SO4)2(OH)2

1 Present address: Faculty of Education, Universiti Malaya, Kuala Lumpur.2 pH and sulphate content being measured after drying the soil in the air for 2 - 3 weeks.

136

SHAMSUDDIN JUSOP AND TUAN OMAR RAJA SENIK

Fig. 1: A map of Peninsular Malaysia shewing the distribution of Quaternary alluvial deposits (shaded area).The dots denote the places where acid sulphate soils are known to occur (adapted from Stauffer, 1973).

137

ACID SULPHATE SOIL FROM MELAKA

The basic ferrisulphate Fe2(SO4)2(OH}2 soformed can easily be converted to jarosite (KFe3(SO4)2(OH)6) in the presence of K^\ Jarositesometimes dehydrates and oxidizes, resulting inthe formation of Fe2O3. These processes areenhanced by a high pH and a low K concen-tration (Breemen and Harmsen, 1975).

The object of this paper is to evaluate theagricultural potential of acid sulphate soil inMalaysia by studying mineralogical compositionof the soil and physical and chemical properties.

MATERIALS AND METHODS

The samples were taken at three depths,representing A, (B) and Cg horizons (Fig. 2).This particular Linau Series which is found atKuala Linggi, Melaka, is derived from Quaternarymarine deposits (Stauffer, 1973; Sooryanarayana,1976) and largely covered with "gelam" (Mela-leuca leucadendron) and or "nipah" (Nipa fruti-can). Taxonomically, the soil is classified asbelonging to the clayey, mixed, isohyperthermicfamily of the Typic Sulfaquept. The groundwater table is below 80 cm depth and yellowjarosite mottles are found in the upper layers indry season. The dried soil is strongly acid. Themean annual temperature of the area is about26°C and the total annual rainfall is about 2000 -2500 mm (Dale, 1963).

(B)

water table

The soil samples were air-dried and groundto pass through a 2 mm sieve. Soil pH(H2O)was measured at a 1:2.5 soil. Particle-size analysiswas carried out by the pippette method, followingthe method of Day (1965). Exchangeable cationswere extracted by NH4 OAc at pH7 (Chapman,1965); Na and K were determined by a flamephotometer and Ca and Mg were determined byatomic absorption spectrophotometer. Exchangecapacity was determined by the NH4OAc methodat pH7 (Chapman, 1965). Exchangeable alumi-nium was extracted by IN KC1 (Maclean, 1965).Time requirement was estimated by the titrationmethod of Dunn (1943). Total sulphur wasestimated by the method of Jackson (1967),sulphate-sulphur (SO4-S) by the method ofHesse (1971) and water soluble sulphate-sulphurby the method recommended by Chow (1968).Organic carbon was determined by the Walkley-Black method (Allison, 1965). X-ray diffraction(XRD) analysis was carried out followig themethod of Whittig (1965).

RESULTS AND DISCUSSION

Mineralogical properties

X-ray diffraction (XRD) investigation ofLinau Series (Fig. 3) shows reflection at 16.6A(montmorillinite), 14.0A (chlorite), lO.lA (illite)7.2A (kaolinite/chlorite), 3.59A (chlorite), etc

(cm)mottle (jarosite)

dark brown, humic clay

H 20

50

reddish brown, humic clay

marine clay with peat

Fig. 2: A sketch showing the profile of Linau Series from Melaka.

138

SHAMSUDD1N JUSOP AND TUAN OMAR RAJA SENIK

Cmusc/HUtc1 quartz halloyslte (001)

kaol (002) nusco-illite (002)

NO TREATMENT

i co- iUi te (004)

K-satiirated

16.6 mont.9.6 *.

,K-55O°C

Mg-solvated

Mg-gly. solv.

Fig. 3: X-ray diffraction pattern of Linau Seriessaturated with K, K-550°Cy Mg andMg-glycerol solvated.

All these reflections point to the presence ofmontmorillonite, chlorite, illite and kaolinite.The presence of pyrite was deduced from thepresence of the total sulphur and sulphate-sulphur.

Diffractogram of Mg-saturated and glycerolsolvated clay does not manifest reflection at

17-18A. Montmorillonite which may be pre-sent in the clay does not expand, probably becauseof the presence of some cementing material whichhad not been removed by the deferrating agent(Tsuneo, 1958). This cementing material wasprobably destroyed when the K-saturated claywas heated to 55O°C, as a result of which, reflectionat 16.6A appears. The 16.6A basal spacing isprobably a reflection of montmorillonite. Thereis no reflection at 10.8A, thus indicating thathalloysite is not present (Whittig, 1965). Treatedmontmorillonite give reflections at about 15A;this shows a high order of crystallinity, whichmay be attributed to the weathering resistivityof montmorillonite itself. Less or low weatheringdegree is indicated by the occurrence of chlorite.

The intensity of reflection at 7.2A, 3.59Aand 2.0A decreased when heated to a temperatureof 55O°C. This phenomenon proves the presenceof kaolinite as heating causes dehydration anddehydroxylation of kaolinite (Fitzpatrick andRoux, 1977). Heating to 550°C does not affectthe reflections at 3.4A (illite) and 2.35A and 2.04A(chlorite). There is no clear evidence of thepresence of goethite and gibbsite; there are noreflection at 4.86A and 4.18A respectively. TheXRD pattern of the upper and lower horizonsare basically the same, indicating that there is noreal mineralogical difference with depth (Fig. 4);but the increase of cation (Na and Mg) andsulphur with depth points to the corresponding

chlo

2.04

musc/illite/quartz

/ 3.59

kaol

Upper horizon( O - 2 O cm)

Lower horizon

( > 50 cm )

muse - illite/halloysite with

H 2 0

Fig. 4: X-ray diffractogram of K-saturated clays of Linau Series from Melaka.

139

ACID SULPHATE SOIL FROM MELAKA

increase of montmorillonite and pyrite withdepth (Table 2).

Mineralogically, the soil may have greateragricultural potential than some upland soils inthe country. Montmorillonite increases theexchange capacity of the soil substantially, butthe presence of pyrite which is easily oxidizableto acid sulphate, makes the soil less suitable foragriculture. The structure of the soil is poor,but it could be improved provided pyrite isabsent. If the pyrite can be destroyed withoutdisturbing the composition of the rest of thecomponent minerals, the soil could be one of thebest in the country. However, effective practicesfor achieving such favourable soil conditions arenot available. Draining the soil exposes thepyrites to the air, causing the pyrite to be oxidisedto sulphate slowly but steadily over a period ofyears. Dilution of the acid with large quantitiesof water and subsequent lime treatment to pH 6.5,is only a short term measure; the remainingpyrite in the soil will eventually be oxidised,rendering the soil unfit for agriculture.

Physical and Chemical Properties

The texture of the soil becomes heavier withdepth; it is sandy clay loam in the A horizon,loam in the (B) horizon and clay loam in the Cghorizon (Table 1). pH in H2O(1:2.5) decreaseswith depth (Table 2). The decrease in pH isconsistent with the increase in sulphate. Theacid formed in the A horizon was probablybrought down to the lower horizon. Higher pHnear the surface may be also due to more waterbeing available in A horizon than in the lowerpart of the profile. The decrease in pH resultsin the release of more aluminium into the solution(Table 2). The increase in acidity is subsequentlyfollowed by the increase of lime requirementwith depth.

The presence of a high amount of K in theA horizon is probably due to the presence ofjarosite which is yellow in colour (Fig. 2).Potassium decreases downward because jarosite

does not form below ground water table. Theincrease of sodium and magnesium with depth isprobably due to the presence of montmorilloniteand or the nature of the parent material. Thehigh organic carbon content is attributed to thepeaty nature of the Quaternary deposits; piecesof wood are frequently spotted in the Cg horizon(Fig. 2).

The CEC of the soil is high, above 16me/lOOg soil (Table 2). This is probably due to thepresence of montmorillonite. Aluminium andhydrogen dominate the exchange sites at low pH.The presence of the excess amount of Al+++ andH+ is undesirable for plant growth. The decreaseof pH with depth is small, but the correspondingincrease of lime requirement is significantly high.This shows that the soil is highly buffered. Highbuffering capacity is also shown by the high CEC.

The traditional practice of liming the soilunder flooded conditions is currently the bestform of management for acid sulphate soil.Growing crops which thrive under such con-ditions is a more logical step than trying to changethe soil by artificial means. Under saturatedconditions, the most suitable crop is paddy.

Flooding acid sulphate soil increases its pHsignificantly (Ting, 1977). The increase in pHis probably brought about by the reduction ofhydrous ferric oxide. The pH increase could bedue to organic matter which under reducedconditions leads to the accumulation of NH| .Ferrous ions are released near the soil surfacejust above the pyritic substratum (Harmsen andBreemen, 1975). Ferrous ions and SO formedin the substratum move upward by diffusion andmass transport. This explains the presence ofFe++ and SO4-S in the upper horizon.

GenesisThe parent material of Linau Series has

probably been subjected to successive loweringand raising of sea level in the Quaternary (Fig. 1).Evidence of eustatic rise and fall (due to fluctua-

TABLE 1

Physical properties of the soil samples

Horizon

A

(B)

Cg

Depth (cm)

0-20

20-50

> 5 0

C-Sand

2.19

3.95

2.77

Particle-size

F-Sand

48.19

50.2

43.9

Distribution

Silt

26.3

28.8

23.2

Clay

23.5

21.6

29.6

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SHAMSUDDIN JUSOP AND TUAN OMAR RAJA SENIK

TABLE 2

Chemical properties of the soil samples.

Depth(cm)

0-20

20-50

> 5 0

pH (H2O)

3.3

3.1

2.8

Exchangeable Cation (me/lOOg)

Na

2.2

2.8

4.4

K

0.33

0.21

0.19

Ca

0.05

0.03

0.02

Mg

0.10

0.11

0.32

Al

2.80

2.93

5.30

CECme/lOOg

17.4

13.8

15.4

BaseSat(%)

15.5

22.7

31.6

4

3

3,

,c

.23

.40

,20

% TotalSulphur

0.30

0.65

2.50

\,SO4-S

0.20

0.58

1.25

%SO4-S(H2O)

0.04

0.11

0.70

Lime(ton/ha)

16.6

39.9

45.3

tion of Pleistocene glaciation) of sea level inPeninsular Malaysia are recorded in the numerousdrowned mangrove swamps, raised beaches, theprograding stream pattern in the continentalshelf (Haile, 1970) and punch cores and foramini-feral data (Biswas, 1973). Further evidence ofsea level rise is seen in the presence of wave-cutnotches and marine beach deposits around theisolated hill of Bt. Kriang, Kedah, which wasonce probably an offshore rockly islet (Tjia, 1973).It is estimated that the lowest Quaternary sealevel was probably about 100 m below and thehighest was probably about 40 m above thepresent one.

When sea level was at its maximum, mostof the lowland areas (particularly those of KualaLinggi) where the present acid sulphate soilsmostly occur, were submerged (Fig. 1). Thesesubmerged deposits are dominantly clay andsandy clay with intercalated layers of sand andpeat (Stauffer, 1973), providing evidence of theexistence of both marine and terrestrial deposits.Such a condition was conducive for the accumu-lation of iron and sulphate, which in reductionresulted in the formation of pyrite when sea leveldropped and the deposits were frequently floodedwith brackish water. Organic matter providedby 'gelam' and 'nipah' palm helped in the reduc-tion of Fe+++ and SO4. The presence of a highamount of bases, especially those of Na and Mg,under slow leaching (lowlying areas) resulted inthe formation of rnontmorillonite.

CONCLUSION

The study of acid sulphate soil from KualaLinggi, Melaka, indicates the presence of mont-morillonite, kaolinite, illite, chlorite and pyrite.The pH of the soil is less than 3.5 and the CECis greater than 16me/100g soil. Total sulphur,SOJ-S and water soluble SO4-S increase withdepth.

The presence of montmorillonite and illitefollowed by high CEC, shows that the soil hasgreat agricultural potential if it was not for thepresence of pyrite. Liming is only a short term

solution. The subsequent oxidation of pyritewill eventually cause the soil to revert to un-favourable conditions for plant growth. Keepingthe soil under anaerobic condition all the timeis probably a logical practice under the presentcircumstances, even though the choice of cropsis limited.

ACKNOWLEDGEMENTS

We gratefully acknowledge the assistance ofthe Staff of the Department of Soil Science,UPM, in the conduct of the laboratory analysis.We would also like to thank Dr. Othman Yaacoband Encik Khanif Yusop for their helpful suggest-ions and criticism of the manuscript.

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(Received 27 June 1978)

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