Pertanika 11(1), 15-23 (1988)

Acidity and Charge Characteristics of MarineAlluvial Soils from Carey Islands, Selangor.

J. SHAMSHUDDIN AND S. PARAMANANTHANSoil Science DepartmentFaculty of Agriculture

Universiti Pertanian Malaysia,43400 Serdang, Selangor, Malaysia.

Key Words: Acidity; aluminium, buffering; negative.

ABSTRAK

Enam siri tanah dari Pulau Carey telah dikaji untuk menentukan ciri keasidan dan cas tanah.Kajian ini telah menunjukkan tanah di Pulau Carey mengandungi kandungan bes kation, Al dan SO42 "yang tinggx Ini ditunjukkan oleh rendahnya kandungan pH dan tingginya konduksian elektrik. Tanah-tanah itu menampan dengan kuat ke bawah pH 5.5 dan didapati berkorelasi dengan baik kepada kan-dungan AL Di samping itu juga, cas negatif di atas permukaan lempung didapati bertambah dengannaiknya pH tanah Pemerhatian ini bercanggah dengan fakta bahawa mineral lempung dalam tanah-tanahini adalah jenis cas tetap.

ABSTRACT

Six soil series from Carey Island were investigated to determine their acidity and charge charac-teristics. The study showed that the soils contained high amounts of basic cations, Al andSo4

2~, whichwere reflected by their low p. I and nigh electrical conductiviy. Vie soils were highly buffered below pH5.5 and this was found to be highly correlated to Al content. Further, it was found that negative chargeson the clay surfaces increased with increase in soil pH, These observations are contrary to the fact that theclay minerals in these soils are of the permanent charge type.

INTRODUCTIONCarey Island is located on the west coast of Penin-sular Malaysia in the Straits of Melaka. It is situa-ted between 2°0' and 3° O'N latitude and between101°15' and 101°30'E longitudes (Figure I).The island is located in the estuaries of the KelangRiver and the Langat River and consists of marine,estuarine and brackish water deposits of recentorigin. The island is flat with an elevation that isbelow mean high tide level. Thus, the island hasbeen reclaimed by the construction of a coastalbund and a network of drainage canals and watercontrol structures.

Carey Island with an estimated area of 11,667ha is almost exclusively owned by Harrison Malay-

sian Plantations. The island is divided into fourestates totaling 10,942 ha. Oil palm is by far thedominant crop (9222 ha), while cocoa/coconutoccupies 1720 ha. A detailed soil survey of thefour estates has been recently carried out (Mano-haran, 1985;Pathumanathan, 1985;Rajasekharam,1985; Yeoh, 1985). Nine soil series were identi-fied on the island. The classification and extent ofthese soils is shown in Table 1. Some of the soilson the island are acid sulfate in nature and henceare agronomically less suited for agriculture unlesssome corrective measures are carried out. Depend-ing on the soils, they are limited by low pH,high aluminium content and high electrical con-ductivity.

J. SHAMSHUDDIN AND S. PARAMANANTHAN

Fig. 1: A map showing the position of Carey Islandin Selangor, Peninsular Malaysia.

minerals are considered to be permanent chargeminerals (Uehara and Gillman, 1980; 1981).

The purpose of this investigation is to charac-terise the acidity and charge characteristics of sixof the soils found on Carey Island. It is hoped thatthe information obtained will supplement othermeasures in the amelioration of the soils for agri-cultural production.

MATERIALS AND METHODS

The soils were described and sampled according topedogenetic horizons and air-dried, ground andpassed through a 2 mm sieve. pH was determinedin water (1.2.5) after 24 hrs. of equilibration.Basic cations were extracted using 1M NH40ACat pH 7; Na+ and K+ were determined by flamephotometer, while Ca2 + and Mg2+ were deter-mined by atomic absorption spectrophotometer.

Aluminium was extracted by 1M KC1 and was

TABLE 1Classification and extent of soils in Carey Island.

Soil Series Classification(Soil Survey Staff 1975) Extent (ha)

Merbok*

Parit Botak*

Tongkang*

Bernam*Linau*

Sedu

Jawa

Selangor*

Carey

Typic Sulfaquent

Typic Sulfaquept

Sulfic TropaqueptTypic Tropaquept

Typic Sulfaquent

Typic Sulfaquept

Sulfic Tropaquept

Aerie Tropaquept

Sulfic Tropaquept

638254

810492

881

722

5609

1115

49

Miscellaneous

Land Units362

•Soils sampled for study

Soils developed\)n marine, estuarine and brac-kish water deposits, especially acid sulfate soils,are highly buffered at low pH. The high bufferingcapacity at that pH is attributed to the presence ofaluminium in the soils (Shamshuddin et al, 1986)and jarosite (Carson et al, 1982). These soilscontain mainly smectite, mica-mixed layers, micaand kaolinite (Shamshuddin etai, 1986). All these

determined colorimetrically. Water soluble sulfatewas determined by turbidimetry after extracting5 g soils with 100 ml H2O. Electrical conductivitywas measured in water at the soil: water ratio of1:5 after equilibration for 24 hours. Free iron wasdetermined by the method of Mehra and Jacksor(1960), while organic carbon was determined bythe Walkley-Black Method.

16 PERTANIKA VOL. 11 NO. 1, 1988

ACIDITY AND CHARGE CHARACTERISTICS OF MARINE ALLUVIAL SOILS

Potentiometric titration curves were obtainedby titrating the soil and soil extracts with 0.1MKOH using an autotitrator. 5 g of soils was equili-brated overnight in 50 ml 1M KC1. Negative andpositive charges at pH 3, 4, 5, 6 and 7 were mea-sured by the method of Gillman and Uehara(1980). Nuclear activation analysis (NAA) wasemployed to determine the total elemental com-position of the soils.

RESULTS AND DISCUSSION

Morphological Characteristics of the Soils

Six of nine soils mapped on Carey Island wereused in this study viz. Merbok, Parit Botak, Tong-kang, Bernam, Linau and Selangor Series. Themain morphological properties of these soils aresummarised in Table 2. From this table it canbe seen that both the Merbok and Linau Serieshave sulfidic materials close to the surface, while

in all the other soils sulfidic materials occur atvarying depths depending on the soil type. Buriedwood is common in the C horizon of the LinauSeries indicating its brackish water origin. Soilsdeveloped over the marine alluvium are light grayin colour, have jarosite mottles at varying depthsand coarse angular blocky structures with stickyconsistence. On the other hand, the SelangorSeries which is developed on brackish waterdeposits, has moderate, subangular blocky struc-tures and friable consistence. The differences inthe soils developed over marine and brackishwater deposits are consistent with those reportedby Paramananthan and Noordin (1986).

Chemical Characteristics of the Soils

The chemical characteristics of six soils in thestudy are given in Table 3. A number of dif-ferences can be ascertained from this table. The C

TABLE 2Morphological properties of the soils studied

Soil Series ParentMaterial

Horizonation DiagnosticSubsurfaceHorizon/Property

Brief Description

Merbok Marine A/Calluvium

SulfidicMaterial

Bluish gray clay, sticky and massive, value low inupper but high in lower horizons. Black materialoozes out in the lower horizons

Parit Botak Marine A/Bw/Calluvium

Sulfuric horizon Light gray, clay, wet sticky, dry hard with coarseover sulfidic angular blocky structures. Yellow Jarosite mottlesMaterial 0-50 cm depth

Tongkang Marine A/Bw/C Sulfuric horizon Light gray, clay, wet sticky, coarse angularalluvium over sulfidic blocky structures. Yellow jarosite mottles

material 50-100 cm depth.

Bernam Marine A/Bw/C Gamble horizon Light gray, clay, wet sticky, coarse angularalluvium blocky structures. No jarosite mottles to 100 cm

Linau Brackishwaterdeposits

O/AC/C Sulfidic Sapric material to depth less than 50 cmoverlying wet, sticky blush gray structureless clay.Many pieces of wood.

Selangor Brackishwaterdeposits

A/Bw/C Cambichorizon

Brown, silty clay, moderate medium subangularblocky, friable, No jarosite mottles to 100 cmdepth.

PERTANIKA VOL. 11 NO. 1, 1988 17

TABLE 3Chemical properties of soils on Carey Island

mH

Z

>^OL

.

2:O*̂1988

Merbok

Parit Botak

Tongkang-

Bernam

Linau

Selangor

HorizonSymbol

ADACC

ApBw2

Bw2

BC2

ApBwj

Bw2

Bw3

ApBWj

Bw2

ApACC

Ap

Bw2

Depth(cm)

0-1111-5050-90+

0-1515-4040-70

70+

0-1010-4040-7070-105

0 - 77-40

40-105

0-2020-35

354

0-1616-4545-104

pH-H2O(1:2.5)

6.33.62.7

3.53.33.23.2

4.04.03.33.3

4.24.03.9

3.32.63.7

3.93.53.2

Basic Cations (meq/lOOg.soil)

Na K

13.70 1.8021.64 2.3420.76 2.29

0.31 0.170.20 0.230.24 0.270.41 0.23

0.09 0.210.06 0.260.23 0.230.44 0.23

0.20 0.230.19 0.300.28 0.07

0.69 0.232.28 0.173.25 0.19

0.12 0.100.10 0.120.32 0.12

Ca

44.6332.1619.27

trtr

0.710.93

4.570.610.540.73

4.491.25tr

1.8017.8823.98

trtrtr

Mg

10.7111.1910.91

0.511.181.631.95

1.112.201.901.4S

2.241.980.46

1.271.874.72

0.100.110.91

Al3+ SO42-

meq/lOOg.soil

tr1 11111

16.68

13.5215.9415.3613.60

10.0415.3815.3813.78

12.7415.804.35

8.0412.0612.28

3.446.08

10.28

2.5011.6021.25

1.381.041.251.33

1.101.000.810.90

1.100.500.40

0.8810.429.58

0.210.380.67

E.C.

msiemen/

cm

2.286.589.04

9.490.610.750.95

0.100.100.320.33

0.070.120.09

0.774.015.25

0.110.260.71

Fe2O3

0.37trtr

1.162.722.911.56

0.310.910.961.99

0.530.98

tr

0.774.015.25

0.110.260.71

Organic

3.874.182.77

2.661.300.750.93

2.590.851.231.54

1.280.881.89

1.280.811.89

1.280.811.88

GOO

5>zoB

X

>H

1

ACIDITY AND CHARGE CHARACTERISTICS OF MARINE ALLUVIAL SOILS

horizons of the poorly drained soils are marineclays which are very juvenile as indicated by thehigh calcium, magnesium, sodium and sulfatecontent, eg. Merbok and Linau Series. Some ofthe Ca in these soils may be present in the formof gypsum (CaSO4.2H2O). The drained soilswhich are developed on marine clays. For exam-ple: Parit Botak,TongkangandBerham,have highermagnesium and calcium values as compared to Se-langor Series which is developed on brackish waterdeposits. This is possibly due to the higher leaching.Note that we do not have Mg and Ca data on theC horizons of Parit Botak, Tongkang and Bernamseries to conclusively prove its marine origin.But from past experience we know that thesesoils are usually found in marine alluvial areas.Selangor Series has a pH of less than 3.5 but nojarosite was observed in the field to a depth of 100cm. However, brownish yellow mottles were pre-sent. It is possible that these mottles were in factjarosite but have browner hues due to the presenceof organic acids. The organic carbon contentvalues may not be a true reflection of the carboncontent as these soils also contain pyrite which

may also be oxidised during the determination oforganic carbon.

Total Elemental Composition

Table 4 gives the total content of Na, K, Mn, Aland Fe in the soils under investigation. The mostimportant determined cation in the soils is Al,with values ranging from 2.44% (Selangor, Ap)to 10.4% (Parit Botak, BC). This is followed byFe and K. The amount of Mn in the soil is alsoquite substantial which could be toxic to crops.

The high amounts of Al and K in the soilsis due to the fact that these elements form impor-tant constituents of silicates. Mica and smectite arethe dominant minerals in soils developed onmarine deposits (Shamshuddin et al., 1986).The presence of high acidity in the soils, as shownby the low pH (Table 3), may result in the clayminerals being attacked by the acid, and as aresult, Al is released into the solution in largeamounts. Similarly, K will be released into thesolution as the mineral weathers, but subsequentlytaken up by the formation of jarosite (KFe3

(SO4)2(OH)6) particularly in acid sulfate soils.

TABLE 4Total elemental composition of soils on Carey Island

Total Elemental Composition

Soil Series Horizon Depth(cm) Na(%) Fe(%) Mn(ppm)

Merbok

Parit Botak

Tongkang

Bernam

Limau

Selangor

ApC

ApBC

Bw3

ApBw2

ApC

ApBw2

0 - 1 150-90

0-1570+

70-105

0-740-105

0-20354

0-1645-104

0.420.80

0.110.11

0.15

0.100.14

0.170.24

0.100.10

1.311.70

0.161.43

L47

1.311.00

1.071.06

0.871.15

8.047.39

3.5210.41

7.73

9.433.92

4.984.90

2.444.25

1.73

2.832.73

-

2.300.93

2.261.45

0.94

100240

3277

119

8849

4757

5338

PERTANIKA VOL. 11 NO. 1, 1988

J. SHAMSHUDDIN AND S. PARAMANANTHAN

Jarosite was mdentified in the soils of the ParitBotak dan Tongkang Series as mottles on pedfaces. The high K values may also be due to illitein these soils.

SoilpH

The pH values for the soils of Carey Island varyfrom 2.66 to 6.28 (Table 3). It appears that pHvalues depend on the amount of Al in the soil.The higher the amount of Al in the soil, the lowerthe pH. For instance when pH is 3.9, the Al con-tent is 3.44 meq/lOOg soil (Selangor, Ap). Whenthe pH goes to 2.7, the amount of Al is 16.68meq/lOOg soil (Merbok, C). On the contrary whenAl content was plotted against pH, the correla-tion between pH and Al content was found to bepoor. This may be partly due to the presence oforganic acids in these soils. However, we cannotdisregard the role of Fe3+ (pka 3) in the bufferingaction of soil although iron is low except inLinau Series. Iron in these soils could exist in theform of (Fe)2(SO4)3. At low pH, the iron goesinto the solution as Fe3+ and this causes soilbuffering below pH4.

Electrical Conductivity

The soils in Carey Island are derived from marineclays and thus salt is an important component ofthe soils. Under such conditions, high electricalconductivity could be a serious limitation to cropgrowth. However, salt can be leached out undera proper system of management. More recent soilssuch as Merbok and Linau Series (Sulfaquents)contain more salt (Table 3) than the drained soils,such as Tongkang and Parit Botak Series, whichare classified as Sulfic Tropaquept and Typic Sul-faquept respectively.

This study shows that there exists a goodcorrelation between electrical conductivity, basiccations and sulfate. This is shown by the equa-tion : -

EC = 0.01 +0.02 basic cation+ 0.38 SO42 ~

R2 - 0.98, F 2 ; i 7 m 392.92**

The relationship between EC and S04

given by the equation:-

FX = -0.06 + 2.11SO42"

R2 = 0.96, F i ; i 8 = 386.30**

2 -IS

EC and basic cations are somewhat less corre-lated as shown by the equation:-

EC = 2.43 + 7.21 basic cations

R2 = 0.64, F i ; i 8 = 32.06**

This study suggests that in order to lower ECto an acceptable level, sulfate has to be removed.For instance, the sulfate in the soils of Linau andMerbok Series, whose EC is rather high in thelower horizons, have to be leached by fresh water.Plant growth is affected when EC is more than 4 msiemens/cm (Wong, 1974).

5a il Buffering

Soils developed over marine and brackish waterdeposits along the coastal plains of the west coastof Peninsular Malaysia, are known to be highlybuffered at a low pH. As a consequence, a highamount of lime is needed to raise the soil pH tothe level suitable for plant growth. According toBloomfield and Powlson (1977) some of thesesoils need about 200 tonnes of CaCo3 to neutra-lize the potential acidity in 1 ha of the soil to adepth of 1 m. This point can be studied in somedetail by using buffer curves.

Some titration curves of selected horizonsfor both soil and soil extract are given in Fig. 2.Other curves are not presented as they show asimilar trend. It appears here that similar curveswere produced when OH was added to soil or tosoil extract. But on closer examination, we foundthat more OH~was needed to raise the pH ofsoil to pH 5.5 than the soil extract. T-test onpaired observations yielded the equation:-

wo.ooi ;i = 3.92 < 7.34

This shows that there is real difference betweentitration curves of soil and soil extract. This in-dicates that when using the curves for interpretinglime requirement, it is better to use the buffercurves obtained from the soil rather than thoseobtained from the soil extract because it willreflect the true reaction taking place in the soil.

For both types of titration curves, the amountof OH "needed to raise the pH to 5.5 and from 5.5to 9.0 were estimated. The limit was set at 5.5

20 PERTANIKA VOL. 11 NO. 1, 1988

ACIDITY AND CHARGE CHARACTERISTICS OF MARINE ALLUVIAL SOILS

15

10-

15

10 '

EXTRACT! IMKCI)

ParitBotak(Bwi)

Tongkang(Ap)

Selangor(Ap)

SOILLinau(AC)

Tongkang(Ap)

Selangor(Ap)

Fig. 2: Potentiometric titration curves of soil extract and soil

because it is known that the end point of Altitration is around that pH (Cabrera and Talibu-deen, 1979) and that the soil is usually limed tothat pH (Sanchez, 1976).

Multiple linear regression analysis was carriedout to relate bases, Al and clay content. There isa good correlation between bases (pH 5.5), Al andclay, as shown by the equations:-

OH" = 2.44+1.33 A1 +0.01 clay (soil)R 2 =0 .81 , F 2 ; 1 6 = 34.80**

and

OH" = 3.36 + 0.94 Al + 0.01 clay (soil extractR2 * 0.83,Fe2;16 = 38.24**

The relationship between OH'and Al alone for the

soil is given by the equation:-

OH' = 0.63 + 0.61 AiR2 • 0.81,F1 ; 1 7 = 73.95**

For soil extract, the relationship between OH'andAl is given by the equation:-

OH" • 0.99 + 0.85 Al

R2 » 0.83,Fx .17 =80.21**

Above pH 5.5, there is no correlation betweenOH", Al and clay either for the soil or for theextract.

This study shows that it is difficult toraise the pH to 5.5 due to the action of Al, whichexists in the solution or on the clay surfaces. Oncethe pH goes up beyond 5.5, it needs only a smallamount of OH"to bring up the soil to pH 9.0. Asimilar conclusion has been reached by Shamshud-din et. al (1986) who studied acid sulfate soilsfrom Perak, Peninsular Malaysia. The effect ofclay minerals, in soil buffering is not significant,either below or above pH 5.5. This is somewhatdifferent from the results obtained for riverinealluvial soils, where OH" is well correlated to claycontent (mainly kaolinite) above pH 5.5 (Sham-shuddin and Tessens, 1983). This difference isprobably due to the interference of Al, SO4

2~andbasic cations which are present in large amountsin the soils on marine deposits.

Charge Characteristics

The soils in Carey Island are poorly drained. Theimpeded drainage condition reduces soil weather-ing, resulting in the dominance of silicates in the

PERTANIKA VOL. 11 NO. 1, 1988 21

J. SHAMSHUDDIN AND S. PARAMANANTHAN

Soil Series

Merbok

Merbok

Parit Botak

Bernam

Linau

Selangor

HorizonSymbol

Ap

C

BC

Ap

C

B22

TABLESNegative charges at pH

Depth(cm)

0 - 1 1

50-90

70+

0 - 7

35+

45-104

3 and 7

PH3

25.1

25.9

21.7

24.2

22.6

24.3

Negative Charge(meq/lOOg Clay)

PH7

58.7

58.4

39.5

41.8

56.5

51.4

soil. The oxides, especially iron oxides, are low.The low iron oxide content is reflected by the lowamounts of positive charges; the positive chargein the soil is about 1 meq/lOOg soil (not shownin table). On the other hand, the negative chargewas found to be quite high with values exceeding50 meq/lOOg clay (Table 5) indicating the pre-sence of substantial amounts of smectite and/ormica-mixed layers. Thus we expect the soils understudy to contain dominantly mica, mica-mixedlayers, smectite and kaolinite, similar to themarine derived soils from Perak studied by Sham-shuddin et al (1986).

Mica, mica-mixed layers and smectite are, bydefinition, permanent charge minerals (Uehara andGillman, 1980; 1981). Even the charges on kao-linite itself are mostly permanent in nature. Itmeans here the charges in the soils will not changevery much with the change in pH. This is not thecase when the charges were determined at variouspH as clearly shown in Fig. 3. At pH 7, the nega-tive charges are rather high, but at pH 3 (aroundthe soil pH under field condition) the values arereduced to about half. For instance, at pH 7, thenegative charge of Selangor Series (Bw2) is 51.4meq/lOOg clay, while at pH 3 the value is 24.3meq/lOOg clay (Table 5).

This phenomenon is probably due to thecharges on mica, mica-mixed layers and smectitewhich are not completely permanent, as suggestedby Hendershot and Lavkulich (1983). Thus, when

24

a

! •

e

1

• Bern* Ap.

. fertx*. L

. Parit Bob*. BC

s

y

s.

, ' * . . . . . - •

Fig. 3: The change of negative charge with pH for

Bernam, Merbok, Linau and Parit Botak Series.

the pH was raised from 3 to 7, some hydrogenfrom the aluminol group was released into thesolution, forming a negative charge. This pheno-menon is of relevance to soil management.

Currently the fertilizer applications are basedon the CEC determined at pH 7. This studyimplies that since the CEC of the soils dependson the pH, the fertilizer rates currently used arean over estimate. An oversupply of nutrients willentail higher costs and losses by leaching mayresult. From the results, it is suggested that thefertilizer rates are better estimated by determiningthe CEC at the pH of the soil,

CONCLUSION

It was found that the soils in Carey Island con-

22 PERTANIKA VOL. 11 NO. I, 1988

ACIDITY AND CHARGE CHARACTERISTICS OF MARINE ALLUVIAL SOILS

tained high amounts of Al, basic cations and sul-fate. High amounts of these materials were re-flected by the low pH and high electrical conducti-vity. Electrical conductivity was well correlated tothe amounts of basic cations and sulfate (R2 =0.98). The soils were highly buffered, especiallybelow pH 5.5, due to the presence of Al. Thecharges on the clay surfaces were found to in-crease with an increase in pH. Fertilizer require-ments based on CEC at pH 7 is considered to givean overestimated value. This study suggests thatthe CEC at the soil pH will give a better estimate.

ACKNOWLEDGEMENTS

The authors wish to record their appreciation toUPM for financial support during the conduct ofthe research and the laboratory staff of SoilMineralogy Section of the Department of SoilScience for the soil analysis.

REFERENCES

BLOOMFIELD, C. and D.S. POWLSON (1977): Theimprovement of acid sulfate soils for crops otherthan padi. Malays. Agric. J., 51(1): 62-76.

CABRERA, F. and O. TALIBUDEEN (1979): The re-lease of aluminium from aluminium silicate minerals.11. Acid-base potentiometric titration. Gays andClay Minerals, 27(2): 113-118.

CARSON, CD., D.S. FANNING and J.B. DIXON (1982):Alfisol and Ultisol with acid sulfate weatheringfeatures in Taxes. In: Acid Sulfate weathering.Kittrick, J.A., Fanning, D.S. and Hossner, L.R.(Eds/). Soil Sci. Soc. Am. pp: 127-146.

GILLMAN G.P. and G. Uehara (1980): Charge charac-teristics of soils with variable and permanent chargeminerals. 11, Experimental. Soil Sci. Soc. Am. J.,44:252-255.

HENDERSCHOT, W.H. and L.M. LAVKULICH (1983):Effect of sesquioxide coatings on surface charge ofstandard mineral and soil samples. Soil Sci. Soc. Am.J., 47: 1252-1260.

MANOHARAN PERUMAL (1985): Detailed soil surveyand land evaluation of north estate, Carey Island,Selangor, B Agric. Sc. thesis, UPM, Serdang.

MEHRA, O.P. and MX. JACKSON (1960): Iron oxideremoval from soils and clays by dithionite-citratesystem with sodium bicarbonate buffer. Clays andClay Minerals, 7:317-327.

PARAMANANTHAN, S. and W.D NOORDIN (1986):Classification of acid sulfate soils of PeninsularMalaysia. Pertanika 9(3): 323-330.

PATHUMANATHAN SHUNMUGAN (1985): Detailedsoil survey and land evaluation of east estate, CareyIsland, Selangor B. Agric. Sci. thesis, UPM, Serdang.

RAJASETHARAN GOPAL (1985). Detailed soil surveyand land evaluation of south estate, Carey Island,Selangor. B. Agric, Sci. thesis, UPM, Serdang.

SHAMSHUDDIN, J. and E. TESSENS (1983): Potentio-metric titration of acid soils from Peninsular Malay-sia. Pertanika, 6(1): 71-76.

SHAMSHUDDIN, J., S. PARAMANANTHAN and NIKMOKHTAR (1986): Mineralogy and surface chargeproperties of two acid sulfate soils from PeninsularMalaysia.Pertanika, 9(2): 167-176.

SANCHEZ, P.A. (1976): Properties and Management ofTropical Soils. Wiley and Sons, New York.

UEHARA, G. and G.P. GILLMAN (1980): Charge charac-teristics of soils with variable and permanent chargeminerals. 1: Theory Soil Sci. Soc. Am. J. 44: 250-252.

UEHARA, G. and G.P. GILLMAN (1981): The Minera-logy, Chemistry and Physics of Tropical Soils WithVariable Charge Clays. Boulder, Colorado, West-view Press.

WONG, I.F.T. (1974): A Soil Crop Suitability Classifica-tion For Malaysia. Bull. No. 1 Department of Agri-culture, Kuala Lumpur.

YEOH, O.M. (1985): Detailed soil survey and land evalua-tion of west estate, Carey Island, Selangor. B. Agric.Sci. thesis UPM, Serdang.

(Received 15 October, 1986)

PERTANIKA VOL. 11 NO. 1, 1988 23