8342937105

MINERAl.OCY. MORPHOI.OGY AND CLASSIFIGATION OF ACID SULPHATE SOILS IN PULAU LUMUT

PARIT

BOTAK    TONGKANG

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Areo reclalmed yeort ago

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Area r«clalm«d 8 years ago

jarosite

Fig 4: Diagramu lir represmtation o) Iłu* presenre oj jarosite ni the and su łja Ir saita ofhilau l.umut

1987). The pl I is < 3.5 and jarosite mottles are present in all the profiles,suggesting that the soils eon tain asulfuric horizon. As thesulfuric horizon in the soils of Parit Botak, Sedu and Sedu (silty) ser i es soils occurs within 50 cm deptli, they are classified as Typie Sulfaquept$ (Table 3) . Others, where the sulfuric horizon occurs at 50-100 cm depth are classified asSulficTropaquepts.The two soil classesdiffer in theiragricultural potential, and thus need different management practices for maximum crop production.

Implieation on Soi/ Genesis

The formation ofsulfide in the alluvial deposits is related to the sea level ehanges in the past. It is believed that sea level in Southeast Asia rosę 3-4 m above the present in the Holocene (Pons et ai 1982). Van Breemen and 1 larmsen (1975) reported that sulfide bearing deposits in Bangkok plains were 3000yearsold. Ii waspossible that at the time ofdeposition much of the lowlands in the Coastal plains of the westcoastofPeninsular Malaysiawere u n d er sea wa te r, wh ere eon d i t i on s w tire co n duc i ve topyritization.Thisisevideneed by the presenceof biorelies in the deposits.

In the soils of Pulau Lumut, pyrite was ob-served in the subsoils or sometimes in the surface horizon of the undrained areas (Fig. 2) , where potential aeid sulfate soils are found. When part of the island was drained and the land given to far-mers, this pyrite was exposed and oxidized, produc-ing a large amount of acidity, thereby lowering soil pH: In the voids and/or root channels, where oxido-reduction often took place jarosite or natrojarosite appeared, formed via precipitation in thesolution. According to Eswaran (pers. comm),

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PERTANIKA VOL. 14 NO.l, 1991