8342937103

M1NERAI.OGY. MORPHOl.OGY AND Cl ASSIKICATION OFACID SULPHATE SOI CS IN PUIAU L.UMLT

pwii Bot«» T KG Tont**ng

SOU S«du

Figi 2: A Map oj hi la u Lumut skauting soil distri bulion

determined by the pipette method (Geeand Bauder

1982).

Water-soluble sułfate wasextracted byshaking 10 g soil with 50 ml watęr for 30 minutes followed by centrifugation ataspeedof 1500 RPM.Total sulfur was extracted by a nitric-perchloric acid method (Tabatabai 1982)..Sulfur in both extractsweredetermined by the method of Freeney (1986) .

Chloride free clay from the particie size analy-sis wasdispersed ultrasonically and used for X-ray diffraction analysisandtransmission electron mic-roscopy (TEM). Yellowishjarositecrystalswere hand-picked from air-dried soil sampled, dispersed ultrasonically and studied underTEM. Undisturbed soil sampleswere taken tostudysoil mineralsandbiore-lics usingscan ni ng electron microscopy (SEM)

RESULTS AND DISCUSSION

Chemical Properties

The central part of the island which has been cultivated about 25 years ago is occupied by soils of Jawa (JWA),ParitBotak (PBK) ,Tongkang (TKG) and Sedu (SDU) Series. This covers an area of approximately 1800 ha (Fig. 2). The Southern part where soils of Sedu series (silty) occuris about 729 ha. As the two areas are subjected to two different periods of drainage, soil Chemical properties are bound to be different.

labie l summarises Chemical properties of soils found in Pulau Lumut. Generally, the soils are very acid, with pH (air-dried) values of 4.0 or less except in the Ap horizon of Tongkang Series. Soil

pi l in the horizon containingjarosite mottleswas< 4.0 in all the soils under study. The pH values decrease with depth indicating higher acid i ty i n the subsoils. The pH values are lower for soils in the newly drained areas than those of the cultivated areas. EC, basie cations, Al and total S are high in the Cg horizon of all soils, reflecting their marinę origin. An ECof>4 dS/m isregarded asdetrimen-tal tocropgrowth (Wong 1986). It wasnoted that Sedu and Jawa Series soils contained very high valuesofex trać labie Al in the B horizon.

M i nera logi ca l Properties

Kaolinite, mica and smectite are the dominant minerals in the clay fraction of Parit Botak and Sedu (silty a) Series (Fig. 3). Other minerals, occurring in minoramounts, include mica-mixed layers and gibbsite. There seems to be no real mineraiogical difference in the soils with depth. The mineralogy of other soils in the island is similar to those of Parit Botak and Sedu (silty a) Series. Studies on acid sulfate soils conducted elsewhere in the country showed a similar mineraiogical composition (Shamshuddin et al 1986).

Mo Tr.oTin.nT    Mo . Olycoł    K Tr.oTHMnT    K ♦ &OO C

A _T,    r* M-ir

Fig. 3: X-ray diffractograms of Ihr clay fraction from Parit Botak Senes (A) and Sedu (silty a) Senes (B).

TEM micrograph (Platę 1A) shows the pre-sence of some tubular halloysites in the clay fraction. These halloysites are of size of about 1 fim. Jarosite cubes was also obsened on TEM micrograph (Platę IB). This jarosite, which is also of size of about 1 /im mm, was found in voidsand/or root channels. They are probably formed via Chemical precipitation in soil solution containingsufRcient

.

PERTANIKA VOL. 14 NO.l, 1991

47