Charge properties of soils in Malaysia dominated by kaolinite, gibbsite, goethite and hematite

Majority of the Malaysian soils in the upland areas of the country are weathered. They are developed from a range of parent materials. These soils, known as Oxisols, are dominated by kaolinite and oxides of Fe and Al (sesquioxides). A study was conducted to determine the charge properties of three common Oxisols in Malaysia. For this study, the mineralogy of the clay fraction of the three soils was determined. It was then followed by the determination of the charge properties, with and without the presence of organic matter and sesquioxides. The results showed that the clay fraction of the soils contained mainly kaolinite, gibbsite, goethite and hematite. The pHo (the pH at which the net charge is zero) decreased with the increase in organic matter contents. On the other hand, it increased with the increase of sesquioxides contents. The negative charge (CEC) increased when soil pH increased. Basalt is a soil amendment. Depending on the rate, its application into the soils had increased soil pH, which concomitantly increased the negative charge of the soils. Simultaneously, the pHo of the soils decreased. This phenomenon further increased the negative charge of the soils under investigation.