Effects of organic content on soil-water characteristic curve and soil shrinkage

Abstract

Organic matters commonly exist in the subsoil within the tree rooting zones. The organic content of soil has been known to affect soil properties. In this study, the soil organic contents at various locations around trees were investigated and found to be variable due to the ground flora and tree roots. The range of soil organic content for the current study was between 0.9–12.5%. The objective of this study was to investigate the effects of the organic content on the shrinkage and Soil-Water Characteristic Curve (SWCC) of the soils during rainy and dry seasons when water content of the soil changes. Soil samples were collected from two locations on Singapore Island at depths of 0.1 m and 0.3 m, one site on the western side of the island and the other site at a coastal area along the eastern shore. Centrifuge was used to measure the water content of the specimens at suction up to 250 kPa and chilled-mirror psychrometry was used for the higher suction. Shrinkage tests were also conducted to obtain the shrinkage properties. The results show that organic content influenced the shrinkage and SWCC where a higher organic content was associated with a greater shrinkage rate and a higher suction corresponding to the residual water content. For the finer soils, a higher organic content comes with a lower air-entry value.