Key indicator tools for shallow slope failure assessment using soil chemical property signatures and soil colour variables

Abstract

Slope failure has become a major concern in Malaysia due to the rapid development and urbanisation in the country. It poses severe threats to any highway construction industry, residential areas, natural resources and tourism activities. The extent of damages that resulted from this catastrophe can be lessened if a long-term early warning system to predict landslide prone areas is implemented. Thus, this study aims to characterise the relationship between Oxisols properties and soil colour variables to be manipulated as key indicators to forecast shallow slope failure. The concentration of each soil property in slope soil was evaluated from two different localities that consist of 120 soil samples from stable and unstable slopes located along the North-South Highway (PLUS) and East-West Highway (LPT). Analysis of variance established highly significant difference (P < 0.0001) between the locations, the total organic carbon (TOC), soil pH, cation exchange capacity (CEC), soil texture, soil chromaticity and all combinations of interactions. The overall CIELAB analysis leads to the conclusion that the CIELAB variables lightness L*, c* (Chroma) and h* (Hue) provide the most information about soil colour and other related soil properties. With regard to the relationship between colour variables and soil properties, the analysis detected that soil texture, organic carbon, iron oxide and aluminium concentration were the key factors that strongly correlate with soil colour variables at the studied area. Indicators that could be used to predict shallow slope failure were high value of L*(62), low values of c* (20) and h* (66), low concentration of iron (53 mg kg) and aluminium oxide (37 mg kg), low soil TOC (0.5%), low CEC (3.6 cmol/kg), slightly acidic soil pH (4.9), high amount of sand fraction (68%) and low amount of clay fraction (20%).

Properties of sandy soil and allelochemical compounds of heath forest in Rantau Abang, Terengganu, Malaysia: Implication for ecological sustainability and biodiversity conservation

“…Several causes affected the availability of heavy metals in the soil, including the region from where the samples were collected (seedling region, semimatured trees region, and matured trees region), the soil's physical appearance and depth, climate, and water bodies. All these factors may be responsible for the reaction of heavy metals because they can be transferred from one place to another place and are non-degradable [22]. Aluminium toxicity at low levels of phenolic compounds and organic matter, low pH levels, and high sand content appear to be the chief limiting factors for plant growth in acidic soils.…”

“…As shown in Table 2, when the soil pH value drops to nearly 4.0, the availability of the majority of plant nutrients diminishes, while aluminium and a small number of micronutrients become more soluble and toxic to plants. According to Othman, et al [24], the correlation between pH and aluminium was determined based on the amount of aluminium that is sufficient for the ion charges to function below pH 5.5. Aluminium compound, Al (OH) 3-, in this hydrolysis reaction at the suitable pH values, reacts with hydrogen ions to free aluminium.…”

“…The impact on the availability of nutrients depends on the charge and size of the nutrient molecules and if they can be dissipated through seepage. Generally, organic carbon and nitrogen (N) are more available in the soil with a value of pH ranging from 6.5 to 8, whereas CEC and phosphorus content are most available in soil with a pH value ranging from 5.5 to 7.5 [24]. Therefore, aluminium toxicity and soil acidity are the major constraints that reduce plant growth efficiency or nutrient obtainability for plant consumption, thereby affecting the growth of most of the target plants in the long run.…”