Characterization of an Alfisol collected from dry zone of Sri Lanka to elucidate the retention mechanisms of pollutants

Characterization of physicochemical properties of a soil enables predicting the behavior of nutrients and pollutants added to the soil. A study was conducted to characterize environmentally important physicochemical properties and processes of an Alfisol (Reddish Brown Earth) collected from the Dry zone of Sri Lanka. Organic carbon content (OC), pH, Electrical Conductivity of soil suspension (EC) and saturated paste (ECe), Cation Exchange Capacity (CEC), and available and total metals (Cu, Zn and Cd) were analyzed. Potentiometric titration and adsorption study were conducted to determine the Point of Zero Charge (PZC) and phosphorus adsorption capacity of the soil. Clay mineralogy of the soil was determined using X-ray diffraction technique. Among the basic soil chemical properties analyzed, CEC (13.2 cmol+ kg-1) showed a low cation retention attributed to low organic carbon percentage (mean 0.37 %) and the predominating of low activity clay minerals of kaolinite and illite. The EC values (EC=0.03 dS m-1, ECe=0.3 dS m-1) indicated a low salinity level. Point of zero charge of the soil was 4.0 indicating net negative charges at the existing soil pH of 6.37. At the near neutral pH of the soil, the cation retention enhanced, subsequently affecting the mobility of metals. Phosphorus adsorption data fitted to Langmuir isotherm gave an adsorption maximum of 14285 mg kg-1 indicating a high P fixing ability. The soil properties studied can be used to elucidate the retention mechanisms of pollutants in this soil.