Assessing soil quality and soil erosion hazards in the Moneragala District, Sri Lanka

Abstract

This study was carried out in order to assess physicochemical properties of soil and to develop a predictive soil erosion hazard zonation map based on the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST)—sediment delivery ratio model (SDR) of the Moneragala District which has been recognized as a highly spreading district of chronic kidney disease of uncertain etiology (CKDu) in Sri Lanka. A total of 68 soil samples were purposely collected from cultivation areas from CKDu prevalence and non-prevalence areas representing the entire district in three soil depths of 0–7, 7–14, 14–21 cm using a soil core sampler for the analyses of moisture content and bulk density. Another subset of soil samples was collected from the depths of 0–15, 15–30, 30–45 cm for the analysis of pH, electrical conductivity (EC), soil texture, major cations, and heavy metals. According to the results, the soil textural triangle shows that the study area consisted of 11 types of soils and the topsoil layer consisted of mainly 4 soil types as sandy loam soil, sandy clay loam soil, loamy sandy soil, and sandy soil, whereas 52 of the soil samples have belonged to the group of sandy loam. Furthermore, the results disclosed that with the increasing depth, the soil pH and EC are increased, the moisture content is decreased, and bulk density is gradually increased. Fe and Mg were found to be the dominant cations in the study area, whereas Cu, Ni, Zn, and Pb were within the tolerable limits, whereas Cd exceeded acceptable levels. Moreover, according to the developed soil erosion hazard zonation map, the predicted mean annual soil loss rate in the study area is 27.8 t/ha/yr and a total of 3.7 t/ha/yr sediment is exported to the stream by erosion. Moreover, the overall study gives an insight that there is no distinct relationship between the spatial distribution of physicochemical properties and the prevalence of CKDu in the Moneragala District. Moreover, the number of CKDu patients recorded is high in the southern part of the study area where soil erosion is found to be low due to its flat low elevated topography where 71% of groundwater quality is poor. However, the ultimate outcomes of this study possibly would be directly used for soil and water conservation (SWC) programs in the Monaragala District.