Distribution patterns of exchangeable aluminium in Sri Lanka’s lowland paddy soils in relation to climate, soil type, and water supply

The presence of excessive amounts of exchangeable aluminium (Ex-Al) in lowland paddy soils poses negative impacts on the growth of rice plants. Even though rice is the most widely grown crop in Sri Lankan lowlands, the distribution of Ex-Al in paddy soils is not known. Therefore, this study was conducted to determine the distribution of Ex-Al concentration and examine the interactive effects of agro-climatic zones (ACZs), soil orders, and water sources in determining Ex-Al concentration in lowland paddy soils in Sri Lanka. A total of 9,280 soil samples representing six ACZs, six soil orders, and three water sources were collected using a stratified random sampling approach. Ex-Al was extracted using 0.01 M CaCl 2 and detected using an Inductive Coupled Plasma Mass-Spectrophotometry. Ex-Al concentration ranged between 0.002 and 101.86 mg kg − 1 with a mean of 4.71 mg kg − 1 . When comparing ACZs, samples collected from the Wet zone Low country had the highest Al concentration ( p < 0.05). Among the soil orders, Histosols had the highest Ex-Al concentration, while that in Inceptisols and Vertisols was the lowest ( p < 0.05). Fields receiving water from major irrigation schemes resulted lower Ex-Al concentration than rainfed fields ( p < 0.05). Moreover, Al concentration was negatively correlated with soil pH and grain yield ( p < 0.05). Therefore, ACZ, soil order, and water source-based strategies need to be developed to minimize further accumulation of Al and/or remediate Al-affected soils.