Effects of agro-climatic zones, soil orders, and irrigation types on the exchangeable cadmium in paddy soils

Even though the concentrations of the total cadmium (Cd) in paddy soils from different countries have been reported, the exchangeable-Cd (Ex-Cd) concentrations in these soils are unknown despite its importance in agriculture. This study was conducted with a total of 5460 soil samples collected in Sri Lanka, representing six agro-climatic zones, six soil orders, and three irrigation types. The Ex-Cd concentrations in soil samples were extracted using 0.01 ​M CaCl₂ and analyzed using an inductively coupled plasma-mass spectrophotometry. The Ex-Cd concentrations were <0.31–163 ​μg ​kg⁻¹, with mean and median concentrations being 14.1 and 8.98 ​μg ​kg⁻¹, respectively, which was affected by both agro-climatic and soil conditions. Samples from the Wet zone, particularly the Wet zone Low country, had higher Ex-Cd (24.1 ​μg ​kg⁻¹) than those from the Dry zone Low country (11.6 ​μg ​kg⁻¹). Among the soil orders, Histosols (21.3 ​μg ​kg⁻¹) and Inceptisols (19.5 ​μg ​kg⁻¹) had the highest Cd concentration while Vertisols had the lowest (6.3 ​ ​kg⁻¹). The irrigation types only affected Ex-Cd concentrations in Dry zone Low country, but not in other agro-climatic zones. Overall, it is important to consider agro-climatic zones, soil orders, and irrigation types when implementing agronomic strategies to mitigate the risk associated with Cd accumulation in paddy fields.