Quantify the effects of water-soluble salts and available fractions of nutrient elements on mobility of cadmium in paddy soil: A case study of the Pearl River Delta

As one of the most toxic heavy metal, soil Cd mobility is crucial to understand Cd transfer in soil-crop system and ensure crop safety production. Water-soluble salts and available fractions of nutrient elements have important influence on soil Cd mobility. However, effects of multi-factor interactions in water-soluble salts and available fractions of nutrient elements on Cd mobility and their quantified contributions haven't been enough emphasized. In this study, conditional inference tree and random forest were adopted to quantify effects of water-soluble salts, available fractions of nutrient elements and their interactions on Cd mobility in paddy soil from Pearl River Delta. The results suggested that cations (K+, Mg2+ and Na+) in water-soluble salts exerted important influence on Cd mobility, especially K+. Cd mobility is enhanced with the increase of K+ concentration and cation exchange capacity and their interaction. Available Si is the primary factor affecting Cd mobility, followed by available K and easily reducible Mn. With increases of their concentrations, interaction of available K and available Si boosts Cd mobility. When available K concentration is higher than 122 mg kg−1, Cd mobility is primarily restricted by available Si. In general, cations improve Cd mobility through competitive adsorption with Cd in soil, and available Si affect Cd mobility by changing Cd fractionation. Therefore, measures can be taken to reduce Cd mobility in paddy soil and promote sustainable development of agriculture. Such as increasing application of organic fertilizer, reducing application of chemical fertilizer, and promoting straw carbonization to return to field and so on. [Display omitted] •Cations exerted important influence on Cd mobility in soil, especially K+.•Available Si in nutrient elements is the primary factor affecting Cd mobility.•Cations improve the mobility of Cd through competitive adsorption with Cd in soil.•Available Si affects Cd mobility by changing the fractionation of Cd in soil.