Spatiotemporal dynamics of labile Cd in soil during rice growth

Labile soil Cd is susceptible to changes over space and time due to the physical and chemical properties of the soil as well as biological processes. In this study, non-disruptive, in situ monitoring was used to explore these changes. We analyzed the mechanism(s) by which Cd is morphologically transformed and its migration patterns, with the goal of preventing soil Cd from becoming labile. The results showed that the concentration of labile Cd in the soil exhibited spatiotemporal variability throughout the rice growth period. Over time, it increased and then declined, while over space, the concentration of labile Cd in rhizosphere is higher than that in non-rhizosphere. As the depth increased, the concentration of Cd increased and then declined, especially during the flowering stage. The change of soil labile Cd concentration showed significant negative correlation with the change in soil pH and easy dynamic S(II) and Fe(II) content. It was also found that root action changed the pH of the soil during rice growth, thereby affecting the morphologies of S(II) and Fe(II), which governed the transformation of Cd and its soil mobility.