Changes in soil cadmium concentrations with time following cessation of phosphorus fertilizer inputs.

Cadmium (Cd) can accumulate in soil from the application of phosphorus fertilizer. However, there is little information on what happens to soil Cd concentrations when Cd inputs stop. This study used soil and pasture samples collected from a long-term field trial to measure changes in Cd concentrations in soil for 22 yr after Cd inputs from fertilizer had stopped and assessed whether the application of nitrogen (N) (50 kg ha  yr ) could increase plant uptake of Cd and reduce soil Cd concentrations. It was found that there was no significant change in total or labile soil Cd (1 M CaCl extractable) concentrations after Cd inputs stopped. The application of N did not significantly (P < .05) increase dry matter yield or increase Cd solubility. As a result, N did not enhance plant uptake of Cd. A mass balance that included Cd loss via plant uptake and Cd leaching confirmed they were insufficient to result in a detectable decrease in soil Cd concentration over the 22-yr interval of the trial. It appears that even an acid soil with low amounts of carbon (2.67%), iron/aluminum oxides, and clay can still strongly retain Cd, preventing Cd depletion from the soil, despite stopping Cd inputs and trying to enhance plant uptake of Cd from the application of N fertilizer.