DGT estimates cadmium accumulation in wheat and potato from phosphate fertilizer applications

Cadmium is a common impurity in phosphatic fertilizers and may contribute to soil Cd accumulation. Changes in total and bioavailable Cd burdens to agricultural soils and the potential for plant Cd accumulation resulting from fertilizer input was investigated. Three year field studies were conducted using three dose levels of cadmium-rich, commercial, phosphate fertilizers applied at four agricultural sites. Labile Cd concentrations, measured using the passive sampling device Diffusive Gradients in Thin Films (Cd(DGT)), increased with increasing fertilizer application rates. Cd also accumulated in the edible portion of wheat and potato crops grown at the sites, and showed strong positive dose response with fertilizer treatment. Regression models were calculated for each site, year, and for individual crops. Model comparisons indicated that soil physical and chemical parameters in addition to soil Cd fractions, were important determinants of Cd(DGT). Significant factors contributing to Cd(DGT) concentrations were Cd from fertilizer input (Cd(fertilizer)), pH, cation exchange capacity (CEC), and total recoverable Cd (Cd(total)). Important factors used to determine Cd concentrations in wheat grain (Cd(wheat)) and in potato (Cd(potato)) were as follows: Cd(wheat):Cd(fertilizer), and Cd(DGT); and Cd(potato):Cd(fertilizer), Cd(DGT), % O.M. The effective concentration, C(E), calculated from DGT did not correlate well with Cd(wheat) or with Cd(potato). Direct measurements of Cd(DGT) correlated better with Cd found in edible plant tissue. The modeling approach presented in this study helps to estimate Cd accumulation in plant tissue over multiple years and in distinct agricultural soil systems.