Prediction of cadmium and zinc concentration in wheat grain from soils affected by the application of phosphate fertilizers varying in Cd concentration

Cadmium is an undesirable contaminant in phosphate fertilizer, and may represent a threat to food safety given its tendency to be taken up by plants and translocated into the edible parts. In this context, predicting wheat grain cadmium concentration from preliminary data would help to prevent exceeding the threshold values. Our study compared different approaches to estimate the concentrations of cadmium and zinc in wheat grains based on either soil solution chemistry of these elements, their quantities added to the soil and various soil parameters. Whereas the predictions based on soil solution chemistry show positive correlations between predicted and measured values of cadmium for some experimental sites, it was more difficult to predict grain cadmium concentrations in other sites. Reverse-wise, predictions based on applied cadmium and some soil parameters yielded systematically good correlations between predicted and measured values. The prediction of the concentration of zinc in wheat grains could not be achieved as its content was neither related to the measured soil solution chemistry nor to the quantities of zinc applied to the soil. We suspect that zinc interacts with the phosphate fertilizer thus obscuring the regressions for plant uptake. The prediction of grain cadmium in wheat cultures is best achieved through empirical modeling from soil parameters and soil inputs rather than through estimates of the bioavailable fractions in the soil solution.