Cadmium concentration in winter wheat as affected by nitrogen fertilization

Cadmium (Cd) is a toxic heavy metal which to a relatively large extent is ingested via wheat-based products. Conflicting results have been reported on how the application of nitrogen (N) fertilizers to winter wheat (Triticum aestivum L.) affects the Cd concentration in grain. The objectives of this study were to investigate how and to what degree application of N fertilizer affected the Cd concentration in winter wheat grain under field conditions and how consistent such effects were between sites and cultivars. Two wheat cultivars fertilized with four rates of nitrate of lime (100. 145. 190 and 235 kg N ha(-1)) were investigated in field trials, where the fertilizer was applied on two occasions as is common for bread wheat. In addition, data on Cd and N concentrations in grain of wheat, oats and barley from a Swedish soil monitoring programme were evaluated. In the field trials the grain Cd concentration increased with increasing N rate, irrespective of the Cd concentration in soil and grain. Each 10 kg increase in N application gave an increased Cd concentration in grain of approximately 0.001-0.003 mg kg(-1). The relative increase in Cd concentration as a function of N rate varied between 6 and 14% across sites and cultivars when the N rate was increased from 145 to 175 kg N. The grain Cd concentration was also positively correlated to the grain N concentration. The data from the Swedish soil monitoring programme showed a significant positive correlation between the N and Cd concentrations in grain of winter wheat, oats and barley. A possible explanation for the increase in grain Cd concentration could be ion exchange reactions in the soil solution, where an increased concentration of the fertilizer cation Ca2+ may have caused an increased concentration of Cd2+ in soil solution and eventually in wheat grain. (c) 2006 Elsevier B.V. All rights reserved.