Trace element concentrations in cereal grain of long-term field trials with organic fertilizer in Sweden

Long-term use of organic fertilizers can lead to slow accumulation of trace elements in arable soil, whereas cropping systems with no return of organic residues to soil can lead to depletion. These changes in soil concentrations may potentially influence crop uptake of both essential and toxic metals over time. The aim of this study was to investigate the long-term use of manure and sewage sludge on trace element composition of cereal grain samples from on-going field experiments. The analyses showed that the organic fertilizers had limited or no impact on grain concentrations of cadmium (Cd), copper (Cu), manganese (Mn), molybdenum (Mo) and selenium (Se). Concentrations of these metals in grain remained low to moderate. However, application of the organic residues resulted in higher grain concentrations of zinc (Zn) at several locations, although results for different sites were contradictory. It was concluded that added trace metals present in organic fertilizer are not easily available to crops and that changes in soil properties, such as pH, and root proliferation often are of greater importance for crop uptake. Application of sewage sludge with a low Cd content to agricultural soil does not pose a high risk of increased Cd concentrations in crops. At low Cd concentrations as in Swedish arable soils, the Cd:Zn ratio seems to have little importance at low to moderate input of Cd and Zn.