4. Conclusions
No accumulation of metals or organic polutants could be determined after 16 consecutive years of adition
of biogas residue and sewage sludge. The metal content in the barley harvest indicates an increased
bioavailability of metals as a result of regular additions of sewage sludge compared to the other fertilizers.
However, the metal concentrations in the barley from the unfertilized control plots indicates high
background levels of metals in the soil.