Use of sewage sludge - nitrogen availability and heavy metal uptake into rape

The results of a three years experiment with large pots in the held evaluating the effects of sewage sludge (sterilised by gamma-irradiation or not sterilised) on rape growth, heavy metal- and N-uptake, using the N-15-dilution technique, are presented. Mobile fractions of Cd, Cu and Zn increased significantly in the substrate due to sewage sludge treatments. However, heavy metal transfer into rape plants did not respond clearly. Rape growth was clearly enhanced in the first and third year due to sewage sludge applications. The average N-utilisation by rape from savage sludge in a three years period decreased from 7.4 % (first year), 1.8 % (second year) to 1.1 % (third year), resulting in an overall utilisation of 10.3 % of savage sludge - N-t by rape plants. Irradiation of sewage sludge did not result in any significant effect on the investigated parameters.