Use of sewage sludge in Austria - II. N-availability and heavy-metal uptake

Results are presented from a 3-year experiment with large pots in the field, evaluating the effects of sewage sludge (sterilized by y-irradiation or not sterilized) on the growth of oil-seed rape and an uptake of heavy metals and of N (using the 15N-dilution technique). Mobile fractions of Cd, Cu, and Zn increased significantly in the substrate due to sewage-sludge application. However, heavy-metal transfer into the plants did not show a clear trend. Rape growth was clearly enhanced in the first and third years due to sewage-sludge applications. Average utilization of sewage-sludge N by rape decreased from 7.4% in the first year to 1.8% in the second to 1.1% in the third year, resulting in an overall utilization of 10% of sewage-sludge N. Irradiation of the sludge had no significant effects on the investigated parameters.