EFFECTS OF DIFFERENT DOSES OF SEWAGE-SLUDGE ON SOIL AND PLANTS OF A CULTIVATED AND A GRASSLAND SITE IN THE LOWER VALLEY OF THE RIVER MURZ

A two years' experiment in Murzhofen and St. Lorenzen in Styria was carried out for measuring the effects of sewage sludge application on soil and plants. In the course, small plots with an area of 20 square meters each were treated with different intensities of application. In the highest intensity 7.5 tons of dry substance per ha and year was applied on the cultivated sites, 3.75 tons per ha and year on the grassland. An enrichment of heavy metals such as zinc, copper, lead and cadmium was noticed on the cultivated soil. Higher contents of lead and mercury could be found in the grassland soil. The plants of the grassland (first reaping) showed a clear increase of zinc and nickel. An increase of zinc and lead was also found in silage-maize. Yet neither the cultivated nor the grassland site showed a more intensive growth of weeds compared to the untreated plots. A better growth of silage-maize as well as grass (first reaping) was quite obvious because of sewage sludge application. The results of this two years' experiment show no significative negative effects on soils and plants according to the present laws and regulations in Styria.