EFFECTS OF COMPOSTED SEWAGE-SLUDGE ON THE RESIDUAL ION CONTENT OF SOILS

Changes occuring in the ion content of two soils of different texture have been studied after their amendment with an urban and an industria l sludge. These sludges hab been subjected to different composting per iods with slivers from tree pruning before their addition to the soils . Organic matter and N contents increased in both soils after the amen dment with the sludges, and this effect was more moticeable in the cas e of the clay soil. It was also found that organic matter from the ind ustrial sludge mineralized after 14-weeks of fermentation, but the per iod of composting with slivers did not affect the organic matter conte nt of the urban sludge. Although the content of macro-elements in soil solution hardly varied after amendment with sludge, the contents of m icro-elements and heavy metals (especially those of Fe and Pb) increas ed significantly when the high rate and the shorter composting period were used; however, Mn and Al were retained in the clay soil. The indu strial sludge increased the content of heavy metals in both soils.