Effects of composted sewage sludge on microbial biomass, activity and pine seedlings in nursery forest.

The investigation was carried out in a 2 year experiment to evaluate the benefits and hazards of the use of composted sewage sludge as a restoration agent for the soil of the nursery forest intended for growing Pinus sylvestris seedlings. The grey forest soil (Haplic Greyzem) was amended with compost at the 25, 50, 75, 100, 150 and 175 t ha(-1) application rates on a dry matter basis. The organic matter content increased with the increase in sludge amendment as well as the metal content. However, the concentrations of individual metals were below the current limits established for Russia and European countries. Sludge amendments enhanced the germination and decreased the mortality of the seedlings. The effects were more obvious for the soil with the highest sludge treatment. The beneficial effects on the biomass of seedlings and the height of the shoots as well as on the length of the roots of the pine seedlings were greater in plots with the highest rates of composted sludge. The application of composted sludge to soil was followed by an increase in microbial biomass and to a lesser extent in basal respiration. In the absence of any detrimental effect on microorganisms, this study lends support to using composted sewage sludge as the organo-mineral fertilizer for the soil of nursery forest.