COUNTS AND ACTIVITY OF MICROORGANISMS PARTICIPATING IN NITROGEN TRANSFORMATIONS IN SOIL, FOUR YEARS AFTER APPLICATION OF SEWAGE SLUDGE

The objective of the study was to determine the direction, intensity and duration of changes in abundance and activity of certain microbial groups active in nitrogen trans-formations in soil subjected to a 4-year fertilization treatment with municipal and indu-strial sewage sludge. The study was conducted on podzolic soil, whose accumulation hori-zon had been fertilized in 1998 with fermented sewage sludge at doses of 30 Mg⋅ha-1(1%), 75 Mg⋅ha-1(2.5%), 150 Mg⋅ha-1(5%), 300 Mg⋅ha-1(10%) and 600 Mg⋅ha-1(20%) and planted with willow (Salix viminalis L.). Four years after the application of sludge, microbiological and biochemical analyses were made in two soil horizons (0-20 cm and 20-40 cm). It was found that in the soil from the 0-20 cm depth significant stimulation of the growth of pro-teolytic fungi and bacteria continued, but only under the effect of the highest dose of slud-ge. Moreover, there was a notable stimulation of protease activity and nitrification process alongside a slight inhibition of ammonification. In the soil from the 20-40 cm layer stimu-lation of the growth of protein-decomposing fungi was observed as well as that of prote-olytic and nitrification activity of soil, while ammonification was inhibited. However, the effect of sludge was generally less pronounced in the deeper soil layer than in the surface soil horizon. Key words: municipal-industrial sewage sludge, podzolic soil, microbiological transforma-tions of nitrogen, content N-NH4 and N-NO3