Soil lipolytic activity under the cultivation of Salix viminalis L. enriched with sewage sludge. Part I

Studies performed in a field indicate that podzolic soil combined with sewage sludge under Salix viminalis L. cultivation exhibited an increase in lipolytic bacteria and fungi numbers as well as a clear stimulation of lipase activity at level A. These changes increased in accordance with the increase of sludge concentration in the soil, and remained in the second and the third year of the experiment. However, a decrease of lipase activity was observed in subjects with a higher sludge concentration in the third year. Disturbances of microbial and enzymatic soil properties after the addition of sewage sludge occurred less intensively at the 20-40 cm than the 0-20 cm layer. In general, a slight stimulation of lipolytic bacteria and fungi and a stronger stimulation of lipase activity was found with higher doses of sludge. As at level A, these changes remained active for two years, showing a decline of lipase activity in the third year.