SHORT-TERM IMPACT OF ORGANOMINERAL FERTILIZERS AND WASTEWATER SLUDGE ON SOIL ENZYME ACTIVITIES AS SOIL QUALITY INDICATORS

Soil enzymatic activities are widely used as bioindicators of soil quality. The objective of this study was to evaluate the effects of organomineral fertilizer (OMF) and wastewater sludge (WS) (with similar properties as OMF) applications on soil enzyme activities during an incubation period of 30 days. To evaluate the effect of OMF and WS concentrations on soil enzyme activities, 200 g soil portions were placed into plastic containers, and distilled water was added to different doses of OMF (50 and 100 t/ha) to bring the soil to 70% of its field capacity. The samples were then incubated under controlled conditions in the dark at 28 degrees C for 15 and 30 days. The results showed that the applications of OMF negatively affected enzyme activities in the short term. In particular, the OMF dose of 100 t/ha inhibited urease activity. The highest enzyme activities were recorded in the control soil for all treatments. Similarly, the WS applications also inhibited soil enzyme activities except for urease activity (UA). At the end of the incubation, the wastewater-sludge application doses of 50 and 100 t/ha increased urease activity by 42% and 40%, respectively. The reduction in alkaline phosphatase activity (APA) and dehydrogenase activity (DHA) for soils amended with 50 t/ha OMF and WS was determined to be 32-6% and 0-56%, respectively. Similarly, soil APA and DHA decreased by 38%-32% and 2.5%-39% in soil amended with doses of 100 t/ha of OMF and WS, respectively. The effects of wastewater sludge and OMF amendments on soil appear to depend on the origin of the contents and application dose. In terms of soil nitrogen and phosphorus cycles, wastewater sludge applications have been found to be more effective than OMF for soil fertility.