BETA-GLUCOSIDASE ACTIVITY IN SOILS AMENDED WITH SEWAGE-SLUDGE

In a laboratory experiment three soil types were treated with two sources of sewage sludge at four rates. Beta-Glucosidase activity was assayed after 0, 7, 14, and 30 days of incubation. At the lower loading rates (10 and 30 mg sludge g-1 soil) beta-glucosidase activity was inhibited but enhanced activity was observed at higher application rates (100 and 200 mg sludge g-1 soil). Inhibition of enzyme was more pronounced with St. Louis sludge (66%) at 30 days of incubation and is attributed to the higher concentration of trace metals in this sludge source. The enhanced activity of beta-glucosidase ranged from 1.2 to 4-fold (Elk soil), 1.21 to 3.67-fold (Lilbourn soil), and 1.13 to 3.28-fold (Waldron soil). This increase in enzyme activity was attributed to the enhanced microbial activity which was stimulated with higher nutrients and organic matter content of sludge-amended soils. Furthermore, binding with humic substances and clay minerals may have played a role in reducing the adverse effects of heavy metals. However, potential hazards associated with land application of sewage sludge such as NO3- leaching into the ground water, accumulation and addition of heavy metals in the soils, germination and plant growth inhibition, remain to be a serious ecological problem.