IMPACT OF SEWAGE-SLUDGE APPLICATION ON SOIL BIOLOGICAL CHARACTERISTICS

This study examines the effect of sewage sludge application on biologi cal and biochemical properties of soil in the plots maintained by the City of Winnipeg at Oak Hammock Marsh, Manitoba. Soils were collected from plots receiving single and multiple applications of 0, 50 and 100 tonnes of sludge ha(-1). Sludge application significantly (P < 0.05) increased the amount of microbial biomass present in the soils. The bi omass N content was uncharacteristically low resulting in a mean micro bial biomass C:N ratio of 36:1. Despite the low C:N ratio of the bioma ss, sludge application enhanced the N mineralization potential of the soil. Potential activities of three soil enzymes (arylsulfatase, acid phosphatase and alkaline phosphatase) were also monitored in this stud y. Sludge application somewhat increased soil enzyme activities. In ad dition, a significant (P < 0.05) temporal variation in potential activ ities was also observed in this study. The functional diversity of the soil community was assessed using Biolog(TM) microplates. The highest rate of sludge application (2 x 100 t ha(-1)) was found to significan tly (P < 0.04) reduce the functional diversity of the soil community. These results suggest that although the sludge application resulted in a reduction in the diversity of the microbial population, the overall size of the soil microbial biomass and its nutrient mineralization po tential were either unchanged or increased. (C) 1997 Elsevier Science B.V.