Impact of sewage sludge application on soil biological characteristics

This study examines the effect of sewage sludge application on biological 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 biomass N content was uncharacteristically low resulting in a mean microbial biomass C:N ratio of 36:1. Despite the low C:N ratio of the biomass, 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 study. Sludge application somewhat increased soil enzyme activities. In addition, a significant (P < 0.05) temporal variation in potential activities 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 significantly (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 potential were either unchanged or increased. (C) 1997 Elsevier Science B.V.