Soil Enzyme Activity and Microbial Dynamics In a Degraded Soil Amended with Biosolids.

Amending soils with composted sewage sludge (biosolids) or yard waste debris has been shown to improve soil quality. Additionally, there is some evidence that biochar (residual charcoal from bio-energy generation) may be helpful in sequestering C in soils to reduce losses of CO₂ to the atmosphere.  However, there is relatively little information in comparing biosolids composts and urban yard waste composts relative to biochar on soil bioremediation.  Therefore, the objective of this study is to determine the microbial response of degraded soils amended with various composted organic amendments derived from urban wastes. Soils were sampled from a degraded soil in Calumet, Illinois in August of 2009 and 2010. The soil was amended with a range of materials including two application rates of a three-year composted biosolid (202 Mg ha^-1 and 403 Mg ha^-1), yard debris vegetative compost (1.15 m³/ plot), and a designer mix consisting of biosolids (202 Mg ha^-1), 13.6 kg biochar, and (1.2 Mg ha^-1 of Fe oxide) drinking water treatment residual. The enzymes were arylsulfatase, acid phosphatase, b-glucosidase, b-glucosaminidase, urease, and fluorescein diacetate (FDA) hydrolase. Biosolid and designer mix treatment plots had significantly higher (P <0.05) enzyme activity compared to control plots, except for urease. The highest activity rates were observed in the biosolid application at 403 Mg ha^-1 for all enzymes in 2009 and 2010. In general, enzyme activities increased for the 2010 samples compared to the 2009 samples (except b-glucosaminidase and urease). There was no statistical difference between the biosolid application at 202 Mg ha^-1 and the designer mix for each enzyme tested. This indicates that there was no short-term effect of biochar additions on the soil microbiological activity. The vegetative compost treatments were statistically similar to the topsoil controls in 2009, however vegetative compost activities for all enzymes increased significantly from the controls in the following year.