Microbial Parameters Related to Soil Quality in Growing Media Assembled from Different Quarry Materials and Organic Amendments.

Topsoil is often unavailable in sufficient amounts during urban soil constructions or during restoration of degraded soils. Artificial soil is increasingly being used as a topsoil replacement. We can construct a growing medium for plants while simultaneously decreasing agricultural and industrial waste by using organic and inorganic by-products of the agricultural and manufacturing industries. Here, a selected suite of agricultural by-products and quarry industry products combinations were evaluated as topsoil replacements in a growth chambers experiment. Our objective was to determine which by-product mix provided the most desirable soil properties for turfgrass growth compared to a commercial topsoil standard. Biological parameters commonly used as indicators of soil quality (microbial biomass and soil enzyme activities) were used to evaluate all the formulations. Based on calculated fungal and bacterial quotients (C_bac/C_org and C_fun/C_org) we determined that the substrates present in the constructed soils promoted bacterial dominance. Also, our data showed that using poultry litter compost increased β-glucosidase activity significantly compared to turkey litter compost or yard litter compost. A strong correlation was found between β-glucosidase and available P. We attributed this correlation to a change in C: Available P stoichiometry. Overall, these data suggest that careful attention must be paid to the source of organic matter and the available nutrient stoichiometric ratios in constructed soils in order to provide sustainable and long-term benefits for the above ground components as well as for nutrient cycling.