Urban Soil Rehabilitation

Yujuan Chen¹, Susan D. Day¹, Abbey F. Wick², W. Lee Daniels², Brian D. Strahm¹, P. Eric Wiseman¹ and Kevin J. McGuire¹

¹ Department of Forest Resources & Environmental Conservation, Virginia Tech, Blacksburg, VA 24061

² Department of Crop and Soil Environmental Sciences, Virginia Tech, Blacksburg, VA 24061

Soil is a significant carbon (C) reservoir globally. The continued storage of C in soils has the potential to contribute to climate change mitigation, but little is known about urban soils. Land use change and urbanization typically result in degraded soils, making soil rehabilitation that incorporates organic matter to improve structure and function over time desirable. This study evaluates the potential to increase C storage in rehabilitated urban soils. In 2007, six replicates of four treatments [minimal effort (10 cm topsoil replaced), enhanced topsoil (10 cm topsoil replaced plus rototilling), profile rebuilding (compost amendment incorporated via subsoiling to 60-cm depth, 10 cm topsoil replaced plus rototilling), and undisturbed (no grading, scraping or improvement methods)] were installed in a completely randomized design, using 84 m² plots, in Montgomery County, VA. Two soil series, Shottower loam (fine, kaolinitic, mesic Typic Paleudults) and Slabtown loam (fine-loamy, mixed, mesic Aquic Paleudalfs), are present at the site.  Prior to treatment installation, all plots except controls (undisturbed) were subjected to typical land development practices to replicate urbanized land: scraping of topsoil and compaction of subsoil to a bulk density of 1.98 Mg m^-3. All plots were planted with five species of trees typically used in urban settings, but otherwise kept free of vegetation or additional organic inputs. In 2010, soil organic carbon (SOC) at depths of 0- 5, 5-15, and 15-30 cm was characterized in the active, slow, and passive carbon pools using density fractionation techniques. At the 15-30 cm depth, profile rebuilding plots contained significantly higher SOC concentrations and greater pool sizes in both active and slow pools relative to other treatments. Soil aggregate size distribution, microbial biomass carbon and three-year SOC results will also be discussed.