Date of Award

9-1-2025

Degree Type

Thesis

Degree Name

Master of Environmental Science (M.Env.Sc.)

Department

Agricultural and Environmental Sciences

First Advisor

Dr. Yujuan Chen

Abstract

Urban land development usually results in compacted soils, creating unfavorable conditions for tree establishment and growth. Soil Profile Rebuilding (SPR) is an urban soil rehabilitation technique to address soil compaction on site. However, the impacts of SPR on urban soils and tree growth in the southeast region remain unexplored. To address this research gap, this study assessed the efficacy of the SPR techniques in improving degraded urban soils including soil physical, chemical, and biological properties, and tree growth. Twelve experimental plots (12.2 m L*0.5 m W; 5.6 m2) were established using a completely randomized experimental design (4 soil treatments; 3 replications; 12 plots in total) in Nashville, Tennessee in 2023. The four soil treatments include: (1) Control (CON): no amendment, only subsoiling, and topsoil removed and partially replaced; (2) SPR: incorporation of four inches of compost to 60 cm, subsoiling, and topsoil removed and partial replaced; (3) Biochar (BC): incorporation of one inch of biochar to 60cm, subsoiling, and topsoil removed and partial replacement; (4) SPR+Biochar (SPR+BC): incorporation of two inches of compost and one inch of biochar to 60 cm, subsoiling, and topsoil removed and partial replacement. Three tree species, Liriodendron Tulipifera (Tulip Tree), Pinus Taeda (Loblolly Pine), and Liquidambar Styraciflua (American Sweetgum), were randomly planted in each plot (3 tree species, 1 tree/species/plot, 36 trees in total). The baseline soil and tree data were collected in 2023, and various soil and tree growth measurements were taken to evaluate the changes in 2024.We found that soil bulk density in SPR, SPR+BC, and BC decreased by 27.5%, 13.2%, and 3.3%, respectively, at 2.5-7.5 cm depth compared to CON, with no differences at greater depths. Moreover, total nitrogen (TN) was significantly higher in SPR+BC treated soils than other treatments, following the similar order of SPR+BC> SPR> BC > CON for soil depths of 0-5cm, 5-10cm, and 10-20cm. Similarly, the soil carbon/nitrogen (C/N) ratio was significantly lowered in SPR and SPR+BC plots than CON and BC plots across soil depths 0-5 cm and 5-10 cm. However, no statistically significant differences were observed in soil moisture, soil temperature, unsaturated hydraulic conductivity (K), soil pH, electrical conductivity (EC), soil organic carbon (SOC), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), soil carbon dioxide (CO2) fluxes and tree growth within the study period. Furthermore, a potential trend or pattern indicated that SPR and SPR+BC outperformed BC alone and CON plots in enhancing various soil properties such as SOC, MBC, and MBN, suggesting the need to extend the study duration to further explore the long-term impacts of SPR techniques. These findings can guide urban foresters/planners, policy/decision-makers, researchers, and practitioners aiming to restore degraded urban soils and enhance urban sustainability.

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