Rapid Remediation of Urban Soil for Trees

2014 | Bryant C. Scharenbroch, The Morton Arboretum

Degraded soil conditions hinder establishment, growth and health of urban trees, leading to premature mortality. Compost and wood chip mulches improve soil quality and tree growth, but the recovery takes many years. Preliminary findings suggest urban soil improvement may be more rapid and effective with biosolids (BS = composted sewage sludge) and/or biochar (BC = charcoal-like substance from pyrolysis of biomass). Basic research of the efficacy of BS and BC on urban trees and soils is virtually non-existent, and those studies have not examined urban tree health (growth ≠ health) or considered potential ramifications on the environment (e.g., water quality). Applied research is needed to determine appropriate application rates and techniques for BS and BC. The proposed research will include four experiments addressing highly relevant questions for arboriculture and urban forestry. Experiments will identify an appropriate BC/BS application rates, identify effective post-processing materials to use to activate BC/BS, compare and contrast mulching and air tillage with BC/BS for remediation of urban soil compaction, and examine BC/BS for remediating contaminated urban soil. Research will be led by The Morton Arboretum and University of Wisconsin – Stevens Point and include collaborators from DePaul University, Gary Comer Youth Center, Metropolitan Water Reclamation District of Greater Chicago, Urban Ecology Center and Bartlett Tree Experts. The research will include undergraduate student mentoring at multiple institutions. Results will be disseminated in papers and at conferences (scientific and industry) and also presented in student symposia.

Study Results
This research was conducted to evaluate two organic materials for potential for rapid remediation of urban soils. The two organic materials investigated were biosolids and biochar. Biosolids are nutrient-rich organic by-products from the treatment of municipal wastewater plants. Biosolids are readily available in cities, are often free to the public and their use in urban soils will reduce landfill pressure. Biochar is a charcoal-like substance derived from heating organic materials at 500-700°C under low oxygen conditions. Woody waste materials from the urban forest might be repurposed as biochar for soil improvement. Because biochar is relatively inert and slow to decompose, its use is beneficial for storing carbon in soil and reducing atmospheric CO2 levels.

When applied to the urban soils, biosolids were found to improve soil organic matter, nutrient availability, water retention and soil microbial activity and biomass. Biochar was found to increase the soil water holding capacity and might also help to retain nutrients in soil. We found that the soil improvements led to healthier and faster growing trees. We found that even though the leaves were greener on trees treated with biosolids and biochar, they were not preferred by leaf-feeding beetles. Future research is needed to refine application rates and identify the best biosolids and biochars for soil improvement for urban trees.

This project would not have been possible without funding from TREE Fund. TREE Fund provided about 50% of the necessary funding to conduct this research. TREE Fund is one of the only sources of funding to conduct research on urban trees and soils. TREE Fund is an invaluable asset for the science of urban trees and soils.

Year: 2014

Funding Duration: 3-5 years

Grant Program: Hyland R. Johns Grant

Grant Title: Rapid Remediation of Urban Soil for Trees

Researcher: Dr. Bryant Scharenbroch

Key words:

Peer Reviewed Publications from Grant:

• Scharenbroch, B.C., Carter, D., Bialecki, M., Fahey, R., Scheberl, L., Catania, M., Roman, L.A., Bassuk, N., Harper, R.W., Werner, L. and Siewert, A., 2017. A Rapid Urban Site Index for Assessing the Quality of Street Tree Planting Sites. Urban Forestry & Urban Greening, 27, pp.279-286.

For more information on this project, contact the researcher via TREE Fund at treefund@treefund.org.