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Compacted soils can be rebuilt to help urban trees thrive


   

A man between a street and a sidewalk uses a specialized probe to extract a column of soil. At a street tree planting site in Arlington County, Virginia, former master’s student David Mitchell uses a specialized probe to extract a column of soil 1 meter deep. Soil carbon was analyzed at sites with and without remediation.


May 15, 2016 – Researchers have developed a soil rehabilitation method that can help fix the compacted, rock-hard soils left behind after land development and building construction. Associate Professor Susan Day and colleagues showed that their method, “Soil Profile Rebuilding,” decreases soil compaction, increases carbon sequestration, and increases the rate at which water moves through the soil, thereby improving storm-water capture.

According to Day, trees planted in rehabilitated soil have as much as 84 percent greater canopy than those in untreated soil. “City soils are much maligned, and with good reason,” she said. “They are stripped and compacted and mixed and layered until they have little in common with their less-disturbed cousins on agricultural and forested lands.”

The Soil Profile Rebuilding method uses compost and a special subsoiling technique adapted for tight urban spaces to create pathways through the soil for root and water penetration. A backhoe is used to break up the compacted soil and incorporate compost to a depth of 2 feet. Then four inches of topsoil are applied and rototilled to a depth of 6 to 8 inches, followed by planting trees or shrubs whose roots help the soil continue to develop.

Unlike many previous approaches to alleviating soil compaction, the effects of Soil Profile Rebuilding persist “because the technique doesn’t just break up the soil physically; it also affects biological activity in the soil,” Day explained. It is a useful tool for designers seeking SITES® (Sustainable Sites Initiative) accreditation from the U.S. Green Building Council.

The rehabilitation process was developed over the course of seven years of research at Virginia Tech and in Arlington County, Virginia. Results were recently published in Urban Forestry & Urban Greening.


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