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Air Spade

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Uploaded on Sep 21, 2011

At the Arnold Arboretum, a tool called the Supersonic Air Knife helps us to safely and efficiently aerate compacted soil, expose and correct tree root problems, and transplant large trees bare-rooted. The air knife converts compressed air (typically 90 to 100 psi) into a supersonic jet, directed through a nozzle especially designed for this purpose. Incredibly, the nozzle can produce exit velocities of over mach 1.6, or nearly 1,200 mph! This tool allows us to remove all of the soil from roots with minimal damage to the root systems of even the smallest trees. A 10-foot tree moved via traditional balling and burlaping techniques would likely have a root ball weighing over 300 pounds, and have perhaps two thirds of its original roots cut away. The same tree extracted from the soil by the Air Knife can retain up to 80% of its original root system during transplanting, and it can be easily picked up and moved by hand.

We also use this tool to examine and correct root issues to improve tree health. Just as a tree's canopy renews itself through occasional pruning, we have discovered similar benefits to managing the tree's complex root system. In heavily trafficked areas of the Arboretum, the Air Knife works very well to loosen up highly compacted soil up to two feet below the surface. In this video, Arboretum Director Ned Friedman lends a hand with the tool to blow away the soil from a Ginkgo biloba tree, wild collected in China by Senior Research Scientist Peter Del Tredici. This tree was moved from Peters Hill to a new location in the landscape of the Weld Hill Research Building.

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