Effects of Four Compaction Remediation Methods for Landscape Trees on Soil Aeration, Mechanical Impedance and Tree Establishment

Abstract

Landscape trees are often planted in heavily compacted soils around newly constructed buildings or in urban areas. Under such conditions, trees frequently die, or decline prematurely. Four techniques for improving tree establishment on such sites were studied: peat-amended backfill; vertical drainage mat panels; radiating trenches filled with sandy loam soil; and vertical, gravel-filled sump drains. Sugar maple (Acer saccharum ‘Seneca Chief’), a species sensitive to soil compaction, and the less sensitive Callery pear (Pyrus calleryana ‘Redspire’) were planted bare root into treatments in a compacted silty clay loam soil. Controls were backfilled with native soil. Shoot and root growth were measured over three growing seasons. Soil air oxygen content was monitored for one year. Effects of treatments on soil compaction were characterized using measurements of both soil strength and bulk density. Shoot growth of pears was greatest for treatments that alleviated mechanical impedance (soil trenches and amended backfill) and least for treatments that did not (controls and vertical drains). Drainage mats, which may alleviate mechanical impedance to a lesser degree, showed intermediate growth. Root growth was well correlated with shoot growth. Length of 2 to 5-mm diameter roots was greater for pears in soil trench treatments than for those with no treatment (controls) at the end of 3 growing seasons. Vertical drainage mats and vertical gravel-filled sump drains were shown to increase O2 percent in surrounding soil. Regardless of treatment, all oxygen levels were usually close to atmospheric levels and never lower than 10%. Maple mortality was high and no treatment effects were shown.