©2023 International Society of Arboriculture Arboriculture & Urban Forestry 49(4): July 2023 179 Arboriculture & Urban Forestry 2023. 49(4):179–189 https://doi.org/10.48044/jauf.2023.012 reduced water-holding capacity, and increased pro- portion of hygroscopic water. Furthermore, soil com- paction results in detrimental effects on soil fl ora and fauna, increasing a tree’s disposition to root-borne diseases such as Phytophthora and Armillaria. Con- sequently, soil compaction is recognised as a major constraint to urban tree survival (Hascher and Wells 2007; Scharenbroch and Watson 2014; Watson et al. 2014). To remediate soil compaction, a few management strategies can be adopted, such as air spading, vertical mulching, soil application of biochar, and/or a wood- chip mulch layer across the compacted soil surface. Air spading is functionally similar to conventional mechanical tilling but uses a hand-held air excavation tool, which transforms pressured air generated from a compressor into a jet of supersonic air. The super- sonic air fractures compacted soil into smaller aggre- gates and has been shown to be highly effective in decompacting soils, increasing soil aeration, and pro- moting root growth while infl icting limited damage to existing tree root systems (Smiley 2005; Day and Harris 2008; Day et al. 2009). INTRODUCTION Soil compaction within the urban landscape is frequently caused by anthropogenic activity (grey infrastructure installation and maintenance, urban development, pedestrian and vehicular traffi c) and is negatively associated with soil quality (Day and Bas- suk 1994; Day et al. 1995; Smiley 2001; Sax et al. 2017; Rahman et al. 2019). Construction activities occurring during urban development and building tasks may intentionally compact soil in order to make grade alterations or construct roads. Soil compaction, however, directly reduces soil pore space and pore continuity, resulting in reduced gas exchange between the atmosphere and soil surface. If soil bulk density exceeds the root limiting bulk density value for the respective soil texture, root elongation decreases, and root branching and radial thickening increases, fur- ther limiting the spread of the root system and decreasing the uptake of essential soil nutrients (Gliński and Lipiec 1990; Day and Bassuk 1994). Trees growing in compacted soils also tend to experi- ence winter waterlogging due to slowed water infi l- tration and percolation, summer drought stress due to The Infl uence of Soil Decompaction and Amendments on Soil Quality By Glynn C. Percival, Sean Graham, and Emma Franklin Abstract. Urban soil is often compacted during anthropogenic activities, which presents a challenging substrate for tree growth. Two tech- niques for decompacting soils (air spading and vertical mulching) were evaluated alone and in combination with the soil amendment biochar and/or a woodchip mulch. Effects on soil quality (bulk density, organic matter, vegetation ground cover, cotton strip degradation, root dry mass, and earthworm counts) were monitored over 5 years. A combined treatment of air spading, biochar, and a woodchip mulch layer proved opti- mal in improving the soil quality of a heavily compacted soil over the 5-year period. This treatment was, however, the most expensive and time-consuming. A woodchip mulch was the most effective of the individual treatments and the most cost-effective. Air spading alone proved reasonably effective in improving soil quality over the 5-year study period. Effects of air spading could be improved by addition of a woodchip mulch. Vertical mulching alone or in combination with biochar had little infl uence on soil quality over 5 years. Results demonstrated that effec- tive long-term soil decompaction measures exist for arborists to improve compacted soils. Keywords. Air Tillage; Compaction; Plant Health Care; Root Growth; Soil Biological Activity; Soil Management; Urban Soils. Scientifi c Journal of the International Society of Arboriculture
July 2023
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