©2023 International Society of Arboriculture 186 quality, these improvements were, in most instances, not significantly greater than air spading alone. Con- sequently, results of this study indicate that biochar addition in combination with air spading and vertical mulching had limited effects on improving soil qual- ity compared to air spading and vertical mulching alone. CONCLUSIONS A combined treatment of air spading, biochar, and woodchip mulch proved optimal in improving a suite of soil physical, chemical, and biological properties in a heavily compacted soil over a 5-year period. This treatment was also the most expensive and time con- suming. A woodchip mulch layer was the most effec- tive of the individual treatments and the most cost effective. Vertical mulching alone had little influence on soil quality. Air spading alone proved effective in improving soil quality over a 5-year period, and the long-term effects of air spading could be improved by the addition of a woodchip mulch layer. In agreement with Fite et al. (2011), results demonstrate effective long-term soil decompaction measures exist that pro- vide arborists with a useful means to improve com- pacted soils within urban landscapes. LITERATURE CITED AHDB. 2018. How to count earth worms. Kenilworth (United Kingdom): Agriculture and Horticulture Development Board. [Updated 2023 March 14; Accessed 2020 July 25]. https:// ahdb.org.uk/knowledge-library/how-to-count-earthworms AHDB. 2019. Biological tests for soil health. Kenilworth (United Kingdom): Agriculture and Horticulture Development Board. [Accessed 2022 March 18]. https://ahdb.org.uk/ knowledge-library/biological-tests-for-soil-health Arideep M, Madhoolika A. 2018. The influence of urban stress factors on responses of ground cover vegetation. Environ- mental Science Pollution Research. 25:36194-36206. https:// doi.org/10.1007/s11356-018-3437-5 Ben-Dor E, Chabrillant S, Dematte JAM, Taylor GR, Hill J, Whiting ML, Sommer S. 2009. Using Imaging Spectroscopy to study soil properties. Remote Sensing of Environment. 113(S1):S38-S55. https://doi.org/10.1016/j.rse.2008.09.019 Blackwell P, Riethmuller G, Collins M. 2009. Biochar applications in soil. In: Lehmann J, Joseph S, editors. Biochar for environ- mental management: Science and technology. London (United Kingdom): Earthscan. p. 207-226. Blanco-Canqui H. 2017. Biochar and soil physical properties. Soil Science Society of America Journal. 81(4):687-711. https:// doi.org/10.2136/sssaj2017.01.0017 Chalker-Scott L. 2007. Impact of mulches on landscape plants and the environment—A review. Journal of Environmental Horticulture. 25(4):239-249. https://doi.org/10.24266/0738 -2898-25.4.239 5, possibly as a result of long-term soil settling com- bined with light foot traffic caused by members of the public (Morris et al. 2009). Similarly, air spading alone or in combination with biochar soil amendment and a woodchip mulch layer had the greatest effects on vegetation ground cover at the end of year 5. Ground cover is widely used as an indirect indicator of soil quality; a soil lacking a cover of living plants is almost certainly indicative of poor soil quality (Zuazo and Pleguezuelo 2009). A lack of vegetation ground cover or smaller stunted plants is also associ- ated with compacted soils (Ben-Dor et al. 2009). By year 5, 100% vegetation ground cover was recorded following air spading in combination with biochar and a woodchip mulch layer compared to 5% in non-decompacted control soils, indicating a signifi- cant improvement in soil quality. Vegetation ground cover observed at year 5 consisted mainly of grass- land species (Lolium perenne, Poa annua) and a few weed species, including white clover (Trifolium rep- ens), dandelion (Taraxacum officinale), nettle (Urtica dioica), and dock (Rumex obtusifolius). The percent composition of each species within each treatment was not quantified in this trial. The application of biochar as a soil amendment has been shown to enhance transplant survival of young trees, improve root growth and health of mature established trees, reduce soil compaction, and reduce the severity of root pathogens such as Armil- laria and Phytophthora (Scharenbroch et al. 2013; Schaffert and Percival 2016; Blanco-Canqui 2017; Yoo et al. 2020; Schaffert et al. 2022). Results of this study, however, show little improvement in soil qual- ity when biochar was added via vertical mulching. Similar results, i.e., little root growth, have been obtained when using other soil amendments such as perlite, an amorphous volcanic glass, in combination with vertical mulching (Kalisz et al. 1994). Indeed, the work of Kalisz et al. (1994) concluded that per- lite-filled vertical mulch channels were actively avoided by tree roots of Acer saccharum. In another study, tree growth responded as well to empty holes as it did those filled with fertilizer following vertical mulching (Smith 1978). Watson et al. (1996) found that replacement of soil within the root zone of mature Quercus alba via radial trenching improved fine root density by 320% and rooting depth by 68%. Although application of biochar in combination with air spad- ing resulted in a significant improvement in soil Percival et al: The Influence of Soil Decompaction and Amendments on Soil Quality
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