City foresters and horticulturists often seek trees suited for urban conditions. Two maples often used were selected to assess response to compacted soil: ‘Armstrong’ Freeman maple and ‘Brandywine’ red maple. Soil physical parameters were assessed to determine effects of high density on movement of gas and water. Rigid-walled lysimeters constructed from polyvinyl chloride pipe were filled with clay subsoil compacted to 1.64 g·cm-3 (MODERATE-density) and 1.78 g·cm-3 (HIGH-density). Compaction decreased total porosity and saturated hydraulic conductivity. In addition, CO2 concentrations in compacted soil were 5–18 times higher than atmospheric concentrations, while O2 concentrations were similar to atmospheric levels despite density. O2 concentration played no real role in plant growth response to compaction. Trees growing in MODERATE-density soils had higher transpiration rates than trees growing in HIGH-density soils, although differences decreased over time. A high soil density did not affect caliper growth, but did reduce annual height growth, leaf area and dry weight, and stem dry weight, but responses varied over time and between species. Root dry weight and volume were unaffected by compaction, but root:shoot ratio was higher for trees growing in HIGH-density soils, which is expected as aboveground biomass is typically reduced by soil compaction.
This study assessed soil compaction effects on aboveground growth of maple cultivars, and compared two nitrogen rates applied pre-planting for their influence on establishment and growth of trees planted into compacted soils. Eight commonly used maple cultivars of Acer rubrum and Acer × freemanii were evaluated. During container production, plants received either 25 or 100 mg·L-1 nitrogen through fertigation twice per day. Trees were planted into non-compacted field plots with a mean bulk density of 1.40 g·cm-3, or into compacted plots with a mean bulk density of 1.60 g·cm-3. In 2002, researchers randomly selected half of the compacted plots and applied an additional soil treatment. At the completion of this treatment, mean bulk density was 1.55 g·cm-3. Trees growing in higher density soils had significantly smaller aboveground biomass measures (P < 0.05), than those growing in non-compacted plots. There was a significant difference between cultivars (P < 0.0001); for example, ‘Celzam’ and ‘Fairview Flame’ had greater aboveground biomass values than other cultivars when grown in compacted soils, but compaction still affected growth. The 100 mg·L-1 nitrogen rate increased leaf dry weight and area, but did not impact height and caliper growth or stem dry weight.
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