Arboriculture & Urban Forestry 33(6): November 2007 429 trees were approximately 25 to 30 years old. All trees were surrounded by turf and had been mulched annually to a di- ameter of 3.7 m (12.21 ft). Soil at the site was a Cecil clay that had undergone sig- nificant disturbance and compaction from past agricultural activity, grading, grounds maintenance equipment, and sea- sonal vehicle parking. Soil bulk densities at the site ranged from 1.38 g/cm3 to 1.86 g/cm3 with an average bulk density of 1.62 g/cm3. For soils of this texture, bulk densities above 1.5 are restrictive to root growth (USDA-NRCS 1999). Two months before treatment application, glyphosate her- bicide (RoundupTM; Monsanto, St. Louis, MO) was sprayed within the diameter of each mulch ring at the recommended label rate, and shredded bark mulch was applied to create a uniform mulch depth of 10 cm (4 in). Herbicide was occa- sionally spot-sprayed thereafter to eliminate weed root con- tamination beneath the experimental trees. Experimental Design The experiment used a randomized complete block experi- mental design with a 2 × 2 factorial treatment structure (± Terravent, ± liquid amendment) in which individual trees served as blocks. Under each tree, a circular sampling area of 24 m2 (259.2 ft2) was identified and divided into four quad- rants centered around the trunk. Five injection sites were marked within each quadrant for a total of 20 injection sites per tree. Treatments included: 1) Terravent injection only (TV); 2) Terravent injection followed by release of MycorTree liquid soil amendment (TV + M); 3) addition of liquid amendment only (M); and 4) an untreated control (C). Each of the four treatment combinations was randomly assigned to one quad- rant beneath each tree for a total of ten replicates per treat- ment. Treatment Application Treatments were applied on 2 April 2002. The TV treatment consisted of five 82.7 bar (1200 psi) N2 injections per quad- rant spaced 88 cm (35.2 in) apart. The Terravent was equipped with a 20 cm (8 in) probe and a clay model power head. TV + M treatment consisted of 83 bar (1200 psi) N2 gas injections followed by the release of 118 mL (3.54 fl oz) of MycorTree Injectable product at a pressure of 10 bars (150 psi). The product had been mixed water at the manufacturer’s recommended rate. The M treatment consisted of liquid amendment addition only. Again, 118 mL (3.54 fl oz) of the suspension was re- leased into each injection site at a pressure of 10 bars (150 psi). No injections of any kind were made in the untreated C quadrants. MycorTree Injectable contains endo- and ectomycorrhizal spores, rhizosphere bacteria, and a variety of abiotic ingredi- ents, including humic acids, seaweed extracts, and interme- diate metabolites. Based on the manufacturer’s ingredient list, each 118 mL (3.54 fl oz) injection contained approximately 64 endomycorrhizal spores, 17.4 × 106 colony-forming units of bacteria, 0.055 g (1.94 × 10−3 oz) of humic acid, and 0.058 g (2.06 × 10−3 oz) of seaweed extract, among other ingredi- ents. Ectomycorrhizal spores were also present in each injec- tion, but the presence of these propagules was not relevant for red maple, which only forms endomycorrhizal associations. Sample Collection and Processing Seven weeks after treatment application, five soil cores (5 cm/2 in diameter, 31 cm/12.4 in depth) were removed from within each quadrant. Coring locations were selected by ran- dom azimuth at a distance of 15 cm (6 in) from each injection site. Immediately after removal, cores were placed in refrig- erated storage until all samples had been collected. A hydropneumatic root elutriation system was used to separate fine roots (less than 2 mm in diameter) from soil in the cores (Hydropneumatic Root Washer; Gillison’s Variety Fabrication, Inc., Benzonia, MI) Roots were immediately transferred to a 50% ethanol solution and refrigerated at 4.4°C (39.92°F) until further processing. Roots greater than 2 mm (0.08 in) in diameter were not considered in this experi- ment. Fine roots obtained from each soil core were suspended in water in a transparent tray and scanned on an Epson Expres- sion 1680 flatbed color scanner (Epson America, Inc., Long Beach, CA). The root length of each sample was measured using WinRhizo software (Regent Instruments, Inc., Quebec, Canada), and this information was used to calculate the root length density (cm root/cm3 soil) of each soil core. The root surface area density (cm2 root surface area/cm3 soil), the root diameter distribution, and the mean root diameter (mm) were also measured. After scanning, root samples were oven-dried for 48 hr at 70°C (158°F) before dry weight measurement and calculation of root mass density (g root dry weight/cm3 soil). Statistical Analyses The effects of soil treatment on root parameters were ana- lyzed using a 2 × 2 factorial analysis of variance with sub- sampling (SAS PRC GLM, SAS version 9.0; SAS Institute, Cary, NC). Mean separations were performed with Fisher’s least significant difference. Treatment main effects and de- pendent multiple comparisons were evaluated at the 0.10 significance level as a result of the marked spatial het- erogeneity that characterizes belowground data. RESULTS AND DISCUSSION Terravent treatment, with or without injection of a liquid soil amendment, did not alter the amount of fine root length pres- ent in a moderately compacted clay loam soil 7 weeks after ©2007 International Society of Arboriculture
November 2007
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