294 Fite et al.: Soil Decompaction and Amendment Process for Urban Trees Boston, Massachusetts (college campus); and Pittsburgh, Pennsylvania (golf course) in the United States. Soils ranged from sand with a bulk density of 1.74 g/cm3 in Myrtle Beach to loam with a bulk density of 1.25 g/cm3 in Pittsburgh (Table 1). At Myrtle Beach and Anderson, soils were approaching the growth limiting bulk density for their texture, and it is likely that root penetration was impaired at these sites (Daddow and Warrington 1983). At Boston and Pittsburgh, bulk densities were lower and less likely to physically restrict root growth. Prior to the experiment, composite soil samples were collect- ed from the upper 15 cm of soil beneath 6–8 trees at each site and analyzed by A&L Analytical Laboratory (Memphis, Tennessee, U.S.) to determine soil pH and mineral nutrient concentrations. Nutrient data were used to create a prescription fertilizer program for each site that complied with ANSI A300 standards (Table 2). Experimental Design and Treatment Application Five treatments [mulch (M), fertilizer (F), air tillage (A), the full decompaction and amendment process (AFM), and control (C)] were applied to ten replicate trees at each site. A completely randomized experimental design was used in Boston. A randomized complete block design was used Soil type (%) Sandy (%) 55 Myrtle Beach, South Carolina Pittsburgh, Pennsylvania 70.8 93 32.9 to control for within-site variability at Anderson, Myrtle Beach, and Pittsburgh. Treatments were applied in Au- gust 2005 in Boston, November 2005 in Anderson, Novem- ber 2005 in Myrtle Beach, and February 2006 in Pittsburgh. At least 14 days prior to treatment, the area surrounding all trees was treated with Roundup Pro herbicide (Monsanto Compa- ny, St. Louis, Missouri, U.S.) in a 1.5 m diameter ring to eliminate competing vegetation. Weed control was maintained throughout the experiment with additional herbicide applications as needed. In Boston, an extensive turf thatch layer remained after her- bicide application. To permit air tillage, thatch was removed to a depth of 3 cm from beneath A and AFM trees using a Ryan® Jr. sod cutter (Jacobsen, Schiller, Wisconsin, U.S.). Some tree fine roots were likely damaged in this process, and trees from other treatment groups did not experience this damage. Soils receiving the M treatment were mulched to a depth of 5–7.5 cm in a 1.5 m radius around the trunk using 0.45 m3 of bagged, shredded hardwood mulch. The specific mulch prod- ucts differed among sites, based on local availability. Soils re- ceiving the F treatment were fertilized with the prescribed materials (Table 2) applied to the soil surface as granular prod- ucts or drenches within a 1.5 m radius around the trunk. Soils receiving the A treatment were air-tilled in a 1.5 m radius and Table 1. Soil particle size distribution, bulk density (BD), and estimated growth-limiting bulk density (GLBD)z Site Silt (%) Anderson, South Carolina Boston, Massachusetts sandy clay loam sandy loam sand loam 19 22.6 3 44.7 Clay (g/cm3 26 6.7 4 22.4 ) BD (g/cm3 ) 1.41±0.02 1.14±0.04 1.74±0.04 1.25±0.03 1.6 1.6 1.8 1.5 z Threshold bulk density above which roots can no longer penetrate the soil (Daddow and Warrington 1983). Root growth is impaired as BD approaches the GLBD. y N = 2–3 for particle size distribution and N =50 for bulk density at each site. Table 2. Fertilizer products applied to 7.1 m2 Product Boost Granular (24-7-7, 6% S, 1% Ca, 0.1% Fe, 0.05% Cu, 0.05% Zn) Manganese chelate (5% Mn, 2%S) Tiger 90 (0-0-0-90 S) Epsom salt (100% MgSO4 ) Pelletized dolomitic lime Pelletized gypsum (20% Ca, 16% S) Disper-Sul (80% S, 3.5% Fe, 1.5% Mn) Manufacturer F.A. Bartlett Tree Expert Co. Stamford, Connecticut Growth Products, Ltd. White Plains, New York Tiger-Sul Products Calgary, Alberta Top Co Associates Skokie, Illinois 0–565 g 0–265 g ASC Mineral Processing 0–1.4 kg Allerton, Illinois ASC Mineral Processing Allerton, Illinois Martin Resources, Inc. Odessa, Texas 3.5 kg 1.1 kg 79 ml 1.3 kg 455 g 169 g 300 ml soil area around the base of each tree receiving the AFM or F treatment. Products and rates were selected for each site based on pre-treatment soil tests. In Anderson, trees were present in three separate por- tions of the Civic Center complex, each of which received slightly different fertilizer rates. Anderson 375–470 g Boston 1.3 kg Myrtle Beach 565 g Pittsburgh 262 g for each study site. GLBD ©2011 International Society of Arboriculture
November 2011
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