Arboriculture & Urban Forestry 40(6): November 2014 subsoil compacted (Caterpillar D4H Crawler Dozer, Caterpillar Inc., Peoria, Illinois, U.S.). A nominal depth of topsoil (3 cm) was replaced on site using a wheel loader (John Deere 444H, John Deere, Moline, Illinois, U.S.) and grader (Fiat Allis 65-B Grader, New Holland Agriculture, Torino, Italy). Following the disturbance, soil descriptions were performed to assess the effect of the site dis- turbance on the soil. A soil pit (2 m wide × 2.5 m deep) was dug bisecting the disturbed and adja- cent undisturbed area and the soils were described. The most dramatic effects of the disturbance were concentrated in the top 20 cm. Soil bulk density of the compacted zone (0 to 20 cm) was increased to likely limiting values for root growth for this clay loam soil (1.62 Mg m-3 ), compared to 1.40 Mg m-3 for the clay loam in the adjacent undisturbed area. The disturbed profile was wetter throughout, with increased redoximorphic features deeper in the profile. The structure of the undisturbed Ap hori- zon was granular departing to subangular in the E and Bt horizons. The disturbed profile had platy and angular blocky soil structure in the top 20 cm. To assess the uniformity of the disturbance across the plot, 30 penetration resistance readings to a depth of 46 cm were measured across the plot at random locations and compared to ten measure- ments from the adjacent undisturbed area using a cone penetrometer (FieldScout SC-900 Soil Pen- etrometer, Spectrum Technologies, Inc., Plainfield, Illinois, U.S.). These measurements were per- formed within a three-hour period on 04/28/2008. Mean penetration resistance in the top 46 cm in the disturbed area was 2.26±0.09 MPa, com- pared to 1.90±0.07 MPa in the undisturbed area. Plant Materials A rectangular experimental grid with 120 square tree plots (3.05 m × 3.05 m) and 1.53 m inter-plot space was laid out on the disturbed area. Sixty Betula nigra and sixty Acer rubrum branched liners (graſted top two-year-old and roots four years old), 1 to 1.5 m height, and 3 to 4 cm diameter, J. Frank Schmidt & Sons, Co., Boring, Oregon, U.S.) were randomly assigned to plots. All Betula nigra trees died aſter planting and had to be replaced with new plantings. Tree planting was performed with a 0.45 m diameter auger mounted on a multi terrain loader (Caterpillar 277B, Caterpillar Inc., Peoria, 321 Illinois, U.S.). These two species were chosen for their ability to tolerate seasonal wetness on the site. Both exhibit chlorosis with typical urban conditions, including extreme soil pH and compaction. Birch is ectomycorrhizal and maple is endomycorrhizal. Aſter trees were planted, the site was seeded with Kentucky bluegrass (Poa pratensis). Trees and lawn were irrigated during dry periods in the establish- ment year (2007). Following the establishment year treatment application began in the spring of 2008. Treatments Treatments were applied May through October, annually, from 2008 through 2010. Treatments and application rates included 1) water control (NULL) at 840 L 100 m-2 yr-1 yr-1 (split evenly over five monthly applications); 2) aerated compost tea (ACT) at 840 L 100 m-2 (split evenly and applied with water over five monthly applications); 3) a commercial biologi- cal product (CBP) diluted with water at 840 L 100 m-2 yr-1 alone in June, July, and August); 4) a NPK fertilizer (FERT) at 1.95 kg N 100 m-2 (applied with wa- (applied in May and September with water yr-1 ter in May and September and water alone applied in June, July, and August) (Smiley et al. 2002; ANSI 2004); 5) compost (COMP) at 2.5 cm as a top dress- ing (applied in May of each year); and 6) double- ground hardwood wood chip (WC) mulch to a 15 cm depth (applied in May of each year). Compost and mulch plots also received water at 840 L 100 m-2 yr-1 terizations were performed and are listed in Table 1. Aerated compost tea was made with a 946 L compost tea brewer (Geotea-250, Greater Earth Organics, Chilton, Wisconsin, U.S.). The brewer was filled with water and aerated for 24 hours prior to adding ingredients to de-gas any chlo- rine in water. Aſter de-gassing, 8 L of compost was added to a mesh bag and placed in the brewer. The compost (Purple Cow Organics, Inc., Oconomo- woc, Wisconsin, U.S.) contained 8,300 mg bacteria kg-1 , 3,547 mg fungi kg-1 of 3.0 µm), 1,883 flagellates g-1 1,134 ciliates g-1 , and 10 nematodes g-1 (mean hyphae diameter , 1,459 amoebae g-1 (fluores- , cence and light microscopic analyses performed by Soil Foodweb, Inc., Corvallis, Oregon, U.S.). Additional ingredients in the brew included 750 ml of liquid humic acid, 700 ml of soluble kelp, 500 ml of fish hydrolysate, and 750 ml of brown ©2014 International Society of Arboriculture when other plots were treated. Treatment charac-
November 2014
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