140 Sax and Bassuk: Tree Growth and Gas Exchange Response of Ficus benjamina 'Evergreen' (approximately 33% v/v) deep into the soil profile using a backhoe, mini-excavator, or shovel (Sax et al. 2017). The practice combines the mechanical fractur- ing of the soil with the incorporation of organic matter. Incorporating compost into soils to improve quality has been extensively examined. Few studies, how- ever, have focused on their effects in the urban envi- ronment (Cogger 2005). A similar technique to the S&D method, known as soil profile rebuilding, has been shown to improve soil bulk density and trans- plant success of trees in the mid-Atlantic U.S.A. Soil profile rebuilding shows improvements in soil quality in as little as eight months, and quality remained ele- vated for as long as five years (Layman et al. 2016). In other studies, the addition of compost to urban soils has been shown to have a species-specific posi- tive effect on basal-area and stem-volume growth. The positive growth response associated with compost additions has been attributed to increased water hold- ing capacity and microbial biomass in compost-amended soils (Oldfield et al. 2015). Previous research on the S&D method has shown improvements in remediated soils by decreasing bulk density, increasing organic matter, and increasing AWHC within a year of compost incorporation (Sax et al. 2017). Based on these results, a study was designed to observe how trees would respond to growing in S&D remediated soils. The first objective of this study was to determine how biomass produc- tion (root, shoot, and leaf-area growth) would respond to the S&D soil environment compared to unamended controls. The second objective was to determine if trees growing in S&D and unamended soils would express differences in leaf water potential and gas exchange during a period of soil-water deficit. MATERIALS AND METHODS The Scoop & Dump (S&D) remediation process was conducted at the time of site establishment for land- scapes adjacent to buildings on the Cornell campus. Landscapes include sites next to the Computing and Communications Center (CCC) in 2012, Mann Library in 2010, and Plant Science building in 2007. For the S&D process, Cornell compost was used and made of greenhouse medium, plant residue, manure, food waste, and animal bedding. Compost was spread across each site to a depth of 15 cm (5.9 in). A bobcat E35 Compact Excavator with a 45 cm (17.7 in) bucket was used to systematically scoop into the ©2019 International Society of Arboriculture compost/soil layer to a depth of 38 to 45 cm (14.9 to 17.7 in) followed by lifting the material 1.2 m (3.9 feet) into the air before dumping the soil/compost back onto the ground. After the Scoop & Dump pro- cess was complete, the site was smoothed with iron rakes before plants were installed. After planting, a 7.5 cm (2.9 in) mulch layer was applied to the site. Mulch was reapplied each year between April to May until canopy closure occurred (Sax et al. 2017). Sample Collection Soil samples were collected from October 8, 2013 through October 15, 2013 on the Cornell Campus, Ithaca, NY, U.S.A. in the northern temperate region USDA Zone 5b. S&D samples were collected on the Agriculture Quadrangle (42.448758, -76.478115) in planting beds adjacent to buildings that had received S&D remediation in the past including the Comput- ing and Communications Center (CCC) (42.449102, -76.479024), Mann Library (42.448692, -76.476697) and Plant Science building (42.448452, -76.477404). Unamended control soils (UN) were taken from turfed landscapes near S&D sites that shared a common land-use history. Ten cores were extracted per study site in S&D and UN soils resulting in a total of 30 S&D and 30 UN samples. For all S&D cores, the samples were collected along a transect at regular intervals in the center of the beds. The first core of each S&D site was extracted five feet from the edge of a designated planting bed. Specific sampling intervals varied depend- ing on the total length of the planting bed and are detailed in Table 1. Unamended soil cores were extracted at equal intervals along the transect to the S&D sam- ples, but in adjacent turfed landscapes directly next to the study sites, and are detailed in Table 1. Soil cores were extracted using lengths of PVC pipe that were 14.4 cm (5.6 in) in diameter and 15.0 cm (5.9 in) in height with a total volume of 2443 cm3 each. When extracting soils, the turf or mulch layer was sliced/scraped away before inserting cores into the ground. To collect UN soil, the core was slowly pushed into the ground using a hydraulic plate compac- tor attached to a backhoe to provide an even compression surface. For S&D soils, cores were driven into the ground using a hand tamper. After cores were tamped or pushed into the ground, they were extracted with a shovel and the core bottoms were secured with a mesh screen and ring clamp to hold the soil in place
July 2019
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