Arboriculture & Urban Forestry 38(2): March 2012 in the field (Sydnor, pers. comm., October 17, 2002, Columbus, Ohio, U.S.) supported this perception, indicating that trees “de- pendent” on fertilizer could not survive under fertility-challenged conditions. Others found that applying high levels of nitrogen fertilizer and adequate irrigation during production improved tree growth and establishment success (Lloyd et al. 2006). In prac- tice, nurseries irrigate, fertilize, and root-prune both container- ized and balled-and-burlapped trees to produce high quality, stress-resistant trees (Alan Erwin, Panther Creek Nursery, Wil- low Springs, North Carolina, U.S.; Mark Gantt, Hefner’s Nurs- ery, Conover, North Carolina, U.S.; Danny Vandevender, Land- scape Design of Goldsboro, Pikeville, North Carolina, U.S., pers. comm., January 11, 2011, Greensboro, North Carolina, U.S.). The primary objectives of this study were to assess the det- rimental effects of soil compaction on growth of various cul- tivars of maple and to determine if pre-planting nitrogen rates affected establishment or growth of trees out-planted into com- pacted soils. Cultivars of Acer rubrum L. (red maple) and Acer × freemanii E. Murr. (Freeman maple), a naturally occurring hy- brid of A. rubrum and A. saccharinum L. (silver maple), were selected because they represent a valuable group of plants used extensively as landscape and street trees (Sydnor and Cowan 2000). The study authors hypothesized that reduced hydrau- lic conductivity and reduced porosity characteristics of high- density soils would reduce aboveground tree biomass, that the Freeman maple cultivars would be less negatively affected by compaction, and that a higher rate of N fertility during produc- tion would benefit tree performance in the compacted soils. MATERIALS AND METHODS Tree Preparation Acer × freemanii ‘Celzam’ (Celebration® Freeman maple), Acer × freemanii ‘Morgan’ (‘Morgan’ Freeman maple), Acer × freemanii ‘October Brilliance’ (‘October Brilliance’ Freeman maple), Acer rubrum ‘Bowhall’ (‘Bowhall’ red maple), Acer rubrum ‘Fairview Flame’ (Fairview Flame™ (Red Sunset® (Burgundy Belle® (October Glory® red maple), Acer rubrum ‘Frank’s Red’ red maple), Acer rubrum ‘Magnificent Magenta’ red maple), and Acer rubrum ‘October Glory’ red maple) were obtained from A. McGill & Son Wholesale Nursery (Canby, Oregon, U.S.), John Holmlund Nurs- ery, LLC. (Boring, Oregon, U.S.), and J. Frank Schmidt & Son Co. (Boring, Oregon, U.S.). Trees were propagated from rooted cuttings and ranged from 25 to 31 cm in height. On April 15, 2001, trees were potted into 13 L black plastic, Root Right™ pots [Mi- bersburg, Pennsylvania, U.S.]. The potting mix was a purchased blend (15% TechnaGro™ is a soil conditioner made of hardwood bark, sawdust, and gratrol™ (active ingredient: cuprous chloride, 5.6% w/w), Cham- , 60% pine bark, 20% rice hulls, and 5% all others (Kurtz Bros., Inc. Groveport, Ohio, U.S.). Techna- Gro™ sewage sludge. Average nutrient contents were as follows: 2.4% total organic nitrogen, 1.3% phosphorous, and 0.2% potassium (Kurtz Bros. 1998). Pre-planting nitrogen (N) treatments began on July 12, 2001, and continued for 13 weeks. Half the trees of each cultivar were randomly assigned to one of two N rates: 25 mg or 100 mg·L-1 ter Soluble Fertilizer [20N-10P2O5 and 12% nitrate N, (O.M. Scotts Co., Marysville, Ohio, U.S.)] applied at 0.50 L in each of two daily irrigation cycles (1 L d-1 N fertigation from 20N-4.3P-16.7K Peters Wa- -20K2 0 with 8% ammonical N 65 total). Rates and times were based on methodology from Struve (1995). Additionally, the 100 mg·L-1 N rate represents the nurs- ery standard application rate for production. Fertilizer was dis- continued at the end of September 2001, prior to field planting. Compaction Procedure and Tree Installation The study was located at the Waterman Research and Education Facility in Columbus, Ohio, U.S. (Latitude 40.01° and Longi- tude -83.04°). The USDA Soil Conservation Service classified the soil at the facility as a Crosby silt loam, fine, mixed, mesic, aeric Ochraqualf type (McLoda and Parkinson 1980). In an un- disturbed Crosby silt loam, the surface soil (down to ~23 cm) is characterized as a silt loam. Below this depth, it would typically be a clay loam or silty-clay loam (McLoda and Parkinson 1980). In October 2001, soil compaction treatments were ran- domly assigned at the Waterman facility. All soil treatment plots were 17.7 × 10.4 m and were arranged in the field in three replicates, from east to west with the three soil treat- ments laid out as whole plots, and split into sub-plots for low and standard nitrogen treatments, and split again into sub sub-plots for cultivar (cultivars were randomly lo- cated throughout nitrogen treatment sub-plots) (Figure 1). For the six areas to be compacted, a loader bucket scraped off the vegetative layer, then removed soil from each to a depth of approximately 1 m, keeping soil separate. A dump truck (4900-Series International, Warrenville, Illinois, U.S.) filled with building rubble and weighing approximately 14 tons was used to compact the base of each area by driving back and forth over each area six times. Three soil lifts of approximately 0.3 m depth were sequentially returned to each area and compacted individually using the same technique as with the base layer. Soil gravimetric water content (θw) at the time of compaction was calculated as the mass of water in the soil per mass of ov- en-dried soil (g·g-1 ), and ranged from 0.10 to 0.15 g·g-1 1.5 g·cm-3 for the compacted plots. At the completion of the compaction treatment, the mean bulk dry density (ρb ) for these plots was approximately . Plots compacted in 2001 will be referred to as C1. Prior to implementing compaction treatments, nine soil samples (approximately 0.91 kg each) were collected from the top 15 cm of the soil from across the entire study area and were air-dried at ambient room temperature for two months. These samples were used to perform a standard Proctor test, which de- termines a soil’s maximum, practically achievable bulk density, following the methodology of the Iowa Department of Trans- portation (2004). Soil was pulverized and then passed through a 2 mm round-hole sieve. A cylindrical brass mold, 10.2 cm di- ameter by 11.6 cm height, was used to perform the Proctor test. A weighted, standardized tamper was used to compact the soil within the mold. Approximately 150 g of water was added to 3000 g of pulverized soil. Approximately one-third of this soil was added to the cylinder. The tamper was placed in the cylin- der, the weight lifted and allowed to free-fall 25 times over the entire surface of the soil. The filled cylinder was weighed, then approximately 30 g of soil from the cylinder was placed in a tin, weighed, and set aside. This process was repeated until the weight of the compacted soil in the cylinder was less than in the previous runs (the point at which no more water could be added). Sample tins were placed in an oven at 105°C for approximately 24 hours to determine gravimetric water content, and these values were used to calculate volumetric water content, and wet and dry ©2012 International Society of Arboriculture
March 2012
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