230 produced with different planting depth strategies and then subject- ed to various root pruning methods at planting into landscape soil. MATERIALS AND METHODS Nursery Growing In March 2005, 110 stem cuttings (22 cm tall, 3 to 4 mm stem diameter) of Quercus virginiana Mill. Highrise® rooted in square 6.9 cm across × 14 cm deep smooth-sided containers (Anderson Die and Manufacturing, Portland, Oregon, U.S., model 03AN- BAN2_7-8 x 5), were planted into 10 L (27 cm across top and bottom, 20 cm deep) Air-Pot™ cylindrical black plastic containers (Caledonian Tree Company, Ltd., Scotland). The point where the top-most woody root emerged from the stem was placed either 13 mm (shallow) or 64 mm (deep) below substrate surface. Trees were spaced pot-to-pot (i.e., touching one another) except for a 1.8 m wide corridor every four rows. Irrigation was applied two or three times daily in the growing season through October 2005, totaling 3.8 L through one Roberts (Roberts Irrigation Prod- ucts, Inc., San Marcos, Idaho, U.S.) Spot-Spitter per container. In late March 2006, trees were shifted into 57 L (47 cm across top and bottom, 30 cm deep) Air-Pot containers, whereby half the trees for each 10 L planting depth were positioned at grade (10 L substrate surface even with 57 L substrate surface ) or deep (10 L substrate surface 64 mm below 57 L substrate surface). A total of four planting depth combinations resulted from the two planting sessions: 1) 13 mm deep into 10 L, 0 mm deep into 57 L; 2) 64 mm deep into 10 L, 0 mm deep into 57 L; 3) 13 mm deep into 10 L, 64 mm deep into 57 L; and 4) 64 mm deep into 10 L, 64 mm deep into 57 L. No roots were pruned or mechanically manipulated in any way at any time during the nursery production phase of the study. Trees in 57 L containers were spaced 2.4 m apart and irrigated three times daily (weather dictating) in the growing season with a maximum of 15 L through two Roberts Spot-Spitters. Trees were pruned and trunks staked in 2006 and 2007 to develop one leader and trees were secured to a trellis system for stability in wind. Substrate was 50:40:10 (New Florida peat: pine bark: sand, volume). New Florida peat is a compost of Florida peat and hardwood bark fines (Florida Potting Soil, Inc., Orlando, Flor- ida, U.S.). Fertilizer (18-5-10 controlled release, Harrell’s Inc., Lakeland, Florida, U.S.) was incorporated into substrate prior to planting at 10.74 kg/m3 Gilman and Wiese: Root System Morphology and Anchorage settling that might occur. Once the root ball was placed in the planting hole, a 15 cm wide volume of undisturbed soil at the edge of hole was loosened as deep as the root ball and pushed into the hole. The rest was filled with soil that came out of the planting hole. Water was added to settle backfill soil and soil was packed firmly with the same person’s foot. The same person did the packing in an effort to standardize compaction of backfill soil. No berm or water ring was constructed around the root balls and no mulch was applied. Weeds were kept clear in a 1 m wide strip down each row with periodic applications of Glyphosate. Trees from each of the four planting depths in containers were root pruned using two different methods and a non-pruned control within a few minutes of planting into the field for a to- tal of twelve treatment combinations. The root pruning methods were: 1) no root pruning; 2) root ball shaved by inserting a sharp square-tip balling spade into the root ball top surface tangent to the trunk 3 to 6 cm inside the periphery all the way to the bottom of the root ball once trees were planted and backfill was added (root ball took on a heptagon shape viewed from above, Figure 1); and 3) root ball radial slicing by cutting 10 to 12 cm radially into the top of the root ball through the bottom in six equidis- tant places with a sharp square-tip balling spade once trees were planted and backfill was added (Figure 1). Prior to planting trees into the landscape in treatments 2 and 3, a hand pruner was used to remove substrate and roots all around the top outer corner of the root ball by cutting at a 45 degree angle about 3 cm deep in an effort to remove circling roots in the very top of the ball. The 48 trees were arranged 1.8 m apart in rows 3 m apart in a randomized complete block design (4 planting depths in containers × 3 root pruning methods at landscape planting ran- domized within each of 4 blocks). Planted trees were irrigated three times daily totaling 11 L through one Roberts Spot-Spit- ter through October 2008. In November 2008, irrigation was changed to 6 L daily. Daily irrigation was applied the follow- ing growing season. Irrigation was applied primarily to the root ball surface, although a small amount landed on landscape soil beyond the root ball. Each tree was fertilized with 200 g of granular 16-4-8 (Diamond R Fertilizer Company, Ft. Pierce, Florida, U.S.) on May 2008 and 400 g on August and Septem- ber 2008, and March and June 2009 by surface application to a circular area with a radius of 45 cm centered on the trunk. , and no other fertilizer was applied. Weeds were periodically pulled from container substrate. Trees did not root out of pots and into the ground. The plot was lo- cated in USDA hardiness zone 8b in Gainesville, Florida. Landscape Planting On March 24 and 25, 2008, 48 trees (12 from each planting depth combination) closest to the mean caliper (3.1 cm caliper, 2.56 m tall) for all trees in 57 L containers in the study were planted into a field soil of Millhopper fine sand (loamy, silica- ceous, hyperthermic Grossarenic Paleudults) with less than 2% organic matter and a bulk density of 1.51 g/cc. Holes 10 to 15 cm wider than the root balls were hand dug with straight sides and flat bottoms and adjusted so the top of the undisturbed root ball was about even with the landscape soil surface. The bottom of the holes were tamped by foot from the same person evenly around the bottom of the planting hole in an effort to standardize ©2012 International Society of Arboriculture Evaluating Anchorage Half of the trees from each of the twelve treatment combina- tions (i.e., two complete blocks chosen at random) were pulled out of the ground in November 2008 (referred to as GS 1) and the other half in September 2009 (GS 2) to evaluate anchorage (lateral stability) approximately one and two growing seasons af- ter planting. An electronic inclinometer (model N4; Rieker Inc., Aston, Pennsylvania, U.S.) was mounted to a fabricated steel plate (5.1 × 7.6 cm) secured to the trunk base 8 cm from soil sur- face, which was above the swollen root flare. A 3,629 kg capac- ity load cell (SSM-AF-8000; Interface Inc., Scottsdale, Arizona, U.S.) was placed in-line with the pulling cable attached to the trunk 30 cm above inclinometer. Trunks were pulled in the 270 degrees Azimuth (from north) direction with the cable parallel to ground. The cable was pulled at a rate of 2 cm • s-1 with an elec- tric winch mounted to a tractor until the roots were completely out of the soil and the trunk was horizontal. Soil moisture con-
September 2012
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