Arboriculture & Urban Forestry 43(1): January 2017 Table 1. Effect of retention time in containerz in containersz 11 L 4 7 9 12 8 10 12 14 visual root imprint rating of Acer. Retention time (months) 57 L 170 L 20 15 11 6 Tree height increase 0.7 bu 0.8 ab 1.1 a 0.7 b 29 on post-landscape planting tree height increase, xylem water potential, and Ψ 5/19/10w 2011y,x (m) -1.59 b -1.56 b -1.61 b -1.69 a (Mpa) Ψ 6/7/10w (Mpa) -1.50 ab -1.45 b -1.45 b -1.58 a Visual root imprint rating from 57 Ly,v 2.9 b 2.2 b 4.0 a 4.2 a z All trees were retained in three progressively larger containers (11, 57, and 170 L) for a total of 32 months with varying retention times in each. y Tree attribute not affected for Magnolia and Ulmus (P > 0.07). x Height increase 2011 growing season; height increase during 2010, 2012, and 2013 growing seasons not significant (P > 0.06). w Ψ not significant October 2010, March and April 2011 (P > 0.08); Ulmus Ψ was not affected by retention time, and Magnolia was not measured. v Imprint imposed on root system by roots deflecting at the 57 L nursery container wall; 1 = little imprint, 5 = highly visible imprint; imprint imposed by 11 L and 170 L containers not significant (P > 0.16). u Means in a column with a different letter are statistically different at P < 0.05; n = 10, mean across root pruning treatment due to insignificant interaction (P > 0.41). formed aſter placing the root ball in the planting hole and stabilizing it with backfill soil half way up the root ball sides. A sharp 36 cm long root-balling shovel removed approximately 5 cm of the periph- ery of the root ball in a process referred to as shav- ing. Roots may not have been cut all the way to the bottom of the container sides because the shovel was slightly shorter (36 cm) than the root ball was tall (47 cm). Substrate and roots severed by shaving remained in the hole as part of backfill soil. Five from the remaining seven Ulmus per retention- time treatment combination (20 trees) were planted in the same manner without root pruning because there were not enough replicates due to cold winter temperatures killing some trees in the nursery. Branches were not pruned at or aſter planting. Trees were surface fertilized with 800 g of 20-0-8 O) in June 2010, and 400 g of 20-0-8 (N-P2 in March and June 2011, on a one meter diameter circle that was centered on the trunk. In order to minimize water stress, trees were irrigated three times daily (with exceptions mentioned hereaſter) until 21 May 2010 when it was changed to every other day. Chipped hardwood branches with live foliage from local utility line-clearance operations, aged several months, were applied as mulch 1.8 m wide and 10 cm deep along the rows. Glyphosate was applied as needed over mulch to control weeds. Vegetation between rows was periodically mowed. O5 -K2 Tree Measurements Each tree was evaluated in early aſternoon by two people, independently, and rated for average pres- ence of actively expanding shoots (1 = no expand- ing shoots, 5 = expanding shoots present across the entire crown) and occurrence of wilting new shoots and/or leaves (1 = no wilting, 5 = most leaves and/or actively growing shoots wilting) on 19 and 28 May and 04 June 2010. Irrigation was withheld and no rainfall occurred two days prior to and during each measurement date. Presence of actively growing shoots was again evaluated by two people and averaged 29 July and 08 September 2010. Foliage density (1 = few live leaves on the tree, 5 = dense crown of live foliage) was rated by two people and averaged in September 2010. Trunk di- ameter was measured at landscape planting 30 cm from the ground (May 2010) and in September of each of four years aſter planting. The difference in diameter between May and September 2010 was reported as trunk diameter increase for that grow- ing season; subsequent diameter increases were calculated as the difference between the previous year and current season’s September measurements. Xylem water potential was measured on all 40 Acer and 20 Ulmus in 2010 on sunny days including 19 and 28 May, 07 June, and 18 October, and on 25 March and 26 April in 2011. Magnolia was not mea- sured because of the large diameter of current-year shoots. Irrigation had been withheld and no rainfall occurred two days prior to the measurement dates. Xylem potential 12:00 to 14:00 hr. was measured with a pressure bomb (Soil Moisture, Inc., Santa Bar- bara, California, U.S.). The terminal portion of one current-year shoot per tree in full sun, about half way up the south side of the crown, was cut about 10 cm long. Pressure in the air-tight chamber was increased at a constant rate of 30 sec·MPa-1 and was recorded when cut stem surface became uniformly wet. All trees (20 Ulmus, 40 each of Acer and Mag- nolia) were winched due east to five degrees trunk tilt from vertical start position to evaluate ©2017 International Society of Arboriculture container (1–5)
January 2017
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