38 Gilman et al.: Effect of Container Type and Root Pruning on Root Architecture were no differences among container types (data not shown); descending was significantly (P = 0.05) less common (32 %) and also did not vary among types. Only 12% of the five largest roots ascended the container wall or kinked to grow back toward the trunk, and there were no differ- ences among container types (data not shown). Shaving the root ball periphery when shifting from either the #3 or #15 containers dramati- cally reduced the percentage of trees graded as culls at either position (#3 and #15) in the root ball (Table 7). Shaving reduced the per- centage of trees with roots >5 mm diameter over the root collar within #3 container dimen- sion, and reduced diameter of the largest roots at #15 container position. In contrast, shaving increased the diameter of roots on the periphery of finished trees in #45 containers. The number of roots growing straight from the trunk (radial roots) between the #15 and #45 con- tainers and diameter of roots at the periphery Diameter of five largest roots on north periphery of #45 root ball (mm)z 6.0 cw 7.8 ab 8.2 a 5.7 c 6.3 bc 6.9 abc 6.4 bc 6.4 bc of the #45 container were larger on the north, rather than south side of the root ball (Table 5). The number of roots growing straight from the trunk between the #15 and #45 contain- ers (radial roots) was approximately double for the shaved than the not shaved treatment for all containers, except RT (Figure 3). Container type had no impact on number of radial roots when root balls were shifted to a larger container with- out shaving. However, SP had more radial roots than CR, FN, RB, and RT when root balls were shaved. Percentage of trunk circled with roots larger than 3 mm diameter depended on con- tainer type and root pruning (Table 8), although in all cases shaving substantially (P < 0.001) reduced root circling at the #3 and #15 positions (Figure 4). In contrast, circling at the #45 posi- tion on shaved trees was greater than or equal to circling without shaving for all container types, except RT and SS, which had a smaller percent- age of the trunk circled as a result of shaving. Table 6. Root ball attributes of ‘Florida Flame’ red maple harvested from eight different #45 container types. Container type Diameter of five largest roots on south periphery of #45 root ball (mm)z APx CR FN JP RB RT SP SS 4.7 b 5.8 ab 7.0 a 5.4 ab 5.6 ab 5.7 ab 7.0 a 4.5 b 6.7 bc 11.0 a 10.7 a 9.5 ab 5.7 c 7.2 bc 10.8 a 6.3 c z Roots in the outer 3 cm in the north or south 180 degree circumference of root ball. Trees in #3, #15, and #45 containers for 7, 9, and 15 months, respectively. y Measured at the position of the #3 container, before descending, circling, kinking, ascending, or growing straight into #15 substrate. x See Table 1 for descriptions. w Means in a column with a different letter are statistically different at P < 0.05; n = 10, averaged across root pruning treatment due to insignificant interaction (P > 0.20). Table 7. Effect of root pruning #3 and #15 root balls when shifting to the larger container size on root attributes of ‘Florida Flame’ red maple in #45 containers. Root pruningz None Shaved % trees graded as cull at #3 container positiony 95.0 av 42.5 b % trees graded as a cull at #15 container mm diameter over positiony 50.0 a 2.5 b 38.0 b % trees with roots >5 root collar within #3 container dimension 90.0 a Diameter of five largest roots at #15 container position (mm)x 10.7 a 6.3 b Diameter of five largest roots on north periphery of #45 root ball (mm)w 5.3 bA 8.1 aA z Shaving removed the outer 3 cm of the root ball periphery and bottom. Trees in #3, #15, and #45 containers for 7, 9, and 15 months, respectively. y Based on roots in the top 5 cm of root ball according to Florida Grades and Standards for Nursery Plants (Anonymous 2005); a cull occurs when there is one (or more) root greater than one-tenth the trunk diameter in the top half of the root ball growing more than one-third around the root ball. No culls occurred in #45 containers. x Measured at the position of the #15 container, before descending, circling, kinking, ascending, or growing straight into #45 container substrate. w Roots in the outer 3 cm in the north or south half of root ball. v Means in a column (lower case) or row (upper case) with a different letter are statistically different at P < 0.001; n = 40, averaged across eight container types due to insignifi- cant interaction (P > 0.15). Diameter of five largest roots on south periphery of #45 root ball (mm)w 4.8 bB 6.7 aB Diameter of five largest roots at position of #3 root ball (mm)y ©2016 International Society of Arboriculture
January 2016
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