34 Gilman et al.: Effect of Container Type and Root Pruning on Root Architecture roots larger than one-tenth the trunk diameter in the top half of the root ball, circling more than one-third around trunk, Anonymous 2015); per- cent trunk circled at #3 and #15 positions; percent trees with roots >5 mm diameter growing over root collar at the trunk; diameter of five largest roots on north and south half of #15 root ball periphery; number of radial roots (roots >2 mm diameter growing straight (with less than a 45 degree turn) from trunk reaching #15 container wall) measured between #3 and #15 container wall positions; and diameter of the five largest roots at position of #3 container before descending, circling, kinking, ascending, or growing straight into #15 substrate. In February 2010, 160 trees (8 container types × 2 root prunings × 10 replicates) were shifted into the identical type #45 containers with the same substrate described above on 1.8 m spacing in a randomized complete block design. Blocks were kept intact when shifting to the larger size. Root balls on half of the trees of each con- tainer type (the same trees shaved when shifting into #15) were shaved, as previously described, and half were not, as they were shifted into #45 containers. The north mark on all trunks was placed due north. Branches on trees were pruned twice using reduction and heading cuts to maintain a dominant leader. The remaining 48 trees from #15 containers (8 container types × 2 root pruning × 3 replicates) were planted directly into the ground (see Gilman et al. 2015b). In May 2011, 80 root balls from the #45 containers (8 container types × 2 root prunings × 5 repli- cates = 80 trees) were washed of substrate before roots were measured in a variety of ways. Some attributes were measured between the position of the #15 and #45 containers; many measured attri- butes resulted from root defections that occurred when trees were in the smaller #3 and #15 con- tainers. Root measurements on #45 root balls included the following: percent trees grading as a cull, according to Florida Grades and Standards for Nursery Plants (Anonymous 2015); percent trunk circled at #3, #15, and #45 positions as indicated by root deflections at the former position of these containers; percent trunk circumference circled by roots at the #3 and #15 positions; percent trees with roots >5 mm diameter growing over root collar at the trunk; diameter of the five larg- ©2016 International Society of Arboriculture est roots on the north and south half (referred to as cardinal direction) of #45 root ball periphery; number of radial roots (roots >2 mm diameter growing straight (with less than a 45 degree turn) from trunk reaching #45 container wall) measured between #15 and #45 container wall positions; and diameter of the five largest roots at position of #3 container before descending, circling, kinking, ascending, or growing straight into #15 substrate. The remaining 80 trees (8 container types × 2 root pruning × 5 replicates) were planted into the ground with the north mark facing due north (see Gilman et al. 2015b). Statistical Analysis Data were analyzed at each harvest date with two- way analysis of variance (ANOVA), with container type and root pruning serving as main effects in a randomized complete block design using the GLM procedure in SAS (1992). Percentages were analyzed in the Genmod procedure within SAS. Two attributes were measured in the northern half of the root ball and compared to those in the southern half; this main effect was referred to as cardinal direction. These attributes included number of roots >2 mm diameter growing straight (with less than a 45 degree turn) from trunk reaching #15 container wall, measured between #3 and #15 container wall positions, and diameter of the five largest roots on the root ball periphery. Three-way ANOVA was used to ana- lyze these data with container type, root pruning, and cardinal direction serving as main effects in a randomized complete block design. Duncan’s multiple range test was used to separate main effect means at P < 0.05; LSD was used to separate interaction means at P < 0.05 unless indicated. RESULTS Shoot Growth Trunk diameter differences for finished trees varied less than 5 mm among container types in #3, #15, and #45 containers (Table 2). Trees in #45 AP, SP, and SS had larger trunk diameters than those in JP and RB at the end of the study; however, differences were small (<5 mm). Tree height differences were less than 15%, 8%, and 4% for trees in the #3, #15, and #45 container types, respectively. There was no
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