150 Etemadi and Nezhad: Production Method and Humic Acid Application in Arid Climate Table 5. Effects of production method and humic acid application on canopy desiccation (CD), canopy color (CC), shoot extension (SE), height increase (HI), and trunk diameter increase (DI) of oriental thuja (Platycladus orientalis) trees in the first and second years following transplanting. CD Production method Biostimulant P-value CG B&B BR C HA Production method Biostimulant Production × Biostimulant 6.2 bz 15.8 b 53.7 a 31 a 19.6 a 0.01 0.20 0.07 CC 7.7 a 7.6 a 5.4 b 6.2 a 7.6 a 0.05 0.06 0.02 First year SE 24.2 a 17.3 b 11.5 c 15.2 b 20.2 a <0.01 0.01 0.05 HI 22.7 a 15.5 b 7.3 c 12.6 b 18.6 a <0.01 0.04 0.18 DI 2 a 1.2 b 0.8 c 1.3 a 1.5 a <0.01 0.36 0.27 CD 2.9 b 9.75 b 54.1 a 27.8 a 16.6 a 0.03 0.18 0.08 CC 8.25 a 7.9 a 5.5 b 6.4 b 8.0 a 0.02 0.03 0.01 Second year SE 13.4 a 11.8 a 10.0 a 10.6 a 12.8 a 0.23 0.11 0.28 HI 26 a 22 a 19.5 a 26.5 a 0.30 0.12 0.35 DI 1.01a 1.2 a 19.8 a 0.5 b 0.8 a 0.9 a 0.02 0.32 0.39 z Treatment means within column in each treatment followed by the same letter are not significantly different according to Duncan’s multiple-range test (P ≤ 0.05). Tree establishment In order to assess the establishment of trans- planted trees, their current-season shoot growth, as well as their visual indices at the end of the second year (i.e., 2012), were compared to untransplanted trees. No significant difference was observed between untransplanted and CG trees in terms of canopy desiccation (Table 6). B&B trees also had low desiccation, although it was statistically higher than desiccation percent- age of CG and untransplanted trees. Further- more, canopy color rates of CG and B&B trees equaled to color rate of untransplanted trees by the end of the experiment. BR trees, however, had still statistically greater canopy desiccation (54.1% versus 0%) and lower color rate (5.5 versus 8.4) than that of untransplanted trees, suggest- ing that BR transplanting method for thuja spe- cies may be more stressful. Based on results from current-season shoot growth, shoot extension was the most on CG trees at 13.4 cm followed by untransplanted, B&B, and BR trees at 12, 11.7, and 10 cm, respectively, although the observed differences were not statistically significant. Table 6. Comparing canopy desiccation (CD), canopy color (CC), and shoot extension (SE) of transplanted ori- ental thuja (Platycladus orientalis) trees from different production methods to un-transplanted (UT) trees. Transplanting method UT CG B&B BR P-value Canopy desiccation 0 cz 2.9 c 9.7 bc 54.1 a <0.01 Canopy color 8.4 a 8.2 a 7.9 a 5.5 b 0.01 Shoot extension 12 a 13.4 a 11.8 a 10 a 0.36 z Treatment means within each column followed by the same letter are not significantly different according to Duncan’s multiple-range test (P ≤ 0.05). DISCUSSION Production Method In the first experiment of the present study, researchers harvested oriental thuja trees as BR (less expensive method) or B&B (more expensive method) and hardened-off the trees in containers for one year before plant- ing into the main field, in order to evaluated the impact of harvesting technique on growth and survival during hardening-off period. Effect of harvesting technique was evident from the early months following transplanting. While trees potted in containers as B&B trees had no mortality, only half of their BR coun- terparts survived by the end of the trial period, and their growth responses were significantly lower than B&B trees. These results suggest that BR transplanting of oriental thuja trees may be more stressful, and BR trees would not be able to successfully withstand transplant shock. Apart from the different climate conditions, soil type, and planting practices, species type is a deci- sive factor in response to transplanting method. Findings of some studies directly comparing BR and B&B trees have shown higher mortality in bare-rooted trees. Survival rates of transplanted evergreen species eldarica pine (Pinus eldarica Medw.), as well as two deciduous trees, white mulberry (Morus alba L.) and smoothleaf elm (Ulmus carpinifolia Gled.), have been reported to be more for B&B trees than their similar-sized BR trees (Etemadi et al. 2013). In contrast to these reports, Anella et al. (2008) found no significant difference in mortality of B&B and BR stocks of ©2017 International Society of Arboriculture
July 2017
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