276 extend the irrigation cycle of recently transplanted, drought- stressed tree seedlings and, if so, at what concentrations were these products effective. The study authors were also interested in whether seedlings representing different production types might respond differently to humectant treatment. Finally, the authors wanted to ascertain whether humectant treatment might alter growth and/or physiological activity, thereby having a potential long term impact on transplant survival. The results of these latter investigations will be the subject of a subsequent research report. All of the studies reported here were conducted in a greenhouse using plant material grown in a soilless substrate to help eliminate some of the environmental variables that often confound the results obtained with field trials. Seedling material was used as an important first step before attempts were made to evaluate the effectiveness of these techniques using larger plant material under field conditions. METHODS AND MATERIALS 2007 Study One-year-old seedlings of both Jiffy Plug™ (seeded and grown in a peat pellet encased in biodegradable mesh) and bare root (seeded and grown in soil) red maple (Acer rubrum L.) and red oak (Quercus rubra L.) were purchased from Vans Pines Nursery, West Olive, Michigan, U.S. In mid-February, fifty 15–30 cm tall Jiffy Plug and fifty 15–30 cm tall bare-root seed- lings of both species were transplanted into 3.8 L plastic pots containing a soilless substrate consisting of composted pine bark, coconut pith coir, sphagnum peat moss, processed bark ash, and perlite (Metromix 560; Sun Gro Horticulture, Van- couver, BC, Canada). The chemical and physical properties of this substrate have been reported elsewhere (Roberts 2006). At planting, the root systems of Jiffy Plug seedlings were left undisturbed (unpruned) while those of bare-root seedlings were pruned back 25%–35% to facilitate placement in the planting con- tainer. To distinguish between seedlings representing the two pro- duction methods used in these studies, the term “production type” is introduced here and is used hereafter to differentiate between plant material seeded and grown in a peat plug and having an intact, un- pruned root system (PPS), versus plant material seeded and grown in soil and having a bare-root, root-pruned root system (BRS). After planting, seedlings were placed in the greenhouse (18°C–26°C; 60 +/- 12% relative humidity) and exposed to 10 hours of light [80–120 W/m2 photosynthetically active radia- tion (PAR; natural day length plus supplemental illumination from 175-W metal halide lamps on a two-hour photoperiod)]. At the end of March, after new foliage had formed, 24 seedlings of each species (red maple; red oak) and each production type (PPS; BRS), a total of 96 seedlings, were selected for treatment. To ensure uniformity in size, seedlings were selected based on comparable growth index measurements (height plus two-dimen- sional crown width; Monterusso et al. 2005). Treatment consisted of soil drench applications of Hydretain ES™ (HydES), a com- mercially available liquid product containing a patented blend of humectant and hygroscopic compounds (Ecologel Solutions LLC, Ocala, FL, U.S.). Six seedlings of each species and each production type were assigned to one of the following four treat- ments: (1) no chemical; (2) HydES at the recommended rate, X, (16 mL/L); (3) HydES at half the recommended rate, 0.5X; or (4) HydES at twice the recommended rate, 2X. Up until the time of ©2010 International Society of Arboriculture 2008 Study Based on the results of the 2007 investigation, an additional greenhouse study was initiated in 2008 using PPS and BRS red maple seedlings similar to those used in 2007 along with 45–60 cm tall bare-root seedlings(BRS) of yellow-poplar (Liriodendron tulipifera L.). HydES was again used as one of the humectants as was a similar product, EcoSentialTM (LESCO, Inc., Cleveland, OH, U.S.). EcoSential™ (EcoS) differs from HydES in that the humectant-containing component of the product is slightly lower while the non-ionic surfactant component is appreciably high- er, a condition which should facilitate greater soil penetration. Plant material (50 each of PPS and BRS red maples and 50 BRS yellow-poplars) was received from the nursery in mid- February, potted in 3.8 L plastic containers in soilless substrate and placed in the greenhouse as described previously. By mid- April the red maples had produced new foliage and were ready for treatment. Using growth index as a method for determining uniformity in size, 35 seedlings of each production type (PPS and BRS) were selected for treatment, seven replications per treat- ment, a total of 70 seedlings. Treatments (350 mL root drench per container) consisted of: (1) no chemical; (2) HydES at the recommended rate, X (16 mL/L); (3) HydES at 0.75X (12 mL/L); (4) EcoS at the recommended rate, X (16 mL/L); or (5) EcoS at 0.75X. As in the 2007 study, all seedlings were hand-watered as needed up until the time of treatment and were fertilized once prior to treatment with a combination of both controlled release and micronutrient fertilizers as previously mentioned. To obtain information on media moisture content during the dry down period, daily moisture readings were taken on one set of seedlings (the PPS red maples) using a moisture meter (HH2) and sensor (SM200) (Delta-T Devices, Ltd., Cambridge, UK). Approximately three weeks after the red maples were treated, the yellow-poplars had broken dormancy and were ready for treat- ment. The same five treatments (0; X and 0.75X HydES; X and 0.75X EcoS) were used in treating 35 poplars, seven replications per treatment, 350 mL drench per container, once again using growth index as the criterion for determining uniformity in seedling size between treatments. As in 2007, initiation of a progressive drought Roberts and Linder: Humectants as Post-Plant Soil Amendments treatment, all seedlings were hand-watered as needed to main- tain media moisture content at field capacity. Approximately one week prior to treatment, seedlings were fertilized with both Os- mocote Plus 15-9-12 controlled release fertilizer (15 g/pot) and Micromax granular micronutrient fertilizer (2.5 g/pot), both ap- plied as a top dressing (Scotts-Sierra Horticultural Products Co., Marysville, OH, U.S.). At the time of treatment, 350 mL of either water (treatment 1) or HydES (treatments 2–4) was applied to each container as a root drench. This amount of liquid was suf- ficient to thoroughly wet the substrate in each container. A 15-cm diameter plastic tray was placed beneath each container to col- lect any excess liquid and to allow for subsequent re-absorption. Seedlings were placed on a greenhouse bench and, start- ing the day after treatment, a progressive drought cycle was imposed by withholding water. The number of days un- til the appearance of foliar wilt (DTW) was then recorded for each seedling. For this investigation, DTW was deter- mined by the appearance of one or more of the following fo- liar symptoms: angle of petiole to stem >90°; angle of leaf blade to petiole >90°; angle of leaf blade to mid-rib >180°.
November 2010
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
