Arboriculture & Urban Forestry 38(1): January 2012 extend the irrigation cycle of newly planted tree seedlings. The authors of the current study wanted to ascertain whether humec- tants have an impact on subsequent growth and/or physiologi- cal activity of treated plant material, thereby determining their potential usefulness as amendments for improving transplant success and establishment for recently transplanted woody plants. The studies reported here were conducted in a green- house over a two-year period using plant material grown in a commercially available soilless substrate in order to eliminate some of the environmental variables that often confound results obtained in field trials. Seedlings were used to provide more consistent and uniform plant material and, as such, represent an important first step in evaluating the effectiveness of humec- tant treatment using larger plant material under field conditions. METHODS AND MATERIALS Growth Measurements (2008 Trials) In mid-February 2008, one-year-old seedlings of both Jiffy Plug™ and bare root red maple (Acer rubrum L.) and one-year-old bare root seedlings of yellow poplar (Liriodendron tulipifera L.) were purchased from a commercial nursery. Both the Jiffy Plug (seed- ed and grown in peat plugs) and bare root (seeded and grown in mineral soil) seedlings 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, Vancouver, British Columbia, Canada). The chemical and physical properties of this substrate have been reported elsewhere (Roberts 2006). At trans- plant, root systems of the Jiffy Plug red maples were left intact (unpruned), while the bare root seedlings, both red maple and yel- low poplar, were pruned back 25%–35% to facilitate placement in the planting container. To distinguish between these two produc- tion methods, the authors will hereafter refer to the plug-grown, non-root-pruned seedlings as PPS (peat plug seedlings), and the soil-grown, root-pruned seedlings as BRS (bare root seedlings). Transplanted seedlings of both species and both production types were placed in a greenhouse (18°–26°C; 60% +/- 12% rela- tive humidity) and exposed to 10 hours of light [80–120 W/m2 photosynthetically active radiation (PAR; natural day length plus supplemental illumination from 175 W metal halide lamps on a two-hour photoperiod)]. The seedlings were hand-watered as needed to maintain media moisture content at or near container ca- pacity. Following bud break, and one week prior to the start of the experiment, all seedlings were fertilized with Osmocote Plus 15-9- 12 controlled release fertilizer (15 g/pot) and Micromax granular micronutrient fertilizer (2.5 g/pot), both applied as a top dressing (Scotts-Sierra Horticultural Products Co., Marysville, Ohio, U.S.). Treatment consisted of a single root-drench application of ei- ther Hydretain ES™ (HydES), a liquid organic product contain- ing 58% humectants, 1.3% non-ionic surfactant, and 40.7% inert ingredients (Ecologel Solutions LLC, Ocala, Florida, U.S.), or EcoSential™ (EcoS), a similar product containing 50% humec- tants, 15% non-ionic surfactant, and 35% inert ingredients (LES- CO, Inc., Cleveland, Ohio, U.S.). Seven seedlings of each species (red maple, yellow poplar) and each production type (PPS, BRS) were assigned to one of the following five treatment groups: 1) water (control); 2) HydES applied at the manufacturer’s recom- mended rate (16 mL/L); 3) HydES at 12 mL/L; 4) EcoS applied at 7 the manufacturer’s recommended rate (16 mL/L); 5) EcoS at 12 mL/L. To assure uniformity in seedling size between treatments, growth index (GI) measurements (average of seedling height and two-dimensional crown width; Monterusso et al. 2005) were used in assigning seedlings to each treatment group. The volume of liquid (350 mL) applied to each pot was sufficient to thoroughly saturate the growing medium without causing substantial runoff; however, a plastic tray (15 cm diameter) was placed beneath each container to collect any excess liquid and to allow for re-absorption. After treatment, seedlings were randomly arranged on a greenhouse bench and, starting the following day, a progres- sive drought cycle was imposed by withholding water. When each seedling wilted (visual observation) it was harvested and the following determinations made: height; canopy size; number of leaves; leaf area; leaf dry weight; length and surface area of roots <1 mm and >5 mm diameter; and root dry weight. [NOTE: on average, untreated seedlings wilted (and were subsequently sampled) about one week earlier than humectant-treated seed- lings.] Leaf area measurements were made with a LI-3100C area meter (LI-COR, Lincoln, Nebraska, U.S.). Root morphological data (length and surface area) were determined using the Win- RHIZO image analysis system (Regent Instruments, Inc., Ste- Foy, Quebec, Canada). Biomass measurements were recorded after oven drying tissue at 70°C for 48 hours. From the raw data collected, the following growth indices were calculated: growth index, specific leaf area, leaf area index, specific root length, fine root:coarse root ratio, and root area index. In a companion experiment, data were collected on changes in substrate mois- ture content (SMC) of unplanted Metromix 560 subjected to a drought period lasting four weeks. In this experiment, SMC was sampled at three fixed locations in each of 12 pots (six HydES-treated; six untreated) using a moisture meter and ma- trix sensor (Delta-T Devices, Ltd., Cambridge, UK). Gravimet- ric measurements of substrate evaporative water loss per unit surface area (evaporative index, EI) were also recorded daily. Physiological Measurements (2009 Trials) In early February 2009, one-year-old PPS and BRS seedlings of red maple and river birch (Betula nigra L.) were purchased from two commercial nurseries. The seedlings were transplanted into 3.8 L plastic pots containing a soilless substrate (Metromix 560) and were placed in a greenhouse under the conditions previously described. After six weeks, all seedlings except the PPS birch had broken dormancy. (NOTE: It was subsequently discovered that the root systems of many PPS birch had frozen during shipment and an insufficient number of plants were available to include in this study). After the remaining seedlings (BRS birch; PPS and BRS maple) had reached full leaf, and about one week before starting the study, they were top-dressed with controlled release and granular micronutrient fertilizers as previously described. The 2009 treatments consisted of a single root-drench ap- plication (350 mL) of either water (control) or humectant (HydES or EcoS at a concentration of 16 mL/L) applied to seedlings with a similar range of GI values. After treatment, seedlings were randomly arranged on a greenhouse bench and drought-stressed by withholding water. As drought progressed, seedlings were sampled in groups of three based on the appear- ance of foliar wilt symptoms in each untreated (control) plant. Thus, each time a droughted, untreated seedling showed wilt ©2012 International Society of Arboriculture
January 2012
| 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
