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Amy N. Wright and Robert D. Wright

Root growth following transplanting allows a plant to exploit water and nutrient resources in the soil backfill (landscape) or container substrate and thus is a critical factor for transplant survival. The Horhizotron, a horizontal root growth measurement instrument, has been developed and evaluated for use in measuring root growth under a variety of root environments. The design of the Horhizotron includes four wedge-shaped glass quadrants that extend away from a plant's root ball allowing measurement of roots as they grow out from the original root ball. The substrate in each quadrant can be modified in order to evaluate the effect of substrate or root environment on root growth. Materials used for construction were lightweight, durable, easy to assemble, and readily available from full service building supply stores. Units were suitable for use on a greenhouse bench or outdoors in contact with the ground. Horhizotrons provided a simple, nondestructive method to measure root growth over time under a wide range of rhizosphere conditions.

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Brian E. Jackson, Amy N. Wright, and Jeff L. Sibley

In the southeastern United States, inconsistent pine bark (PB) supplies and overabundance of cotton gin by-products warrant investigation about the feasibility of replacing PB with cotton gin compost (CGC) for container horticultural plant production. Most research on the use of composted organic substrates for horticultural plant production has focused on shoot growth responses, so there is a need to document the effect of these substrates on root growth. In 2004, `Blitz' tomato (Lycopersicon esculentum), `Hot Country' lantana (Lantana camara `Hot Country'), and weeping fig (Ficus benjamina) were placed in Horhizotrons to evaluate root growth in 100% PB and three PB:CGC substrates containing, by volume, 60:40 PB:CGC, 40:60 PB:CGC, and 0:100 PB:CGC. Horhizotrons were placed in a greenhouse, and root growth in all substrates was measured for each cultivar. Physical properties (total porosity, water holding capacity, air space, and bulk density) and chemical properties (electrical conductivity and pH) were determined for all substrates. Physical properties of 100% PB were within recommended guidelines and were either within or above recommended ranges for all PB:CGC substrate blends. Chemical properties of all substrates were within or above recommended guidelines. Root growth of all species in substrates containing CGC was similar to or more enhanced than root growth in 100% PB.

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Amy N. Wright, Stuart L. Warren, and Frank A. Blazich

Root growth is a critical factor in landscape establishment of container-grown woody ornamental species. Kalmia latifolia (mountain laurel) often does not survive transplanting from containers into the landscape. The objective of this experiment was to compare rate of root growth of mountain laurel to that of Ilex crenata `Compacta' (`Compacta' holly) and Oxydendrum arboreum (sourwood). Six-month-old tissue-cultured liners (substrate intact) of mountain laurel, 1-year-old rooted cutting liners (substrate intact) of `Compacta' holly (liner holly), 6-inch bare root seedling liners of sourwood, and 3-month-old bare-root rooted cuttings of `Compacta' holly were potted in containers in Turface™. Prior to potting, roots of all plants were dyed with a solution of 0.5% (w/v) methylene blue. Plants were greenhouse-grown. Destructive harvests were conducted every 2 to 3 weeks (six total harvests). Length, area, and dry weight of roots produced since the start of the experiment, leaf area, and dry weight of shoots were measured. Sourwood and liner holly had greater rate of increase in root length and root dry weight than mountain laurel and bare root holly. Rate of increase in root area was greatest for sourwood, followed by (in decreasing order) liner holly, mountain laurel, and bare-root holly. Increase in root length and root area per increase in leaf area was highest for liner holly, possibly indicating why this species routinely establishes successfully in the landscape. Increase in root dry weight per increase in shoot dry weight was lowest for mountain laurel. The slow rate of root growth of mountain laurel (compared to sourwood and liner holly) may suggest why this species often does not survive transplanting.

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Amy N. Wright, James A. Robbins, and Mengmeng Gu

An online survey was conducted to gain information about nursery management and production (NMP) course content and enrollment, attitudes regarding the use of multimedia resources in the classroom, and opinions about the use of virtual field trips to supplement or replace traditional field trips. Results reflected current organizational and curriculum changes within colleges of agriculture that have impacted traditional horticulture courses such as NMP and in many cases have resulted in the merging of NMP courses with other courses such as greenhouse or garden center management. The number of departments with “horticulture” in the department name was similar to the number of departments with “plant science” in the department name (and not “horticulture”). The five topics covered most frequently included container production, container substrates, fertility, field production, and pot-in-pot production. Most of the respondents indicated that the NMP course in their department included at least one field trip. The top criteria used for selecting field trip locations included type of nursery, distance, innovation, reputation, and the number of aspects that could be viewed. Accessibility and distance to nurseries were listed as primary limitations for providing comprehensive field trips. Most respondents currently use multimedia resources in courses other than NMP, and a majority of respondents indicated that multimedia resources such as DVDs or web-based videos would be valuable for supplementing instruction in NMP, particularly for aspects not observed during field trips.

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Amy N. Wright, Robert D. Wright, Brian E. Jackson, and Jake A. Browder

Rhizosphere pH preferences vary for species and can dramatically influence root growth rates. Research was conducted to determine the effect of root zone pH on the root growth of BuxusmicrophyllaSieb. & Zucc. `Green Beauty' (boxwood) and KalmialatifoliaL. `Olympic Wedding' (mountain laurel). Boxwood plants removed from 3.8-L containers and mountain laurel plants removed from 19-L containers were situated in the center of separate Horhizotrons™. The key design feature of the Horhizotron is four wedge-shaped quadrants (filled with substrate) that extend away from the root ball. Each quadrant is constructed from glass panes that allow the measurement of roots along the glass as they grow out from the root ball into the substrate. For this experiment, each quadrant surrounding a plant was filled with a pine bark substrate amended per m3 (yd3) with 0.9 kg Micromax (Scotts-Sierra, Marysville, Ohio) and 0, 1.2, 2.4, or 3.6 kg dolomitic limestone. All plants received 50 g of 15N–3.9P–9.8K Osmocote Plus (Scotts-Sierra), distributed evenly over the surface of the root ball and all quadrants. Plants were grown from May to Aug. 2003 in a greenhouse. Root lengths were measured about once per week throughout the experiment. Root length increased linearly over time for all species in all substrates. Rate of root growth of boxwood was highest in pine bark amended with 3.6 kg·m3 lime and lowest in unamended pine bark. Rate of root growth of mountain laurel was lowest in pine bark amended with 3.6 kg·m3 lime. Results support the preference of mountain laurel and boxwood for acidic and alkaline soil pH environments, respectively.

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Amy N. Wright, Alex X. Niemiera, J. Roger Harris, and Robert D. Wright

The objective of this study was to determine the effect of micronutrient fertilization on seedling growth in pine bark with pH ranging from 4.0 to 5.5. Koelreuteria paniculata (Laxm.) was container-grown from seed in pine bark amended (preplant) with 0, 1.2, 2.4, or 3.6 kg/m3 dolomitic limestone and 0 or 0.9 kg/m3 sulfate-based micronutrient fertilizer (Micromax ®). Initial pine bark pH for each lime rate was 4.0, 4.5, 5.0, and 5.5, respectively. Final pH (week 10) ranged from 4.7 to 6.4. Ca and Mg supply in irrigation water was 10.2 and 4.2 mg·L–1. Seedlings were harvested 10 weeks after planting, and shoot dry weight and height were determined. Pine bark solution was extracted using the pour-through method at 3, 7, and 10 weeks after planting. Solution pH was measured, and solutions were analyzed for Ca, Mg, Fe, Mn, Cu, and Zn. Shoot dry weight and height were higher in micronutrient-amended bark than in bark without added micronutrients. Lime (1.2 kg·\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{m}^{-_{3}}\) \end{document}) increased growth only in the absence of micronutrient additions. In general, adding micronutrients increased pine bark solution Ca, Mg, and micronutrient concentrations. Adding lime increased pine bark solution pH and Mg concentration and either had no effect on or decreased solution Ca and micronutrient concentrations. Regardless of pine bark pH, micronutrient additions resulted in improved growth and adding lime was not necessary.

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Amy N. Wright, Alex X. Niemiera, J. Roger Harris, and Robert D. Wright

The objective of this study was to determine the effects of lime and micronutrient amendments on growth of seedlings of nine container-grown landscape tree species in two pine bark substrates with different pHs. Acer palmatum Thunb. (Japanese maple), Acer saccharum Marsh. (sugar maple), Cercis canadensis L. (redbud), Cornus florida L. (flowering dogwood), Cornus kousa Hance. (kousa dogwood), Koelreuteria paniculata Laxm. (golden-rain tree), Magnolia ×soulangiana Soul.-Bod. `Lennei' (magnolia), Nyssa sylvatica Marsh. (blackgum), and Quercus palustris Müenchh. (pin oak) were grown from seed in two pine bark substrates with different pHs (pH 4.7 and 5.1) (Expt. 1). Preplant amendment treatments for each of two pine (Pinus taeda L.) bark sources were: with and without dolomitic limestone (3.6 kg·m–3) and with and without micronutrients (0.9 kg·m–3), and with and without micronutrients (0.9 kg·m–3), supplied as Micromax. Seedlings were harvested 12 and 19 weeks after seeds were planted, and shoot dry weight and tree height were determined. The same experiment was repeated using two of the nine species from Expt. 1 and pine bark substrates at pH 5.1 and 5.8 (Expt. 2). Seedling shoot dry weight and height were measured 11 weeks after planting. For both experiments, pine bark solutions were extracted using the pour-through method and analyzed for Ca, Mg, Fe, Mn, Cu, and Zn. Growth of all species in both experiments was greater in micronutrient-amended than in lime-amended bark. In general, adding micronutrients increased nutrient concentrations in the pine bark solution, while adding lime decreased them. Effect of bark type on growth in Expt. 1 was variable; however, in Expt. 2, growth was greater in the low pH bark than in the high pH bark. In general, nutrient concentrations in bark solutions were higher in low pH bark than in high pH bark for both experiments. Under the pH conditions of this experiment, micronutrient additions stimulated growth whereas a lime amendment did not.

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Amy N. Wright, Robert D. Wright, Jake F. Browder, and Brian E. Jackson

Posttransplant root growth is critical for landscape plant establishment. The Horhizotron provides a way to easily measure root growth in a wide range of rhizosphere conditions. Mountain laurel (Kalmia latifolia L.) plants were removed from their containers and planted in Horhizotrons in a greenhouse in Auburn, Ala., and outdoors in Blacksburg, Va. Each Horhizotron contained four glass quadrants extending away from the root ball, and each quadrant within a Horhizotron was filled with a different substrate (treatment): 1) 100% pine bark (Pinus taeda L., PB), 2) 100% soil, 3) a mixture of 50 PB: 50 soil (by volume), or 4) 100% soil along the bottom of the quadrant to a depth of 10 cm (4 inches) and 100% PB layered 10 cm (4 inches) deep on top of the soil. Root growth along the glass panes of each quadrant was measured biweekly in Auburn and weekly in Blacksburg. Roots were longer in all treatments containing pine bark than in 100% soil. When pine bark was layered on top of soil, roots grew into the pine bark but did not grow into the soil. Results suggest that amending soil backfill with pine bark can increase posttransplant root growth of container-grown mountain laurel.

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Julie Guckenberger Price, Amy N. Wright, Robert S. Boyd, and Kenneth M. Tilt

Planting shrubs above-grade with organic matter has shown potential for improving landscape establishment. To further investigate this technique, wax myrtle [Morella cerifera (syn. Myrica cerifera)] (3 gal) and mountain laurel (Kalmia latifolia ‘Olympic Wedding’) (5 gal) were planted on 30 Oct. 2006 (fall planting) and 12 Apr. 2007 (spring planting) in the ground in a shade house in Auburn, AL. At each planting date, plants of each species were assigned one of four treatments. Three of four treatments used a modified above-grade planting technique in which shrubs were planted such that the top 3 inches of the root ball remained above soil grade. Organic matter, either pine bark (PB), peat (PT), or cotton gin compost (CGC), was applied around the above-grade portion of the root ball, tapering down from the top of the root ball to the ground. In the fourth treatment, plants were planted at-grade with no organic matter (NOM). In general, both species had higher shoot dry weight (SDW) and root spread (RS) when planted in the fall than when planted in spring. Among all treatments, plants also typically had larger RS when planted above-grade with PB or PT. For easy-to-transplant species (such as wax myrtle) and especially for difficult-to-transplant species like mountain laurel, fall planting using this modified above-grade planting technique with PB or PT may improve post-transplant root growth and speed establishment in the first growing season.

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Julie Guckenberger Price, Amy N. Wright, Kenneth M. Tilt, and Robert L. Boyd

The need for reliable planting techniques that encourage posttransplant root growth in adverse conditions has prompted research into planting above soil grade (above-grade). Container-grown Morella cerifera (L.) Small (syn. Myrica cerifera L.) (wax myrtle), Illicium floridanum Ellis (Florida anise tree), and Kalmia latifolia L. (mountain laurel) plants were planted in Horhizotrons (root observation chambers) in a greenhouse in Auburn, AL, on 1 Mar. 2006, 6 June 2006, and 3 Jan. 2007, respectively. The experiment was repeated with all three species being planted 18 June 2007. Horhizotrons contained four glass quadrants extending away from the root ball providing a nondestructive method for measuring root growth of the same plant into different rhizosphere conditions. Each quadrant was filled with a native sandy loam soil in the lower 10 cm. The upper 10 cm of the quadrants were filled randomly with: 1) milled pine bark (PB); 2) peat (P); 3) cotton gin compost (CGC); or 4) more native soil with no organic matter (NOM). Horizontal root lengths (HRL, length measured parallel to the ground from the root ball to the root tip) of the five longest roots visible along each side of a quadrant were measured weekly for M. cerifera and I. floridanum and biweekly for K. latifolia. These measurements represented lateral growth and penetration of roots into surrounding substrates on transplanting. When roots of a species neared the end of the quadrant, the experiment was ended for that species. M. cerifera had the fastest rate of lateral root growth followed by I. floridanum and then by K. latifolia. In most cases, roots grew initially into the organic matter rather than the soil when organic matter was present. In general, HRL and root dry weight (RDW) of I. floridanum and K. latifolia were greatest in PB and P, whereas for M. cerifera, these were greatest in P. Differences in root growth among substrates were not as pronounced for M. cerifera as for the other species, perhaps as a result of its rapid increase in HRL. Increased root growth in PB and P may be attributed to the ideal physical and chemical properties of these substrates. Results suggest that planting above soil grade with organic matter may increase posttransplant root growth compared with planting at grade with no organic matter.