58 Bryan et al.: Transplant Season, Irrigation, and Planting Depths on Landscape Establishment high soil water content fluctuations when grown in a sandy soil (Gilman et al. 1998). In addition, when live oaks were frequently irrigated after field transplanting into sandy soil, they grew twice as much (diameter and height) in the first growing season as trees which were infrequently irrigated (Gilman 2004). However, posi- tive effects of irrigation on live oak growth rates disappeared in the second season, possibly as a result of tree establishment (Gil- man 2004) or possibly due to low fertility (no fertilizer applied during study) as a result of nutrients leaching out of the root zone. Similarly, red maple (Acer rubrum L.) subjected to frequent ir- rigation after transplanting had greater trunk diameter, increased root number, root diameter, and uniform root distribution, than trees irrigated less frequently (Gilman et al. 2003). Results from the above-mentioned research indicate that irrigation frequen- cy is important to tree growth and survival after transplanting. What remains unclear is the effect of planting depth and potential interactions with either transplant season or irriga- tion on plant growth and survival. Therefore, it is important to determine the effects of planting practices on tree survival at transplant, and to assess the effects of these practices on subsequent landscape performance. Baldcypress [Taxodium distichum (L.) Rich.] and sycamore (Platanus occidentalis L.) are majestic trees of considerable ornamental value in urban and riparian environments (Bailey and Bailey 1976; Simpson 1988; Liu et al. 2007). Baldcypress is known to tolerate a wide range of soil moisture conditions, ranging from periodic flood- ing to mild drought (Elcan and Pezeshki 2002). Sycamore is flood tolerant (Kozlowski and Pallardy 2002), and is known to have the ability to adjust its osmotic potential in response to drought (Tschaplinski et al. 1995). The broad objectives of the present experiments were to explore the effect of plant- ing depth and transplant season on baldcypress growth and establishment, and the effect of planting depth and irriga- tion rate on sycamore growth and landscape establishment. MATERIALS AND METHODS Experiment 1: Effect of Planting Depth and Trans- plant Season on Growth and Landscape Estab- lishment of Baldcypress Cultural Conditions Baldcypress seeds were collected in Poteet, Texas (29°2’23.11”N, 98°34’27.45”W), and stored under ambient conditions until required (approximately two months). Seeds were immersed in a heated [43°C (109°F)] water bath (180 Series Water Bath, Precision Scientific Inc., Chicago, IL) and left to soak for approximately 24 hours in cooling water [to 23°C (73°F)]. Seeds were then removed and rinsed in reverse osmosis (RO) treated water. This procedure was repeated five times. Seeds were then stratified in a cold room at 1.7°C (35°F) for 90 days in moist peat (Premier® Pro Moss® TBK Professional, Premier Horticulture Inc., Red Hill, PA), and then planted in 10 cm × 36 cm × 51 cm (height x width x length) (18.4-L) black plas- tic flats (Dyna-flat™ vermiculite (Sunshine® Strong-Lite® , Kadon Corp., Dayton, OH) containing Medium Vermiculite Pre- mium Grade, SUN GRO™ Horticulture, Pine Bluff, AR), and placed in a greenhouse at Texas A&M University Horticul- tural Gardens, College Station, TX (30°36’5”N, 96°18’52”W). Emerging seedlings were irrigated with RO water as required. ©2010 International Society of Arboriculture After approximately 100 days, uniform seedlings, approxi- mately 11 cm in height, were transplanted into 0.85 L black plas- tic containers (Kinney Bonded Warehouse, Inc., Donna, TX) with their root collars at substrate surface (grade) (Metro-Mix® Series, SUNGRO® 700 , Bellevue, WA). Root collars were defined as the area between the stem and the root system. Transplanted seedlings were maintained under shade (55% light exclusion) in a graveled nursery at Texas A&M University Horticultural Gardens. Plants were fertigated (0.27 L·min-1 50 mg⋅L-1 flow rate), as required with (50 ppm) N from a water soluble fertilizer (Peters Pro- fessional® Acid Special water soluble fertilizer, 21N-3.1P-5.8K, Scott’s Company, Marysville, OH). Irrigation water was injected with concentrated sulfuric acid to lower pH to a target of 6.5. Young trees (liners) were transplanted, after approximately 80 days, into 2.6 L (#1) black plastic containers (C-300S Classic, Nursery Supplies, Inc., Chambersburg, PA) with their root collars at substrate (composted pine bark mulch; Landscapers Pride® , New Waverly, TX) surface (grade). Container substrate was amended with the following: 7 kg·m-3 tilizer (Scotts Osmocote® 15N-3.9P-9.9K controlled release fer- Plus 15-9-12, Scotts-Sierra Horticultural Products Co., Marysville, OH), 4 kg·m-3 dolomitic limestone (Austin White Lime Company, Austin, TX), 2 kg·m-3 gypsum (Hoedown™ Standard Gypsum LP, Fredericksburg, TX), and 1 kg·m-3 micro- nutrients (Scotts Micromax® micronutrients, Scotts-Sierra Horti- cultural Products Co., Marysville, OH). Liners were maintained in the nursery under shade and fertigated as previously described. Trees were transplanted, after approximately 225 days, into 10.8 L (#3) (28 cm top diameter; 24 cm height) black plastic con- tainers (1200C Classic, Nursery Supplies, Inc., Chambersburg, PA), with the substrate (composted pine bark mulch; Earth’s Fin- est Black Diamond Mulch, The LetCo Group, Dallas, TX) sur- face maintained at grade. Container substrate was amended as described previously. Trees were maintained in the nursery under shade and fertigated as previously described. Trees were staked (1.2 m bamboo stakes) and tied to maintain a central leader. Trees were transplanted into field conditions at the Texas A&M University Horticulture Farm, after approximately 210 days (November 19, 2005) for the autumn transplant, and 320 days (March 12, 2006) for the spring transplant. Trees were trans- planted at various depths in relation to the root collar, at grade (at soil surface), 7.6 cm below grade, or 7.6 cm above grade. Trees were drip-irrigated (T-Tape® , T-Systems Intl. Inc., San Diego, CA) as required. Field soil had a textural analysis of 74% sand, 16% silt, and 10% clay (sandy loam), contained 2.73% organic matter (OM), pH 6.4, electrical conductivity (EC) 0.201 dS·m-1 , and nutrient levels with the following µg·g-1 (ppm): 11 NO3 -N, 47 P, 70 K, 490 Ca, 47 Mg, 17 S, 294 Na, 87.4 Fe, 0.87 Zn, 8.69 Mn, 0.28 Cu, and 0.15 B (Soil, Water, and Forage Test- ing Laboratory, Texas A&M University, College Station, TX). Daily precipitation events during the active growing season (March to September) at nearby Easterwood Air- port (Office of the Texas State Climatologist, Department of Atmospheric Sciences, Texas A&M University, Col- lege Station, TX) in 2006 and 2007 are presented in Figure 1. Assessment of Plant Growth Tree height, from soil line to apical tip, and trunk diam- eter (15 cm above soil) were measured in March and Novem- ber 2006, and again in March and November 2007. Rela- tive growth rates were calculated (Hoffmann and Poorter
March 2010
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