Browsing by Author "Stuart L. Warren, Committee Co-Chair"

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Clay Amended Soilless Substrates: Increasing Water and Nutrient Efficiency in Containerized Crop Production
(2007-03-05) Owen, James Stetter Jr.; Ted E. Bilderback, Committee Co-Chair; D. Keith Cassel, Committee Member; Dean L. Hesterberg, Committee Member; Stuart L. Warren, Committee Co-Chair
Current management practices in containerized crop production maximize plant growth by supplying adequate or excess nutrient and water inputs. In the United States, nursery production input use efficiency remains ≤ 50%, in part, because of the inert softwood bark used as a primary component of soilless substrate. One technique to increase input use efficiency would be to engineer a substrate that increases nutrient and water buffering capacity of the substrate. Clay may be such a component. Clay has been used in the past to generically describe an inorganic mineral aggregate to amend a peat- or bark-based soilless substrate that increased water and nutrient buffering capacity. Industrial mineral aggregates with various chemical composition, aggregate size, mineralogy, and temperature pretreatment have been used effectively as chemical absorbents, fertilizer carriers, or barrier clays to contain heavy metals. Experiments herein were conducted to determine which physical and chemical attributes of industrial mineral aggregate could increase input use efficiency in containerized crop production and at what amendment rate plant growth and water and nutrient use efficiency are maximized. Field experiments were conducted using Cotoneaster dammeri C.K. Schneid. "Skogholm" as an indicator plant for growth, net photosynthesis (P[subscript n]), stomatal conductance (g[subscript s]), and mineral nutrient content. Plant were potted into 14 L containers in a pine bark based (PB) substrate with known physical properties and grown for approximately 120 days in 2002, 2003, and 2004 on outdoor facilities in Raleigh, NC that allowed for collection of effluent and influent, which was used to calculate a water budget. In the laboratory, effluent NO₃-N, NH₄-N and dissolved reactive P (DRP) were quantified to determine effluent daily concentration and cumulative content which allowed for calculation of nutrient budgets. In 2002, a bentonite palygorskite industrial amendment with contrasting particle size and temperature pretreatment was evaluated for its effect on growth, and water and nutrient use efficiency. Substrate amended with a low volatile material (LVM) amended substrate leached 35% less dissolved reactive P (DRP) than the regular volatile aggregate amended substrate. In addition, a 0.25 to 0.85 mm aggregate amended substrate required 11 L less water applied per container when compared to 0.85 to 4.75 mm aggregate amended substrate. In 2003, 0% to 20% (by vol.) rate of the 0.25 to 0.85 mm LVM palygorskite bentonite mineral aggregate were compared. Plant growth and P[subscript n] increased curvilinearly and linearly with the maximum occurring at 12% and 11%, respectively. Container capacity and available water (AW) increased linearly with increasing amendment rate, whereas, unavailable water and air space decreased linearly with increasing rate of mineral aggregate. Water use efficiency of productivity and g[subscript s] was maximized at 11% clay amendment rate. Plant elemental nutrient content of P, K, Ca, and Mg increased when PB was amended with clay. In 2004, cotoneaster was grown in PB amended with 11% (by vol.) sand or 0.25 to 0.85 mm LVM palygorskite bentonite clay mineral aggregate. The PB amended with sand is representative of a typical industry substrate. Treatments included a leaching fraction (LF) of 0.1 or 0.2 and P fertilization rate of 1.0x or 0.5x. Pine bark amended with 11% (by vol.) clay increased AW 4% when compared to sand amendment. Water use efficiency and plant growth increased if PB was amended with clay rather than sand. Plant content of all macro-nutrients, with the exception of N, increased when PB was amended with clay versus sand. Reduction of LF from 0.2 to 0.1 decreased effluent DRP concentration and content 8% and 64%, respectively. A PB substrate amended with 11% (by vol.) 0.25 to 0.85 mm LVM palygorksite-bentonite clay mineral aggregate can grow an equivalent plant with half of the water and P inputs.
Physiological Responses of Selected Taxa of Salvia, Taxus, Cephalotaxus, and Syringa to Heat and/or Flooding
(2004-05-31) Lasseigne, Francis Todd; Thomas G. Ranney, Committee Member; Frank A. Blazich, Committee Co-Chair; Stuart L. Warren, Committee Co-Chair; Udo Blum, Committee Member
High-temperature stress impacts plant growth in warm-temperate climates. Landscape plants are subjected to extreme conditions in urban environments, due to reflected light and retained heat from brick and concrete. Two experiments were conducted to ascertain heat tolerance across a range of Salvia L. taxa. In the first study, Salvia chamaedryoides Cav., S. greggii A. Gray 'Furman's Red', S. guaranitica St.-Hil. ex Benth., S. leucantha Cav., S. nemorosa L. 'Ostfriesland', S. pratensis L., S. splendens Sell. ex Roem. & Schult., and S. x sylvestris L. 'Mainacht' were grown under 15-hour days of 20, 25, 30, 35, or 40 °C and 9-hour nights of 15 or 25 °C. American taxa performed poorly — S. chamaedryoides, S. greggii 'Furman's Red', S. guaranitica, S. leucantha, and S. splendens — exhibiting chlorosis and growth distortions at 35 and 40 °C. European taxa, S. nemorosa 'Ostfriesland', S. pratensis, S. x sylvestris 'Mainacht', maintained shoot and root dry weights at 35 and 40 °C and exhibited lesser physical symptoms. The second study demonstrated that S. x sylvestris 'Mainacht' and S. nemorosa 'Pusztaflamme' were better able to maintain net photosynthetic rates (P[subscript n]) at 35 and 40 °C than S. guaranitica and S. leucantha. In regions with hot, humid climates, plant growth is limited by tolerance of root systems to hot, wet conditions in poorly drained soils. A third study measured flood and heat tolerance of Taxus canadensis Marsh., T. x media Rehd. 'Brownii', T. x media 'Densiformis', T. x media 'Tauntonii', T. wallichiana Zucc. var. chinensis (Pilg.) Florin, and Cephalotaxus harringtonia (Knight ex Forbes) K. Koch 'Prostrata'. Despite anecdotal evidence that Taxus are intolerant of heat and poor soil drainage, cultivars of T. x media, especially 'Densiformis', survived a 30-day flood and grew better than other taxa at 30/26 °C. In a fourth study, Syringa x hyacinthiflora (Lemoine) Rehd. 'California Rose', S. x persica L., and S. vulgaris L. were subjected to flooding at 16-hour days/8-hour nights of 25/20, 30/25, or 35/30 °C. No plants survived a 10-day flood. Both S. x persica and S. x hyacinthiflora 'California Rose' exhibited greater growth and higher P[subscript n] rates at day temperatures up to 35 °C, compared to S. vulgaris.
The Physiology of Landscape Establishment of Kalmia latifolia
(2002-05-10) Wright, Amy Noelle; Stuart L. Warren, Committee Co-Chair; Frank A. Blazich, Committee Co-Chair; Thomas G. Ranney, Committee Member; Udo Blum, Committee Member
Although native to the eastern United States, with a broad geographic range, mountain laurel (Kalmia latifolia L.) frequently does not survive transplanting from containers into the landscape and is generally regarded as a difficult-to-transplant species. In an effort to understand poor transplant success and to improve landscape establishment of the species, four experiments were conducted to describe some of the critical factors associated with transplanting mountain laurel. In some cases, research included comparison of mountain laurel to that of an easy-to-transplant species, Japanese holly (Ilex crenata Thunb.). In the first study, root growth of mountain laurel was compared to that of Japanese holly over the course of 1 year. Root length and root surface area of mountain laurel increased in the fall but decreased in the spring, while root length and root surface area of Japanese holly increased linearly throughout the year. Root : shoot ratio increased linearly for Japanese holly but did not increase during the spring for mountain laurel. The second study compared the effects of root-zone temperature on root growth of mountain laurel and Japanese holly. When mountain laurel and Japanese holly were grown hydroponically in the fall and the spring at 9 hour days/15 hour nights of 26/22C with root-zone temperatures of 16, 24, or 32C, percent increase in root length and root surface area were highest at 16C for mountain laurel and 24C for Japanese holly. At each root-zone temperature, percent survival was higher for Japanese holly than mountain laurel. More root growth occurred in the fall than in the spring for both species. Root : shoot ratio of mountain laurel was higher in the fall than in the spring, whereas root : shoot ratio of Japanese holly was similar for both seasons. A third investigation compared drought tolerance of mountain laurel to that of Japanese holly. In response to several drought treatments, shoot dry weight decreased more rapidly with increasing drought stress for mountain laurel than Japanese holly. Pre-dawn plant water potential decreased faster for mountain laurel than Japanese holly. Although both species appeared to osmotically adjust, mountain laurel was less drought tolerant than Japanese holly. Osmotic adjustment occurred only in more severely stressed plants. The fourth experiment investigated the influence of root : shoot ratio on survival and subsequent growth of transplanted, container-grown mountain laurel. Landscape exposure and initial root : shoot ratio of transplanted mountain laurel influenced plant survival and growth over three growing seasons. Shoot growth (stems and leaves) and visual quality were highest for plants with largest initial root : shoot ratio. In general, plant growth, survival, and visual ratings were higher on north and east exposures than on south and west exposures.
Propagation by Stem Cuttings and Nitrogen Nutrition of Eastern Redbud (Cercis canadensis)
(2008-05-28) Wooldridge, John Michael; Frank A. Blazich, Committee Co-Chair; Stuart L. Warren, Committee Co-Chair; Barry Goldfarb, Committee Member; Dennis J. Werner, Committee Member