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John M. Ruter and Dewayne L. Ingram

Plants of `Rotundifolia' holly (Ilex crenata Thunb.) were grown for 3 weeks with root zones at 30,34,38, or 42C for 6 hours daily to evaluate the effects of supraoptimal root-zone temperatures on various photosynthetic processes. After 3 weeks, photosynthesis of plants grown with root zones at 38 or 42C was below that of plants grown at 30 or 34C. Chlorophyll and carotenoid levels decreased while leaf soluble protein levels increased as root-zone temperature increased. Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) activity per unit protein and per unit chlorophyll responded quadratically, while RuBisCO activity per unit fresh weight increased linearly in response to increasing root-zone temperature. Results of this study suggest that `Rotundifolia' holly was capable of altering metabolism or redistributing available assimilates to maintain CO2 assimilation rates in response to increasing root-zone temperatures.

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Chris A. Martin and Dewayne L. Ingram

A three-dimensional computer model was developed to simulate numerically the thermal environment of a polyethylene container-root medium system. An energy balance was calculated at the exterior container wall and the root medium top surface. Thermal energy exchanges at the system's boundaries were a function of radiation, convection, evaporation, and conduction energy flaxes. A forward finite difference form of a transient heat. conduction equation was used to calculate rates of temperature changes as a result of thermal energy exchanges at the system's boundaries. The χ2“goodness-to-fit” test was used to validate computer-generated values to actual measured temperature data. Probabilities for the null hypothesis of no association ranged from P = 0.45 (Julian day 271), to P = 0.81 (Julian day 190), with P ≥ 0.70 on nine of 10 validation days in 1989. Relative to net radiation and convection, conduction and evaporation had little effect on thermal energy exchanges at the root medium top surface during sunlight hours. The rate of movement of thermal energy (thermal diffusivity) was slower and generally resulted in lower temperatures in a pine bark medium than in a pine bark medium supplemented with sand when volumetric water content (VMC) ranged from 0.25 to 0.45.

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Susmitha S. Nambuthiri and Dewayne L. Ingram

The demand for groundcover plants for landscape use is increasing. Plantable containers are becoming available in sizes appropriate for groundcover plants. Landscapers are seeking ways to decrease the time required to prepare and plant groundcover beds. Studies were conducted in 2011 and 2012 to evaluate plantable containers for a variety of groundcover plants. The study has shown that ‘Bronze Beauty’ ajuga (Ajuga reptans), ‘Herman’s Pride’ lamiastrum (Lamiastrum galeobdolon), ‘Beacon Silver’ lamium (Lamium maculatum), ‘Immergrunchen sedum (Sedum hybridum), ‘Red Carpet Stonecrop’ sedum (Sedum spurium), and ‘Vera Jameson’ sedum (Sedum telephium) were grown to a marketable size from 1.5-inch plugs in 8 weeks in Lexington, KY, when transplanted in May through August. ‘Big Blue’ liriope (Liriope muscari) from bare root bibs required 12 weeks. Plant growth in a 90-mm paper container and 80-mm bioplastic container was similar to that of plants grown in standard 3-inch rigid plastic containers and required 20% less time to transplant into the landscape and grew rapidly after transplanting in the field. Peat containers in this production system yielded smaller plants and slower ground coverage after transplanting in the field than plants grown in the other containers.

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John M. Ruter and Dewayne L. Ingram

Respiration of excised Ilex crenata (Thunb.) `Rotundifolia' roots as influenced by root-zone growth temperature and buffer solution temperature was measured in the presence and absence of salicylhydroxamic acid (SHAM) and potassium cyanide (KCN). Respiration rates of roots excised from plants grown for 3 weeks with root-zones at 30, 34, 38, or 42C decreased linearly with increased root-zone growth temperatures when the buffer solution was maintained at 25C. When the buffer solution was the same temperature as the root growth temperature, respiration rates were similar. Respiration in roots from plants grown with the root zone at 30C was maximal with the buffer solution at 34C and decreased to a minimum at 46C. Above 46C, a presumably extra-mitochondrial stimulation of O2 consumption occurred. The activity of the CN-resistant pathway was fully engaged (P' = 0.99) when roots were grown at 30C and buffer solution was at 25C (30-25). CN-resistant pathway activity decreased with `the buffer solution at 46C.

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William J. Foster, Dewayne L. Ingram, and Terril A. Nell

Rooted stem cuttings of Ilex crenata Thunb. `Rotundifolia' were grown in a controlled-environment growth chamber. Root-zone temperatures were controlled with an electric system. Shoot carbon exchange and root respiration rates were determined in response to root-zone temperatures of 28, 32, 36, and 40C for 6 hour·day–1 for 7 days. Photosynthesis was decreased by root zones ≥ 32C, while root respiration increased with increasing root-zone temperature. Decreased photosynthetic rates were not due to increased stomatal resistance.

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Thomas H. Yeager, Rebecca H. Harrison, and Dewayne L. Ingram

Ilex crenata Thunb. `Rotundifolia' grown in sand culture with the root zone at 40C for 6 hours daily had smaller root and shoot dry weights after 6 weeks than plants grown with root zones at 28 or 34C. Root and shoot N accumulation (milligrams N per gram of dry weight) decreased when root-zone temperatures were increased from 28 to 40C and plants were fertilized twice dally with either 75, 150, or 225 mg N/liter. Nitrogen application rates of 150 or 225 mg·liter-1 resulted in increased root and shoot N accumulation for plants grown with root zones at either 28, 34, or 40C compared with the 75 mg N/liter treatment. Increased N fertilization rates did not alleviate reduced plant growth due to the high root-zone temperature.

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Chris A. Martin, Dewayne L Ingram, and Terril A. Nell

Trees were grown for 2 years as a function of three container volumes (10, 27, and 57 liter) the first year and six shifting treatments (10 liter both years, 10 to 27 liter, 10 to 57 liter, 27 liter both years, 27 to 57 liter, or 57 liter both years) the second year when containers were spaced 120 cm on center, Height and caliper were greatest for magnolias grown in 27- or 57-liter containers both years. Caliper was greater for trees shifted from 10-liter containers to the larger container volumes compared to trees grown in 10-liter containers both years, Trees grown in 10-liter containers both years tended to have few roots growing in the outer 4 cm at the eastern, southern, and western exposures in the grow medium, During the second year, high air and growth medium temperatures may have been primary limiting factors to carbon assimilation during June and August. Using large container volumes to increase carbon assimilation and tree growth may be even more important when daily maximum air temperatures are lower during late spring or early fall compared to midsummer.

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Chris A. Martin, Dewayne L Ingram, and Terril A. Nell

Trees were grown for 2 years as a function of three container volumes (10, 27, and 57 liter) the first year and six shifting treatments (10 liter both years, 10 to 27 liter, 10 to 57 liter, 27 liter both years, 27 to 57 liter, or 57 liter both years) the second year when containers were spaced 120 cm on center, Height and caliper were greatest for magnolias grown in 27- or 57-liter containers both years. Caliper was greater for trees shifted from 10-liter containers to the larger container volumes compared to trees grown in 10-liter containers both years, Trees grown in 10-liter containers both years tended to have few roots growing in the outer 4 cm at the eastern, southern, and western exposures in the grow medium, During the second year, high air and growth medium temperatures may have been primary limiting factors to carbon assimilation during June and August. Using large container volumes to increase carbon assimilation and tree growth may be even more important when daily maximum air temperatures are lower during late spring or early fall compared to midsummer.

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Dewayne L. Ingram, Charles R. Hall, and Joshua Knight

The production components of an evergreen shrub (Ilex crenata ‘Bennett’s Compacta’) grown in a no. 3 container in an east coast U.S. nursery were analyzed for their costs and contributions to carbon footprint, as well as the product impact in the landscape throughout its life cycle. A life cycle inventory was conducted of input materials, equipment use, and all cultural practices and other processes used in a model production system for this evergreen shrub. A life cycle assessment (LCA) of the model numerated the associated greenhouse gas emissions (GHG), carbon footprint, and variable cost of each component. The LCA also included the transportation and transplanting of the final product in the landscape as well as its removal after a 40-year useful life. GHG from input products and processes during the production (cutting-to-gate) of the evergreen shrub were estimated to be 2.918 kg CO2e. When considering carbon sequestration during production weighted over a 100-year assessment period, the carbon footprint for this model system at the nursery gate was 2.144 kg CO2e. Operations, combining the impact of material and equipment use, that contributed most of GHG during production included fertilization (0.707 kg CO2e), the liner and transplanting (0.461 kg CO2e), the container (0.468 kg CO2e), gravel and ground cloth installation (0.222 kg CO2e), substrate materials and preparation (0.227 kg CO2e), and weed control (0.122 kg CO2e). The major contributors to global warming potential (GWP) were also major contributors to the cutting-to-gate variable costs ($3.224) except for processes that required significant labor investments. Transporting the shrub to the landscaper, transporting it to the landscape site, and transplanting it would result in GHG of 0.376, 0.458, and 0 kg CO2e, respectively. Variable costs for postharvest activities were $6.409 and were dominated by labor costs (90%).

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Dewayne L. Ingram, Charles R. Hall, and Joshua Knight

The components for two production systems for young foliage plants in 72-count propagation trays were analyzed using life cycle assessment (LCA) procedures. The systems differed by greenhouse type, bench size and arrangement, rainwater capture, and irrigation/fertilization methods. System A was modeled as a gutter-connected, rounded-arch greenhouse without a ridge vent and covered with double-layer polyethylene, and the plants were fertigated through sprinklers on stationary benches. System B was modeled as a more modern gutter-connected, Dutch-style greenhouse using natural ventilation, and moveable, ebb-flood production tables. Inventories of input products, equipment use, and labor were generated from the protocols for those scenarios and a LCA was conducted to determine impacts on the respective greenhouse gas emissions (GHG) and the subsequent carbon footprint (CF) of foliage plants at the farm gate. CF is expressed in global warming potential for a 100-year period (GWP) in units of kilograms of carbon dioxide equivalents (kg CO2e). The GWP of the 72-count trays were calculated as 4.225 and 2.276 kg CO2e with variable costs of $25.251 and $24.857 for trays of foliage plants grown using Systems A and B, respectively. The GWP of most inputs and processes were similar between the two systems. Generally, the more modern greenhouse in System B was more efficient in terms of space use for production, heating and cooling, fertilization, and water use. While overhead costs were not measured, these differences in efficiency would also help to offset any increases in overhead costs per square foot associated with higher-cost, more modern greenhouse facilities. Thus, growers should consider the gains in efficiency and their influences on CF, variable costs (and overhead costs) when making future decisions regarding investment in greenhouse structures.