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Roger Kjelgren

Growth and water relations of Kentucky coffee tree [Gymnocladus dioica (L.) K. Koch] whips in translucent tubelike shelters were investigated. In a container study, 1.2-m-high shelters were placed over whips following transplanting, then diurnal microclimate, water relations, and water use were measured. Shelter air temperature and vapor pressure were substantially higher, and solar radiation was 70% lower, than ambient conditions. Sheltered trees responded with nearly three-times higher stomatrd conductance than nonsheltered trees. However, due to substantially lower boundary layer conductance created by the shelter, normalized water use was 40910 lower. In a second experiment, same-sized shelters were placed on whips following spring transplanting in the field. Predawn and midday leaf water potentials and midday stomatal conductance (g,) were monitored periodically through the season, and growth was measured in late summer. Midday gs was also much higher in field-grown trees with shelters than in those without. Sheltered trees in the field had four times greater terminal shoot elongation but 40% less stem diameter growth. Attenuated radiation in the shelters and lower specific leaf area of sheltered trees indicated shade acclimation. Shelters can improve height and reduce water loss during establishment in a field nursery, but they do not allow for sufficient trunk growth.

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Roger Kjelgren

I investigated perceptions of Agricultural Experiment Station (AES)-supported faculty and administrators regarding faculty involvement in placing AES-supported research on the World Wide Web (Web). Four populations were surveyed with a Web-based survey: all AES-supported faculty at Utah State University; AES-supported faculty in distinct horticulture departments at land-grant universities; AES state directors; and department heads/chairs in AES-supported horticulture departments. The survey queried the merits of placing research results on the Web and the degree of institutional support and actual faculty involvement in this process. All four groups agreed that placing AES-supported research results online was important and that faculty will need to become more conversant with the Web to do so. Overall, department heads were the least supportive of faculty involvement with placing research findings on the Web, and faculty were ambivalent regarding whether it interfered with other work. Most respondents reported little in the way of institutional support, policies, and mechanisms to help faculty get research online. About one-third of both faculty groups were able to balance an online AES-supported research presence with existing duties, and interest in doing so was high in the rest. Developing an online research presence is an opportunity for AES-supported faculty to make more of their agricultural research findings available in new and interpretive way to a broader constituency, both traditional and new. Doing so will likely require leadership from state AES directors in terms of policies and technical support.

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Roger Kjelgren

Supplemental watering of shade trees in field production nurseries is needed, even in summer-rainfall climates, to achieve maximum growth. Scheduling the timing and amount of supplemental watering makes more efficient use of financial and water resources while maintaining maximum growth. Methods of scheduling supplemental watering based on uniform canopy and rooting in production agriculture must be modified, however, for shade trees in a production setting. Nursery trees are non-uniform in canopy and rooting compared to an agricultural crop. Applying the water budget method can be effective with sprinkler systems if tree water loss and rooting depth can be properly estimated. A measure of reference evapotranspiration and a species-specific multiplier are typically used to estimate water loss. Since species diversity in a field nursery is quite high, however, estimates of both tree transpiration and rooting depth must necessarily be simplified assumptions less accurate than for a uniform agricultural crop. If supplemental water is to be applied with drip irrigation, estimates of tree transpiration and soil water depletion need to be converted to volume units with information on total tree leaf area.

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Roger Kjelgren

Technology allows educators to convey information more flexibly and visually. How to access and make use of technological teaching tools is the challenge facing educators. HortBase provides the framework for educators to create and access educational chunks. How to make use of the information in HortBase in distance teaching is a three-step process. 1) Before assembling the teaching material, the educator must decide on who the target audience is and what information to convey. Audiences on campus have higher expectations of how they learn, as they are used to live teaching and guidance, and often do not have a clear idea of what they want to learn. Off-campus audiences have lower expectations and are more focused on the information they want. 2) The educator then decides how much of the information to convert into digital form individually and how much to draw from elsewhere. Pieces of digitized information can be created by scanning existing images into the computer or created on computer with authoring-illustrating programs. Once digitized, images can be manipulated to get the desired look. This is a very time-consuming step, so much effort can be saved by taking created “chunks” from HortBase. 3) Finally, what medium and tools to use must be decided. Course content can be presented with slide-show software that incorporates digitized slides, drawings, animations, and video footage with text. Lectures can then be output to videotape or broadcast over an analog rework. Alternatively, the digitized information can be incorporated into interactive packages for CD-ROM or the World Wide Web.

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Roger Kjelgren

Changes in foliage temperature with environmental conditions were investigated for use in detecting water stress and scheduling irrigations of woody nursery plants. Midday leaf-minus-air temperature (Tl-Ta) and vapor pressure deficit (VPD) were monitored seasonally for container-grown shrubs--prostrate juniper, upright juniper and dwarf red-stem dogwood--at open and closed spacings. There was an inverse relationship between Tl-Ta and VPD for all species and spacings but with substantial scatter. Slopes for openand closed-spaced shrubs were not significantly different for any species. As container moisture and predawn leaf water potential declined during a dry-down cycle Tl-Ta increased significantly over well-watered levels for open-spaced plants and closed-spaced dogwood. In a field experiment Tl-Ta and VPD were monitored in young London plane, flowering pear, and redbud with-and-without irrigation. Only irrigated London plane Tl-Ta was inversely related to VPD. Leaves coated with petroleum jelly, however, had Tl-Ta levels consistently greater than uncoated leaves in all species, and non-irrigated Tl-Ta rose to those levels during a mid-summer drought. These results suggest that irrigation of container shrubs can be timed to increases in Tl-Ta with VPD, while comparing coated and non-coated Tl-Ta may be more successful for irrigated field production.

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Roger Kjelgren

Shade acclimation response of Emerald Queen Norway maple street trees to variable urban irradiance levels was investigated. Specific leaf area, trunk growth, and crown density were measured from trees in 13 sites ranging from urban canyons in the business core to open exposures in residential areas of Seattle, Wash. Percentage of potential seasonal input of global shortwave radiation for each site was modeled based on the azimuth and elevation angles of the surrounding horizon topography. Building height in the business core reduced estimated irradiance to a range of 27% to 90% of that for an unobstructed horizon topography, while those outside the business core had 90% to 95% irradiance. As estimated potential irradiance decreased, growth of these maple street trees exhibited responses characteristic of shade acclimation in a dose-response pattern. Specific leaf area increased and trunk growth and crown density decreased to acclimated levels at -70% of potential irradiance. These acclimation responses did not degrade the function of the trees in their urban-canyon locations. Their foliage was healthy, and reduced crown density was not apparent since there were no full-sun-grown trees for comparison.

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Mike Caron and Roger Kjelgren

We investigated growth, water relations, and water use of bare root (BR) and balled-burlapped (BB) Patmore green ash following transplanting into an irrigated landscape setting in a high desert climate. Treatments were green ash harvested as larger (40 mm caliper) BB and BR trees, and smaller BR stock (25 mm caliper). During establishment, we measured canopy growth for 3 years, and for 2 years plant water relations [predawn water potential and midday stomatal conductance (g S)] and water depletion within the root zone. All treatments expressed varying degrees of isohydric responses to root loss by reducing g S that maintained water potential nearly constant, but least so for the smaller BR trees. g S was greater than that of all larger trees, meaning that for the same cost in water potential as the larger trees, BR-Small benefitted from more open stomates and presumably greater carbon gain. Greater initial conductance apparently translated into more growth. Year 1, BR-Small trees had the least total leaf area, but by Year 3 total leaf area was not different among all treatments. Also during Year 1, the ratio of water use to local reference evapotranspiration [plant factor (PF)] was 0.36 for large BR trees vs. 0.56 for BB trees, similar to the recommended PF of 0.5 for trees in dry climates. These results suggest smaller BR trees are a cheaper alternative for high desert landscapes while reaching nearly equivalent growth to BB trees after 3 years. Achieving high growth of BR trees would need careful scheduling of irrigation amount and frequency based on leaf area, root zone size, and local reference evapotranspiration.

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Roger Kjelgren and Larry Rupp

Computer technology allows horticultural educators to convey information more flexibly and visually to a greater audience. However, accessing and making use of technological teaching tools is as much a hurdle as it is an opportunity. HortBase provides the framework for educators in horticulture to easily access and contribute to quality chunks of horticultural educational by computer. Engaging computer-based instruction such as HortBase in distance or on-campus teaching is a three-step process. First, before assembling the teaching material, the educator must decide on who the target audience is and what information to convey. Audiences on campus often have higher expectations of how they want to learn, being accustomed to face-to-face instruction and guidance, but may not have a clear idea of what they want to learn. Off-campus audiences may have lower expectations but generally are more focused on the information they want. Second, the educator then must decide on how much of the information to bring into digital form oneself and what to draw from elsewhere. Chunks of digitized information can be created by scanning existing images into the computer or created on computer with drawing programs. Once digitized, images can be manipulated to achieve a desired look. This is laborious, so much effort can be saved by taking created chunks from HortBase. Finally, choose a medium for dissemination. Course content can be presented with slide-show software that incorporates digitized slides, drawing, animations, and video footage with text. Lectures can then be output to videotape or broadcast via an analog network. Alternatively, the digitized information can be incorporated into interactive packages for CD-ROM or the World Wide Web.

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Roger Kjelgren and Mike Foutch

Growth and water relations of seedlings grown in protective tree shelters were investigated during establishment in a field nursery. Shelters, 1.2 m high, were placed over 0.5 m Kentucky coffee tree seedlings following spring transplanting in a field experiment. Predawn leaf water potential (ψ) and stomatal conductance (gs) were monitored periodically through the season and growth was measured in late summer. In a second experiment diurnal microclimate, and seedling water relations and use, in the shelters were studied under controlled conditions. In the shelters, leaf and air temperature, humidity, and gs exceeded non-sheltered levels while solar radiation was 70% lower. Despite greater gs, normalized water use was 40% lower in the sheltered trees. While midday gs was similarly high in the field-grown trees, no differences in predawn ψ were detected through the season. Sheltered trees in the field had four times more shoot growth but 40% less caliper growth. Sheltered trees had leaf thickness lower than control trees, and together with the growth and radiation pattern, indicated that they were shade acclimated. Shelters can improve height growth and reduce water loss during establishment, but may not allow sufficient trunk development or taper for upright support