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  • Author or Editor: Roger Kjelgren x
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As populations become increasingly urbanized, landscape water conservation becomes more important. Landscape water consumption can increase municipal water use up to 4-fold during the growing season, and account for half the total yearly water use. Landscape water conservation is important in decreasing peak summer water demand to reduce the strain on delivery systems, and to reduce total demand so that development of new sources can be forestalled. Potential water savings from existing landscapes can be estimated by comparing historical usage gleaned from water meter readings to plant water needs estimated from reference evapotranspiration. Estimating water needs for turf is straightforward because of the few species involved and the uniformity of turf landscapes. Estimating water needs of woody plants is more difficult because of the heterogeneity of woody plants and how they are used, and woody plants respond to evaporative demand differently than turfgrass. Many woody plants will actually use less water as reference evapotranspiration increases due to stomatal closure induced by high leaf-air vapor pressure gradients. Landscape water is then conserved by either applying water more effectively in scheduling when and how long to irrigate based on estimating water use again from reference evapotranspiration, or by replacing areas in turfgrass with plants more-adapted to the existing conditions. Encouraging water conservation by end users is the final and largest challenge. Automated irrigation systems makes wasting water easy, while conserving water takes more effort. Education is the key to successful landscape water conservation.

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Technology allows educators to convey information be conveyed 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 bring into digital form oneself and what to draw from elsewhere. Pieces 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 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, drawing, animations, video footage with text. Lectures can then be outputted to videotape or broadcast via over 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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We investigated growth and water relations of London plane and corkscrew willow irrigated at 80% and 0% replacement of potential evapotranspiration (ETo). In Spring 1991, whips were planted in a randomized complete-block design in a silt loam soil that was clean-cultivated through two seasons. In 1992, tree response was measured in water relations [water potential (ψ)] at predawn and midday and dawn-to-dusk stomatal conductance (gs), trunk growth, and total leaf area. Soil-water depletion was monitored with a neutron probe. Measured ETo was 98.6 mm, and actual water applied based on final leaf area was 92% and 38% of ETo for plane trees and willows, respectively. Nonirrigated trees received 4% of ETo from rain. Soil water content at the 0.90-m depth was lower in the 0% ETo treatment. There were, however, no differences in predawn ψ through the season. Plane trees had consistently higher dawn-to-dusk gs than the willows, but there were no differences in gs or midday ψ between irrigation treatments for either species. Despite lower gs, willows had greater total leaf area and trunk growth than the plane trees, but again, there were no differences among irrigation treatments. Lack of detectable water-stress effects suggests that, in the absence of competition from other species, an expanding perimeter of root growth explored new soil and allowed nonirrigated trees to exploit soil water ahead of moisture depletion within the root zone.

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In 1992 and 1993, we taught the course “Landscape Management in the Interior West” by satellite in four states in the mountain west. The broadcast originated from an on-campus studio without students present, but with a two-way audio link. About one-third of the students viewed the course for credit and were located both on and off campus, while the remainder were not on campus and took the course for personal knowledge. In 1992, the course was broadcast live, but in 1993 it was restructured in a modular format and videotaped before broadcast. In 1994, videotapes from the previous year were used to offer the course on a semi-independent study basis on the Utah State Univ. campus. Videotaping the course in discrete content modules substantially improved the quality of the course by eliminating production problems and creating better content flow. The videotapes in turn provided a readily usable off-the-shelf course. Student response, however, varied with location and degree of involvement. On-campus students were critical of a perceived lack of face-to-face contact with faculty. Positive responses came from viewers in remote locations where access to college-level courses is otherwise limited. Distance education through studio-produced, videotaped lectures provides a visually engaging format that is easily disseminated. Such courses will less likely succeed on client campuses, however, unless there is an onsite individual mediating between the tapes and students.

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Limited root development of nursery stock in root-control bags facilitates harvest but without irrigation may predispose stock to water stress. The effect of bags and irrigation on growth and water relations of field-grown Malus sieboldii var. zumi were investigated following transplanting as large liners into a silty-clay soil. Predawn leaf water potential (ψ), and midday stomatal conductance (gs) and ψ, were measured periodically through the season. Late-season osmotic potential (ψπ), caliper, leaf area, and root growth were also measured. Non-irrigated treatments exhibited water stress during an extended mid-summer drought, as predawn ψ and particularly gs were less than irrigated treatments, resulting in lower vegetative growth and ψπ. For combined bagged treatments water relations did not differ, but leaf area, root growth, and ψπ, but not caliper, were less than non-bagged trees. Growth measurements and ψπ of non-irrigated bagged trees, however, were consistently lower but nonsignificant than the other treatments. Bag-induced root reduction can limit some top growth even with optimum soil water. Moreover, in terms of potential Type-II errors extrapolated over a conventional production cycle, trees grown in root-control bags in normally non-irrigated soils may be more susceptible to water stress and subjected to further cumulative growth limitation.

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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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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

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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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Growth of woody landscape plants is strongly affected by the underlying surface. In urban areas, plants are subjected to energy balance characteristics of a variety of surfaces. This research investigated energy balance properties of six common urban surfaces: Kentucky bluegrass, pine bark mulch, concrete, asphalt, lava rock mulch, and gravel rock mulch. Each summer over a 2-year period incoming global radiation (GW), relative humidity, and air temperature were measured over each surface, and surface reflectivity (AW), surface temperature (TS), soil temperature (TO), and soil heat flux (SF) were measured below each surface. Thermal conductivity (K) and emitted surface longwave radiation (LW) were also calculated. Surface property differences were determined by regression analysis. Incoming global radiation (independent variable) versus TS, TO, SF, LW data (dependent variable) were analyzed. Linear or quadratic curves were selected according to significance of each variable and the coefficient of determination (R2). Surface reflectivity was greatest for concrete and least for lava rock mulch, and K was greatest for asphalt and concrete and least for lava rock and pine bark mulch. Under maximum GW, regression data indicate that SF and TO would be greatest under asphalt and least under lava rock and pine bark mulch. Under similar circumstances, TS and LW would be greatest for pine bark mulch and least for Kentucky bluegrass. This research revealed that more energy was conducted into the soil below asphalt and concrete, and that a greater portion of GW was prevented from entering the soil below pine bark and lava rock mulch than below other surfaces. Due to these effects, and the lack of evaporative cooling, surface temperatures were greater, and more longwave radiation was emitted from, non-vegetative surfaces than from turf.

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