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  • Author or Editor: David R. Sandrock x
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Salt tolerance of landscape plants is important to ornamental growers as well as residents and landscapers in coastal communities. Damage to ornamental plants from salt spray can be prevented by evaluating and selecting plants that exhibit tolerance to aerosol salts. Ornamental grasses are frequently recommended for low-maintenance landscape situations and may be candidates for coastal plantings once they are evaluated for their salt spray tolerance. The objective of this study was to determine the salt spray tolerance of Miscanthus sinensis `Gracillimus' and Pennisetum setaceum `Hamelin'. The experiment was conducted for 90 days from 7 July to 5 Oct. 2005 in a polyethylene greenhouse in Gainesville, Fla. Plants were subjected to four treatments (100% seawater, 50% seawater, 25% seawater, or 100% deionized water) applied by spraying each plant to runoff three times per week. Plant heights, flower number, and aesthetic ratings were recorded biweekly for the duration of the experiment. Root and shoot dry weights were determined at the initiation and completion of the study. Significant growth rate differences were found between treatments. Growth rates of plants treated with 100% seawater were significantly lower than the control and other seawater concentrations. Root and shoot dry weights of the plants treated with 100% seawater were significantly lower than the other treatments. In addition, significant differences were found between the 100% seawater treatment, the 25% seawater treatment, and the control in the aesthetic ratings of plants at the end of the study.

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Horticulture graduates entering the landscape industry will be faced with a multitude of complicated management decisions where they will need to integrate their understanding of plant science, site constraints, state and federal environmental regulations, and the human impact on the built landscape. To help students develop and refine their problem-solving skills, an interactive online case study was created. The case study was used in two different landscape horticulture courses at Iowa State University and Oregon State University. The case study centers on a residential backyard with eight landscape problem scenarios. Each scenario is identified on the clickable landscape map of the area and contains links to audio files, PDF documents, images, and Internet links. After investigating each scenario, students submit an analysis, diagnosis, and recommendation about the landscape problem via WebCT or Blackboard, depending on the institution. Student evaluation of the case study as a teaching tool was positive (3.5, where 1 = poor; 5 = excellent). Students answered additional questions using a scale where 1 = strongly disagree and 5 = strongly agree. As a result of using this teaching tool, students felt that they were able to summarize the data (3.9), diagnose the landscape problem (3.9), and make a recommendation to the homeowner (3.6). Further, they felt this teaching tool was an effective way to deliver information (3.9); the interactive format aided their learning (3.7); that they were comfortable using a web-based format (4.2); and they liked learning using case studies (4.1). Our goal is to make the case-study framework available to other teaching colleagues who can then add their own data.

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Nitrogen (N) management in container nurseries is part of a complex system. Working within this system, nursery owners, managers and employees routinely make N management decisions that have consequences for the immediate nursery environment (e.g., plant growth, yield, disease susceptibility, water quality) as well as areas beyond nursery boundaries (e.g., surface and groundwater quality, public perception). Research approaches often address parts of the system associated with the immediate nursery environment and purpose. As a result, best management practices that contribute to greater N use efficiency have been developed. Research approaches that consider the whole system reveal novel relationships and patterns that identify areas for future research and may direct future management decisions. To investigate N management from a whole system perspective, a group of nursery managers from Oregon and scientists from Oregon State University met three times between 2001 and 2003. Growers drew their N management systems and identified components, relationships and feedback loops using an ActionGram technique. From this information, researchers developed Group-based On-site Active Learning (GOAL). GOAL combines Action-Grams and the Adaptive Cycle at container nursery sites. In this case, N flow and management in container production systems served as the topic of active learning. Managers and employees from four wholesale container nurseries evaluated the GOAL exercise. After completing GOAL, 94% of participants indicated that they learned a new idea or concept about N cycling in their container nursery. Of those, 100% gained new ideas and concepts from peers and colleagues present at the meeting. In addition, 60% gained new ideas and concepts from researchers and 60% developed their own ideas and concepts. GOAL is a learning tool that provides a simple, convenient, interactive format for investigating complex systems.

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Two approaches for estimating the amount of nitrogen (N) in plant tissues derived from labeled fertilizer were evaluated for two tissue types (root and shoot) in three different genera. In the first, atom percentage values obtained by mass spectrometry were converted to the portion of N derived from the fertilizer (NDFF). In the second, the slope of the regression line for the relationship between total N and labeled fertilizer N was used to represent the incremental increase in fertilizer N for each unit increase in total N. These two approaches were applied to data collected during container experiments. Unless a plot of total N versus labeled fertilizer N passes through the origin, conventional ratio-based estimates of the amount of NDFF for plants or tissues are often misleading. When nonzero intercepts occur, NDFF is dependent on the size (total N content) of the tissue or plant. Nonzero intercepts were frequently encountered. An analysis of regression lines describing the relationship between total N gain and fertilizer N produces a different interpretation than evaluations of the NDFF for treatment means. When an analysis of covariance was used to account for differences in total N between tissues and genera, results were generally consistent with the graphical observations and regression analysis. If only ratio-based approaches are used, it is difficult to determine if there are real physiological differences among treatments, genera, and tissues or if differences in NDFF are size-related. Because the data easily can be analyzed several ways, simultaneously evaluating data with ratio-based NDFF, covariates, and regression is appropriate.

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Water use is the most important environmental issue facing the horticulture industry. As a result, many water management districts are recommending native plants for their putative low-water requirements. Numerous textbooks and trade journals claim native plants use less water than non-natives; however, previous research found no difference in water use efficiency in the field between native and non-native species. Furthermore, recommendations of ornamental grasses for use as low-maintenance and low-water-requiring landscape plants have recently escalated. This study evaluated non-native Miscanthus sinensis `Adagio' and the native Eragrostis spectabilis for irrigation requirements and drought response in a landscape setting. To simulate maximum stress, both species were planted into field plots in an open-sided, clear polyethylene covered shelter. Each species was irrigated on alternating days at 0, 0.25, 0.5, or 0.75 L for a 90-day period. Growth index and height were recorded at biweekly intervals, and final shoot and root dry masses were taken at completion of the study. Significant treatment and species effects were found for height, growth index, shoot dry weight, and biomass. Plants receiving 0.75 L of irrigation had the greatest growth, and non-irrigated plants grew significantly less. Comparisons between species found growth was greatest among Eragrostis spectabilis plants for all parameters.

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Fifty-four taxa of Atlantic white cedar [Chamaecyparis thyoides (L.) B.S.P.] were assembled and maintained. A protocol for propagation of Atlantic white cedar was established. Plants were grown in containers and in a replicated field plot. Height and width data were recorded from container- and field-grown plants and all taxa were evaluated for growth habit, growth rate, and summer and winter color. Color descriptions of foliage are provided based on the Royal Horticultural Society colour chart. Exceptional taxa were identified based on needle color, texture, growth habit, and growth rate. Superior green forms include Dirr Seedlings 1 and 2, `Emily', `Rachel', and `Okefenokee'. The superior variegated form is `Webb Gold'. Superior blue forms include `Blue Sport', `Glauca Pendula', and `Twombly Blue', and superior slow-growing forms include `Andelyensis', `Meth Dwarf', `Red Star', and `Heatherbun'. These taxa are recommended to growers, landscapers, and gardeners for production and use.

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Five taxa of Atlantic white cedar [Chamaecyparis thyoides (L.) B.S.P.], `Blue Sport', `Okefenokee', Raulston Form, `Emily', and `Rachel', and one cultivar of Leyland cypress [×Cupressocyparis leylandii (Jacks. and Dallim.) Dallim.], `Haggerston Grey', were screened for resistance to Botryosphaeria and Seiridium cankers. Treatments consisted of Seiridium unicorne (Cke. And Ell.) Sutton, Botryodiplodia Sacc. sp., Fusicoccum Corda. sp. and the non-inoculated control. After 8 weeks, plants were measured for change in caliper at the wound site, change in plant height, and length and width of surface and interior cankers. Seiridium and Botryosphaeria canker development on Atlantic white cedar taxa was not significantly different than that on Leyland cypress. Seiridium unicorne was more pathogenic than Botryodiplodia sp. and Fusicoccum sp. on Atlantic white cedar and Leyland cypress with infection percentages of 100%, 84%, and 80%, respectively. Well-defined, sunken, resinous cankers developed on Leyland cypress plants infected with Seiridium unicorne, whereas Atlantic white cedar showed no visible surface canker.

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Nitrogen accumulation patterns were established for Weigela florida (Bunge.) A. DC. `Red Prince' (fast growth rate) and Euonymus alatus (Thunb.) Sieb. `Compactus' (slow growth rate). From these, daily and biweekly N delivery schedules were designed to match N supply with N accumulation patterns of each taxon. Delivery schedules were sliding scales in that total N applied was controlled by independent increases (or decreases) of N concentration and solution volume. Daily and biweekly N delivery schedules were tested against a constant N rate (200 mg·L-1) and Osmocote 18N-2.6P-9.9K (The Scotts Co., Marysville, Ohio). Plants were grown in 3.8-L containers in 7 douglas fir bark: 2 sphagnum peatmoss: 1 silica sand (0.65 mm; by volume) outdoors in full sun on a gravel pad for 142 d. Within each taxon, Weigela and Euonymus grown with sliding-scale N fertilization schedules had similar total dry weights, leaf areas, and total plant N contents to plants grown with a constant N rate (200 mg·L-1) or Osmocote 18N-2.6P-9.9K. Sliding-scale liquid fertilization based on plant N requirements introduced less total N to the production cycle and resulted in higher N uptake efficiency than fertilization with a constant N rate of 200 mg·L-1. In general, liquid N fertilizer treatments resulted in plants with higher shoot to root ratios than plants treated with Osmocote 18N-2.6P-9.9K. Weigela and Euonymus treated with biweekly schedules were similar to plants treated with daily schedules (same total amount of N delivered with each treatment).

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Cornus sericea L., Weigela florida (Bunge) A. DC., and Euonymus alatus (Thunb.) Sieb were grown outside in 3.8-L plastic containers for 345 days (1 Apr. 2001 to 11 Mar. 2002). Nitrogen (N) was applied at rates (NAR) of 25, 50, 100, 200, and 300 mg·L–1 and delivered as aqueous double-labeled 15N depleted NH4NO3 (min 99.95% atom 14N). In all species, root, shoot, and total plant dry weight increased with increasing NARs while root to shoot ratios decreased. Similarly, root, shoot, and total plant N increased with NAR for each species, and at each NAR more N was stored in the roots than in the shoots. Estimation of fertilizer N uptake determined by the total N method was higher for all species and at each NAR than estimation of N uptake determined by the fertilizer 15N tracer method. Fertilizer N uptake efficiency determined by the total N method was highest at 25 mg·L–1 and decreased as NARs increased. In contrast fertilizer N uptake efficiency determined by the fertilizer 15N tracer method was lowest at 25 mg·L–1 and increased or remained relatively constant as NARs increased. Differences in N uptake and N uptake efficiency can be attributed to overestimation by the total N method due to the inclusion of nonfertilizer N and underestimation by the fertilizer 15N tracer method due to pool substitution. Corrected N uptake efficiency values can be calculated by adjusting the original data (total N or 15N uptake) by the distance between the origin and the y intercept of the regression line representing the data.

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Accurate methods for determining the fate and recovery of nitrogen (N) fertilizer applied to container-grown nursery crops are essential to comply with regulations and develop innovative fertilizer programs. The objectives of this study were (i) to use 15N techniques to determine the fate of fertilizer N, (ii) to compare nonisotopic and isotopic methods of determining N recovery, and (iii) to determine the relative importance of fertilizer and non-fertilizer N at rates of 25, 50, 100, 200, and 300 mg·L-1 in container-grown Euonymus alatus (Thunb.) Sieb., Cornus sericea L., and Weigela florida (Bunge) A. DC. In all species, root and shoot N increased with N rate, and at each rate more N was stored in the roots than in the shoots. Estimation of N recovery determined by the total N method (Kjeldahl N/applied N) was significantly higher for all species and at each N rate than estimation of N recovery determined by the labeled fertilizer N method (labeled N/total applied N). Increasing fertilizer rates up to 100 mg·L-1 resulted in increased uptake of N derived from other sources (NDFO). NDFO at low N concentrations was a significant portion of the total N in the plant. As a result, the difference in estimation of percent N recovery between each method was larger at lower N concentrations for all species. The nonisotopic total N method produces higher fertilizer N uptake estimates, as much as three to four times the isotopic based estimates, in container-grown plants at N concentrations of 25 mg·L-1. Actual fertilizer N loss increases dramatically from 25 to 300 mg·L-1 (due to dramatic increases in N applied), despite small gains in fertilizer N recovery efficiency.

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