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Sarah A. White

The need to protect our water resources and increasing public awareness of the importance of cleaner water for ecological and human health reasons are driving regulations limiting nutrient release from traditionally exempt, non-point source agricultural contributors. Modification of production practices alone may not be adequate to meet regulated nutrient criterion limits for irrigation and stormwater runoff entering surface waters. Three constructed wetland technologies are well suited to help agricultural producers meet current and future regulations. The first two technologies, surface- and subsurface-flow constructed wetlands, have been in use for over 40 years to cleanse various types of wastewater, whereas floating treatment wetlands are an emerging remediation technology with potential for both stormwater and agricultural runoff treatment applications. The mechanisms driving removal of both nitrogen (N) and phosphorus (P) in constructed wetland systems are discussed. Surface-flow constructed wetlands remediate N contaminants from both container nursery and greenhouse production wastewater, whereas P remediation is variable and tied most closely to active plant growth as the constructed wetland ages. Subsurface-flow constructed wetlands effectively remediate N from production wastewater and can be tailored to increase consistency of P remediation through selection of P-sorbing root-bed substrates. Floating treatment wetlands effectively remediate both N and P with a designed surface area of a pond covered depending on the target effluent concentration or regulated total maximum daily load. The choice of treatment technology applied by growers to meet regulated water quality targets should be based on both economic and site-specific considerations.

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Youping Sun, Sarah A. White, David Mann and Jeffrey Adelberg

Veratrum californicum, a native of the western United States, has long been used in herbal medicine and now also has potential pharmaceutical uses. As a result of a projected increasing demand for V. californicum biomass for pharmaceutical purposes, the development of a chilling protocol for enhanced cultivation efficiency is needed. To study the effects of chilling on the growth of V. californicum, field-collected rhizomes with attached bulbs and roots were potted, stored at 10 °C for 2 weeks, and subsequently chilled at 5 °C for 30 to 180 days before transfer to a greenhouse or growth room. Twenty plants were transferred to the greenhouse every 30 days to observe growth. Ten plants were harvested at shoot emergence and the remaining 10 when leaves were fully expanded. In addition, 10 plants were transferred from 5 °C to a growth room every 30 days where net photosynthetic rates were measured. Longer chilling duration correlated with a reduction in days to shoot emergence and leaf expansion. The net photosynthetic rates of V. californicum plants chilled for 120, 150, or 180 days were higher than those of plants chilled for only 30, 60, or 90 days. Plants exposed to longer chilling durations were taller and had larger, more numerous leaves. Interestingly, V. californicum shoot emergence was also observed in the dark at 5 °C after the bulbs had been stored for 210 days. Growth of the root systems of plants was also observed during chilling. In conclusion, chilling was necessary at 5 °C for a minimum of 120 days to force early emergence and vigorous growth of V. californicum.

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Laura A. Warner, Alexa J. Lamm, Peyton Beattie, Sarah A. White and Paul R. Fisher

Nursery and greenhouse growers have an important role to play in conserving water resources. Many technologies are available to help growers conserve water. Yet, within the industry, there may be varying levels of knowledge about a specific strategy, along with inconsistent adoption and continued use. An understanding of these factors can be incorporated into educational programming for this audience. This study evaluated the reported knowledge level of U.S. greenhouse and nursery growers about eight specific water conservation technologies and then explored the rate at which growers had adopted and continued or discontinued their use. Technologies were ranked from high to low adoption rate, beginning with drip irrigation, rainwater capture, water reuse, and microirrigation, followed by soil moisture sensors, climate-based irrigation, subirrigation, and finally an irrigation audit. Overall, greater levels of knowledge corresponded to both greater adoption and continued use of a technology. Other factors, such as economic cost and technical feasibility are undoubtedly important. Findings highlight an opportunity to focus educational programs on the systems-based strategies that are beneficial to growers, but growers are least knowledgeable about to increase adoption of effective water conservation methods that currently have low levels of grower implementation.

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Milton D. Taylor, Sarah A. White, Stewart L. Chandler, Stephen J. Klaine and Ted Whitwell

Substantial quantities of water and nutrients are required for the production of high value nursery and greenhouse crops. As water quality criteria are strengthened locally and nationally, horticultural enterprises will have to meet stricter limits on nutrients in discharge water. This study examined the efficacy of an established vegetated surface-flow constructed wetland to mediate nitrogen (N) and phosphorus (P) in runoff water from a commercial nursery over a period of 38 months. Maximum oxidized nitrogen [nitrate-N (NO3-N) + nitrite-N (NO2-N)] inputs occurred during the spring fertilization period of March through May (11.1 to 29.9 mg·L–1 N) and minimum inputs occurred during winter plant dormancy between December and February (2.8 to 5.2 mg·L–1 N). Nitrogen remediation efficiency averaged 94.7% for March through November sampling dates but declined to a mean of 70.7% between December and February when mean wetland water temperature dropped below 15 °C. Orthophosphate phosphorus (PO4-P) concentrations in nursery runoff showed no dramatic changes over months, seasons, or years. Mean wetland influent orthophosphate concentration ranged from 0.7 to 2.2 mg·L–1 PO4-P with an overall mean of 1.41 mg·L–1 PO4-P for all months sampled. Mean discharge orthophosphate concentration ranged from 0.5 to 2.1 mg·L–1 PO4-P with a mean of 1.45 mg·L–1 PO4-P. Phosphorus remediation efficiency varied widely and there was no correlation with water temperature. This 9.31-acre surface-flow constructed wetland was highly efficient at removing N from nursery runoff from a 120-acre catchment (large container production area), although it failed to consistently lower orthophosphate levels in runoff. This type of constructed wetland is suitable for removing oxidized N forms from nursery runoff and, depending on size, is capable of handling the large volumes of runoff generated by medium to large nursery and greenhouse operations.

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Amy Fulcher, Anthony V. LeBude, James S. Owen Jr., Sarah A. White and Richard C. Beeson

Nursery and greenhouse producers, research and extension faculty, and representatives from allied fields collaborated to formulate a renewed vision to address water issues affecting growers over the next 10 years. The authors maintained the original container irrigation perspective published in “Strategic vision of container nursery irrigation in the next ten years,” yet broadened the perspective to include additional challenges that face nursery crop producers today and in the future. Water availability, quality, and related issues continue to garner widespread attention. Irrigation practices remain largely unchanged due to existing irrigation system infrastructure and minimal changes in state and federal regulations. Recent concerns over urbanization and population growth, increased climate variability, and advancements in state and federal regulations, including new groundwater withdrawal limitations, have provided an inducement for growers to adopt efficient and innovative practices. Information in support of the overarching issues and projected outcomes are discussed within.

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Sarah A. White, Holly L. Scoggins, Richard P. Marini and Joyce G. Latimer

Little information is available on cultural requirements for greenhouse production of Tradescantia virginiana L. We tested three plant growth regulators (PGRs) at ascending rates on T. virginiana `Angel Eyes,' `Blue Stone,' and `Red Cloud' in an effort to find appropriate application levels for height suppression. Treatments applied two weeks after transplant. Each PGR was applied once at the following rates: paclobutrazol at 0, 40, 80, 120, or 160 mg·L-1, uniconazole at 0, 15, 30, 45, or 60 mg·L-1, or flurprimidol at 0, 15, 30, 45, 60, or 75 mg·L-1. Repeated measures experimental design and multivariate analysis was used to examine plant responses to PGRs over time. The most effective paclobutrazol rate for adequate height suppression was 120 mg·L-1. Uniconazole at 30 to 45 mg·L-1 and flurprimidol at 45 to 60 mg·L-1 resulted in adequate height control. `Blue Stone' and `Red Cloud' appeared more responsive (greater suppression of height at rates applied) to both uniconazole and flurprimidol than `Angel Eyes.' These results suggest that cultivars respond in a different manner to PGRs applied to them; more compact growth can be obtained for cultivars tested using these suggested rates. Chemical names used: trifuloromethoxy phenyl-5-pyrimidinemethanol (flurprimidol); [(±)-(R*,R*)-ß-((4-chlorophenyl) methyl)-?-(1,1,-dimethylethyl)-1H-1,2,4,-triazole-1-ethanol)] (paclobutrazol); uniconazole.

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Milton D. Taylor, Sarah A. White, Stephen J. Klaine and Ted Whitwell

Container-grown plants require large amounts of water and nutrients during their production cycle. This results in substantial runoff that is contaminated with nitrogen and phosphorus. At our study site, nutrients were delivered through incorporation in the potting media as timed-release prills and through liquid feeding by injection into irrigation water. Mitigation of nutrients in runoff water was dealt with proactively by the container nursery with construction of 3.77 ha of planted wetlands to receive runoff from a 48.6-ha drainage basin and excess water diverted from adjacent watersheds. Water flowed though drains between wetland cells and eventually into stilling ponds before it was allowed to exit the property. Water flow through the wetlands ranged from 1.1 to 3.1 million liters per day over the period. Three years of monitoring data indicate some seasonal differences in nitrogen removal efficiencies. Nitrogen removal between March and November averaged ≥95% while removal during winter (December through February) averaged ≥72%. Nitrogen (as nitrate) varied from 4.28 ppm to ≤0.01 ppm in wetland discharge, well below drinking water quality standards, but occasionally above levels that may cause downstream eutrophication. Orthophosphate phosphorus removal was highly variable with greatest removal occurring during late spring, late fall, and winter. There was a significant net export of phosphorus during some summer months for years 2 and 3. Phosphorus levels in wetland discharge ranged between 0.84 and 2.75 ppm. While there is currently no legal water quality standard for phosphorus, these levels were above the generally accepted level for preventing downstream eutrophication.

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Robert F. Polomski, Milton D. Taylor, Sarah A. White, Ted Whitwell, Stephen J. Klaine and William C. Bridges Jr.

Commercial nurseries use large amounts of water and nutrients during production cycles. Runoff contaminated with N and P can adversely impact surface and groundwater quality. A 3-year monitoring study of nutrient mitigation by a constructed wetland at a container nursery found nitrogen removal was highly efficient. However, orthophosphate-P removal was highly variable. Partial removal occurred during some months, but net export also occurred. P levels in wetland discharge—between 0.84 and 2.75 ppm—were well above the generally accepted level for preventing downstream eutrophication. Therefore, identifying landscape plants that remediate nutrients, especially P, could be useful in improving constructed wetlands. A 2003 greenhouse study screened commercially available landscape plants for their phytoremediation potential. Among the 17 taxa and 19 cultivars examined were woody shrubs, e.g., Cornusamomum, Myricacerifera`Emperor', and Salix integra `Hakura Nishiki'; herbaceous semiaquatics, e.g., Canna(two cultivars), Colocasia esculenta `Illustris', Rhyncospora colorata, Iris`Full Eclipse', Pontederia cordata `Singapore Pink', and Thalia geniculata `Red Stem'; and floating aquatics, e.g., Myriophyllum aquaticum, Eichhornia crassipes, and Pistia stratiotes. Plants were grown in pea gravel media and kept saturated with one of five concentrations of Hoagland's. Herbaceous and woody plants were harvested after 8 and 13 weeks, respectively. Experiments were replicated twice for each cultivar. The nutrient uptake efficiency was determined for each taxon from the total amount of N and P applied and the biomass dry weight and N and P content.