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Yun Kong and Youbin Zheng

Suaeda glauca is an annual halophyte growing in saline–alkali environment in North China. To evaluate the potential of producing S. glauca as a vegetable at moderate NaCl concentrations, plants were grown in nutrient solutions with 6, 8, and 10 mm NaCl, and with 200 mm NaCl as a control. Results showed that main stem length, true leaf number, side branch number, and canopy width of plants in 6–10 mm NaCl were not significantly different from those in 200 mm. Also, no significant differences in fresh and dry weights of individual plants, marketable yield, and water use efficiency of the plants were observed between 6–10 and 200 mm NaCl treatments. Despite remarkable decreases in sodium uptake, similar water consumptions by the plants were obtained in 6–10 vs. 200 mm NaCl. The results suggest that S. glauca is a potential candidate for hydroponic production as a vegetable at moderate NaCl salinity, since growth attributes and biomass accumulation were not reduced when grown at lower salinity levels, despite with decreased sodium uptake.

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Yun Kong and Youbin Zheng

Salicornia bigelovii is a halophyte that is capable of growing under high salinity. To evaluate the potential of producing S. bigelovii hydroponically as a vegetable at moderate NaCl concentrations, plants were grown in nutrient solutions with 6, 8, and 10 mm NaCl, and with 200 mm NaCl as a control. Results showed that plants had a reduced main stem length, canopy width, stem diameter, and root system length in 6 to 10 mm NaCl compared with those in 200 mm. Also, fresh weight increase, fresh and dry weights of individual plants, marketable yield, and water use efficiency of the plants grown in solutions with 6 to 10 mm NaCl were significantly lower than those grown in 200 mm. Associated with the reduced growth attributes, remarkable decreases in sodium uptake by the plants were also obtained in 6 to 10 vs. 200 mm NaCl. The results suggest that S. bigelovii is not a good candidate for hydroponic production as a vegetable at moderate NaCl salinity resulting from reduced growth attributes, which are possibly associated with decreased sodium uptake.

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Erin Agro and Youbin Zheng

Region-specific trials examining optimum controlled-release fertilizer (CRF) rates for the Canadian climate are limited. This study was conducted to determine an optimum range of CRF application rates and the effect of the application rate on growth, nitrogen (N), and phosphorus (P) losses of six economically important container-grown woody ornamental shrubs using typical production practices at a southwestern Ontario nursery. Salix purpurea ‘Nana’, Weigela florida ‘Alexandra’, Cornus sericea ‘Cardinal’, Hydrangea paniculata ‘Bombshell’, Hibiscus syriacus ‘Ardens’, and Spiraea japonica ‘Magic Carpet’ were potted in 1-gal pots and fertilized with Polyon® 16N-2.6P-10K (5–6 month longevity) incorporated at rates of 0.8, 1.2, 1.7, 2.1, and 2.5 kg·m−3 N in 2012. The experiment was repeated for the 2013 growing season with rates of CRF incorporated at 0.05, 0.35, 0.65, 0.95, and 1.25 kg·m−3 N. Plant performance (i.e., growth index) and leachate electrical conductivity (EC) and pH were evaluated once every 3 to 4 weeks during the respective growing seasons. The amount of N and P lost to the environment was determined for the 2012 growing season. The interaction between nutrient supply rate and target species affected most response variables. Although higher levels of fertilization produced larger plants and had the potential to decrease production time, increased losses of N and P and higher EC leachate values occurred. Results of this study indicate that an acceptable range of CRF application rates can be used for each species depending on the production goals, i.e., decreased production time, maximum growth, or decreased nutrient leachate. Overall, the highest acceptable CRF rates within the optimal range were: 1.25 kg·m−3 N for Spiraea; 1.7 kg·m−3 N for Hydrangea; 2.1 kg·m−3 N for Cornus; and 2.5 kg·m−3 N for Weigela, Salix, and Hibiscus. The lowest acceptable rates within the optimal range were: 0.35 kg·m−3 N for Hibiscus; 0.65 kg·m−3 N for Cornus, Weigela, Salix, and Spiraea; and 0.80 kg·m−3 N for Hydrangea.

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Yun Kong and Youbin Zheng

To evaluate the potential of producing purslane (Portulaca oleracea L.) as a sodium (Na)-removing vegetable hydroponically at moderate NaCl salinity, two cultivars (Green and Golden) were grown in solutions with added 0, 6, 8, and 10 mm NaCl (the actual Na+ concentrations ≈2, 8, 10, and 12 mm, respectively). At harvest, 26 days after transplanting, apparent growth and biomass accumulation were not negatively affected by 6 to 10 mm added NaCl compared with 0 mm added NaCl. However, with the increase of added NaCl concentration from 0 to 6 to 10 mm, the sodium removal showed a 1- to 3-fold increase up to 0.26 to 0.41 mmol/plant, and 225.7 to 300.2 mmol·kg−1 dry weight (DW) or 0.90 to 1.32 mmol·L−1 H2O, respectively. ‘Green’ produced greater biomass and removed more sodium per plant than ‘Golden’. ‘Golden’ had more of a dwarfed and compact canopy than ‘Green’. Sodium removal rate (mmol/plant/day) was the highest during the first 7 days after transplanting, but the fresh weight increase rate (g/plant/day) increased gradually as growth progressed. Results suggest that it is possible to hydroponically produce purslane in nutrient solutions with 8 to 12 mm Na+. Despite the high sodium-removal capability, purslane cannot be used to reduce Na+ concentrations in NaCl-rich hydroponic solutions. The biomass yield and the sodium removal of individual plants were affected by different cultivars and time after transplanting.

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Xiuling Tian and Youbin Zheng

In vitro testing was conducted to evaluate the inhibition potential of three compost teas (pine bark, manure, and vermicasting), Root Rescue Landscape Powder® (a mix of mycorrhizae and other beneficial microbes), waste diatomaceous earth (DE; from beer brewing), and a greenhouse nutrient solution, which had been reused for 20 years on six plant pathogens: Fusarium foetens, Rhizoctonia solani, Sclerotinia sclerotiorum, Phytophthora cryptogea, Pythium intermedium, and P. ultimum. The test materials showed in vitro inhibition on most of the test pathogens. Pine bark tea suppressed growth of all six pathogens, and inhibition exceeded 50% after 10 days of coincubation. Vermicasting tea showed over 40% inhibition against S. sclerotiorum and F. foetens; manure tea showed 42% inhibition against F. foetens; DE showed 40% inhibition against F. foetens, S. sclerotiorum, and R. solani; whereas reused greenhouse nutrient solution showed 56.7% inhibition against R. solani and 43.4% inhibition against F. foetens; Root Rescue showed 66% inhibition against P. intermedium. The results suggest that the six test materials have potential in the control of these soil- and water-borne pathogens in plant production system.

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C. Siobhan Dunets and Youbin Zheng

Phosphorus (P) pollution from greenhouse wastewater is currently a major issue. A treatment method that can efficiently remove P concentrations ([P]) that fluctuate between greenhouse systems and throughout the year is required. An ideal method would also recover nutrients in a reuseable form. A combined precipitation/flocculation process incorporating addition of lime and a biodegradable flocculant (guar gum, cationic starch, or chitosan) was investigated for providing optimized P removal and recovery. Effectiveness of this process was evaluated in simulated wastewater of low and high alkalinity, as well as real greenhouse wastewater. Precipitation via lime addition reduced total P to below 1 mg·L−1 in low-alkalinity simulated wastewater, but high alkalinity slightly inhibited separation. This inhibition was overcome by flocculation via guar gum or cationic starch addition, which improved separation efficiency and reduced separation time, although chitosan was ineffective as a flocculant. The precipitation/flocculation method was found to be effective for treating real greenhouse wastewater, although effectiveness varied with variation in wastewater composition. Recovered precipitate contained 57.4 g·kg−1 P as well as high levels of Ca, Mg, K, Fe, and Zn. This study demonstrates a P separation process incorporating lime and biodegradable flocculants could provide a means of reducing P in greenhouse wastewater below a 1 mg·L−1 regulatory limit in a settling time of less than 30 minutes, while simultaneously recovering P and other nutrients in a form that could be reused as fertilizer. An evaluation of viability of full-scale application of this technology is now warranted.

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Mary Jane Clark and Youbin Zheng

The objectives of the current study were to 1) determine the best topdressed controlled-release fertilizer (CRF) application rates for quality and growth of two nursery crops under temperate climate outdoor nursery production conditions in the Niagara region, Ontario, Canada, and 2) evaluate the nutrient status of the growing substrate following topdressing of two CRF types during the growing season. Fall-transplanted Goldmound spirea (Spiraea ×bumalda ‘Goldmound’) and Wine & Roses® weigela [Weigela florida (Bunge) A. DC. ‘Alexandra’] were grown in 2-gal (7.56 L) containers and topdressed on 7 May 2015 with Osmocote Plus 15N–3.9P–9.9K, 5–6 month CRF or Plantacote 14N–3.9P–12.5K, 6 month Homogeneous NPK with Micros. CRF was applied at rates of 1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 g nitrogen (N)/pot for both species. The best plants at the end of the growing season (i.e., 23 Sept. 2015) were spirea at 3.0–4.5 and 3.0–6.0 g N/pot, and weigela at 3.0–4.5 and 6.0 g N/pot, with Osmocote and Plantacote, respectively. At CRF rates above these rates, the majority of plants showed no increase in growth or quality attributes. All weigela plants, despite CRF application rate, showed K deficiency symptoms during the study. Using marketable-size criteria and plant growth data over time, estimates of production timing are presented for fall-transplanted, spring-topdressed weigela and spirea. These estimates may assist growers in choosing CRF application rates to meet time-sensitive production goals. Early in the growing season, NO3-N and P concentrations in the growing substrate were highest at CRF rates ≥4.5 and ≥6.0 g N/pot, respectively, and P continued to be high in August and September at 9.0 g N/pot. NH3-N and K concentrations at all CRF application rates were greater early in the growing season and decreased over time. At high CRF rates toward the end of the growing season, concentrations of NO3-N, NH3-N, and P once again increased. Considering crop-specific CRF application rates and understanding changes in growing substrate nutrient status during the growing season may help nursery growers prevent negative environmental impacts from over-fertilizing.

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Mary Jane Clark and Youbin Zheng

The objective of this study was to determine the optimal controlled-release fertilizer (CRF) application rates or ranges for the production of five 2-gal nursery crops. Plants were evaluated following fertilization with 19N–2.6P–10.8K plus minors, 8–9 month CRF incorporated at 0.15, 0.45, 0.75, 1.05, 1.35, and 1.65 kg·m−3 nitrogen (N). The five crops tested were bigleaf hydrangea (Hydrangea macrophylla), ‘Green Velvet’ boxwood (Buxus ×), ‘Magic Carpet’ spirea (Spiraea japonica), ‘Palace Purple’ coral bells (Heuchera micrantha), and rose of sharon (Hibiscus syriacus). Most plant growth characteristics (i.e., growth index, plant height, leaf area, and shoot dry weight) were greater in high vs. low CRF treatments at the final harvest. Low CRF rates negatively impacted overall appearance and marketability. The species-specific CRF range recommendations were 1.05 to 1.35 kg·m−3 N for rose of sharon, 0.75 to 1.05 kg·m−3 N for ‘Magic Carpet’ spirea, and 0.75 to 1.35 kg·m−3 N for bigleaf hydrangea and ‘Green Velvet’ boxwood, whereas the recommended CRF rate for ‘Palace Purple’ coral bells was 0.75 kg·m−3 N. Overall, species-specific CRF application rates can be used to manage growth and quality of containerized nursery crops during production in a temperate climate.

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Youbin Zheng and Mary Jane Clark

To determine the optimal growing substrate pH values for Sedum plants, Sedum album, Sedum reflexum ‘Blue Spruce’, Sedum spurium ‘Dragon’s Blood’, Sedum hybridum ‘Immergrunchen’, and Sedum sexangulare were grown in containers using peatmoss and perlite-based substrates at five target pH levels (i.e., 4.5, 5.5, 6.5, 7.5, and 8.5). Optimal pH levels, calculated from dry weight regression models, were 6.32, 6.43, 5.71, 6.25, and 5.91 for S. album, S. reflexum, S. spurium, S. hybridum, and S. sexangulare, respectively, and 5.95 overall. Sedum spurium dry weight varied the most among pH treatments (i.e., 9.5 times greater at pH 6.3 vs. 8.3), whereas S. reflexum varied the least (i.e., 1.3 times greater at pH 6.3 vs. 4.4), indicating species-specific growth responses to growing substrate pH. These findings identified a narrow range of optimal growing substrate pH levels within a wider pH range tolerated by five Sedum spp. Therefore, by adjusting substrate pH to optimal levels, Sedum growth can be maximized.

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Mary Jane Clark and Youbin Zheng

Vegetation success on green roofs in northern climates is challenged by extreme weather conditions, especially in winter, and is influenced by season of installation and substrate fertility. Appropriate fertilization with phosphorus (P) and potassium (K) can reduce winter injury for some plant species. The objectives of this study were to identify both the effect of P and K fertilizer rates on Sedum spp. survival over the first winter and the response of Sedum spp. growth to fertilizer rates when applied at installation. In a fall-installed extensive green roof system, survival, growth, and visual appearance of Sedum mats in non-fertilized plots (control) were compared with plots fertilized with 16–6–13 POLYON® Homogenous NPK plus Minors 3-4 month controlled-release fertilizer at 20.0 g nitrogen (N)/m2 either alone or with additional P to total 28.8, 54.4, or 80.0 g P/m2 or K to total 32.5, 51.6, or 70.6 g K/m2. Sedum mats were installed on 8 Oct. 2010 and plants in all plots survived the winter and the next year. During the 2011 growing season, vegetative coverage was not significantly different among any individual fertilized treatments; however, vegetative coverage data combined for all fertilized treatments was larger than the control. Fertilized treatments also showed larger plant height and biomass after one year, taller S. acre and S. sexangulare inflorescences, increased leaf greenness, and higher visual appearance rankings compared with the control. For individual Sedum species, S. album showed the greatest coverage in P-fertilized treatments, and effects on S. acre and S. sexangulare were treatment-dependent. Application of a controlled-release N–P–K fertilizer, without additional P or K, can be used to encourage vegetative coverage, plant growth, leaf greenness, inflorescence height, and visual appearance in fall-installed extensive Sedum green roof systems.