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  • Author or Editor: Youbin Zheng x
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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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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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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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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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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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Hanging basket (HB) production alters the light environment in the lower canopy of ornamental greenhouses by intercepting and altering the spectral quality of incoming light. If shading is sufficiently high, the quality of the lower crops can be reduced. This work investigated changes in light quantity and quality at the lower crop level caused by HB production in Ontario, Canada. Light sampling occurred at three commercial greenhouse facilities throughout the Spring 2012 HB season. The greenhouses represented a range of HB densities (1.8, 2.4, and 3.0 baskets/m2) and different HB canopy architectures (one, two, and three tiers of HBs). Light samples were taken at three fixed locations within each greenhouse facility: outside, HB level, and lower crop level. Photosynthetically active radiation (PAR) was logged continuously at each location within each greenhouse environment. Spectral scans were made at each sampling location, within each greenhouse facility, at various times throughout the season to assess how HB production altered the red to far red ratio (R:FR) at lower crop level. As the season progressed, outdoor daily light integrals (DLIs) more than doubled from <20 to >40 mol·m−2·d−1. Light reduction caused by polyethylene films and structural components varied among locations, but remained steady throughout the season, averaging 48.3% for the three locations. As the HB crops matured, the rate of decrease in PAR at lower crop level varied according to facility and HB density with mean reductions of 42.5%, 32.6%, and 37.7% for the one-, two-, and three-tiered facilities, respectively. Mean lower crop level DLIs were all very similar, between 9.4 and 9.9 mol·m−2·d−1. Accordingly, there may be insufficient light below HB canopies to produce high-quality crops of many varieties of bedding plants that are commonly grown in Ontario. The one- and two-tiered systems reduced the R:FR at lower crop level by 14% and 10%, respectively, whereas the three-tiered system caused no reduction. More work is required to determine if the observed far red shift is sufficient to alter crop quality. These case studies provide a backdrop against which to help determine and interpret horticultural management strategies for a variety of greenhouse crops.

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To evaluate the performance of four newly developed high-intensity-discharge lamp types on plant growth and production, tomato (Lycopersicon esculentum cv. Tradiro F1) plants were grown indoors under 100% artificial lighting for 17 weeks. The four lamp types were: high-pressure sodium high output [HPS(HO)], high-pressure sodium standard [HPS(STD)], metal halide warm deluxe [MH(WDX)] and metal halide cool deluxe [MH(CDX)]. All the lamps tested were 1000 W. HPS(HO) had the highest electrical energy use efficiency (EUE) (0.98 μmol·m–2·s–1·W–1 at 40 cm directly under the lamp); HPS(STD), MH(WDX) and MH(CDX) had 93%, 72% and 61% of the EUE of the HPS(HO), respectively. The photosynthetically active radiation (PAR) outputs of different lamp types had the following order: HPS(HO) > HPS(STD) > MH(WDX) > MH(CDX). The percentage red of PAR of the four tested lamp types had the same order as above, but the percentage blue of PAR of these lamp types had exactly the opposite order. As a result, plants growing under the two HPS lamp types were taller and flowered and fruited earlier than plants under the two MH lamp types. Chlorophyll content index was generally greater in leaves under MH lamps than in leaves under HPS lamps. We recommend that the HPS lamp be used for flowering and fruiting crops and the MH lamp would be better used for foliar and compact crops.

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To investigate plant growth and quality responses to different light spectral combinations, cabbage (Brassica oleracea L. var. capitata f. rubra), kale (Brassica napus L. ‘Red Russian’), arugula (Eruca sativa L.), and mustard (Brassica juncea L. ‘Ruby steak’) microgreens were grown in a controlled environment using sole-source light with six different spectra: 1) FL: cool white fluorescent light; 2) BR: 15% blue and 85% red light-emitting diode (LED); 3) BRFRL: 15% blue, 85% red, and 15.5 µmol·m−2·s−1 far-red (FR) LED; 4) BRFRH: 15% blue, 85% red, and 155 µmol·m−2·s−1 FR LED; 5) BGLR: 9% blue, 6% green, and 85% red LED; and 6) BGHR: 5% blue, 10% green, and 85% red LED. For all the light treatments, the total photosynthetic photon flux density (PPFD) was set at ≈330 µmol·m−2·s−1 under a 17-hour photoperiod, and the air temperature was ≈21 °C with 73% relative humidity (RH). At harvest, BR vs. FL increased plant height for all the tested species except arugula, and enlarged cotyledon area for kale and arugula. Adding high-intensity FR light to blue and red light (i.e., BRFRH) further increased plant height for all species, and cotyledon area for mustard, but it did not affect the fresh or dry biomass for any species. Also, BRFRH vs. BR increased cotyledon greenness for green-leafed species (i.e., arugula, cabbage, and kale), and reduced cotyledon redness for red-leafed mustard. However, BGLR, BGHR, and BRFRL, compared with BR, did not affect plant height, cotyledon area, or fresh or dry biomass. These results suggest that the combination of 15% blue and 85% red LED light can potentially replace FL as the sole light source for indoor production of the tested microgreen species. Combining high-intensity FR light, rather than low-level (≤10%) green light, with blue and red light could be taken into consideration for the optimization of LED light spectral quality in microgreen production under environmental conditions similar to this experiment.

Open Access
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To determine whether supplemental blue light (B) or far-red light (FR) overnight can promote microgreen elongation to facilitate machine harvesting and improve microgreen quality and yield, two common microgreen species, mustard (Brassica juncea) and arugula (Eruca sativa), were grown in a greenhouse in Guelph, Ontario, Canada, during January 2019. Low-intensity (14 μmol·m−2·s−1) B or FR was applied to microgreens overnight from 1730 hr to 0630 hr, and no supplemental lighting (D) was used as a control. After 2 weeks of light treatments, B compared to D promoted stem elongation by 16% and 10%, respectively, and increased crop yield by 32% and 29%, respectively, in mustard and arugula. B compared to D also increased the cotyledon area in mustard and leaf mass per area in arugula and enhanced cotyledon color in both species despite having no effects on total chlorophyll, carotenoid, and phenolic contents. However, FR did not increase stem length or fresh weight compared with D, reduced plant height compared with B in both species, and reduced the cotyledon area in arugula. FR, compared with D and B, reduced the stem diameter and phytochemical contents of both species. Therefore, low-intensity B can be applied overnight for winter greenhouse microgreen production because of its beneficial effects on appearance quality and crop yield without negatively affecting nutritional quality.

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The objectives of this study were to compare fertilizer rates and types to identify an optimum rate to maintain green roof vegetative coverage and encourage plant growth (i.e., plant performance) while minimizing the amount and concentration of nutrients leached from a green roof module system. Sedum-vegetated modules with no added fertilizer (control) were compared with modules fertilized with 5, 7.5, 10, 15, 20, 30, and 60 g·m−2 nitrogen (N) of 16N–2.6P–10K POLYON® Homogenous NPK plus Minors, 5–6 month controlled-release fertilizer (CRF), 5 g·m−2 N of a 2.9N–2.2P–2.3K fly-larvae processed chicken manure fertilizer (5-Sus), or 5 g·m−2 N of 4N–4P–4K Gaia Green All Purpose organic fertilizer (5-OR). The total amount and concentration of aluminum (Al), calcium (Ca), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), mercury (Hg), potassium (K), magnesium (Mg), sodium (Na), NH4 +, nickel (Ni), NO3 , phosphorus (P), lead (Pb), sulfur (S), and zinc (Zn) in leachate as well as plant overall appearance, winter injury, vegetative coverage, shoot height, bloom duration, and leaf color of green roof modules were evaluated between July 2011 and Aug. 2012. A CRF fertilizer rate of 15 g·m−2 N maximized vegetative coverage and overall plant appearance while maintaining leachate quality within Ontario and Canadian guidelines for most of the measured elements. The amount of Zn in the CRF appeared to be higher than plant demand and the high amount and concentration of P in leachate was likely the result of release from the growing substrate. The 5-Sus fertilizer resulted in increased coverage the first spring and increased greenness soon after application compared with the same rate of CRF. Overall, 15 g·m−2 N of CRF was the best treatment based on vegetative coverage and plant growth in sedum-vegetated green roof modules.

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