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Yuqi Li and Neil S. Mattson

The objective of this study was to evaluate the growth and flowering of petunia (Petunia ×hybrida) transplants in response to seven commercial substrates with two water sources (fertigation and clear water irrigation). Seven commercial substrates used were Sunshine #1 Natural & Organic (SS), Metro-Mix 360 (MM), AgriTech (AT), Cornell Peat-Lite Mix B (CB), Jeff’s Organic (JO), LM-18, and LM-111. The experiment was a completely randomized 2 × 7 factorial design with six single-pot replications per treatment. With fertigation, substrate electrical conductivity (EC) decreased over time to 38 days after transplanting (DAT), and then did not further change. The AT substrate EC value was greater than others during the first 38 DAT. With clear water irrigation, substrate EC decreased over time to 31 DAT, and then did not further change. The AT substrate EC value was greater than other substrates during the entire petunia growth period. With fertigation, all substrate pH values were between 6.5 and 7.5 except AT and CB. The AT substrate had the greatest pH ranging from 7.5 to 8.0 during the petunia growth period. The CB substrate exhibited the lowest pH, which was between 5.8 and 6.3. Clear water irrigation had greater substrate pH values than fertigation. There was a substrate and water interaction for calcium (Ca), potassium (K), ammonium-nitrogen (NH4 +-N), nitrate-nitrogen (NO3 -N), and sodium (Na) concentrations in substrate leachate. At 52 DAT, the shoot dry weight (DW), root index (RI), and flower number of petunia grown in AT substrate were greatest among all the substrates, but chlorophyll index (SPAD) was the lowest under either the fertigation or clear water irrigation treatments. The DW and RI of petunia grown in AT substrate were greater when fertigation was used than clear water irrigation, but the water source had no effect on flower number. For SS, MM, CB, JO, LM-18, and LM-111 substrates, fertigation increased petunia DW, RI, and flower number as compared with clear water irrigation, but not SPAD readings.

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Yuqi Li and Neil S. Mattson

Seaweed extracts are widely used as plant growth regulators in agriculture and horticulture for improvement of plant growth and development. This study investigated the effects of rockweed (Ascophyllum nodosum) extract application method (foliar spray or substrate drench) and rate on growth and postharvest drought tolerance of petunia (Petunia hybrida) and tomato (Solanum lycopersicum) transplants grown in a commercial peat/perlite substrate. Foliar sprays significantly affected growth of petunia and tomato, but did not improve drought tolerance of petunia and tomato. Whereas, substrate drenches significantly improved drought tolerance of petunia and tomato compared with the control. Shoot fresh weight (FW), shoot dry weight (DW), root index (RI), and chlorophyll index (SPAD) of petunia and tomato increased significantly with increasing concentration of foliar spray rate up to 5 mL·L−1, but did not change significantly with further higher foliar spray rates. Weekly substrate drenches at 20 mL·L−1 significantly decreased FW, DW, RI, and SPAD values of petunia and tomato. In this study, substrate drench at 5–10 mL·L−1 significantly increased flower number of petunia and tomato. The results of this study suggested that substrate drenches at 5–10 mL·L−1 are appropriate for the improvement of postharvest life of petunia and tomato transplants, and that foliar applications can increase plant growth.

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Yuqi Li and Neil S. Mattson

Fertility management of seedlings and transplants is considered a key challenge in organic greenhouse production. This study was conducted to determine response of greenhouse-grown cucumber (Cucumis sativus) and nutrient release profile to two organic fertilizers and their combinations applied at three different concentrations in organic substrate. The organic fertilizers used were a turkey litter–based compost (TC) and a dairy manure vermicompost (VC). In addition, two control treatments [no fertilization (CK), conventional liquid fertilizer (CF)] were included. For TC, substrate leachate pH decreased for the first 17 days after addition and then increased, whereas electrical conductivity (EC), and calcium (Ca) and nitrate-nitrogen (NO3 -N) concentrations increased and then declined. For VC, EC decreased continuously over time from days 0 to 52, whereas pH increased. The Ca and NO3 -N concentrations decreased over time to 24 days and then did not change further. For TC/VC combinations, EC was stable for the first 17 days and then declined. For all organic fertilizer applications, potassium concentration was stable for the first 17 days and then decreased, whereas most of the sodium, ammonium-nitrogen, and chloride were no longer leached by 24 days. The VC and TC/VC combinations did not affect cucumber seed germination rate, seedling survival rate, seedling height, and leaf greenness (SPAD) as compared with CF. The stem length, leaf number, dry weight (DW), root index, and SPAD readings of cucumber transplants increased with increasing TC and VC fertilizer applications. The TC/VC combinations increased the biomass of cucumber transplants compared with CK, and did not differ from CF. The results of this study indicated that the 28.32 lb/yard3 of VC (high rate) or the 9.44 lb/yard3 of VC combined with 4 lb/yard3 of TC (medium rate) can be substituted for CF for the cultivation of cucumber seedlings. Based on DW, the 12 lb/yard3 of TC (high rate) or the 4 lb/yard3 of TC combined with 9.44 lb/yard3 of VC (medium rate) fertilizers were suitable replacements for CF for the cultivation of cucumber transplants.

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Soohyun Kang, Yating Zhang, Yuqi Zhang, Jie Zou, Qichang Yang and Tao Li

Ultraviolet-A (UV-A) is the main component of UV radiation in nature. However, its role on plant growth, to a large extent, remains unknown. In this study, tomato (Solanum lycopersicum ‘Beijing Cherry Tomato’) seedlings were cultivated in an controlled environment in which UV-A radiation was provided by UV-A fluorescent lamps (λmax = 369 nm) with a fluence rate of 2.28 W·m−2. The photoperiod of UV-A radiation was 0, 4, 8, and 16 hours, which corresponds to control, UV-A4, UV-A8, and UV-A16 treatments, respectively. The photosynthetic photon flux density (PPFD) was 220 μmol·m−2·s−1, which was provided by light-emitting diodes (LEDs) with a blue/red light ratio of 1:9, the photoperiod of PPFD was 16 hours. We showed that supplementing 8 and 16 hours of UV-A to visible radiation (400–700 nm) stimulated plant biomass production by 29% and 33%, respectively, compared with that of control. This resulted mainly from larger leaves (i.e., 22% and 31% in 8 and 16 hours UV-A, respectively), which facilitated light capture. Supplemental UV-A also enhanced photosynthetic capacity, as indicated by greater net photosynthesis rates in response to CO2 under saturating PPFD. Furthermore, the greatest stomatal conductance (g S) value was observed in UV-A16, followed by UV-A8, which correlated with the greater stomatal density in the corresponding treatments. Moreover, supplemental UV-A did not induce any stress, as the maximum quantum efficiency of photosynthetic system II (PSII) (F v/F m) remained ≈0.82 in all treatments. Similarly, chlorophyll content and leaf mass area (LMA) were also unaffected by UV-A radiation. Taken together, we conclude that supplementing reasonable levels of UV-A to visible radiation stimulates growth of indoor cultivated tomato seedlings.