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  • Author or Editor: Seonghwan Kang x
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Sulfur (S) is an essential plant nutrient that regulates plant growth and metabolism. However, S is often absent from certain one-bag hydroponic fertilizers designed to provide a complete and balanced mixture of nutrients. We quantified the effects of S supplementation on the growth, morphology, and photosynthesis of lettuce grown in a deep-water culture hydroponic system. Two lettuce (Lactuca sativa) cultivars, green butterhead Rex and red oakleaf Rouxai, were grown using a prepackaged fertilizer specially formulated for reverse osmosis (RO) and other low-alkalinity water sources. The base nutrient solution was mixed using Jack’s FeED 12–4–16 fertilizer and RO water at a nitrogen concentration of 100 mg⋅L−1 (control). Three S supplementation treatments were implemented over a 4-week production period: 10 mg⋅L−1 supplemental S (provided using MgSO4); 20 mg⋅L−1 supplemental S (MgSO4); and a treatment using H2SO4 (instead of nitric acid) for pH adjustment. In both lettuce cultivars, shoot fresh and dry mass, total leaf area, leaf photosynthetic rate, total chlorophyll content, and leaf S concentration with all three S supplementation treatments increased significantly compared with those of the control. In contrast, the ratio of shoot dry mass to fresh mass, root dry mass, and percentage of root dry mass (i.e., root dry mass/total shoot and root mass) were significantly higher with the control treatment. Notably, ‘Rouxai’ lettuce grown in the control treatment had intense red coloration with a 216.6% to 288.9% increase in the anthocyanin index. There were no statistical differences in any of the growth and morphological parameters among the three S supplementation treatments. Overall, we observed significantly enhanced lettuce growth and photosynthetic performance with S supplementation, resulting in a 144.0% to 215.9% increase in shoot fresh mass in the two cultivars compared with the control. Thus, we recommend that at least 10 mg⋅L−1 of S should be supplemented when growing lettuce hydroponically to ensure optimal plant growth, especially when S is absent or low in the fertilizer and water source.

Open Access

Automated irrigation systems based on soil moisture sensor measurements can reduce water and fertilizer use while adequately meeting plant water requirements. In this study, the effects of substrate volumetric water content (θ, v/v) on the flowering of 17-month-old Doritaenopsis Queen Beer ‘Mantefon’ (from the time of deflasking) were examined. The plants were transplanted in plastic pots (10.5 cm width × 9.5 cm height) filled with sphagnum moss and the θ of sphagnum moss was maintained at 0.2, 0.3, 0.4, or 0.5 m3·m−3 using an automated drip irrigation system. Plants grown at a θ threshold of 0.2 m3·m−3 had thinner leaves and lower SPAD value than those grown at higher θ thresholds. The net CO2 uptake of the uppermost fully expanded leaf increased with increasing θ between 0.2 and 0.4 m3·m−3, but there was no significant difference in the net CO2 uptake between plants grown at 0.4 and 0.5 m3·m−3 thresholds. The number of flower buds at the time of the first open flower was lower in plants grown at θ thresholds of 0.2 and 0.3 m3·m−3 as compared with that in the plants grown at 0.4 and 0.5 m3·m−3 thresholds. Early flower abscission, flower bud dropping, and flower senescence during the 2 weeks after flowering occurred in 55% and 30% of the plants at 0.2 and 0.3 m3·m−3 thresholds, respectively, whereas plants at θ thresholds of 0.4 and 0.5 m3·m−3 had negligible flower abscission. Although vegetative growth parameters were similar among θ thresholds of 0.3 m3·m−3 or higher, plants grown at a θ threshold of 0.3 m3·m−3 produced fewer flowers than those grown at 0.4 and 0.5 m3·m−3 thresholds. During the 83-day experimental period, the system irrigated the plants ≈0.79, 1.93, 2.46, and 2.84 L/pot at θ thresholds of 0.2, 0.3, 0.4, and 0.5 m3·m−3, respectively. Overall, 0.4 m3·m−3 was considered to be an optimal threshold θ level for producing high-quality Doritaenopsis Queen Beer ‘Mantefon’ during the flowering period with most efficient water use.

Free access