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Abstract
Photoradiation plays a major role in plant growth processes, especially photosynthesis and nutrient uptake. Light intensity and photoperiod affect temperature and caused more transpiration in plants, which influences nutrient uptake. This study aimed to examine the effects of photoradiation on the growth and K, Ca, and Mg uptake of lettuce (Lactuca sativa L.). Lettuce was hydroponically grown in a walk-in growth chamber, and the experiment was performed using eight treatments with eight replications. A combination of eight fluorescent lamps was used to provide a photon flux density of 128±20 umole m-2 s-1 for 15/15 minutes, 45/15 minutes, 345/15+15/15 minutes of black UV, and 345/15+15/45 minutes of black UV of light/dark periods. A combination of ten fluorescent lamps was used to provide a photon flux density of 194±28 umole m-2 s-1 for 30/30 minutes, 15/15 minutes, and 45/15 minutes of light/dark periods and 24 hours of light period. Continuous illumination with higher light intensity gave the greatest shoot fresh weight, plant height and number of leaves. Whereas a shorter photoperiod and lower light intensity gave the lowest shoot fresh weight. Shortened UV light radiation gave better result in lettuce growth performance such as shoot fresh weight, plant height and number of leaves. UV light also damaged the lettuce leaves. The leaves turned brown (brown spot) at the tip of the old leaves. Molar concentrations of K, Ca and Mg in the lettuce leaves were in the order of K > Ca > Mg for all of the treatments. The steep gradient and highest K accumulation at bottom leaves were found at lower light intensity and short photoperiod (15/15 minutes of light/dark). Extended photoperiod improved K and Ca movement and reduced K and Ca accumulation in the bottom leaves. High K in the leaves reduced Ca uptake. Continuous illumination with higher light intensity resulted in the lowest concentrations of K, Ca and Mg. The mole ratio of K/Ca decreased from the top to bottom leaves, whereas the mole ratio of K/Mg tended to be stable except in the treatment with lower light intensity and short photoperoid. The best growth performance was found in the treatment with consistent K/Ca ratio.
Highlights
Urban farming provides fresh food to customers, reduce loss of products and reduce cost of transportation
Lettuce was grown by a deep flow technique (DFT) in a 54 cm width, 60 cm length and 10 cm depth of growing basin
Room temperature was maintained at 16 °C, the temperature above the growing beds differed because of the influence of light intensity and photoperiod
Summary
Urban farming provides fresh food to customers, reduce loss of products and reduce cost of transportation. The cost and limitations of land areas can be minimized through intensive cultivation. Growing plants under controlled environment have a number of advantages, such as higher quality of yields, shorter production periods, and smaller labor force, relative to conventional growing systems (Kozai, 2013; Kang, Krishna Kumar, Atulba, Jeong, & Hwang, 2013). The fresh weight of turnip can be increased by more than 10 times within 1 week when it was grown under a continuous illumination of 237 μmol m-2 s-1 and elevated CO2 concentration to 2100 μL L-1 (Ikeda, Nakayama, Kitaya, & Yabuki, 1988). Sunlight is unsuitable for multilayer cultivation and has various limitations such as its limited availability only in the daytime and its inconsistant intensity. Responses to continuous illumination depend on plant species
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