Abstract
To achieve clean and high-quality spinach production, the effects of daily light integral (DLI) and light spectrum on growth, nutritional quality, and energy yield of hydroponic spinach (Spinacia oleracea L.) were investigated in a closed plant factory under light-emitting diode (LED) lighting. The hydroponic spinach plants were grown under 16 combinations of four levels of DLI (11.5, 14.4, 17.3, and 20.2 mol m−2 day−1) with four light spectra: LED lamps with ratio of red light to blue light (R:B ratio) of 0.9, 1.2, and 2.2 and fluorescent lamps with R:B ratio of 1.8 as control. The results show that total fresh and dry weights, energy yield, and light energy use efficiency (LUE) of harvested spinach were higher under D17.3-L1.2 treatment compared to other treatments. The higher net photosynthetic rates were shown at DLI of 17.3 mol m−2 day−1 regardless of light quality. Higher vitamin C contents of spinach in all LED treatments were obtained compared with the control. L1.2 treatments with higher fraction of blue light led to more vitamin C content, lower nitrate content, and higher LUE independent of DLI. L2.2 treatment with more fraction of red light was beneficial to reduce oxalate accumulation. Power consumption based on increased total fresh weight under LED lamps with R:B ratio of 1.2 in different DLIs was over 38% lower than that under the fluorescent lamps and 1.73 kWh per 100 g FW at DLI of 17.3 mol m−2 day−1. In conclusion, lighting environment in DLI of 17.3 mol m−2 day−1 using LED lamps with R:B ratio of 1.2 is suggested for the design of a LED plant factory for hydroponic spinach production.
Highlights
The nutritional quality of leafy vegetables, especially spinach, is significantly affected by environmental variables such as light condition [1,2]
46.82 ± 3.99 g FW kWh−1, respectively. These results show that both higher and lower daily light integral (DLI) would reduce energy yield and increase power consumption based on increased total fresh weight, but an optimized spectral formula in Light-emitting diode (LED) lamps could effectively promote light energy use efficiency (LUE) in plant factory
This study revealed that LEDs with different R:B ratios had significant impacts on growth, and nutritional component accumulation, and energy yield in hydroponic spinach
Summary
The nutritional quality of leafy vegetables, especially spinach, is significantly affected by environmental variables such as light condition [1,2]. Higher yield and nutritional quality of leafy vegetables could be achieved through plant factory with artificial lighting (PFAL) due to controlled environments [3]. Spinach is suitable to produce in PFAL because of its shorter growth cycle, lower plant height, and higher planting density. Higher initial investment and production cost of PFAL are the biggest obstacles to industrialization promotion. Lighting cost accounting for 70–80% of the total electricity consumption in PFAL directly led to higher vegetable production cost [3]. It is necessary to reduce lighting cost through adopting
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