The purpose of this paper is to determine the conditions that promote denitrification using silicate iron fertilizers, which are conventionally used in paddy fields. Denitrification incubation experiments were conducted in an incubator to evaluate the denitrification gas generation (amount of denitrification) and gas composition (nitrogen and nitrous oxide) in four different soils (Yabe, Koshi, Aso and Matsubase were soil collected in Kumamoto), three different silicate iron fertilizers (Silicate Iron fertilizers with different iron concentrations), different initial soil pH (pH 5, 6, 7, 8, 9). Also, the ratio of denitrification substrate (carbon and nitrogen; C/N 1.2, 1.7, 2.3, 3.5, 5.2, 6.9, 10.4) was to be added. Nitrous oxide was below the detection limit in some of the soils in the treatments with the addition of the Silicate Iron. In soils with relatively low soil C/N, the effect of silicate iron fertilizers was observed and nitrogen gas generation increased. In addition, silicate iron fertilizers were more effective in fertilizers with higher iron and calcium oxide concentrations. As an effect from the soil, nitrogen gas production increased with the addition of silicate iron fertilizers for soil pH in the 5–7 range and low added denitrification substrate (C/N 1.2 to 2.3).

　This comparative study investigated the effects of various aeration treatments on lettuce cultivation in a plant factory using artificial light (PFAL). A deep-water culture (DWC) hydroponic system was used in the present study. Three aeration treatments, namely macrobubbles (MA), microbubbles (MI), and ultrafine bubbles (UFB), were compared. We examined the influence of different aeration methods and fertilizer doses on lettuce growth and measured electricity consumption. The results showed that MI and UFB treatments significantly increased the yield and accelerated lettuce growth in PFAL. Relative to the MA treatment, the UFB treatment increase the SFW of lettuce by 1.5 times bigger in PFAL. Despite the increased energy consumption, UFB treatment demonstrated high energy efficiency compared to MA treatment. Notably, lettuce treated with UFB and 25% less fertilizer grew as well as lettuce given the full fertilizer dose without UFB. These findings suggest that UFB application has significant potential in PFAL. UFB enhances yield and accelerates lettuce growth.

　The growth of different lettuce varieties in response to the application of ultrafine bubbles (UFB) was investigated inside a plant factory with artificial light (PFAL). Six different types of lettuce (greenwave, frilly, green leaf, butterhead, romaine, and lamb lettuce) were cultivated under UFB and control treatments using a deep flow technique (DFT) hydroponic system. As a result, the effect of UFB treatment was found to vary depending on the type of lettuce cultivar. UFB treatment was found to promote growth in greenwave, frilly, and romaine lettuce but not in green leaf, butterhead, or lamb lettuce. Compared to the control treatment, the temperature of the nutrient solution and the dissolved oxygen (DO) concentration were higher by 1.61℃ and 59.5% in the UFB treatment, respectively. These findings suggest that an increased temperature and a high DO content during UFB generation are factors that enhance lettuce growth. Taken together, these results indicate that the application of UFB in the DFT hydroponic culture system can significantly promote lettuce growth in PFAL.