Intermittent Root Flushing with Ozonated Water Promotes Growth of Japanese Mustard Spinach (Brassica rapa var. perviridis) grown in a Nutrient Film Technique Hydroponic Culture—Preliminary Results

ABSTRACT Japanese mustard spinach with 4–5 unfolded leaves were transplanted in a nutrient film technique hydroponic system to investigate the effects of washing roots intermittently with ozonated water (OW) on plant growth. The high concentration of OW generated electrolytically was mixed in the nutrient solution tank, showed 5.8 mg.L−1, and circulated through the culture beds for 1 h every week. After washing the roots with OW or tap water (TW) as a control for 1 h, Otsuka house A solution (NO3-N: 16.8 me.L−1, NH4-N: 1.8 me.L−1, P: 5.1 me.L−1, K: 8.6 me.L−1, Ca: 8.2 me.L−1, Mg: 3.0 me.L−1) at 1.2 dS.m–1 was provided for plant cultivation in hydroponic culture systems. The OW or TW was replaced every week. The fresh and dry weights of the leaves, number of leaves, leaf length, and leaf width of plants treated with OW were significantly higher than those of the plants treated with TW at 1, 2, and 3 weeks after transplanting (WAT). The ratio of the shoot and root dry weights at 1, 2, and 3 WAT was significantly higher in plants grown in the OW flushing treatment compared with the control treatment. However, the roots dry weights were not significantly different between the OW- and TW-treated plants. Moreover, the number of coliform bacteria and aerobic plate count (APC) in the solution and plants were not significantly different between the two treatments. These results indicate that washing roots intermittently with 5.8 mg.L−1 dissolved ozone concentration of OW for 1 h per week promotes aerial plant growth without physiological disorder and is not accompanied by a decrease in the number of coliform bacteria and APC in the solution and plants.