Photocatalytic treatment of waste nutrient solution from soil-less cultivation of tomatoes planted in rice hull substrate

摘要

The effectiveness of photocatalytic treatment under solar light irradiation of waste nutrient solution emitted from a soil-less cultivation system of tomatoes planted in rice hull substrate was investigated from the viewpoint of conservation-oriented agriculture. As a model experiment, the phytotoxically active extract from rice hulls was treated with a TiO2-coated porous alumina filter irradiated with ultraviolet light at an intensity of 2.0 mW/cm(2), and the phytotoxic activities before and after irradiation were evaluated from the germination rate of lettuce seeds. The germination rate was 0 % before irradiation, demonstrating the strong inhibitory effect of the rice hull extract, but recovered to 100 % after 4 days of irradiation. The growth of tomatoes planted in rice hull substrate under actual cultivation conditions was also observed in six repeated experiments over a 3-year period by comparing tomatoes grown in a closed soil-less cultivation system with photocatalytically treated waste nutrient solution under solar light (photocatalytically treated system), with tomatoes grown in a closed system with untreated waste nutrient solution (untreated system). The results showed that tomato growth in the photocatalytically treated system was significantly higher than that in the untreated system in six experiments over 3 years, and yields in the photocatalytically treated system were comparable to those in a currently used open cultivation system using rockwool substrate. These results suggest that incorporating photocatalytic treatment of waste nutrient solution under solar light irradiation will allow conservation-oriented closed soil-less cultivation systems to be realized.