Development of environmentally friendly soilless cultivation system by photocatalytic treatment

From the viewpoint of environmental conservation agriculture, it is desirable not only to switch nutrient solutions from opened to closed systems in soilless cultivation, but ,（F1）also to switch culture substrates from rockwool to organic substrates. This study investigated for development of closed soilless cultivation system using rice hull substrate by TiO2 photocatalytic treatment of the waste nutrient solution. First, performance of the photocatalytic treatment for closed soilless cultivation system using rice hull substrate was tested. The treatment successfully controlled the phytotoxicity eluted from the rice hull substrate and significantly increased growth and yield of tomato and rose comparing to closed system without the treatment. In addition, the yield was comparable with conventional open system using rockwool substrate at greenhouse under sun light . Second, photocatalytic decomposition and detoxification of phytotoxic compounds released from only plant roots investigated. The phytotoxic activity of the phytotoxically active fraction extracted either from asparagus roots or from the recycled nutrient solution of an asparagus soilless cultivation system using inorganic substrate was decreased by photocatalytic treatment . Finally, to enhance disease control in the closed soilless cultivation system using rice hull substrate, the suppression of bacterial wilt disease in a waste nutrient solution with photocatalytic and silver treatments was investigated. The untreated waste nutrient solution had a high Total Organic Carbon (TOC) concentration, and silver in the untreated solution had no antibacterial activity. By contrast, silver in the photocatalytically treated solution showed a high antibacterial effect via the low TOC of the treated solution. A similar trend of disease onset was observed when pathogenic bacteria were inoculated into the solutions used to cultivate tomato seedlings. From these results, it is expected that combining photocatalytic and silver treatments can contribute to stable crop production in closed soilless cultivation.