Control measure against the injury of lettuce [Lactuca sativa] seedlings caused by salt accumulation on polyurethane cube surface used as root substrate in hydroponics

There are two important technologies to maintain intensive plant production. These are the cultivation technique to decrease plant growth deviation, and the monitoring technique to detect abnormal plants. The lettuce (Lactuca sativa L. var. capitata L. non-heading type) cotyledons suffered by the disease, and/or by the injury of shoot tip have been observed at their seedling stage cultivated hydroponically in plant factory using fluorescent lamps. The growth injuries were caused by the contact with salt accumulation on polyurethane cube surface. The cube was utilized as root substrate support the plant. The injuries inflicted on the cotyledons prior to reaching to its leafing stage have been made delay of later growth. Not only the growth delay, but growth deviation among the plants has increased. The proper measure to prevent the cotyledons from contacting with salt accumulation on cube surface has been considered. The vinyl film applied to cube surface has efficiently prevented cotyledons from contacting with salt accumulation. The result is satisfied.