Effects of Supplemental Lighting on the Quality of Tomato Seedlings Raised in Greenhouses

High-quality seedling supply is essential for the production of tomatoes in greenhouses using high density (5 plants per m(2)) and continuous planting (8 cycles per year) with double-tiered beds and cultivation until the fourth truss, compared to the conventional case of annual planting until higher truss harvest. In this study, the seedling period from seed germination to fixed transplant size was divided into two stages. Seedlings were then placed into an artificial weather room with fluorescent lamps and then into a greenhouse with natural light until the seedling reached transplant size. In the latter periods of growth, the quality of the seedling deteriorated due to weak natural light in the rainy and winter seasons. Thus, a ceramic metal halide lamp (150 W 4,300 K) used for outdoor signboards that was able to uniformly illuminate a horizontal surface was attached to the greenhouse eaves to avoid the formation of shaded areas. A computerized lighting control system was also implemented to compensate for the PPF fluctuation of the natural light. The average PPF on the plant canopy was increased to 94.0 mu mol m(-2) s(-1) using supplemental lighting, and the input electric power density was 166 W m(-2). The planting density during this period was 108.6 plants m(-2) and the experiments were repeated four times. The average supplemental lighting time was 6.30 h d(-1). We found that the cumulative PPF on the plant canopy was increased by 33% using supplemental lighting, and its daily coefficient of variance (CV) was improved from 53 to 29%. The top dry weight of the seedling was increased from 17 to 35%, while the total plant height tended to be short. Supplemental lighting during the cultivation period also improved the quality of the tomato seedlings. The average total cost of supplemental lighting was 17.3 yen per seedling.