Abstract
Water balance of the closed-type transplant production system with artificial lighting was investigated. Sweetpotato (Ipomoea batatas (L.) Lam. cv. Beniazuma) plants were grown for 15 days at photosynthetic photon flux (PPF) on the tray surface of 100, 200 and 300 μmol m-2 s-1 on days 0-2, 3-11 and 12-14, air temperature of 30°C, CO2 concentration of 1000 μmol mol-1, relative humidity of 80/100% (photoperiod/dark period) inside the system and photoperiod of 16 h d-1. Daily amounts of evapotranspirated and dehumidified water were increased with time due to increases in evapotranspiration area and PPF. Daily amount of dehumidified water was 90-95 % of the sum of evapotranspirated and humidified water. The amounts of irrigated, evapotranspirated, humidified and dehumidified water during the experiment were 49.5, 36.7, 24.3 and 55.9 kg m-2, respectively. Water contents of plants and soil at the end of the experiment were 1.6 and 10.8 kg m-2, respectively. Water utilization efficiency of the system was 0.93. These results show the amount of water use for transplant/plant production can be decreased to 24% of the amount of irrigated and humidified water when dehumidified water was reused for irrigation and humidification. Thus, the closed-type transplant production system is suitable for minimizing the water use in transplant/plant production.
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