Abstract
A closed hydroponic system was established in the cultivation of single-truss tomato, where the drainage was utilized for improving the fruit quality. Tomato (Lycopersicon esculentum Mill) plants were grown in a “wet-sheet culture” (WSC) bed, where a water-retaining sheet (non-woven fabric) was used as a growing medium to supply nutrient solution. Nutrient solution with EC 1.2 dS m-1 was applied by tube irrigation. Supply of the solution was controlled with a level sensor, and surplus solution was overflowed from the bed and preserved into a reservoir tank. Tomato seedlings were transplanted to the WSC bed in a density of 10 400 plants 10 a-1 at early June in 1997, and main shoots were pinched after the anthesis of the first truss. On an average, 20 to 30% of daily-supplied nutrient solution was overflowed as drainage. At the final stage of ripening, the preserved drainage in the tank was concentrated to EC 5.0 dS m-1, and re-supplied to the bed instead of fresh solution. By the end of the harvest, all the preserved drainage was used up by the plants, and no waste solution was drained out of the greenhouse. Moreover, fruit cracking, which frequently occurred under high temperature conditions, could be completely prevented by the application of the concentrated drainage, possibly due to the salinity effect.
