抄録
Irrigation control system using relative stem diameter (RSD) as the index of water stress was developed to stabilize a tomato production of high-Brix fruits by restricted root-zone hydroponics. This experiment has been conducted to investigate the effectiveness of this irrigation control system on characteristics of growth, yield and fruit quality of tomato plants. In this control system, irrigation starts when RSD is lower than the set point (SP) in the irrigation time period. Irrigation timing has been controlled with high SP (H-SP) and low SP (L-SP) in double-truss tomato cultivation by the hydroponics. As a result, RSD, amount of irrigation, plant height, leaf area, total fruit number and weight in L-SP were smaller than those in H-SP. However, Brix and acid content of tomato fruit in L-SP were higher than those in H-SP. Although a significant positive relationship was observed between evapotranspiration rate and amount of irrigation during growing period, the correlation coefficient in L-SP was higher than that in H-SP. These results suggested that amount of irrigation in L-SP was controlled with evapotranspiration rate under high intensity water stress and that application of optimum water stress by this irrigation control system was effective for the tomato production of high-Brix fruit.
