Abstract
A simple irrigation control system with a fabric sensor was developed for high-Brix tomato production in the restricted root-zone hydroponics. The fabric sensor is composed of a L-shape acrylic unit (LAU) with a non-woven fabric (NWF, thickness: 2 mm, width: 20 mm) and an electrode unit (EU) . The vertical part of NWF in LAU is in contact with a pair of electrodes of EU, and the horizontal part of the NWF is placed under the rooting substrate in the bed. In this irrigation control system, electrification between the electrodes of fabric sensor is detected by a float-less level switch (FLS) . When water content in the substrate is high, the electrodes are charged with electricity because the NWF absorbs ionic water by capillarity. An irrigation pump starts working when the substrate becomes too dry to maintain the electric current in the electrodes. Water content in the substrate at the beginning of irrigation (IP) increased with increasing the height of placement of EU (HEU) and variable resistance (VR) between the electrodes as well as with decreasing the electric conductivity of nutrient solution (ECn) . Using the irrigation control system, the amount of irrigation changed automatically in response to substrate water content, which was affected by solar radiation and plant growing stage. Tomato fruits with Brix values higher than 9% were produced by using this irrigation control system under appropriate conditions of HEU, VR and ECn to optimize the water stress level of the plants.
