Abstract
This study was carried out in order to develop electro-conductivity (EC) sensor for rock-wool culture. The EC sensor was developed according to the method of Ito (1982) . The sensor consisted of a ceramic plate (1×10×30mm), on which two electro-conductive pastes were printed as electrodes. The power of the EC sensor, measured by the standard EC measuring amplifier, was 1/3 of that of a conventional one, and the dead time in the measurement was approximately 15 min. The linearity between the measured value of each sensor was maintained in the range of 1.0 to 8.0 mS/cm. The degree of water saturation in the rockwool mat surrounding the ceramic plate affected the power of the EC sensor. However the effect was negligible for practical use when the ceramic plate was placed in the lower layer of the .rockwool mat.
The EC value was measured automatically early in the morning when the fluctuations of the temperature and nutrient solution in the mat were minimal. The values obtained gave adequate information for the irrigation control system of rockwool culture.
