In hydroponic systems or those that use the fertigation, the total amount of soluble salts in the nutrient solution has a significant impact on crop productivity. An adequate fertilizer concentration can be modified in response to stages of plant development through indirect monitoring of electrical conductivity of nutrient solution. The objective of this work was to evaluate a low cost electronic circuit to measure the electrical conductivity based on frequency measurements. The electronic circuit was connected to a computer using the parallel interface and calibrated with 16 KCl solutions. The solutions temperature was maintained at desired levels with a controlled temperature equipment. Regression analysis was used to obtain relationships between frequency and resistance in order to measure the electrical conductivity and the solution temperature based on measured data of frequency. The coefficients of determination obtained from this study showed excellent correlations (R² > 0.997). The results demonstrated that the proposed circuit is capable of measuring the electrical conductivity of the solution from 0.10 to 10.15 dS m-1 with considerable accuracy, compensating automatically instantaneous temperature variations.
conductivity meters; hydroponic; fertigation
