In soilless culture, water and nutrients must be frequently and precisely applied due to the reduced volume and low water holding capacity of the substrate. For this reason, irrigation scheduling is an important and difficult task. The use of an irrigation control tray with two electrodes (level sensor) is a simple way for controlling irrigation. Irrigation operation is triggered when the water level in the tray decreases below a preset level. This is a simple on-off control but inflexible

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... se it requires periodic manually calibrations. This work aims at developing a more efficient control system for the irrigation management of soilless culture. The control system is based on a Proportional Integral Derivative (PID) algorithm and it allows for fully automatic operation with a minimum set of variables in order to reduce the cost of the equipment. The results obtained demonstrate that the PID control algorithm can efficiently be used to control irrigation in soilless culture. The calculated average daily leaching fractions fit reasonably well to the target values. Nevertheless, some improvements of the control algorithm are required to reduce the variability of the calculated leaching fractions during the initial stage of crop development.