Abstract
To feedback plant water requirement into control of solution supply in hydroponics, we developed a method to measure drainage flow rate continuously. Drainage accumulates in an apparatus which we have developed, and its weight is measured continuously by a balance. Continuous measurement of drainage makes real-time monitoring of water uptake by plants practicable. We examined the usefulness of this method for controlling the supply of nutrient solution in an aeroponics of cucumbers (Cucumis sativusL.) . We compared two methods of controlling the nutrient solution supply. As a new method, to determine the amount of solution supply on the following day, we fit an equation relating water uptake to solar radiation. As a conventional method, solution was supplied whenever the integrated solar radiation reached 0.0926 MJ m-2 and fed back daily leaching fraction of a previous day into the control. In the first half of the experimental period, the water uptake in the new method was higher than the conventional method. In the second half, water uptake was similar for the two methods. Fruits yield of the new method was significantly higher than the conventional method.
