Abstract
A new type of the nutrient sensor using ISFET (ion-sensitive field-effect transistor) has been investigated. Measuring the ion concentration of a solution in plant growh media (ex. rockwool) is difficult and has not been carried out in practice. The authors anticipated that an ISFET, with its advantages of small size and low output resistance, could be used to measure the ion concentration of such a solution in growth media. In this study, the authors examined the basic characteristics of ISFET-based nutrient sensor probes in rockwool as follows : 1) response characteristics for nitrate ion concentration changes in rockwool, 2) reproducibility of the output when they were inserted into rockwool repeatedly, 3) output dependence on the rockwool water content, 4) output dependence on the distance between the ISFET and a reference electrode, 5) long-term stability of the sensitivity and output baseline in rockwool. These experiments have shown that the sensors have sufficient stability for use in this kind of measurement. The authors have found that ISFETs are able to measure the ion concentrations for a nutrient solution in growth media such as rockwool.
