ISE and Chemfet sensors in greenhouse cultivation

The development and market introduction of ion-specific sensors, like the ion selective electrode (ISE) and ion selective field effect transistor (ISFET) sensor, has paved the way for completely new systems for application of fertilisers to crops in greenhouses. This paper illustrates the usefulness of these sensors, by elaborating on a new fertigation strategy in greenhouses aiming at less pollution, more efficient use of fertilisers and eventually, crop quality control. The basic idea of this strategy is to keep the concentration of the individual ions in the drainage water of a set of plants constant at a level that is non-limiting to ion-transport and nutrient uptake. In this way, the uptake of ions by the plants is intrinsically compensated for, thus, satisfying the demand of the plant by exploiting its self-regulatory behaviour. Measuring ion concentrations also enables the design of even more advanced feedback-controlled nutrient dispensers, functioning on the basis of a model-based control strategy that uses sensors connected to the plant.