THE DYNAMIC BEHAVIOUR OF SALINITY CHANGES IN A CLOSED NFT GROWING SYSTEM

In the Netherlands a law will enforce the use of closed growing systems in greenhouses. A project is initiated at IMAG-DLO to introduce ion-selective measurement and controlled injection of singular liquid nutrients in closed growing systems.

As part of this project step and impulse response tests are carried out to study the dynamic behaviour of salinity changes in an NFT growing channel. The paper describes a time delay algorithm for the trickle irrigation system and an aggregated dead zone model for the growing channels in closed NFT growing systems. It suggests a Smith Predictor as a controller for a nutrient dispenser system.

Ion-selective measurement on a practical scale will only be available for a few nutrient ions. Controlled injection of singular liquid fertilizers will need information on plant uptake of ions which cannot be measured in relation to ions which can be measured.