Abstract
An optimization-based methodology for irrigation control and nutrient supply is devel-
open using common measurements of greenhouse climate: The process measurement has a
long time delay, and a feedforward (FF)control loop based on a mobel-based estimate of
water losses is used. A long feedback loop, by which the FF model is adapted using output
error feedback , is the mechanism used to minimise The control error. To read the output
error, a drain measuring device, or soil moisture meter, is necessary. The optimisation
method used is ageneral tool developed for real-time application and is capable of
optimising linear and non-linear systems.The minimisation algorithm used is based on a
variant of the powell direction set method in multiple dimemsions. It compares favourably in
speed of conrergence and accuracy when compared with linear regessors for linear systems.
It is therefore used as a generalised tool embedded in a modern greenhouse management
system. The method allows on-site on-line identification fo plant water needs. As a added
benefit, the method provides information for the caeaotion of crop transpiration models.
2001 Elsevier Science B.V. All rights reserved.