Prediction of production, requisite of an integrated approach.

In modern greenhouse industry the grower besides being a good grower also has to be a good manager. In fact the annual cost of labor, energy and capital investments is such that proper decision making is of primary importance. It is in this context that the problem of energy saving should be considered. The complexity and the range of many of these decisions make it highly desirable to provide the grower with suitable tools for making optimal choices. Depending on the time scale three levels can be distinguished where decisions are made: strategical decisions: one - many years tactical decisions: months - year operational decisions: days - weeks - minutes - 24 h At each of these levels prediction of production may play an important role. Crop growth models therefore are a tool that may assist the grower in decision making. The present state of the art in crop growth models for horticultural applications will be discussed briefly. Depending on the decision- level and the type of decisions different models can be used. Examples of decisions and the involvement of models will be given. Ultimately the grower aims at certain goals. It is the task of future decision support systems to take these goals into account at each decision level, but integrated within an overall decision structure. Speculations on how modern information technology may be involved in future greenhouse management will be made with an emphasis on the role of crop growth models.