SEASONAL OPTIMIZATION OF THE GREENHOUSE ENVIRONMENT FOR A SIMPLE 2-STAGE CROP GROWTH-MODEL

A simple, single-state-variable, two-stage crop model has been develop ed to investigate a possible change in the optimal control policy when the crop switches from the vegetative stage to the reproductive stage . The costate variable (marginal value) of dry matter, was transformed in a way that made the resulting control policy constant over the sea son. The policy remains constant, independent of weather variation and crop development, and can be easily adjusted to price changes. Applyi ng this simplified approach to real crops, requires the determination of the appropriate parameter values. This is demonstrated by fitting t he simple model to data obtained by simulation with a comprehensive gr eenhouse tomato model, TOMGRO. The results show that, at least for a s tationary (periodic) weather, the behaviour of the simple model is rem arkably similar to that of TOMGRO. Consequently, the optimal control p olicy of the simple model could serve as a sub-optimal control for TOM GRO. (C) 1998 Silsoe Research Institute.