Seasonal Optimization of the Greenhouse Environment For a Simple Two-stage Crop Growth Model

A simple, single-state-variable, two-stage crop model has been developed to investigate a possible change in the optimal control policy when the crop switches from the vegetative stage to the reproductive stage. The co-state variable (marginal value) of dry matter, was transformed in a way that made the resulting control policy constant over the season. The policy remains constant, independent of weather variation and crop development, and can be easily adjusted to price changes. Applying this simplified approach to real crops, requires the determination of the appropriate parameter values. This is demonstrated by fitting the simple model to data obtained by simulation with a comprehensive greenhouse tomato model, TOMGRO. The results show that, at least for a stationary (periodic) weather, the behaviour of the simple model is remarkably similar to that of TOMGRO. Consequently, the optimal control policy of the simple model could serve as a sub-optimal control for TOMGRO.