Contribution to the Optimization of the Plant Growth Factors in the Greenhouse and in the Open Land

Abstract

With regard to the modelling of plant growth processes, a distinction is suitably made between plant-physiological descriptive models and control models which are appropriate for the control design. The first part of the paper is concerned with the setting up of a control model on the basis of a plant-physiological model of the greenhouse cucumber developed by biologists of the Academy of Agricultural Sciences of the GDR, and with designing a strategy for the climate control ensuring optimum yields at limited expenditure of energy. This is performed by simulating the complicated descriptive model on a digital computer (substitute of the original) and parameter identification of a simplified non-linear multivariable Hammerstein and Wiener type resp. control model. On the basis of this model and of a multilevel control conception, a strategy is designed for achieving optimum climate control under “normal” environmental concitions. In order to take the actual and past outside climate into account, some repetitive optimizations with shortened horizon are performed. In the second part, a growth model of the sugar-beet developed by the Academy of Agricultural Sciences is processed such that mathematical optimization techniques can be used for maximizing the final yield. This model was already available as control model. The control variables are in this case the water stress (state of the water supply of the plant) and the nitrogen content of the leaves (nitrogen supply The off-line control design is carried out using a method of variable metrics without direction minimization.