GROWTH AND YIELD CONTROL OF GREENHOUSE VEGETABLES ON THE BASIS OF YIELD MODELS IN THE GDR

The Institute for Vegetable Production Großbeeren belonging to the Academy of Agriculture Sciences of the GDR has for a longer time aimed at controlling growth and yield of greenhouse vegetables on the basis of models. The following report deals with the strategy and results obtained so far under the direction of Heissner.

The work can be diveded in the three main steps:

1. Development of plant-physiologically founded models describing growth an yield formation. In the following they will be called functional models, they were developed by Augustin till 1980 for cucumbers (Augustin and Schmidt, 1980; Augustin, 1984) and till 1986 for tomatoes (not published).
2. Development of aggregated control models on the basis of the functional models as well as simulative tests of different control strategies and target functions. This work has been done at the Technical College by Reinisch, Puta, Schmidt, Arnold and Markert from 1980 and is still being continued.
3. Yield control tests of cucumber production in vegetative experiments since 1985.

Giving the chief points only, the following results have been obtained:

1. Models of growth and yield formation

Having examined different ways of development models of growth and yield formation of fruit bearing vegetables considering the long vegetative phase and the permanent relationship between vegetative growth and fruit development, we decided to explain the yield formation by the important plant-physiological subprocesses. It was expected that a logically founded, functional, that is dynamic, model could describe the connections in a form suitable for optimization.

Figure 1 shows the input and output variables of the models as well as the main physiological parameters derived. For the other important influence factors, above all water and nutrient supply, we presumed optimal conditions, for example by the use of automated