METHODOLOGY OF COMPARISON OF GREENHOUSE-TYPES

In 1956–1957 in the Netherlands the glasshouse-area increased very rapidly and as a consequence the question concerning the best type of glasshouse, especially for the growing of tomatoes, became urgent.

This problem can be approached in two essentially different manners. The first possible approach has a more direct character. A crop is grown in different glasshouse types and data regarding the yield are collected. These data are used for an economic comparison of the glasshouses concerned. This method is directly related to what occurs in practice and produces an answer within a relatively short time.

The other method involves an indirect approach by which the problem is split into two parts. On one hand the climatological requirements of the crops to be grown are determined by ecological experiments, on the other hand the essential differences in climate between various glasshouse constructions are determined.

This method has a more fundamental character and the results have a more general use than the results of the indirect approach. The results of the indirect method, however, will only be available after a longer time.

In 1958 we started an experiment using the direct method, the choice being dictated by the great need for information at short notice. Two other reasons have also influenced this choice: firstly the basic question: Venlo-block or a wide span glasshouse for heated tomatoes and secondly the expectation that the differences between these glasshouse types would not be too difficult to detect.