In The Netherlands there are almost 15,000 farms growing greenhouse vegetables.
The average areas of greenhouse grown vegetable crops per farm are comparatively small.
Table 1 gives the number of farms which produce vegetables, according to their size, for 1960 and 1966.
The number of these farms has not varied much between 1960 and 1966. However, the distribution of these farms in the different size classes has been changed.
The number of farms with less than 1,000 m2 of greenhouse vegetable producing area has greatly decreased, in favour of farms of greenhouse areas over 5,000 m2 and mainly over 7,500 m2. The average greenhouse area has increased from 2,600 m2 to 3,400 m2.
Individual farms vary greatly in respect to their methods of management and in their interior and exterior conditions of production, due to which the economic results are also quite different, not only in the various regions of the country, but in one and the same region, and even of the same economic type.
Table 2 illustrates the financial results of 32 specialized greenhouse vegetable producing farms in the Berkel municipality.
All these greenhouses are exclusively artificially heated ones, designed mainly for growing tomatoes and cucumbers.
The reasons for the discrepancies of the economic results in The Netherlands are elucidated by means of comparative economic studies.
As a result of such studies, it has been established that with comparable vegetable varieties, the differences in the economic results can be explained in most cases (often in two thirds of the cases) with the differences in the level of their net profits.
By the term 'Level of net profit' we understand the net profit in percentage of an accepted norm, actually received by the farm.
This notion can easily be explained by the following example:
Figure 1 illustrates the differences in the net profits, derived from tomatoes, grown in heated greenhouses at different planting dates in the Westland region in 1966. Every point represents an individual farm.
Farm "A" planted its tomato seedlings on 20 December and received a net profit of 1710 guilders.
We accept as a norm the line drawn over figure 1. The net profit norm on 20 December was 1530 guilders.
Thus the level of net profit in farm "A" was 1710/1530 x 100 = 112.
Due to the great effect of the level of net profit on the economic result we tried to establish by means of a comparative economic investigation, based on the factorial analysis, which is the cause of the differences in the level of net profits of growing tomatoes in heated greenhouses.
We could not reach concrete explanations for all the differences displayed.
It was established, however, that separate factors were clearly connected with the level of the net profits.
These factors were, among others, the type of the greenhouse, the expenditure of fuel and of CO2.