C.H.M. van Bavel
In discussing the theme, it appears necessary to distinguish between two broad climate zones in which greenhouses are used commercially. In the cool and temperate zone, typified by N.W. Europe, light is at a premium during the winter and the associated solar energy, that is not actually used in dry matter production, cannot furnish the energy needed for heating. In the warm and subtropical zone, typified by Southern Japan or the Mediterranean, light is less at a premium, solar energy can, in theory, supply normal heating needs, and excessive plant temperatures are a problem.

Thus, in the first or cool area, the value-in-use of light energy exceeds that of the value-in-use of any form of thermal energy. The challenge is to increase the effectiveness of the light resource, that itself cannot be augmented, by ever-increasing perfection of conventional approaches to energy conservation for a greenhouse area that appears essentially stable. It is obvious that this process requires analysis of its economics, rather than to be confined to engineering and horticultural measurements.

On the other hand, in the second, warmer area that is generally situated south of 40°N, the greenhouse industry has rapidly expanded and continues to do so. Precedent and transferable technology are often lacking, and the research opportunities are in the areas of innovative use of materials and of solar and industrial waste energy utilization.

In regards to research methodology, it is noted at this and at previous symposia, that much experimentation takes place without the benefit of previous analysis. A number of physical models of greenhouses are available. Some incorporate plant productivity as well, and can be amplified to sort out the economic options. The use of the theoretical method to intelligently plan and design experiments ought to be greatly increased.

The second suggestion that is made is that the behavior of green-house crops should be more intensively studied during their growth cycle. New greenhouse technologies cannot be appreciated from standard measurements of yield, earliness, quality and so on. An energy saving technology is likely to affect light levels, plant temperatures, humidity and CO2 levels in the greenhouse at the same time as it reduces energy losses. Therefore, it is necessary to have information about actual plant temperatures and water potentials, transpiration and photosynthesis rates, among others, to understand the integrated and commercially important test results. It seems certain that this goal cannot be accomplished without automatic, computer-controlled data collection systems.

van Bavel, C.H.M. (1981). FUTURE OUTLOOK AND RESEARCH NEEDS. Acta Hortic. 115, 705-706
DOI: 10.17660/ActaHortic.1981.115.80

Acta Horticulturae