GREENHOUSE MICROCLIMATE AND ITS MANAGEMENT IN MILD WINTER CLIMATES

In the last decades, protected crops have experienced a very strong development in the mediterranean area (Spain, Greece, Italy, South of France, Turkey, North Africa…). This development is due firstly to the favorable winter climate of these regions, where levels of temperature and radiation are significantly higher than in the North-European countries.

In most cases, cheap simple structures and equipments are used, mainly in order to increase day temperature in wintertime and to protect against wind damages.
This is a very first step in modifying microclimatic conditions.
It is clear that this step is not sufficient for high productivity, good quality, or if a precise crop planning has to be respected.
In order to achieve these goals, other climatic parameters have to be controlled and managed :

1. In winter :

   • night temperatures (heating systems, better insulation, solar energy storage…),

   • air humidity and condensation control (ventilation, heating, dehumidifying systems…),

   • CO₂ and light levels (CO₂ enrichment, cover optical properties, greenhouse structure and orientation…).

2. In summer :

   • very high temperatures occur under greenhouse during late spring and summertime in the mediterranean areas, with negative consequences on production and quality : ventilation, shading, fog or mist systems can be used in order to control these high temperatures,

   • together with the increase in air temperature, vapor pressure deficits are increasing also, and induce water stress, stomata closure, low photosynthetic rate… A good control of air humidity and water supply is necessary in order to get humidity levels suitable to a given crop (ornemental crops are among the most sensitive to this parameter).

In this paper, some technical solutions to improve the microclimatic conditions under greenhouses are presented.
The evolution of structures and equipment in the next years will be discussed, taking into account the specific economic conditions of the mediterranean and mild – winter countries.

International Symposium on Protected Cultivation of Ornamentals in Mild Winter Climates

B. Alain

https://doi.org/10.17660/ActaHortic.1989.246.1