Coltura e clima : effetto microclimatico dell'ambiente serra

The aim of a greenhouse is modification of the environment, to warrant improved conditions (with respect to field) for crop productivity. We start with a brief review of present knowledge about the effect of relevant climate factors on production, with particular attention to (sporadically) non-optimal tem- peratures, on the short- and long-term production pro- cesses. In the next section we consider the effect of a shelter (cover) and of its physical properties on the temperature within. We show that the energy balance makes it possible to determine the temperature within a passive greenhouse in given meteorological condi- tions, as it follows from two independent components: one solely determined by the radiative and thermal properties of the cover, the other only by the ventila- tion rate. In order to get the widest possible short-term manage- ment range, the properties of the cover should be selected through an analysis of the long-term climate. Short term management of temperature within this range is done through regulation of ventilation, once number, area, place and type of openings has been determined in such a way that enough ventilation is possible also in the conditions of maximum load. Particular attention is given to the effect of limited ven- tilation on carbon dioxide concentration inside the house, and on the consequences in terms of producti- vity. Thereafter we discuss the criteria on which a cost-benefit analysis of active vs passive greenhou- ses should be based. Finally, after a short introduction of the critical success factors of a horticultural holding, it is pointed out that the climate may be not the most important one, but certainly it is a factor with a large bearing on produc- tion costs. A careful analysis of the design parameters that affect conditions within a greenhouse makes it possible to select the most efficient combination, once the climatic conditions are known.