THE EVAPORATIVE POWER OF AIR AND THE POSSIBILITIES OF CONTROLLING ITS ACTION IN GREENHOUSES

This paper is a compendium of data obtained regarding temperature, hygrometry and evaporation within plastic tunnels and glazed greenhouses handled in several ways in order to determine the conditions essential to a minimum possible cuticular transpiration and to avoid losses in net assimilation caused by a stomatal regulation.

The results show that a sideway ventilation exercises a substantial influence upon the evaporation under the area’s mild wind conditions, making it advisable to dispense as far as possible with side ventilation.
Using glazed greenhouses, essentially enclosed and humidified, and PVC tunnels, lower evaporation values are obtained than with open greenhouses during the months of the warm season.
In autumn and winter periods the enclosed and non-humidified greenhouses show evaporation rates perceptibly lower than the external ones, in spite of the fact that the temperatures involved exceed the external ones by 10–12° C, whereby the evaporation-promoting effect of ventilation becomes evident once again.

The conclusion can be drawn that for our area it is advisable to furnish the greenhouses with a good ridge ventilation and to omit the lateral one in order to avoid high evaporation rates.
It is even better to use ventilation to a minimum extent and to maintain high rates of hygrometry by using humidifiers.

Symposium on Cultivation of Flowers under Protection in the Mediterranean Regions

A. García-Homs, J. Cardús

https://doi.org/10.17660/ActaHortic.1974.43.5