ALTERNATIVE GREENHOUSES FOR MILD WINTER CLIMATE AREAS OF SPAIN PRELIMINARY REPORT
During the last decade, plastic greenhouses have expanded, in the mild winter climate areas of the world. In south-eastern Spain, the greenhouse industry (over 13 000 Ha in 1987, in the province of Almeria alone) is based on the use of polyethylene (PE) film placed on very simple wood or metallic structures of low cost, most of them with a flat roof. Climate inside these plastic greenhouses is far from optimal for vegetable production, because insufficient ventilation and lack of heating lead to inappropiate extreme temperatures. As alternatives to the conventional one two new prototypes of unheated greenhouses are been evaluated (a north-south orientated multispan of symmetrical 17° roof slope and an east-west orientated singlespan of asymmetrical roof - 18° and 8° - angles), in Almeria, Spain at 36° 48' N latitude. Preliminary results show that, around the winter solstice, the highest light transmission is obtained in the asymmetrical singlespan followed by the multispan. Roof ventilation reduced notoriously maximum air temperatures in the alternative greenhouses relative to those in the conventional flat roof structure, during the high radiation period. Significant differences in yields, 5 % level, were detected among greenhouses for an autumn-winter cucumber crop, during some cropping periods, being higher in the asymmetrical singlespan (total and high size yield) than in the conventional structure. The latter yielded less large-sized fruits than the multispan in one of the cropping periods. Around the winter solstice, crops growth rates were lower in the conventional than in the alternative structures.
Castilla, N., Lorenzo, P., Montero, J.I., Fereres, E., Bretones, F., López-Gálvez, J. and Pérez-Parra, J. (1989). ALTERNATIVE GREENHOUSES FOR MILD WINTER CLIMATE AREAS OF SPAIN PRELIMINARY REPORT. Acta Hortic. 245, 63-70