VEGETABLE CROP RESPONSES IN IMPROVED LOW-COST PLASTIC GREENHOUSES

Two new unheated prototype greenhouses were evaluated (a north-south oriented multispan of symmetrical 17-degrees roof slope and east-west oriented singlespan of asymmetrical roof angles, 18-degrees and 8-degrees), as possible alternatives to the conventional flat-roofed greenhouse, using a sequence of three crops (cucumber, indeterminate beans and sweet pepper), in Almeria, Spain. Around the winter solstice, when the vegetables reach their best prices in the market, the higher light transmission in the asymmetrical singlespan significantly increased higher cucumber and pepper yields, relative to the conventional plastic house. The additional light reducing materials of the multispan structure generated lower radiation transmisivity in spring and, subsequently, lower yields in the bean and pepper crops. The asymmetrical greenhouse should be more profitable than the conventional one if its building cost does not exceed 24% (equivalent to 1.45 US dollar m-2) of the building cost of the conventional plastic house.