EFFECT OF SHADING ON GROWTH AND QUALITY OF SUMMER SPINACH

Spinach (Spinacia oleracea L. cv. Active) was cultivated four times during the summer season (from June to September) in four plastic houses with different aluminum coated polyethylene nets which had 0%, 30%, 45%, and 60% shading ratios, respectively, to prevent the increase of air and soil temperature in plastic houses. Integrated solar radiation in plastic houses was decreased as shading ratio increased. Air and soil temperatures were kept the same. Spinach growth was the best under 45% shading ratio in June, August, and September and 60% in July. Sugar and ascorbic acid (vitamin C) contents were decreased as shading ratio increased in all seeding times. Nitrate content was highest under 45% shading ratio in July, August and September and 30% in June. Soluble oxalate content was highest in June, July, and August and lowest in September in the non-shaded house.