EFFECTS OF GREENHOUSE COVERS ON SEEDLESS CUCUMBER GROWTH, PRODUCTIVITY, AND ENERGY USE

Effects of single-glass (glass), double inflated polyethylene film (D- poly), and rigid twin acrylic (acrylic) panels, as greenhouse covers, on seedless cucumber growth, productivity and energy use were investig ated over three spring seasons (1988, 1990 and 1992), The early and fi nal marketable yields of plants grown in D-poly houses were similar to or higher than those grown in glass houses. Also, plants grown in D-p oly houses produced a similar or higher percentage of large and a lowe r percentage of small fruits than the plants grown in glass houses. Th e early and final marketable yield and percentages of fruit grades wer e similar in D-poly and acrylic houses; an exception was the early mar ketable yield in 1992 which was higher in the acrylic houses, Light tr ansmission was the highest in glass houses, intermediate in acrylic ho uses and the lowest in D-poly houses. Relative humidity was highest in D-poly, intermediate in acrylic, and the lowest in glass houses. The plants in D-poly houses grew and developed faster (more leaves and flo wers) than those in glass houses. The leaf size of plants in D-poly ho uses and glass houses was similar, but the dry matter content and spec ific leaf weight of plants grown in D-poly houses were significantly l ower (40% less) than those in glass houses. Plants in D-poly houses mi ght have acclimated to the low light conditions by reducing specific l eaf weight and increasing their light interception efficiency. Plant g rowth and development in acrylic and D-poly houses was similar, For cu cumber production in climatic conditions similar to South Western Onta rio, the D-poly greenhouse is strongly recommended, because there is n o loss of productivity in comparison with a glass house, while great s avings on initial investment and energy use are achieved. (C) Elsevier Science B.V.