Effects of Insect-Proof Screens Used in Greenhouse on Microclimate and Fruit Yield of Tomato (Solanum lycopersicum L.) in a Mediterranean Climate

The main objective of this study was to investigate how the screens influence ventilation, temperature and humidity inside the greenhouse, and analyse their effect on tomato yield. Four tomato (Solanum lycopersicum L.) crops were grown in three multispan greenhouses over two seasons (2007/08 and 2008/09) in southern Spain. The experimental greenhouses were divided in two by a low-density polyethylene (LDPE) film of 180 mu m thickness. The sidewalls and roof vents of the greenhouses were covered with different insect-proof screens in the two halves of each greenhouse, with porosities phi ranging from 0.32 to 0.47. In order to quantify the ventilation reduction due to the screens we have calculated the openings' discharge coefficient C-d by testing in a wind tunnel. We have also analysed the screens' effect on the greenhouse ventilation rate R by means of a two-dimensional Computational Fluid Dynamics (CFD) model. The results indicate maximum differences of 27% for R and 38% for C-d between the different screens analysed. However, the wind and temperature conditions in the experimental greenhouse are generally less extreme than those simulated, reducing the effect of the ventilation on the inside climate. Consequently, the statistical analysis of experimental data obtained from four tomato crops in the three experimental greenhouses, showed that mean daily temperature, mean daily water vapour pressure deficit (VPD) and marketable yield were not significantly correlated with porosity. http://www.actahort.org/members/showpdf?booknrarnr=927_88