Covering materials to improve greenhouse microclimate during summer in hot climate

The use of nets and photoselective materials are two of the methods used for providing an acceptable microclimate inside the greenhouse during summer cultivations in hot climates, though the efficacy of these materials in improving the microclimate conditions has still to be verified. To this aim this study is focused on the comparison of three different greenhouse covering materials (a PE film, an insect-proof net and a photoselective red-coloured film) used in an experimental trial of tomato cultivation during summer, in order to analyze the effects on microclimatic conditions. During the growing cycle climatic variables inside and outside the greenhouse were continuously recorded. Besides, laboratory measurements of perpendicular spectral transmissivity of the materials were performed in the waveband of the solar radiation and in the infrared range. From these measurements some parameters characterizing the transmitted light were calculated, showing that the PE film is the most transparent in the solar waveband, the red film is the most opaque in the infrared range and it causes a decrease of the cryptochrome-related parameters. From in situ measurements, vapour pressure deficit, air and soil temperature frequencies over the experimental period were calculated to identify stress conditions for the crop. The results showed that in the greenhouse covered with the insect-proof net, the temperatures were very similar to those recorded outside while the photo-selective film was not effective to control temperature rise during summer period.