Shading methods for crop protection under greenhouse in mediterranean areas

Mediterranean areas are characterized by hot summers, which can determine unfavorable environment for the growth and quality of the crops which are cultivated inside a greenhouse. In order to control the greenhouse air temperature raise, one of the most common traditional solutions utilized by growers is the shading of the greenhouse against excessive solar radiation through the use of calcium hydroxide (i.e., slaked lime) or other paints applied on the greenhouse cover (so-called, whitening) with the aim to reduce the incoming solar radiation and limit the inside air temperature. More recently, the use of plastic shading nets is progressively affirming due to their cheaper price and photo-selective properties, as a way to effectively control the microclimatic conditions inside greenhouses and tunnels. Thanks to a specific formulation of their chemical and physical properties, plastic nets may indeed combine the shading effect with some specific features useful for creating more favorable microclimatic conditions for the crop growth. With the aim to analyze the efficacy of the shading effect of plastic nets in different climates, two experimental trials have been carried out by comparing five identical smallscale tunnels; two installed in Southern Italy, and three in an arid climate (Saudi Arabia), in which the inside air and soil temperatures have been measured. The two tunnels were covered with EVAC plastic film, one of them also covered with plastic net, in contact with the external side the film. The three tunnels were covered with PE film; two of them were covered with two different plastic nets, fixed at 20-cm apart from the film cover. The radiometrical characteristics of the plastic films and nets were determined. The results obtained through these experimental trails enabled to start a comparative analysis of the performances of the tested net, highlighting the role that a selective filtering of solar radiation may play on crop protection from high temperatures and quality of light arriving to the crops.