Micro-climatic effect of shading nets for crop protection in Mediterranean areas.

Mediterranean areas are characterized by hot summers that can determine bad environmental conditions for the growth of vegetable crops cultivated inside greenhouse. In Southern Italy, the traditional technique often employed by farmers during summer to reduce sun radiation and excessive internal air temperature is the whitening of the external side of the greenhouse plastic film through painting it with liquid calcium carbonate. More recently, the use of plastic shading nets is progressively affirming, thanks to a cheaper price and improved photo-selective properties, as a way to more effectively control the micro-climatic conditions inside closed greenhouse and tunnel. Thanks to a specific formulation of their chemical and physical properties, plastic nets may indeed combine the shade effect with some specific features useful for creating more favourable microclimatic conditions for the crop growth. With the aim to analyze the efficacy of different greenhouse shading techniques, an experimental trial was carried out by comparing two commercial plastic nets characterized by different shade effects, respectively equal to 60 % and 36%. These two plastic nets were tested in laboratory, where their radiometrical characteristics were determined. The same plastic nets were then installed on two different small-scale tunnels located in Southern Italy, in which inside air and relative humidity were measured during some late spring days. The results obtained through these experimental trails enabled to start a comparative analysis of the performances of the two tested shading nets, highlighting the role that a correct selection of the most suitable net may play on the final results in terms of crop protection from high temperatures and sunburns.