Effect of shading and insect proof nets on screenhouse light environment

Abstract

Screenhouses covered by shading or insect proof screens are becoming popular among growers in arid and semiarid regions like the Mediterranean area, due to the environmental, economic and agronomic benefits they offer. The positive impact of a net-covering on plant behaviour can be mostly explained by the more favourable microclimate under a screen-house than outdoors. However, manipulation of light environment by shading using screens requires the knowledge of the characteristics and parameters of the modified light regime, on both the quantitative and qualitative aspects of light environment under the screens. Thus, the effects of cover optical properties on screenhouse radiative environment were investigat-ed, under Mediterranean conditions during summer in Central Greece, under three net-screen materials (i) a pearl insect-proof screen (IP-78), (ii) a white insect proof screen (IP-59) and (iii) a green shade-screen (GS-62) with values of the transmittance to photosynthetically active radiation (τPAR) of 78%, 59% and 62%, respectively. All screens induced impover-ishment in the blue wavelength band (B, 400-500 nm) and enrichment in near-infrared broadband (NIR, 700-1100 nm) with respect to PAR (400-700 nm), and modified photomor-phogenetic parameters such as the ratios B:FR (Blue vs Far-Red), R:FR (Red vs Far-Red) and the phytochrome ratio, ζ.