Effects of External Coloured Shade Nets on Sweet Peppers Cultivated in Walk-in Plastic Tunnels

Shading effect of external nets of different colours (white, green, yellow and red) on the yield of two “kapija” pepper (Capsicum anuum L.) cultivars was examined in walk-in plastic tunnels in Hungary under real cultivation circumstances. Shading nets decreased incoming radiation by 23-39% and reduced photosynthetically active radiation by 32-46%. The highest retention was obtained by yellow and green nets, in the range of 450-550 nm and 550-670 nm, respectively. Relation was reported between the degree of shading and the average air temperature of the tunnels, however, treatments did not decrease tunnel air temperature significantly, compared to that of unshaded and paint-shaded control tunnels. This can be explained by the applied proper ventilation and mist irrigation. A strong and negative relation was noted between the intensity of shading and the relative chlorophyll content (SPAD value) of leaves. Shading net treatments did not increase yields, yellow and green nets even decreased it. Instead of tunnel air temperature, yield was mainly affected by photosynthetically active radiation in the experiment. Strong positive linear relation was declared between the chlorophyll content of the leaves and the yield. Results of the current research led to the conclusions that under Hungarian climatic conditions the use of shading nets was less justified if proper cooling techniques (ventilation and mist irrigation) were applied; even under the relatively high incident radiation experienced during the trials. In greenhouses of less favourable climatic conditions, red or white shading nets are recommended instead of commonly used green ones in Hungary.