Photoselective shade nets for pepper cultivation in southeastern Spain

The high temperatures that occur during summer in the southeast of Spain produce a reduction of and difficulties in the setting of the fruits of pepper (Capsicum annuum); as a consequence, there is a decrease in the crop yield and quality. The use of shading nets can induce a drop of temperature, and consequently a decrease in the incidence of malformations in fruits produced by excess radiation in the summer months. The photoselective shade nets currently available contain spectral filters with differential light-scattering properties that alter the red/far-red wave-band (R/FR) ratio. The actual functions of coloured shade nets depend on the chromatic additives incorporated into the plastic and the knitting design. The physiological responses linked to light, such as photosynthesis and photomorphogenesis, produce effects on stem growth, leaf expansion, chloroplast development, chlorophyll synthesis, secondary metabolites, and harvest time. The objective of this work was to study the behaviour of a pepper crop with an extra-late cycle grown under various photoselective shading nets, placed on simple greenhouse structures. The nettings used were: silver in colour with 30% shading, pearl with 30% shading, red with 30% shading, red with 40% shading, and black with 30% shading, using as reference the crop without shading. The initial results show that with the photoselectivity provided by the pearl-coloured netting with 30% shading the fruits were harvested earlier and the yield was greatest, followed by that of the plants cultivated under the silver-coloured netting with 30% shading. For the red-coloured netting, the results were similar for the 30 and 40% shading, being inferior to those of the pearl and silver nettings. However, the nutritional values of the fruits, both those harvested when green and those harvested when red, were best with the silver-coloured photoselective mesh. It is worth highlighting that it was the contents of Fe, K, Na, Mg, Mn, and Zn that differed most greatly between the different shade net treatments and according to the maturation at harvest (red or green fruits).