PHOTOSELECTIVE ANTI-HAIL NETTING FOR IMPROVED CITRUS PRODUCTIVITY AND QUALITY

Nets are commonly used to protect agricultural crops from excessive solar radiation, environmental hazards and pests. The netting approach was further developed for differential filtration of sunlight, concomitant with the desired physical protection. A series of photoselective nets (ColorNets) was developed for outdoor use, each one differentially absorbing the ultraviolet, blue, green, red, far red or infrared spectral regions, and at the same time enriching the relative content of scattered/diffused light. This spectral manipulation is aimed at specifically promoting desired photomorphogenetic/physiological responses, while light scattering improves light penetration into the inner canopy. Enriching the intercepted light with productive parts of the spectrum, while reducing the less productive parts, allows better utilization of solar energy. We investigated the photoselective-net approach in citriculture in a commercial ‘Ori’ mandarin orchard. The experiment included four ColorNets (red, yellow, white and transparent) and a control plot. The effects of the nets were investigated by analyzing the following groups of variables: climatic (temperature, relative humidity, wind), tree physiology (photosynthesis, stomatal conductivity, water consumption, water potential, chlorophyll content) and productivity (flowering, fruit set, yield, fruit quality). Nets slightly increased the minimal temperature and slightly reduced the maximal temperature. However, more significant effects were an increase in relative humidity and reduction in wind. All of the nets, especially the white and transparent ones, significantly reduced water consumption, up to 20% relative to non-netted controls. Interestingly, ¹³C-discrimination measurements suggested that stomata are more open in trees grown under red and yellow nets. A significant, up to twofold increase in yield was evident with the white and transparent nets. Fruit external quality was remarkable enhanced by all nets. These and other results demonstrate the unique potential of photoselective, light-dispersive netting in citriculture.