Top netting as a practical tool to mitigate the effect of climate change and induce productivity in citrus: summary of experiments using photo-selective nets

In many areas around the globe, climate change seems to be resulting in increased numbers of extreme heat waves during the spring and summer, and in warmer winters, which together might reduce the productivity of many fruit trees. The technology of top netting, which mitigates microclimate and protects outdoor crops from environmental hazards, might well serve as a practical solution for unfavorable climate change. Use of photoselective (color) nets, which differentially absorb various spectral regions and enrich the relative content of scattered/diffused light, have additional photo-morphogenetic/physiological effects. Therefore, the technology of top netting has three elements to be considered in evaluating its benefits: microclimate, shading and color. In a series of experiments, we examined the effect of color nets on microclimate, productivity, fruit quality, physiology, morphogenesis and water consumption of citrus trees during various stages of plant development. Experiments were conducted in 'Orri' mandarin and 'Valencia' orange orchards. By further including differential irrigation in a mature orchard, we also attempted to estimate water-use efficiency for a given net color. Here, we summarize published and unpublished results, and evaluate the effects of microclimate, shading and color on citrus productivity. Most of the effects could be attributed to microclimate mitigation and shading, but an overall increase in multiannual fruit number, size and yield was associated with red nets.