The impact of deficit irrigation on transpiration and yield of mandarin and late oranges

Citrus is a major evergreen fruit crop around the temperate areas and in the tropics. In the Mediterranean area, its production is largely dependent on irrigation, and given the current water supply situation and future scenarios, it is important to delineate strategies for optimizing water use. Regulated deficit irrigation (RDI) strategies have been widely studied in citrus and, although the results have been variable, they are often proposed as a means for improving water use and productivity under irrigation. We report here the effects of two RDI regimes on transpiration rate, yield and quality parameters in a 4-year experiment in two citrus species. Additionally, we present a meta-analysis of past research that investigated RDI applied during summer in citrus. Our results indicate that transpiration rate was decreased in the more stressed treatment as a consequence of the water shortage. Yields of mandarin and late orange were sustained when irrigation was decreased to 50-55% (related to control treatment) during the RDI period, making RDI a valuable tool for decreasing water application in citrus. Nevertheless, it is necessary to characterize the effects of water stress on transpiration and yield for the correct implementation of deficit irrigation strategies. The relationship between yield and relative transpiration observed in this study indicates that mandarin is less sensitive to water stress than late orange. It was probably related to a change in the dynamics of fruit growth and development. The results with different species and cultivars suggest that the RDI strategy must be fine-tuned for each cultivar according to its phenology. Once the sensitive phases are well-identified, citrus species are suitable for successful application of RDI regimes in most situations.