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.

Irrigated agriculture is the primary user of water worldwide. Any method that reduces the consumption of water in irrigated agriculture without a reduction in yield and fruit quality would be highly desirable. One of the approaches currently being implemented in fruit trees and vines is regulated deficit irrigation (RDI). It consists of the application of water below the full crop-water requirements during periods of crop growth that are less sensitive to water deficit, which is a viable strategy during periods of water shortage. The results of on-farm experiments indicated that RDI based on stem water potential can be used successfully on nectarine trees in the area of Cordoba (Southern Spain) in deep soils. This strategy reduced the amount of irrigation water without reducing yield or crop value. One of the main limitations to the application of RDI to commercial orchards is the need of plant water status indicators like water potential. But to measure the latter is time consuming and therefore the number of trees that can be monitored continuously is a limiting factor. New tools should be developed for the early detection of water stress and one such tool is the high spatial resolution thermal remote sensing imagery.

XXVIII International Horticultural Congress on Science and Horticulture for People (IHC2010): International Symposium on CLIMWATER 2010: Horticultural Use of Water in a Changing Climate.

The daily course of leaf photosynthesis, stomatal conductance and water potential was followed in drip-irrigated olive trees, cv. Picual between 1993 and 1995 in Cordoba, southern Spain. The results indicate that leaves fully open stomata early in the morning, when vapour pressure deficit (VPD) is low, showing high assimilation and low transpiration rates. Maximum CO2 assimilation ranged from 7 to 18 mu mol m(-2) s(-1), depending on the time of the year. Some time before noon stomata partially close reducing leaf photosynthesis as well as transpiration. Such closure occurs in all seasons although it is less evident in spring and autumn. While in spring, summer and autumn midday stomatal closure appears to be related mainly to VPD and air temperature, in winter, low soil temperatures effect low leaf water potential (Psi(l)) and stomatal closure despite high soil water potential (Psi(s)).