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size distribution toward more favourable fruit value and thus, increasing grower revenue.On the other hand, in a small citrus fruit such as Clementina de Nules, it was concluded thatthe best RDI strategy was irrigation at around 50 percent ET c from July (after June fruit drop)to the beginning of September when late summer autumn rainfall helped to quickly releaseplant water stress (Gonzalez-Altozano and Castel, 1999). The usefulness of this strategy hasalso been recently corroborated in commercial situations (Ballester et al., 2011).It should be noted that the utility of ET c -based RDI regimes depends, in part, on soil conditionsand the amount and storage of winter rainfall in the root zone, especially early in the season.For example, with relatively high winter rainfall, deep soils, and a full coverage irrigationsystem that promotes roots in the entire potential root zone, reducing applied water early inthe season may not induce tree water deficits and will not have much impact on tree waterstatus. On the other hand, with the opposite conditions — low winter rainfall, shallow soils,and localized (drip, microsprinkler) irrigation, there will likely be a rapid decline in tree waterstatus in response to deficit irrigation soon after is imposed.For this reason, the use of a plant-based indicator of tree water status is highly recommendedwhen applying RDI for validating that the desired stress level is being achieved in the tree.In conclusion, given the very wide diversity of combinations of species, cultivars, market andgrowing conditions that exist in citrus, the need to tailor RDI strategies to specific conditions iseven more pressing that for other fruit trees and makes it difficult to recommend generalizedRDI programmes.ReferencesAllen, R.G., S. Pereira, L., Raes, D. & Smith, M. 1998. Crop evapotranspirations-Guidelines for computing waterrequirements. In: FAO Irrigation and drainage paper No. 56. Rome, FAO.Ballester, C., Castel, J., Intrigliolo, D.S. & Castel, J.R. 2011. Response of Clementina de Nules citrus trees to regulateddeficit irrigation. Yield components and fruit composition. Agricultural Water Management. 98:1027-1032.Barbera, G, & Carimi, F. 1988. Effects of different levels of water stress on yield and quality of lemon trees. In:Proceedings of the sixth international citrus congress, pp. 717-722.Brych & Luedders. 1988. Citrus responses to different irrigation levels in South Portugal (Algarve). Proceedings SixthInternational Citrus Congress 1831-1836.Castel, J.R. 1997. Evapotranspiration of a drip-irrigated Clementine citrus tree in a weighing lysimeter. ActaHorticulturae, 449 (1), 91-98.Castel, J. R., Bautista, I., Ramos, C. & Cruz, G. 1987. Evapotranspiration and irrigation efficiency of mature orangeorchards in Valencia (Spain). Irrigation and Drainage Systems, 1(3):205-217.Castel J.R. & Buj, A. 1989. Response of mature ‘Salustiana’ oranges to high frequency deficit irrigation. IrrigationScience 11:121-127.Chartzoulakis, K., Michelakis, N. & Stefanoudaki, E. 1999. Water use, growth, yieldand fruit quality of ‘Bonanza’ orangesunder different soil water. Advances in Horticultural Science 13:6-11.Davies, F.S. & Bower, J. 1994. Water Stress, gas exchange and fruit set of ‘Olinda’ Valencia orange trees in EasternTransvaal area of South Africa. Acta Horticulturae 365:121-127.Eliades, G. 1994. Response of grapefruit to different amounts of water applied by drippers and minisprinklers. ActaHorticulturae 365:129-146.FAO. 2011. FAOSTAT online database, available at link http://faostat.fao.org/. Accessed on December 2011.Fereres, E., Cruz-Romero, G., Hoffman, G. L. & Rawlins, S. L. 1979. Recovery of orange trees following severe waterstress. Journal of Applied Ecology 16:833-842.García-Petillo, M. & Castel, J. R. 2007. Water balance and crop coefficient estimation of a citrus orchard in Uruguay.Spanish Journal of Agriclutural Research, 5(2):232-243.328crop yield response to water