Response of citrus trees to deficit irrigation during different phenological periods in relation to yield, fruit quality, and water productivity I. Garcı ´a-Tejero *, R. Romero-Vicente, J.A. Jime ´ nez-Bocanegra, G. Martı ´nez-Garcı ´a, V.H. Dura ´ n-Zuazo, J.L. Muriel-Ferna ´ ndez IFAPA Centro ‘‘Las Torres-Tomejil’’. Ctra. Sevilla-Cazalla, Km. 12,2. C.P. 41200, Alcala ´ del Rı´o, Sevilla, Spain 1. Introduction Climatic conditions of the Guadalquivir river basin (SW Spain) promote an annual accumulated water deficit, necessitating irrigation for several crops such as citrus trees. The high demand for agricultural products for food, fodder, and fuel with a growing human population are requiring more efficient water use in agriculture. In this context, there is an increasing challenge for scientists to develop innovative soil-water-nutrient-crop-man- agement practices that foment sustainable agricultural systems (Anapalli et al., 2008), maximizing water savings and improving its productivity. Irrigation water productivity (IWP) is defined as the ratio of yield to water applied (Seckler, 1996), and can be improved by augmenting yield or reducing crop evapotranspiration (Fereres et al., 2003). Deficit irrigation (DI) has been widely investigated as a valuable and sustainable production strategy in dry regions. These practices save water by reducing crop evapotranspiration and increasing IWP. Such water-management methods cause different effects in the crop, altering the potential development of the plant, by depressing photosynthetic rates, reducing the sources of carbon (Hsiao, 1973), and exerting a negative impact on the crop development and production (Gonza ´ lez-Altozano and Castel, 2000a). Nevertheless, not all DI strategies have these negative consequences. Many authors have reported that the response of the citrus trees to water-stress depends mainly on the crop phenology, and the different effects observed are closely related to the moment, duration, crop physiological status, irrigation water quality, plant genotype, and the degree of stress endured by the crop (Doorenbos and Kassam, 1979; Ginestar and Castel, 1996; Garcı ´a-Tejero et al., 2008). The negative impact could be mitigated by an improvement in fruit quality, as has been shown by several authors in the citrus crop (Sa ´ nchez-Blanco et al., 1989 in verna lemon trees; Gonza ´ lez-Altozano and Castel, 2000b in ‘Clementina de Nules’; Verreynne et al., 2001 in ‘Marisol Clementines’). Agricultural Water Management 97 (2010) 689–699 ARTICLE INFO Article history: Received 3 August 2009 Accepted 19 December 2009 Available online 12 January 2010 Keywords: Citrus trees Deficit irrigation Water-stress ratio Fruit quality ABSTRACT Four strategies of deficit irrigation based on a different water-stress ratio (WSR) applied in each phenological stage, and a control treatment were implemented in 11-year-old citrus trees (Citrus sinensis L. Osb. Cv. Navelina) grafted onto carrizo citrange (C. sinensis L. Osb.  Poncirus Trifoliata L. Osb.). The midday stem-water potential and stomatal conductance were measured during the periods considered, and these parameters were used to estimate the plant-water status. Integrated stem-water potential (C Int ) and integrated stomatal conductance (g Int ) were calculated for all treatments and used as a water- stress indicator for the crop. Reference equations were formulated to quantify the relations between water-stress indicators (WSR, C Int , g Int ) and the crop response, expressed as yield, yield components, and fruit-quality parameters under limited seasonal water availability. Significant differences in yield were found in the second year of experiment between the stressed treatments and control, although these differences were evident during the first year. The main effects were detected in treatments with a water-sever stress applied during the flowering and fruit-growth phases. When this degree of stress was applied during the maturity phase, it was reflected mainly in fruit-quality parameters (total soluble solids, and titrable acidity). These results lead to the conclusion that, in mature orange trees, deficit irrigation affects yield and fruit quality, while enabling water savings of up to 1000 m 3 ha 1 . Therefore, yield declined on average 10–12% but boosted water productivity 24% with respect to the fully irrigated treatment. Regarding the water-stress indicators used, C Int and g Int showed highly significant correlations with the yield and fruit-quality parameters. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +34 95 5045556; fax: +34 95 5045625. E-mail address: ivanf.garcia@juntadeandalucia.es (I. Garcı ´a-Tejero). Contents lists available at ScienceDirect Agricultural Water Management journal homepage: www.elsevier.com/locate/agwat 0378-3774/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2009.12.012