Response of orange trees to deficit irrigation strategies: effects on plant nutrition, yield and fruit quality

Environmental and economic sustainability of agricultural systems has to face the general decreasing trend of water resources through the adoption of strategies aimed at improving water-use efficiency. In the study, during three consecutive summer seasons, the effects of deficit irrigation (DI) treatments applied on mature orange trees [Citrus sinensis (L.) Osbeck] cv. “Tarocco Meli” were analyzed. Two different DI strategies supplying 70 and 50% of crop evapotranspiration (ETc) were compared with irrigation at the full rate of ETc; the comparisons were carried out in terms of plant physiological response, crop production, quality, and nutritional status. The orange trees became less sensitive to moderate water restrictions (DI = 70% ETc) permitting approximately 80 mm of water saving (i.e., corresponding to a threshold for water stress integral of 60 MPa) per season without any significant impact on their water status and on agronomic performances. Severe water restrictions (DI ¼ 50% ETc) reduced fruit weight and crop production every year, with water-use efficiency values similar to those of the moderate DI (70% ETc). The study does not evidence crop mineral nutrition imbalances and yield decrease caused by mild water reductions. A moderate water restriction can be applied in commercial orange orchards because it saved water and improved fruit quality by increasing total soluble solids and titratable acidity while the fruit maturity was delayed.