Long-term impact of sustained-deficit irrigation on yield and fruit quality in sweet orange cv. Salustiana (SW Spain)

Long-term impact of different sustained-deficit irrigation (SDI) treatments on a 13-year-old orangeorchard (Citrus sinensis L. Osbeck, cv. Salustiana) was studied from 2004 to 2008. The experimentconsisted of a control irrigation treatment which was applied at 100% of the crop evapotranspiration(ETc) values for the whole season, and three SDIs imposed as a function of different water-stressindex (WSI) values, defined as the ratio of the actual volume of water supply to the ETc rate. Thevalues defined by the WSI were 0.75, 0.65, and 0.50. The plant-water status was measured throughthe midday stem-water potential (ΨStem). Yearly, yield and fruit quality were evaluated at harvestin each treatment, and a global analysis was carried out using the whole dataset. Overall, nosignificant differences were found in fruit yield between SDIs and control treatments, althoughsignificant differences appeared in some of the fruit-quality parameters (total soluble solids andtitrable acidity) which also showed significant relationships with integrated stem-water potential(ΨInt) and irrigation water applied. These findings lead us to conclude that SDIs have important andstatistically significant effects on fruit quality. Thus, the application of sustained-deficit irrigation (SDIwith WSI of 50) provides promising possibilities for optimising citrus irrigation and boosting the waterproductivity for citrus orchards in a semiarid Mediterranean climate.