Deficit irrigation for enhancing 'Tarocco' orange fruit quality

This study focused on the application of deficit irrigation (DI) strategies to orange orchard species [Citrus sinensis (L.) Osbeck] in semi-arid areas. The impact of DI application on nutritional status, fruit yield, and quality of orange trees ('Tarocco') was evaluated during two field trials carried out in Sicily (Italy), in the period 2009-2013. In the first experiment, a sustained DI strategy was conducted on a mature orange orchard ('Tarocco'). The second trial studied the use of regulated DI and partial root-zone drying (PRD) on young, but not mature, orange trees ('Tarocco'). In both the trials, micro-irrigation techniques (i.e., surface and sub-surface) were employed to increase water use efficiency by the orchards. Results of the experiments revealed that the nutritional status of the orange trees was modified according to the severity of the imposed water deficit. Nitrogen leaf content was reduced by the imposed water deficit, whereas P, K and micronutrient leaf contents, in most of the cases, indicated the opposite behaviour. A light trend in fruit size reduction was noticed in the deficit irrigated trees; it was less pronounced for mild water restrictions. Finally, the study suggests that a moderate water stress can be profitable for enhancing key fruit quality characteristics (i.e., antioxidant compounds).