Deficit Irrigation and Partial Root-Zone Drying Techniques in Processing Tomato Cultivated under Mediterranean Climate Conditions

Due to climate change, the application of water saving strategies is of particular interest. The aim of this study was to evaluate the effects of deficit irrigation (DI) and partial root-zone drying (PRD) techniques on the crop water stress index (CWSI), water use efficiency (WUE), and quality parameters in processing tomatoes grown in open field conditions in a Mediterranean climate. Two cultivars were grown for two growing seasons under four irrigation regimes as follows: (i) IR100: full irrigation by restoring 100% of the maximum tomato evapotranspiration (ETc); (ii) IR70DI: 70% of the amount of water given to the IR100; (iii) IR70PRD: 70% of the amount of water given to the IR100 by applying partial root-zone drying and (iv) IR0: irrigation only at transplanting and during fertigation. During the flowering period, the first growing season was characterized by an absence of rainfall and by higher temperatures also showing a higher CWSI. Despite, under IR70PRD, the CWSI was significantly higher than under IR70DI, the marketable yield obtained was significantly higher. Both IR70DI and IR70PRD regimes received approximately 24% less water than IR100, but the yield reduction with relation to the optimum regime was equal to 16.2% under IR70DI, and only 7.6% under IR70PRD. The WUE increment of IR70PRD with respect to IR100 was equal to 27% in the first growing season and to 17% in the second one, showing that the positive effect of PRD on the WUE is more evident in the more stressed year. Finally, the results from the principal component analysis (PCA) showed that the two cultivars had different qualitative responses in the two extreme regimes (IR100 and IR0) but not under PRD and DI regimes.