Research PaperEvaluation of crop water stress index on Royal table grape variety under partial root drying and conventional deficit irrigation regimes in the Mediterranean Region

- Full irrigation resulted in higher yields than PRD and deficit irrigations.
- PRD-75 and PRD-50 produced significantly higher yields than DI-75 and DI-50.
- PRD-75 might be a suitable strategy for irrigation under water scarcity.
- Royal table grape variety should be irrigated when CWSI is 0.20.

This research was conducted during 2009, 2010 and 2012 growing seasons in the experimental vineyard of the Department of Horticulture at Cukurova University in Adana located in the Eastern Mediterranean Region of Turkey on 12 years old Royal table grape variety to evaluate the crop water stress index under various deficit and partial rootzone drying irrigation strategies applied with drip system. In the study, six different treatments were considered; namely full irrigation (FI), deficit irrigations (DI-75 and DI-50), partial rootzone drying (PRD-75 and PRD-50) and rainfed (RF). In FI soil water deficit in the 80 cm within the seven-day intervals was replenished to the field capacity. DI-75, DI-50, and PRD-75, PRD-50 treatments received 75 and 50% of water applied to FI. In PRD plots, drip laterals on both sides of the vine rows operated alternately. Experimental design was randomized blocks with three replications. Canopy temperatures were measured throughout the growing season with an infrared thermometer, and vapor pressure deficit of air was used for calculating the crop water stress index (CWSI). Lower and upper limits of basic graphic, which is necessary to CWSI calculation, were developed for grapevine. The effect of irrigation treatments on yield, vine growth and juice quality differred significantly among the treatments. Highest yield was obtained from the full irrigation (FI) as 30.2 t ha−1, and the lowest yield was obtained from the RF treatment as 14.2 t ha−1. PRD vines exhibited a stronger control over vegetative growth as compared with DI and FI plants. This was expressed by lower values of total leaf area at harvest. Higher water use efficiency (WUE) was observed in RF and PRD-75 treatments while the lowest WUE was obtained from DI-50 treatment. Results showed significant differences in grape quality components among treatments and seasons studied. The highest brix value was obtained in RF while the lowest brix value was from the FI treatment. Three years seasonal average CWSI values ranged from 0.20 in FI to 0.77 in RF. Significant linear relations were found between yield and CWSI in three experimental years. The results revealed that Royal variety should be irrigated when average CWSI value is approximately 0.20 for high yield. According to the experimental findings, PRD-75 application with water savings as compared to full irrigation might be a suitable strategy for irrigation under water scarcity.