Ünlü, M., Çukurova University, Adana, Turkey
Kanber, R., Çukurova University, Adana, Turkey
Levent Koç, D., Çukurova University, Adana, Turkey
Özekici, B., Çukurova University, Adana, Turkey
Kekeç, U., Çukurova University, Adana, Turkey
Yeşiloğlu, T., Çukurova University, Adana, Turkey
Ortaş, I., Çukurova University, Adana, Turkey
Ünlü, F., Çukurova University, Adana, Turkey
Kapur, B., Yüzüncü Yıl University, Van, Turkey
Tekin, S., Kahramanmaraş Sütçü İmam University, Kahramanmaraş, Turkey
Käthner, J., Leibniz Institute for Agricultural Engineering, Potsdam, Germany
Gebbers, R., Leibniz Institute for Agricultural Engineering, Potsdam, Germany
Zude, M., Leibniz Institute for Agricultural Engineering, Potsdam, Germany
Peeters, A., Agricultural Research Organization, Bet-Dagan, Israel
Ben-Gal, A., Agricultural Research Organization, Bet-Dagan, Israel

In this study, 1 full irrigation regime (100% of crop evapotranspiration, I100) and 2 deficit irrigation regimes (70%, I70, and 50%, I50) were evaluated in a Rio Red grapefruit (Citrus paradisi Macfad. ‘Rio Red’) orchard in Adana, Turkey. Fruit yield, leaf water potential (LWP), and soil water depletion (SWD) were measured among trees from each treatment. Actual evapotranspiration was calculated in 3 ways, using 2 energy balance methods (eddy correlation and Bowen’s ratio) and water balance. Evapotranspiration rates of I70 and I50 treatments were 10% and 18% less than I100, respectively. Average irrigation amount for I50 was less than half of the average irrigation amount for I100. Considering that yield for the experimental treatments did not change statistically significantly, the I50 treatment provided about 50% more irrigation water savings than full irrigation conditions. Grapefruit tree LWP was highly correlated to soil water status and significantly associated with irrigation treatment. Average LWP values for treatments were -2.70 MPa for I100, -2.96 MPa for I70, and -3.28 MPa for I50. LWP increased up to a threshold level equivalent to 60%-66% of SWD, above which LWP decreased linearly with a continuous increase of SWD. This indicates that an average LWP of -3.28 MPa can be allowed for grapefruit under these experimental conditions while keeping the crop yield at that of full irrigation levels. The research findings showed that an enhanced understanding of physiological parameters is essential for irrigation scheduling of fruit plants. These will result in obtaining the optimum yield of fruit while conserving water. © TÜBİTAK.