The effects of different drip irrigation regimes on watermelon [Citrullus lanatus (Thunb.)] yield and yield components under semi-arid climatic conditions

This study was conducted to investigate the effects of drip irrigation on yield and yield components of watermelon [Citrullus lanatus (Thunb.) Crimson Tide F-1] under semiarid conditions in the Southeastern Anatolian Project Region, Harran Plain, Sanliurfa, Turkey, during 2002 and 2003. Using a 4-day irrigation period, 4 different irrigation regimes were applied as ratios of irrigation water/cumulative pan evaporation (IW/CPE): 1.25 ( I-125), 1.00 (I-100), 0.75 (I-75), and 0.50 (I-50). Seasonal crop evapotranspiration (ETc) rates were 720, 677, 554, and 449 mm in the first year and 677, 617, 519, and 417 mm in the second year for irrigation treatments I-125, I-100, I-75, and I-50, respectively. Amounts of irrigation water applied to the 4 respective treatments were 764, 642, 520, and 398 mm in 2002 and 709, 591, 473, and 355 mm in 2003. Maximum yield was obtained from I-125, with 84.1 t/ha in 2002 and 88.6 t/ha in 2003. Yield was reduced significantly as the irrigation water was reduced. The values of water use efficiency ranged from 9.6 to 11.7 kg/m(3) in 2002 and 10.8 to 13.1 kg/m(3) in 2003. The unstressed I-125 treatment produced 10.1 kg marketable watermelons/m(3) irrigation in 2002, and 11.3 kg/m(3) in 2003. By comparison, the least irrigated (I-50) treatment produced 12.4 kg/m(3) in 2002, and 14.9 kg/m(3) in 2003. A yield response factor (k(y)) value of 1.15 was determined based on averages of 2 years, and watermelon was found to be sensitive to water stress. This result showed that yield loss (1-Y-a/Y-m) is more important than evapotranspiration deficit (1-ETa/ETm). The study demonstrates that 1.25 IW/CPE water applications by a drip system in a 4-day irrigation frequency might be optimal for watermelon grown in semi-arid regions similar to those in which the work was conducted.