Plant tolerance to salinity stress is vital for irrigation scheduling, decision-making, planning and operation, and water resource management. This study is aimed to investigate the effects of irrigation water salinity on water use, growth, physiology, and yield parameters of drip-irrigated tomatoes in two different growing seasons. In addition to control (0.7 dS m⁻¹), three irrigation water salinity levels: 2.5 (low), 5.0 (moderate), and 7.5 (high) dS m⁻¹ were used. In both seasons, autumn 2021 and spring 2022, increased water salinities caused an increase in soil salinity, while a decrease in seasonal crop evapotranspiration. Plant heights did not show significant differences under different salinity levels in autumn 2021, while a meaningful difference among treatments was found in spring 2022. Marketable and total tomato yields, and the leaf area index showed significant decreases under increased salinities in both seasons. Stomatal conductance was not affected by salinity levels. The salt tolerance models for marketable and total fruit yields showed a low threshold and slope value in autumn 2021, contrasting with a high threshold and slope value determined in spring 2022. The results suggest that the salinity slope value should be considered, as well as the salinity threshold value, for decision making in tomato production at different growing seasons.

Accurate information regarding crop evapotranspiration (ET_c) and its components is essential for proper water management. Salinity has become increasingly serious in many parts of the world, affecting the use of saline water in irrigation for various biochemical processes, hence the importance of understanding the effects of soil and water salinity on ET_c. This study aimed to determine the transpiration (T_r) and soil evaporation (E_s) components that constitute ET_c in tomatoes irrigated by drip irrigation and to investigate the effects of irrigation water salinity levels on ET_c and its components, as well as on the crop coefficient (K_c) used to determine ET_c. In addition, the reference evapotranspiration (ET_o) values determined by the measurements obtained with the lysimeter system were compared with the ET_o values calculated using the Almeria (ET_{o_Alm}), FAO Radiation (ET_{o_FAO-Rad}), and Hargreaves (ET_{o_Harg}) models. During the spring growing period of 2022, tomatoes were cultivated under four different irrigation water salinity levels: S₀ = 0.7 (control), S₁ = 2.5 (low), S₂ = 5.0 (medium), and S₃ = 7.5 (high) dS m⁻¹. The T_r values in S₀, S₁, and S₂ treatments were measured by the sap flow method. Radiation-based ET_o prediction models had strong relationships with lysimeter-measured ET_o values (R² > 0.977 and RMSE < 0.53 mm). The results indicated that increasing salinity levels led to a decrease in both T_r and ET_c while causing an increase in E_s. In the S₀, S₁, and S₂ treatments, E_s accounted for 16.3, 45.0, and 36.2%, respectively. Actual K_c values also decreased with increasing salinity. The results indicate that different actual K_c values can be used when calculating evapotranspiration in decision-making processes in greenhouse tomato production in Antalya and when irrigation water with different salinity levels is used. Additionally, actual ET_c responses of tomatoes to salinity can be used to manage saline water in irrigation scheduling.