Effect of Regulated and Controlled Deficit Irrigation on Yield and Yield Response Factor of Processing Tomato

Deficit irrigation (DI) can contribute to water conservation and help alleviate water scarcity. For this purpose, two field experiments were conducted in 2023 and 2024 to adopt a strategy that involves lower water use without compromising yield. In 2023, regulated deficit irrigation (RDI) was applied at 100% (V100), 80% (V80), 60% (V60), 40% (V40), and 0% (V0), while in 2024, controlled deficit irrigation (CDI) was applied at 100% (V100) or 50% (V50) during the whole growing season, 50% reduction up to the first fruit set, then 100% restoration (V50-100), and 100% until the beginning of ripening, then 50% reduction (V100-50), and 0% (V0) of evapotranspiration (ET). In 2023, RDI decreased yield by 9.1, 26.2, and 51.1% for V80, V60, and V40, respectively, with a remarkable increase in water productivity (WP) for all treatments compared to V100. In 2024, CDI included a reduction of water early in the season (V50-100) did not lead to significant losses in yield but resulted in a water saving of 25% compared to (V100), while the yield was negatively affected by the reduction of water late in the season (V100-50). WP was positively affected by both treatments, but (V50-100) appreciably increased WP. The sensitivity of tomato to DI was higher when water was applied at different intensities with RDI ( K y = 0.96) than at individual growth stages with CDI ( K y = 0.87). These results indicated that DI during the vegetative growth stage was a better strategy to optimize yield, coupled with water saving and improving WP.