Effect of regulated and controlled deficit irrigation on yield and yield response factor of processing tomato.

Deficit irrigation (DI) can help conserve water and alleviate the issue of water scarcity. For this purpose, two field experiments were conducted in 2023 and 2024 to evaluate a strategy involving reduced water use without compromising the yield production of processing tomato (cv. Castle Rock) in a typical arid environment of Egypt. In 2023, regulated deficit irrigation (RDI) was applied at 100% (V100), 80% (V80), 60% (V60), 40% (V40), and 0% (V0) of evapotranspiration (ET) following plant establishment. 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) as in the previous year. In 2023, RDI decreased yield by 9.1, 26.2, and 51.1% for treatments 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). Water productivity was positively affected by both treatments but V50-100 appreciably increased WP. Yield response factor (Ky) with values less than one in both years showed relative tolerance of tomato to water deficit. The sensitivity of tomato to deficit irrigation was higher when water was applied at different intensities with RDI (Ky = 0.96) than at individual growth stages with CDI (Ky = 0.87). These results indicate the priority of deficit irrigation during the vegetative growth stage to improve crop yield, conserve water and enhance water productivity.