Mediterranean regions play a central role in lemon (Citrus x limon (L.) Osbeck) production, but increasing water scarcity and temperature extremes under climate change have made orchards highly vulnerable. Deficit irrigation (DI) has been proposed as a strategy to improve water use efficiency without compromising productivity.

In this experiment, three irrigation regimes were compared: a Control at 4.0 L/h, DI1 at 3.5 L/h (≈12% reduction), and DI2 at 2.7 L/h (≈32% reduction). Each treatment consisted of ten trees, irrigated twice weekly with two drippers for 90–120 minutes over an eight-month period. All trees were mulched with black plastic. Growth dynamics, photosynthetic efficiency, and fruit organoleptic attributes were monitored.

Results showed that DI1 maintained yields at levels comparable to the Control, with only minor decreases (≈5–7%) in photosynthetic rates, vegetative growth, and fruit quality traits. In contrast, DI2 produced substantial declines, with photosynthetic activity reduced by up to 25%, vegetative growth by 30%, and fruit sensory properties (flavor and juiciness) significantly affected. Nevertheless, DI2 ensured tree survival under severe water restriction.

The study demonstrates that a moderate water reduction (DI1) can be applied to young orchards (0–7 years old) during seasons with average or above-average rainfall, optimizing water use without compromising production. Severe restriction (DI2) is not suitable for commercial yield but may serve as an emergency strategy under extreme drought conditions.

These findings emphasize the potential of carefully adjusted DI strategies as an adaptation measure for Mediterranean lemon orchards, contributing to sustainable management in water-limited environments.