Optimizing Lavender (Lavandula angustifolia Mill.) Yield and Water Productivity with Deficit Irrigation in Semi-Arid Climates

Irrigation optimization is critical for sustainable agriculture in water-scarce regions, particularly for drought-tolerant crops like lavender (Lavandula angustifolia Mill.), where strategic water management can enhance productivity. This study evaluated the impact of different irrigation regimes on yield, yield components, essential oil content, water productivity, and irrigation water productivity of drip-irrigated lavender under the semi-arid conditions of Niğde, Turkey, over five growing seasons (2020–2024). Treatments included full irrigation (T1), moderate deficit irrigation (T2, 33% water deficit), severe deficit irrigation (T3, 66% water deficit), and rainfed conditions (T4). Results demonstrated that T2 achieved fresh yields (144–227 kg da−1) and oil yields (2.7–6.9 kg da−1) comparable to T1, with crop water consumption ranging 781.5–923.6 mm. Rainfed conditions significantly reduced yields but maximized water productivity, highlighting the potential for efficient water use even under substantial water deficits. Essential oil content remained stable (1.88–3.04%) across treatments, except in 2022 (p < 0.05). Lavender exhibited low drought sensitivity, with a yield response factor (ky) of 0.25, indicating adaptability to controlled water deficits. Regression analyses revealed significant positive linear relationships between crop water consumption and fresh yield. Overall, the findings emphasize that improving water productivity through moderate-to-severe deficit irrigation strategies can support sustainable lavender production under semi-arid conditions, even when absolute yields are partially compromised. Results indicated that T2 is recommended for optimizing water productivity with minimal yield reduction. However, in water-limited regions, T3 provided viable productivity, offering a suitable balance for sustainable lavender production in semi-arid climates.