Agronomical, physiological and water use efficiency changes of lettuce in response to deficit irrigation regimes

Deficit irrigation occurrence while maintaining acceptable yield represents a useful tool for vegetables production wherever irrigation water is limited. Lettuce (Lactuca sativa L.) ‘Corsica’ was grown in the field from May to July in order (1) to investigate the daily and seasonal evapotranspiration (ET_c) of lettuce using drainage lysimeter, (2) to determine the crop coefficients (K_c) values, and (3) to study the effects of deficit irrigation on growth, marketable and water use efficiency (WUE). Treatments were: well-watered treatment receiving 100% of ET_c (C), water-stressed treatment receiving 80% of ETc (WS₁), water-stressed treatment receiving 60% of ETc (WS₂), water-stressed treatment receiving 40% of ET_c (WS₃). Lysimeter measured crop evapotranspiration (ET_c) totaled 422 mm, for total irrigation period of 81 days. Seasonal evapotranspiration (ET) of lettuce treatments, varied from 351 mm in the WS₁ treatment to 305 mm in the WS₂ treatment and 259 mm in the WS₃ treatment, while in the control ET totaled 397 mm. The highest yield was recorded in C and WS₁, with no significant differences between treatments followed by WS2, while the lowest value was recorded under the severe water stress treatment. A yield response factor (k_y) value of 1.17 was determined, and lettuce was found to be sensitive to water stress. The highest values of water use efficiency (WUE), was recorded on WS₁ (18.8 kg m^‑3), followed by the C (17.8), WS₂ (16.3) and finally WS₃ (15.5) treatment. Applying 80% of ETc resulted in water saving, with the least yield reduction, making more water available to irrigate other crops, and thereby considered optimal strategies for drip-irrigated lettuce in the semi-arid climate.