Timer versus moisture sensor-based irrigation control of soilless lettuce: Effects on yield, quality and water use efficiency

We compared the effects of: 1) timer- ('Timer') and soil moisture sensor-controlled irrigation on soilless lettuce; 2) two volumetric water content (?) thresholds for irrigation (0.30 ('?=0.3') and 0.40 m3?m-3 ('?=0.4')). The most nutrient solution (NS) was applied in 'Timer' where the lowest water use efficiency was observed, with 17 and 42% less NS used in '?=0.4' and '?=0.3', respectively. Irrigation volumes followed the plant water needs in the sensor-controlled treatments, with little or no leaching, while 18% of leaching was recorded in 'Timer'. Plants in 'Timer' and '?=0.4' had higher fresh weights (24%) and leaf area (13%) than plants in ?=0.3. Similar dry weight was observed among treatments but percent dry matter was 20% higher in '?=0.3'. Gas exchanges and leaf tissue chemical composition were similar in all treatments, but nitrate concentration was lower in the '?=0.3' plants. Precision sensor-controlled irrigation based on ? measurements is an effective tool to increase the overall WUE and to improve the quality of soilless-grown lettuce by acting on the substrate moisture level.