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

The study compares the effects of: timer ('Timer') and soil moisture sensor-controlled irrigation on soilless lettuce; two volumetric water content (Theta) thresholds for irrigation (0.30 ('Theta = 0.3') and 0.40 m(3)/m(3) ('Theta = 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 'Theta = 0.4' and 'Theta = 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 'Theta = 0.4' had higher fresh weights (24%) and leaf area (13%) than plants in 'Theta = 0.3'. Similar dry weight was observed among treatments but percentage of dry matter was 20% higher in 'Theta = 0.3'. Gas exchanges and leaf tissues chemical composition were similar in all treatments, but nitrate concentration was lower in the 'Theta = 0.3' plants. Precision sensor-controlled irrigation based on Theta measurements is an effective tool to increase the overall water use efficiency and to improve the quality of soilless-grown lettuce by acting on the substrate moisture level.