Quantifying the Effects of Sensor-based Irrigation Strategies and Harvest Techniques on the Growth, Physiology, and Palatability of Romaine Lettuce in Coarse-textured Turface Medium

Sustainable lunar crop production will likely require coarse-textured media to mitigate waterlogging under reduced gravity, although larger particle sizes reduce water retention and availability. Maintaining a target root zone water content via sensor-based irrigation may improve plant water status in such media. For harvest management, the standard multiharvest “pick-and-eat” method enables continuous production, whereas a single-harvest “cut-and-sow” alternative may limit root buildup. The objective of this study was to assess the effects of sensor-based vs. time-based irrigation on growth, physiology, mineral content, and palatability of Lactuca sativa ‘Little Gem’ using pick-and-eat and cut-and-sow harvesting techniques in a coarse calcined-clay medium (Turface) to quantify interactions among plant performance, rhizosphere water availability, root zone salinity, and sensory outcomes. Forty-eight greenhouse-grown plants and 24 nonplant controls were randomly assigned to either sensor-based irrigation (maintaining a volumetric water content of 0.40 m³·m − ³) or time-based irrigation (daily application until leaching occurred). Within each irrigation treatment, the plants were subjected to either the pick-and-eat or the cut-and-sow harvesting technique. Plant growth and physiology were recorded throughout the experiment, and a sensory evaluation was conducted at termination. Within the pick-and-eat technique, sensor-based irrigation increased photosynthesis, stomatal conductance, and transpiration and lowered leaf–air temperature, resulting in higher cumulative fresh and dry mass and larger leaf area and leaf mineral contents, including phosphorus, potassium, and magnesium, than time-based irrigation. In the cut-and-sow technique, reseeding into the same medium promoted salt accumulation, particularly under sensor-based irrigation due to lack of leaching, and subsequently depressed gas exchange, total leaf area, and leaf dry and fresh weights compared with the pick-and-eat technique. The lowest palatability was reported on lettuce receiving time-based irrigation with pick-and-eat due to unpleasant mouth feel and flavor, which was attributed to early bolting. Overall, pairing sensor-based irrigation with a pick-and-eat harvest strategy maximized yield, stabilized physiology, limited premature bolting, and preserved sensory quality in coarse Turface media. Cut-and-sow harvesting technique under nonleaching irrigation minimized the risks of salinity buildup and performance impairment. These results highlight the importance of closed-loop water management and harvest strategy codesign when translating crop systems to reduced-gravity, regolith-based agriculture.