Morpho-physiological, water productivity and hyperspectral responses of lettuce to regulated deficit irrigation and mulching: Plastic mulch sustains yield under a 14-day pre-harvest deficit at 70% ETc

Regulated deficit irrigation (RDI) combined with soil mulching may reduce irrigation requirements while limiting yield losses in leafy vegetables. This study evaluated the morpho-physiological, productive, and hyperspectral responses of lettuce subjected to pre-harvest RDI under different mulching conditions. The experiment was conducted in a protected environment using a randomized block design with three soil cover conditions (no mulch, double-sided black-and-white plastic mulch, and rice straw mulch), four periods of RDI imposed before harvest (0, 7, 14, and 21 days), and four replications. During the deficit periods, irrigation was reduced to 70% of crop evapotranspiration (ETc), which was determined daily using constant water-table lysimeters. A 14-day RDI period reduced the irrigation depth from 131.6 to 110.9 mm without mulch and from 47.2 to 39.4 mm with plastic mulch, corresponding to water savings of 15.8 and 16.5%, respectively. Plastic mulch resulted in the highest overall yield (2.05 kg/m²) and water productivity (49.91 g/L), compared with 1.90 kg/m² and 16.49 g/L without mulch. Lettuce maintained shoot fresh mass and yield under plastic mulch when irrigation at 70% ETc was imposed during the 14 days preceding harvest, whereas extending the deficit to 21 days reduced plant growth and yield and increased electrolyte leakage. These responses were also reflected in the spectral behavior of the plants. Therefore, combining plastic mulch with irrigation at 70% ETc during the final 14 days before harvest reduced irrigation water use by 16.5% while maintaining lettuce yield, indicating a defined pre-harvest window for reducing water application without a significant productive penalty.