Water Productivity and Seasonal Performance of Floating-Root Hydroponic Lettuce Under Coastal Desert Conditions in Northern Chile

Water scarcity increasingly constrains horticultural production in coastal desert regions. This study provides a site-specific characterization of the seasonal performance and water productivity of a pilot-scale floating-root hydroponic lettuce system under coastal desert conditions in northern Chile, where air temperatures ranged from 0.98 to 27.1 °C during the study period. Four seasonal production cycles were conducted using two commercial cultivars. Because all seasonal observations were obtained from a single hydroponic bench and shared nutrient-solution reservoir without independent system-level replication, seasonal comparisons were interpreted descriptively. Fresh weight ranged from 230 to 265 g plant−1, marketable yield exceeded 93% in all production cycles, and water productivity ranged from 7.1 to 12.5 L kg−1 fresh biomass, with the highest value observed during autumn. Fractional canopy cover was strongly associated with cumulative system water use (R2 = 0.89), suggesting the potential application of non-destructive imaging tools for irrigation monitoring. In a separate winter experiment with statistical analysis, a four-day pre-harvest nutrient flushing reduced nitrate concentration by 15% without affecting yield or total polyphenol content. Water utility descriptively varied among seasons, reaching a maximum of 401 CLP L−1 during summer. Overall, the study provides a preliminary characterization of the technical performance, water-use indicators, and economic potential of a floating-root hydroponic system under coastal desert conditions, while highlighting the need for independent multi-bench and multi-location experiments to validate seasonal responses.