Suitable Water–Fertilizer Management and Ozone Synergy Can Enhance Substrate-Based Lettuce Yield and Water–Fertilizer Use Efficiency

Abstract

As living standards rise, enhancing quality has become a central objective for many researchers. Soilless cultivation, known for its efficient use of resources, is increasingly used in vegetable production. It is critical to develop effective water and fertilizer management strategies to achieve high-quality yields and promote sustainable development in modern agriculture. This study employed an orthogonal experimental design to assess the impact of varying nutrient solution concentrations (50%, 75%, 100%, and 125% of Hoagland’s), lower irrigation thresholds (40%, 55%, 70%, and 85% field capacity (FC)), and ozone concentrations (0, 1, 2, and 4 mg·L−1) on lettuce growth, yield, quality, and water–fertilizer use efficiency. The results indicated that fixed nutrient solution concentrations and lower irrigation thresholds enhanced growth metrics for lettuce. Similarly, increasing ozone concentrations initially improved, then reduced growth metrics when the lower irrigation threshold was constant. Furthermore, maintaining stable ozone concentrations while raising the nutrient solution concentration initially boosted, then diminished, growth indicators. Optimal conditions for water and fertilizer management were identified at a nutrient solution concentration of 75% to 100% and an ozone concentration of 0 to 1 mg·L−1. Variance analysis highlighted the significant effects of nutrient solution concentration, lower irrigation thresholds, and ozone concentrations on lettuce yield, quality, and water and fertilizer use efficiency. Range analysis revealed the optimal management combination to be a nutrient solution concentration of 100%, an 85% lower FC irrigation threshold, and an ozone concentration of 1 mg·L−1, yielding 16.82 t·ha−1 of lettuce and a water use efficiency of 40.14 kg·m−3. These findings provide theoretical support for the sustainable advancement of soilless cultivation in contemporary agriculture.