Screening Surfactant and Calcium-Mobilizing Biostimulant Formulations for Growth Enhancement and Tipburn Mitigation in Hydroponic Lettuce

Abstract

Controlled-environment hydroponics enables year-round production of leafy greens while conserving water and nutrients. Hydroponic lettuce (Lactuca sativa) is prone to tipburn, a localized calcium-deficiency disorder affecting emerging leaves. Even with sufficient nutrient supply, environmental and physiological factors can limit calcium uptake and distribution within the plant. Biostimulants and surfactants that modify nutrient use efficiency or calcium mobility represent potential chemical approaches to mitigate tipburn and improve crop performance. We conducted a winter greenhouse study with butterhead lettuce ‘Nancy’ to evaluate four experimental surfactant formulations and one calcium-mobilizing biostimulant (CC US-2101–2105) applied to deep-water culture hydroponic nutrient solutions. Seedlings were grown in rockwool cubes and transplanted to hydroponic trays arranged in a randomized complete block design with three simultaneous replications. In addition to an untreated control, most experimental products were evaluated at two concentrations (0.5 and 2 mL·L−1), whereas the biostimulant CC US-2105 was applied at 0.022 and 0.22 mL·L−1. Shoot fresh mass, marginal tipburn severity, and bolting were recorded at harvest. CC US-2101, CC US-2102, and CC US-2103 caused phytotoxicity and severely reduced shoot growth, indicating that these surfactant formulations were unsuitable for hydroponic lettuce at the tested concentrations. In contrast, CC US-2104 increased shoot fresh mass by 11% to 12% and reduced tipburn severity, with the higher concentration being more effective. The calcium-mobilizing biostimulant CC US-2105 reduced tipburn severity at the higher concentration without affecting shoot fresh mass. Bolting occurred under the control, CC US-2104, and CC US-2105 treatments, whereas stunted plants exposed to other formulations exhibited minimal bolting. These results indicate that selected surfactant formulations and a calcium-mobilizing biostimulant can exhibit biostimulant activity in greenhouse hydroponic lettuce, either by enhancing growth or mitigating tipburn, whereas other surfactant chemistries may be phytotoxic under hydroponic conditions.