Macroporous alginate-based hydrogels to control soil substrate moisture: Effect on lettuce plants under drought stress

Abstract

The aim of this study was to develop alginate-based hydrogels for application in horticultural field as bio-based substrate additives to control moisture. For this purpose, a 2-level factorial design was performed to select the appropriate levels of significant variables, i.e. polymer concentration (2–3% w/v), CaCl2 concentration (0.2–0.4% w/v), and cross-linking time (10–30 min). Statistical analysis showed that CaCl2 concentration and cross-linking time were the most significant variables affecting the swelling properties of the alginate-based hydrogels. Hence, two formulations (2 or 3% w/v of alginate, cross-linked with 0.2% w/v of CaCl2 for 10 min) were chosen for further analysis. A complete characterization of each material was performed in terms of swelling degree (SD) and kinetics in distilled and tap water, gel fraction, thermal properties, morphology, and Fourier transformed infrared spectroscopy. SD after 24 h in distilled water was above 55 g/g dry hydrogel in both formulations. Bioassays performed in lettuce plants as well as substrate microbiota provided evidence for the putative application of alginate-based hydrogels in horticultural systems, with an 80% increase in fresh weight of the plants grown in substrate supplemented with 5% hydrogels compared to control substrate after 7 days under drought conditions.