Novel Polysaccharide Hydrogels Enriched with Humic Acid for Sustainable Agricultural Applications

This study deals with the development of humic acid (HA)-enriched hydrogels aimed at enhancing water retention and promoting plant growth for agricultural applications. A set of hydrogels based on spermidine (SPD)-ionotropically cross-linked gellan gum (GG) were formulated with and without the addition of karaya gum (KG). The hydrogels were structurally characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, mechanical assays, scanning electron microscopy, and swelling kinetic measurements. Water retention tests indicated that both GG/HA and GG/KG/HA hydrogels preserve higher soil moisture levels compared to commercial polyacrylate hydrogels. Biodegradation studies showed that the biopolymer hydrogels lost more than one-third of their weight after 30 days of immersion in a soil aqueous extract. Both GG/HA and GG/KG/HA hydrogels exhibited no phytotoxicity on cultivation trials of Triticum aestivum L. var. Borlaug 100, but the plant growth was promoted with the GG/KG/HA network compared to GG/HA sample. The overall results support the potential use of GG/KG-based hydrogels enriched with HA as sustainable materials for improving soil quality and crop productivity in agricultural systems.