Selection of matrix material for hydrogel carriers of plant micronutrients

This research paper presents a technology for preparing hydrogels based exclusively on natural materials (alginate, carboxymethylcellulose and starch) as carriers of micronutrients (Cu, Mn and Zn). Experiments were performed to select the hydrogel matrix components, including a comparison of the viscosity and density of sodium alginates purchased from different manufacturers, as well as the effect of additives (carboxymethylcellulose and starch) on the swelling properties and strength of the structures. Finally, a solution containing 2 wt% alginate, 2 wt% carboxymethylcellulose and 10 wt% starch was used to prepare reproducible spherical hydrogels. The influence of hydrogel preparation methods on their sorption capacity and strength (either direct dropping into micronutrient solution or two-step, i.e., dropping into calcium chloride and later sorption in micronutrient solution) was also explored. The study revealed that the enrichment of hydrogels with micronutrients by the two-step method is slower, but the structures have better mechanical strength (Young's modulus more than 4 times higher) than those enriched by the one-step method. A series of analyses (FTIR, TGA, XRD and TEM) showed that obtained hydrogels have a semicrystalline structure, are thermally stable and mainly involve carboxylic acid groups in the enrichment process. The effectiveness of the designed hydrogel matrix for the slowed release of micronutrients has been preliminarily proven in winter wheat germination tests. The best results (12.2 cm stem length and 47.9 cm roots) were obtained for the group, where hydrogels were applied at a dose equivalent to 50% of the wheat’s Cu, Mn and Zn requirements. Graphical Abstract