Silk sericin-based emulsion gel as a novel coating material for controlled-release NPK fertilizer

In this study, a novel bio-based hydrophobic coating technology was developed to prepare controlled-release fertilizers (CRF). The emulsion was formed using beeswax (BW), an aqueous solution of silk sericin (SS) and polyvinyl alcohol (PVA). The particle size, microstructure, contact angle, and rheological properties of the colloidal systems were analyzed. Fertilizer granules (F) were coated with an SS-based emulsion (FBWE), and the resulting nutrient release kinetics in water and performance in an agricultural model were investigated. The amphiphilic character of SS promoted the stabilization of the colloidal system with BW, leading to the formation of an emulsion gel that combined the barrier properties of the SS/PVA hydrogel and the hydrophobic character of BW. This was confirmed by microstructural and rheological analyses and correlated with the slowest nutrient release rate observed in the FBWE coating. Moreover, the developed CRF system successfully promoted overall plant growth, as evidenced by a 78 % increase in leaf area compared with soil + F, along with higher biomass accumulation (≈1.5 g vs. 0.9 g in control and 1.1 g in soil + F). These results indicate that SS-based hydrophobic coatings could be a promising strategy for prolonging water and nutrient availability in soil.