A Green Temperature-Responsive Hydrogel Derived from Rosin-Stabilized N-Vinylcaprolactam and Agrochemicals for Synergistic Pesticide-Fertilizer Release

The practical use of agricultural hydrogels remains limited by poor mechanical strength, incompatibility with hydrophobic agrochemicals, and weak environmental responsiveness, although they have advanced in retaining water and delivering nutrients. In this study, a thermoresponsive hydrogel was synthesized, with urea incorporated as a nutrient source, by copolymerizing the hydrophobic monomer N-vinylcaprolactam (NVCL) with the fungicide azoxystrobin (Azo), using amphiphilic disproportionated rosin acid soap (DRAS) as both an emulsifier and a structural modifier. This dual role of DRAS enabled it to not only disperse the hydrophobic components but also regulate the hydrogel’s network architecture, thereby enhancing its mechanical strength, swelling behavior, and controlled release kinetics. Below the lower critical solution temperature (LCST), the hydrogel demonstrated effective soil moisture retention and reduced water evaporation. Upon heating above the LCST, it facilitated the controlled release of urea and Azo compounds. This temperature-responsive behavior allows for the on-demand coordination of water, fertilizer, and pesticide delivery in alignment with crop growth stages and disease prevention needs. Biosafety evaluation revealed that the unloaded hydrogel exhibited low toxicity toward earthworms. In antifungal tests, the drug-loaded hydrogel showed strong inhibitory activity against Fusarium oxysporum f. sp. niveum (FON). Pot experiments further confirmed that the drug-loaded hydrogel effectively suppressed FON infection, increased watermelon biomass, and improved fruit quality. These results highlight the potential of this multifunctional hydrogel as an environmentally sustainable and stimulus-responsive carrier for smart agrochemical delivery in modern agriculture.