Mechanistic insights into NPK release from biodegradable starch/Na-alginate hydrogel: Synthesis, characterization, and agricultural efficacy under drought stress

The development of advanced functional materials for synchronized water and nutrient delivery is crucial for addressing resource scarcity in agriculture. This study presents a biodegradable starch/alginate-CaCl 2 macroporous hydrogel loaded with NPK (NPK-hydrogel), designed to enhance resource-use efficiency under drought stress. The hydrogel exhibited a high equilibrium swelling ratio (165 g g −1 ) and sustained NPK release (58.5% over 20 days in soil). Agronomic evaluation on wheat ( Triticum aestivum L.) under two irrigation regimes and three fertilizer treatments over 40 days revealed that under drought stress, NPK-hydrogel significantly increased chlorophyll a by 22% compared to conventional NPK and significantly reduced the root-to-shoot ratio (R/S), indicating a shift in biomass allocation toward shoot development under drought stress. Under well-watered conditions, conventional NPK dramatically reduced ascorbate peroxidase activity by 56%, while NPK-hydrogel reduced it by 11%. Moreover, NPK-hydrogel moderated soil NO 3 − accumulation and buffered pH decline, suggesting a potential to reduce leaching risk compared to conventional NPK. However, root biomass did not improve, and soil available K transiently decreased, likely due to K + binding to the alginate matrix, although gradual hydrogel degradation may release the bound K + over time. Correlation analysis confirmed strong associations between soil nutrients, shoot biomass, and antioxidant responses. These findings highlight the dual potential of polysaccharide-based hydrogels as soil conditioners for sustainable agriculture, while identifying key limitations requiring further optimization. These findings offer a bio-based strategy that may contribute to mitigating fertilizer-induced environmental pollution in water-limited agroecosystems.