Urea-Functionalized Polyacrylic Acid-Acrylamide Hydrogel for Sustainable Crop Cultivation

Abstract Fertilizers and water are critical inputs in modern agriculture, directly influencing crop productivity and food security. However, nitrogen loss from conventional urea fertilizers and poor soil water retention limit sustainable cultivation. In this study, a nitrogen-releasing plant growth material (NPGM) hydrogel was developed to enhance soil moisture retention while enabling controlled nitrogen release. The hydrogel was synthesized from acrylic acid and acrylamide, cross-linked with diethylenetriamine, and functionalized via covalent bonding of urea. FTIR, TGA, and SEM analyses confirmed its chemical structure and morphology. The hydrogel exhibited high nitrogen content (21 g/g) and excellent swelling capacity, with equilibrium swelling ratios of 3644.31 g/g in distilled water and 540.87 g/g in 0.9% saline solution. No phytotoxic effects were observed in mung bean (Vigna radiata) plants. The incorporation of NPGM significantly enhanced gravimetric water retention, increasing it by 119%, 125%, and 259% in sandy soil and by 53%, 37%, and 31% in loam soil at 1, 5, and 15 bar, respectively. Chili cultivation trials showed improved plant growth compared to conventional urea application. Overall, NPGM serves as a dual-function material combining controlled nitrogen release and water conservation, offering a sustainable solution for agriculture under water-limited conditions.