In this study, a multifunctional superabsorbent hydrogel with synergistic effects of water retention, slow-release fertilizer, and metal-ion adsorption capabilities was synthesized through a green, one-step irradiation method (gamma-SAHs). The synthesis was conducted at room temperature without initiators or crosslinking agents, using potato soluble starch (PSS, 0.5-5 g) and acrylic acid (AA, 5 mL) as raw materials, with urea (1-4 g) incorporated (urea/PSS-g-PAA) to enhance physical crosslinking and enable controlled-release fertilization. The addition of PSS and urea significantly increased the cross-linking density and porosity of the hydrogel. As a result, urea/PSSg-PAA exhibited improved water retention, salt tolerance and broader pH adaptability. Plant growth experiments in sandy soil demonstrated that gamma-SAHs effectively retained moisture, reduced evaporation, and substantially promoted maize growth under dry conditions. The hydrogel displayed segmented urea-release kinetics, offering a safe germination environment followed by a sustained nutrient supply. Degradation experiments further confirmed the synergy between the degradability of gamma-SAHs and their metal-ion adsorption capacity, with a maximum Cu2+ ions adsorption capacity of 84.37 mg/g. With its integrated functions, this material demonstrates great potential for sustainable agriculture and ecological restoration in arid regions.