Inducing surface secondary gradient cross-linking coupled with doping starch carbamate derivatives for improving the property of the acrylamide hydrogel-based slow-release fertilizer

The extensive application of acrylamide hydrogel (AMH) as a matrix in slow-release fertilizers (SRFs) remains a significant challenge owing to its numerous disadvantages such as non-renewable raw materials, non-degradability and unsatisfactory slow-release performance. Herein, semi-interpenetrating network (SIPN) structural starch carbamate (SC)/acrylamide/sodium alginate hydrogel (SC/AM/SAH) and its corresponding SC/AM/SAH-SRF were successfully constructed by incorporating the as-synthesized SC into the hydrogel and then inducing secondary gradient cross-linking among SA and AM. In view of the high swelling ratio and favorable water retention of the synthesized SC/AM/SAH, the corresponding SC/AM/SAH-SRF exhibits stable nitrogen (N) nutrient slow-release behavior, achieving N cumulative release rates of 78.5% within 50 h in water and 85.1% within 30 days in soil. Kinetics fitting analysis indicates that the N release behavior of SC/AM/SAH-SRF conforms to the Korsmeyer–Peppas model in water (R 2 = 0.994) and a first-order kinetic model in soil (R 2 = 0.992), both of which are governed by a non-Fickian diffusion mechanism. In addition, pot experiments consolidate that the SC/AM/SAH-SRF could effectively facilitate the growth of maize seedlings based on the variations of plant growth parameters (plant heights, stem diameters and leaf numbers). In conclusion, this work presents a feasible strategy for further strengthening the performance of AMH SRF with abundant biomass materials.