Hydrogel Nanocomposite Based Slow-Release Urea Fertilizer: Formulation, Structure, and Release Behavior

To enhance the nitrogen utilization efficiency of fertilizers, we developed a novel slow-release fertilizer hydrogel through free radical polymerization, incorporating lignin-containing cellulose nanofiber (LCNF), clinoptilolite (CL), urea, and acrylic acid (AA)-co-acrylamide (AAm) polymer. Various analytical techniques were utilized to examine the structure, swelling, and release behaviors of the fabricated hydrogels with varying LCNF concentrations. The results indicated that the addition of 10% LCNF led to a decrease in water absorption from 72.44 g g⁻¹ to 24.04 g g⁻¹. However, re-swelling was significantly enhanced, with a reduction in re-swelling capacity loss from 32.91% to 23.52%. Concurrently, water retention capacity notably increased from 18.03% to 39.20%. The hydrogel containing 10% LCNF exhibited a slower urea release over 30 days. The kinetic studies revealed that the swelling and urea release behaviors align well with the second-order kinetics model and the Peppas-Sahlin model, respectively. In summary, the developed LCNF/CL/(AA-co-AAm)/urea hydrogel nanocomposites present a novel strategy for the future production and utilization of slow-release fertilizers in agricultural and horticultural fields.