Preparation and Properties of <scp>pH</scp> ‐Responsive Starch‐Based Gel Coated Slow‐Release Fertilizer

ABSTRACT pH‐responsive fertilizer is an innovative slow‐release fertilizer that can regulate the release of nutrients according to changes in soil pH, which is designed to improve the applicability of fertilizers according to environmental changes during crop growth. It has research and development potential in the field of smart agriculture in the future. This study developed a starch‐based pH‐responsive hydrogel (SA) using starch (St) as the matrix and acrylic acid (AA) as the functional monomer, which was subsequently employed to encapsulate urea particles for controlled nutrient delivery. The effects of St/AA ratios and crosslinker concentrations on the hydrogel's water retention, absorption capacity, and swelling behavior were systematically investigated. The fertilizer's release kinetics were evaluated in both aqueous and soil environments, with particular emphasis on pH‐dependent responsiveness. Experimental results demonstrated that under typical soil conditions (pH 7 and 9), formulations with St:AA = 3:1 and St:MBA = 500:1 exhibited optimal pH‐responsive characteristics. These formulations achieved equilibrium cumulative nitrogen release rates of 80.43% and 80.51%, respectively, with sustained release durations extending to 30–35 days. The findings highlight the potential of starch‐based pH‐responsive hydrogels as effective carriers for smart fertilizer systems in precision agriculture applications.