Stimuli-Responsive Starch-Based Biopolymer Coatings for Smart and Sustainable Fertilizers

The quest for sustainable agriculture demands nutrient delivery systems that align productivity with environmental responsibility. This review critically evaluates stimuli-responsive starch-based biopolymer coatings for controlled-release fertilizers (CRFs), highlighting their structure, functionality, and agronomic relevance. Starch, an abundant and biodegradable polysaccharide, offers intrinsic advantages such as modifiability, film-forming ability, and compatibility with green chemistry. The paper discusses starch's physicochemical characteristics, its functionalization to achieve responsiveness to environmental triggers (pH, moisture, temperature, ionic strength), and coating strategies like in situ polymerization, grafting, and nanocomposite integration. A comprehensive analysis of release kinetics, swelling behavior, biodegradability, and water retention is provided, followed by evaluations under simulated field conditions, encompassing various soil types, environmental stressors, and crop responses. Comparative insights with other smart biopolymers such as chitosan, alginate, and cellulose underscore starch's unique position in CRF technology. Despite promising developments, the review identifies critical research gaps, including limitations in scalability, coordination of multi-stimuli responses, and the need for extensive field validation. This work serves as a consolidated platform for researchers, policy makers, and agro-industrial stakeholders aiming to design smart, eco-friendly fertilizers that address global food security while minimizing ecological footprints.