Nanomaterials in slow/controlled-release fertilizers: mechanisms, material designs, and future directions

Slow- and controlled-release fertilizers (S/C-RFs) were developed to address the well-recognized inefficiencies of conventional fertilizers by providing nutrient delivery systems capable of synchronizing release with plant physiological demand. Contemporary S/C-RF technologies encompass several distinct product architectures, including coated fertilizers (e.g., sulfur-coated, polymer-coated, and multilayer hybrid coatings), matrix-based systems (including hydrogels, composite matrices, and biodegradable polymer networks), and nanoencapsulated or core–shell architectures, each exhibiting distinct structural features that govern nutrient diffusion and release kinetics. However, traditional coating and matrix technologies still face limitations in achieving precise, environmentally responsive release profiles. Recent advances in nanomaterials (NMs) have introduced transformative opportunities for engineering next-generation S/C-RFs, owing to their high specific surface area, tunable surface chemistry, and nanoscale interactions with fertilizer matrices. These materials reinforce polymer networks, generate tortuous diffusion pathways, and introduce electrostatic or coordination interactions that collectively modulate nutrient mobility and enhance release control. This review presents current progress in nanotechnology-enabled S/C-RFs, with emphasis on coating strategies, hydrogel systems, and composite formulations, while evaluating their agronomic, economic, and environmental implications. In hydrogel-based systems, nanofillers densify polymer networks, reduce porosity, and suppress burst release, whereas in coated fertilizers they enhance barrier integrity, mechanical durability, and water uptake regulation. These mechanisms contribute to improved nutrient use efficiency, reduced leaching, and better alignment between nutrient availability and plant uptake. Overall, NMs are positioned as key contributors to advanced S/C-RF technologies that support more efficient, sustainable, and climate-responsive agricultural practices.