Controlled-Release Fertilizers: Innovations, Challenges, and Practical Applications

Ensuring high crop productivity while reducing nutrient losses and environmental impacts remains a central challenge of modern fertilization strategies. Controlled-release fertilizers (CRFs) have emerged as a key tool to synchronize nutrient availability with plant demand by embedding soluble nutrient sources within coatings or matrices that modulate water penetration and ion diffusion. This narrative review synthesizes recent advances in CRF materials and technologies, with particular emphasis on biodegradable and bio-based systems, hydrogels, nanostructured carriers, and extrusion-based matrix formulations. It outlines the main classes of coating and matrix materials, their release mechanisms, agronomic performance, and documented benefits for nutrient-use efficiency, crop yield and quality, and soil and water protection. The review also analyzes major scientific, technical, environmental, and economic barriers that currently limit the large-scale deployment of CRFs, including microplastic pollution from persistent polymer coatings and the difficulty of tailoring release profiles under variable field conditions. Emerging directions are highlighted, such as composite and multilayer bio-based coatings, superhydrophobic and stimuli-responsive structures, biochar- and compost-based matrices, nutrient recovery from waste streams, and integration with precision agriculture and sensor technologies. The paper identifies priorities for future research needed to translate promising CRF concepts into robust, field-validated and sustainable fertilization solutions.