Fuente: Journal of applied polymer Lugar: REVIEW Coating-engineered urea fertilizers regulate nitrogen release through diffusion-controlled barriers, enhancing efficiency and reducing environmental losses. Performance is governed by coating microstructure, mechanical integrity, and permeability evolution rather than thickness alone. Emerging strategies such as self-healing and biodegradable polymers address durability and sustainability, highlighting the transition from conventional coatings to next-generation, environmentally compliant fertilizer systems.

ABSTRACT
Urea accounts for over 50% of global nitrogen fertilizer use, yet its efficiency is limited by rapid dissolution and nitrogen losses through volatilization, leaching, and gaseous emissions. This review systematically analyzes 34 peer-reviewed studies on coating-engineered controlled-release urea fertilizers, selected through a Scopus-based search and evaluated using a six-criterion methodological framework. Approximately 41% of studies exhibit low risk of bias, while 59% are moderate, indicating generally robust but heterogeneous evidence. Most systems employ granular urea (2.5–5.0 mm) with coating thicknesses of 40–170 μm, achieving release durations from 20 to 150 days. Diffusion-controlled release dominates (> 70%), while swelling- and degradation-assisted mechanisms occur mainly in biopolymer-based coatings. Compared with uncoated urea, coated systems reduce ammonia volatilization by 30%–90% and nitrate leaching by 40%–90%. However, only 30%–40% of studies include field validation, and fewer than 15% assess mechanical durability. The findings demonstrate that coating integrity, permeability evolution, and process control are more critical than coating thickness alone. Persistent gaps in standardized testing, scale-up validation, and life-cycle assessment limit comparability and practical implementation. This review provides a mechanistic framework to guide the design of efficient and sustainable controlled-release urea fertilizers.