Role of Nanocomposite Structure in Polyurethane Coatings for Slow-Release Fertilizers: A Case Study with <i>Brachiaria brizantha</i>

We developed a nanocomposite coating system based on castor oil-derived polyurethane (PU) and montmorillonite for the controlled release of urea. The incorporation of low amounts of nanoclay effectively slowed nitrogen diffusion through an ion exchange mechanism, resulting in a reduction from 70 to 20% in 215 h (treatment with less than 5%). Greenhouse experiments using Brachiaria brizantha demonstrated that the coated fertilizers promoted improved nitrogen uptake and biomass production compared to uncoated urea. Sequential harvests showed that the benefits were consistent across growth stages, with a more evident cumulative effect over 135 days. The results highlight the critical role of nanocomposite structure in enhancing nutrient use efficiency and reducing environmental losses. This approach enables the use of thinner coatings without compromising performance, providing a sustainable alternative for the development of advanced controlled-release fertilizers.