Abstract This study aimed to formulate enhanced-release urea fertilizers using carbon-based matrices derived from cocoa pod husks (CPH) to evaluate their nitrogen release kinetics and establish correlations between physicochemical properties and release parameters. As support matrices to enhance urea retention and nutrient delivery, biochar, compost, a biochar–compost mixture, and a co-composted substance (COMBI) were examined. Fertilizers were prepared by incorporating urea through physical mixing and infusion methods to assess their influence on urea–matrix interactions. Physicochemical characterization showed that biochars produced by controlled pyrolysis developed ordered macroporous structures and abundant surface functional groups (carboxylic acids, ketones, and alcohols), which promoted strong chemical interactions with urea. These interactions significantly improved urea anchoring and slowed nitrogen release, particularly in infused formulations. Although compost-based matrices exhibited limited macroporosity and weaker interactions, it is noteworthy that all synthesized fertilizers showed improved nitrogen release behavior compared to commercial urea. Release kinetics revealed that biochar with infused urea exhibited the best performance, reducing the urea release rate by a factor of 472 relative to commercial fertilizer. Macroporosity, surface functionality, and kinetic release characteristics were found to be strongly associated. This controlled-release behavior was attributed to a combined mechanism involving diffusion through the porous structure and chemical interactions with surface functional groups. Overall, these results demonstrate that CPH-derived carbonaceous matrices, particularly biochar, are effective for developing enhanced-release urea fertilizers, providing a sustainable strategy for agricultural residue valorization within a circular economy framework. Graphical Abstract
Carrillo et al. (Thu,) studied this question.