The present study describes the preparation and characterization of a novel urea slow-release nanocomposite, based on urea intercalation into montmorillonite clay by an extrusion process at room temperature. Nanocomposites with urea contents ranging from 50 to 80 wt % were successfully produced and characterized. Analyses by XRD, DTA, and SEM-EDX confirmed the effectiveness of this simple process to exfoliate the clay lamellae into the urea matrix, forming a product that can be classified as a nanocomposite, due to the exfoliation degree attained. Diametral compression tests showed that the samples were very deformable, and the release rate of active components in water showed that the nanocomposite showed a slow release behavior for urea dissolution, even in low montmorillonite amounts (20% in weight).

Efficient use of fertilizers, especially nitrogen, is essential and strategic to agricultural production. Among the technologies that can contribute to efficient use of fertilizers are slow- or controlled-release products. This study describes the impact on structure, urea release rate, and function in the field of urea nanocomposites associated with an exfoliated clay mineral prepared using various concentrations of hydrophilic or hydrophobic polymers. The nanocomposites have a high nutrient load (75% by weight), which itself acts as a structural matrix. Our manufacturing processthe extrusion of a plastic mixtureis simple and can be scaled up, allowing granule production without high costs. Nanocomposites were prepared by adding varying amounts (less than 4% by weight) of polyacrylamide hydrogel or polycaprolactone, which influenced mechanical properties and urea release profiles. Nitrous oxide (N2O) emissions in the field were reduced substantially for nanocomposites, whether composed of polyacrylamide hydrogel or polycaprolactone.

The rapid hydrolysis of urea applied to the soil surface causes high rates of NH3 volatilization, leading to adverse environmental impacts and decreased uptake of N by crops. One approach that can be used to improve the efficiency of urea use involves strategies to control its release, such as the coating of granules with polymers. However, the effectiveness of this method can be limited by poor interaction between the coating and the granule surface. We, therefore, propose a novel class of nanocomposite fertilizers, based on clay exfoliation in urea matrices, with or without polymerization using formaldehyde as a strategy to increase the interaction between urea and the additives. A comparative study was performed using various slow-release fertilizers, determining the amounts of volatilized ammonia, dry matter production, and efficiency of urea-N uptake by ryegrass, in a trial carried out in a greenhouse. Interaction, such as solubility, thickness, and chemical composition of the composites revealed aspects of the interaction that affected the slow-release behavior of urea in soil and the availability of N for plants. It could be concluded that the controlled release of urea from the nanocomposites decreased NH3 volatilization, resulting in a more constant N availability in the soil and better synchronization with the nutritional demands of the plants. The new fertilizers offer a practical option for increasing urea-N efficiency, reducing environmental impacts caused by NH3 loss and improving the quality of forage grown on low fertility soils, such as oxisols.