Controlled Urea Release Employing Nanocomposites Increases the Efficiency of Nitrogen Use by Forage

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.