The nitrogen slow-release fertilizer based on urea incorporating chitosan and poly(vinyl alcohol) blend

Abstract

For mitigating environmental pollution caused by excess usage of urea fertilizer, this paper reports a new fertilizer formulation, based on urea incorporating chitosan (CS) and poly (vinyl alcohol) (PVA) blend, for the slow release of urea. The urea/CS/PVA formulations were prepared by cross-linking CS and PVA blend in the presence of urea with glutaraldehyde as a cross-linker. The results indicated an interaction between urea and the functional groups of CS and PVA through hydrogen bonding, which has significant effects on the thermal properties of urea/CS/PVA formulation. The surface morphology of urea/CS/PVA formulations showed that the quantity of urea crystals anchored on the surface increased with the contents of urea and the cross-linking agent. Urea/CS/PVA formulations with a high degree of cross-linking had low water absorbency in the early stage. Meanwhile, they improved hydrolytic stability in the latter stage upon being immersed in water. The sustained release of urea from urea/CS/PVA formulations was prolonged to 10 days. The amount of urea released from urea/CS/PVA formulation with low urea contents followed the first order and Hixson–Crowell models. In contrast, urea/CS/PVA formulation with high urea contents fitted well to the Higuchi and Korsmeyer–Peppas​ models. This study provides a simple process to produce urea/CS/PVA formulation, a potential slow-release fertilizer used in agriculture to minimize adverse environmental and economic impacts. • This study developed a fertilizer formulation for the slow release of urea. • Urea was added in the matrix of cross-linked chitosan/poly (vinyl alcohol) hydrogel. • Urea interacted with chitosan and poly (vinyl alcohol) through hydrogen bonding. • Composition of formulation affected on its morphology and the release rate of urea. • The sustained release of urea from the formulation was prolonged to 10 days.