Development and characterization of slow release N and Zn fertilizer by coating urea with Zn fortified nano-bentonite and ZnO NPs using various binders

The fertilizer use-efficiencies particularly of nitrogen (N), phosphorus (P), and zinc (Zn) in alkaline soils are often seriously low. The surplus N released from the conventional fertilizers pollutes the environment and causes climate change. Slow or controlled release N fertilizer can improve its use efficiency and decrease its environmental impacts. Previously, we have shown that the ZnO nanoparticles (ZnO NPs) has higher use efficiency than the conventional Zn fertilizers. In this study, we focused on the development of Zn coated slow-release urea fertilizer. For this purpose, ZnO NPs and Zn fortified nano-bentonite were coated on urea by using various binders. The coated fertilizers ZU1& ZU2: nano-bentonite (4%) & ZnO NPs (2%) + vegetable oil respectively, ZU3 & ZU4: nano-bentonite (4%) & ZnO NPs (2%)+stearic acid+ paraffin oil+ paraffin wax respectively was prepared. The coated granules were characterized by using SEM, XRPD techniques. Zn and N release was evaluated in a soil incubation experiment. The results showed that ZU4 and ZU2 released higher amounts of Zn (3.9 and 3.42 mg kg −1) respectively while the prolonged release of Zn (>30 days) was observed from ZU3 and ZU4. Similarly, a significant reduction in N release from ZU3 and ZU4 (15 days) was observed while the rapid release of N from ZU1, ZU2, and control (first 5 days) was recorded. It was concluded that coated urea with ZnO NPs and Zn fortified nano-bentonite using stearic acid, paraffin oil, and paraffin wax as binder can act as an efficient slow-release macro micronutrient fertilizer.