Glauconite-Urea Nanocomposites As Polyfunctional Controlled-Release Fertilizers

This investigation aims to design controlled-release nanocomposites based on mechanical activation of a mixture of glauconite and nitrogen nutrients in a 1:1 ratio. The methods include mechanochemical preparation of composites, X-ray diffraction analysis, scanning electron microscope with energy-dispersive X-ray spectroscopy (SEM-EDS), high-resolution transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), differential thermal analysis (thermo-gravimetric analysis and differential scanning calorimetry, TG-DSC), and soil column leaching experiments with the prepared nanocomposites for 56 days and growth of oat (Avena sativa) using manufactured nanocomposites were tested. The nanocomposites display increasing intercalation between nitrogen substances and glauconite with increasing duration of the operation. The amount of intercalated nitrogen in the glauconite interlayer increases from 21.2 to 23.1% as the operation time increases from 3 to 14. The adsorbed nitrogen on glauconite flakes thickens with time. Analytical results record the frequent structural modifications of the nanocomposites. A substantial increase in the interlayer thickness of the unit structure of glauconite compared to its original state indicate the intercalation of urea into the structure of glauconite. Nitrogen occurs as intercalations in the exchangeable site (interlayer space) of the glauconite unit structure, remains an absorbed part within micro-flakes, or may be adsorbed on the surface of mineral particles. Soil leaching experiments, spanning over 56 days, reveal the release of nitrogen and potassium initially at a fast rate, which slows down with time. The nanocomposites leach nutrients at a slower rate than the urea sample. The plant height grows faster with the application of urea than nanocomposites. However, the reduced release of nitrates and ammonium from the nanocomposites decreases the leaching of nutrients downstream to soil layers. It prohibits the emission of greenhouse gases like nitrous oxides into the atmosphere. Therefore, the nanocomposites are classified as polyfunctional controlled-release fertilizers saving 50% of the urea. Further, the simultaneous release of potassium makes the composite a complex controlled-release fertilizer.