Slow release fertilizers based on polyphosphate/montmorillonite nanocomposites for improving crop yield

Nanocomposites are promising materials for the development of novel and environmentally friendly fertilizers that can delay the release of nutrients. In this study, a novel high-strength spherical nanocomposite fertilizer was prepared via agglomeration and granulation using montmorillonite, urea phosphate, urea, and potassium chloride as raw materials. The properties and morphology of the prepared fertilizer were characterized by Fourier Transform Tnfrared Spectroscopy (FT-IR), X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Thermogravimetric Analysis (TGA) and X-ray Computed Tomography (XCT) techniques. FT-IR analysis identified the formation of polyphosphate in fertilizer and hydrogen bonds between polyphosphate and montmorillonite. XRD analysis showed increased montmorillonite interlayer spacing and confirmed the formation of polyphosphate-montmorillonite nanocomposites. The effects of raw material mass ratio, reaction time, and reaction temperature on the strength and fluidity of nanocomposite fertilizer granules and the optimum preparation process was obtained by the response surface method (RSM-CCD). The optimum preparation process was obtained as follows: reaction temperature, 103 °C; reaction time, 237 min; and mass ratio, 1:1:0.93:1 (urea phosphate: urea: potassium chloride: montmorillonite). Under these optimum conditions, the particle hardness and angle of repose of the prepared fertilizer were 64.75 ± 0.48 N and 30.84 ± 0.95°. Nutrient release and agronomic effectiveness of the fertilizer was evaluated using column leaching and pot experiments, respectively. The column leaching experiment and XCT analysis demonstrated that the nanocomposite structure was responsible for the slow nutrient release. The pot experiment showed that compared with the traditional fertilizer, the soil nitrate and available phosphorus was increased by 28.02% and 43.45%, respectively, and the maize yield was increased by 24.27% with the application of prepared fertilizer. This work provides support for the preparation of high-strength spherical nanocomposite fertilizers and their large-scale applications in modern mechanical agriculture.