Urea intercalated halloysite/sodium alginate composite hydrogels for slow-release fertilizers

The application of nanotechnology in the field of agrochemicals release is an effective way to reduce the use of fertilizers and improve their utilization. Here, different ratios of urea were successfully intercalated into halloysite (Hal) by solid-phase milling method, and the maximum loading of urea was calculated as 14.99 ± 1.33 wt%. X-ray powder diffraction (XRD) demonstrated the distance of the Hal (001) plane increased from 0.7 to 1.0 nm by the urea intercalation. Subsequently, urea-Hal‑sodium alginate (SA) hydrogel beads (UHS) were fabricated by Ca2+ crosslinking method. SA and Hal content has a significant influence on the morphology and surface properties of the hydrogel. The optimal ratio of UHS was found as 2 wt% CaCl2, 2 wt% SA, and 2 wt% Hal. UHS had good water retention and slow release properties, and the water retention rate of UHS was increased by 13% compared with that of raw soil. The release curve showed that the release time of urea in UHS was 60 times longer compared to pure urea. Furthermore, using wheat as a plant model, UHS can provide slow-release nitrogen nutrients to promote the growth of wheat. In virtue of good swelling and slow-release properties, low cost, simple preparation process and environmental friendliness, UHS has a promising future in slow-release fertilizers for modern agriculture technology.