Biodegradable CMC/ZnO/Ni Cross-Linked Hydrogel Beads for Enhanced Plant Growth and Increased Soil Urease Activity

The development of biodegradable and biocompatible hydrogel systems to improve agricultural production has garnered significant public attention in recent years. In extension to our work on the optimization of carboxymethyl cellulose (CMC), zinc oxide (ZnO), and nickel (Ni) based hydrogel beads (HB), we have tried to load dipotassium hydrogen phosphate (PHB) and urea onto these hydrogels as multinutrient slow-release fertilizer for soil application. At optimized conditions, ∼60.2 and ∼53.8% urea was loaded in both HB and PHB to obtain UHB and UPHB, respectively. To gain insight into the properties, structures, and morphology, the synthesized samples were characterized using FTIR, SEM-EDX, XPS, TGA, and XRD analysis. The release of urea from UHB and UPHB in water was found to be 74.71 and 72.67%, respectively, within 7.8 h, whereas in the soil it was found to be 72.91 and 63.62%, respectively, within 15 days. The application of hydrogel also enhances the urease enzyme activity in soil, along with the increase in the water holding and water retention capacity of soil as compared to the control. Three months of soil biodegradability study of the hydrogel beads showed a slight increase in the cation exchange capacity (CEC) and electrical conductivity (EC) of the applied soil. A plant growth study was conducted on sandy soil with Oryza sativa (rice) plant using randomized pot trials. Among all treatments, a 0.5 wt % hydrogel/soil mixture of UHB showed the best results in growth profile for rice. Moreover, under water stress conditions, UHB also showed excellent results. All our data confirm the composite’s ability to promote plant growth and maintain its functionality throughout the trial period.