Development of a Nanosulfur–Biopolymeric Coating Composite for Rock Phosphate: Transforming a Mineral into a Fertilizer

Securing global food supplies requires the use of fertilizers to sustain crop production. Current agricultural practices rely on the excessive use of phosphorus (P) fertilizers, which, unfortunately, have been implicated in surface and groundwater contamination due to their high solubility in water. This study aimed to develop a nanoenabled polymeric coating technology for pristine rock phosphate (RP) mineral. A chitosan gel matrix with tannic acid, citric acid, and nanosulfur (CTS) was designed to harness the chelating properties of organic acids and the abrasion resistance of sulfur to generate slow-release RP fertilizers. Furthermore, kinetic studies were conducted to provide insights into the surface interactions of the coatings and RP and the kinetics of phosphate desorption from the coated RP. The CTS-coated RP exhibited nonphytotoxicity, reduced P leaching, and increased plant height, plant biomass, and yield compared to a commercial P fertilizer. Loss of P from soil was reduced by 71% in CTS-coated RP treatment compared to the commercial P fertilizer application. In addition, there was a 12% enhancement in soil postharvest cation exchange capacity, corroborating the impact of the coating on the dissolution of cationic nutrients present in RP. The release kinetics elucidated a pseudo-first-order desorption process driving the available P release mechanism with a Pearson R correlation value of 0.983. Altogether, this study demonstrated the suitability of nanoenabled coating technology to develop an alternative for P fertilizers with improved P use efficiency, with benefits in sustainable crop production and reduced environmental impact.