Smart Fertilization Based on Sulfur–Phosphate Composites: Synergy among Materials in a Structure with Multiple Fertilization Roles

Sulfur is currently a bottleneck for agronomic productivity. Many products are based on the application of elemental sulfur (S°), but the ability of the soil to oxidize them is variable and dependent on the presence of oxidizing microorganisms. In this work, a composite was designed based on a matrix of S° prepared by low-temperature extrusion, reinforced by rock phosphate particles acting as P fertilizer, and with encapsulation of Aspergillus niger as an oxidizing microorganism. This structure was shown to be effective in significantly increasing S° oxidation while providing P by rock phosphate dissolution in an acid environment. X-ray absorption near-edge structure (XANES) spectra provided information about P fixation in the soil after dissolution, showing that the composite structure with A. niger modified the nutrient dynamics in the soil. This fully integrated material (a smart fertilizer) is an innovative strategy for eco-friendly agronomic practices, providing high nutrient delivery with minimal so...