Unveiling the Role of Polysulfide Matrices in Phosphate Diffusion for Controlled Release Fertilizers

Phosphate rock and struvite (ST) dispersion in a polysulfide (PS) matrix offers a sustainable alternative for phosphorous (P) fertilization, as it can favor P dissolution and control its release, while also being a sulfur fertilizer. Herein, we discuss the PS permeability mechanism as well as the chemical and structural factors that affect P diffusion from PS composites. SEM and contact angle showed that P particles increased PS porosity and hydrophilicity, which favors P release. Within 7 days in soil, Fe-oxide papers revealed that the P-diffusion diameter was only 0.3 cm for ST against up to 2.3 cm from the PS composite. In 28 days, available P in soil from the apatite increased from 6 to up to 79 mg/dm3 due to its dispersion in PS. In the adapted Ussing Chamber permeability test, PS displayed higher affinity toward anion permeability and a negligible cation diffusion, which might contribute to the gradual P release and higher availability in soil.