KPO ₃ -Silica Nanocomposite for Eco-Friendly Smart Fertilization

Coating fast-effective fertilizers with recalcitrant organic polymers, which are the main sources of microplastic particles, is a preferred commercial approach to controlled release (CR) compound fertilizers, mainly because of the absence of available potassium sources. This study focused on developing a CR K source in the form of a potassium metaphosphate (KPO3)–silica nanocomposite for pollution-free CR compound fertilizers. A KPO3-silica nanocomposite was successfully fabricated from phosphoric acid and potassium silicate at a temperature range of 450 to 500 °C, consisting of KPO3 nanoparticles embedded within a silica matrix along with 30% of fast-release orthophosphates and diphosphates. In citric acid, the accumulated fractions of released phosphate over time were well-fitted to zero-order release kinetics, whereas the concentration of released phosphate in dynamic water was inversely correlated with the flow rate. In particular, the nanocomposite exhibited a prolonged and reliable release of phosphorus and K, even in the presence of Ca2+ and Al3+, highlighting the protective role of silica matrix against these cations in soil. A pot experiment using black beans clearly showed that nanocomposite-supplied K and P were sufficient to promote more sustainable growth than the corresponding fast-effective fertilizers. Therefore, the results of this study demonstrate that KPO3–silica nanocomposites can be utilized as eco-friendly CR sources for K and P to offer reliable nutrient release performance and compatibility with the environment.