Effect of Urea: Hydroxyapatite Composites for Controlled-Release Fertilization to Reduce P Complexation in Soils

Phosphorous fixation in the soil is the most limiting factor for P-management, and previous studies have indicated that coupling nanoparticulated P sources (e.g. hydroxyapatite) in adequate matrices (nanocomposites) can increase nutrient uptake. However, how the nanocomposite affects the P fixation is still an open question. Herein we describe X-ray absorption near edge structure (XANES) experiments to investigate the role of phosphate fertilizer (P) composite in reducing P complexation in soil. Experiments in a greenhouse (maize cultivation) and soil incubation comparatively revealed that a composite formed by the dispersion of hydroxyapatite (phosphate source) into urea could increase the production of dry matter (compared to monoammonium phosphate, MAP), keeping the residual P available in the soil for future cultivations (i.e. not strongly bonded to minerals). This behavior was evidenced by P-XANES, which indicated that the composite induced the bonding of remnant P to more labile organic fractions instead of mineral phases, as seen in MAP cultivation.