Functionalization of Amorphous and Crystalline Calcium Phosphate Nanoparticles with Urea for Phosphorus and Nitrogen Fertilizer Applications

The development of nanofertilizers has gained significant attention for their potential to enhance nutrient delivery to plants while mitigating the environmental impact of intensive agriculture. In this study, we investigated the urea functionalization of two types of calcium phosphate nanoparticles, hydroxyapatite (HAP) and amorphous calcium phosphate (ACP), as nanofertilizers capable of simultaneously releasing phosphorus and nitrogen in a controlled manner. Leaching experiments using a vermiculite column revealed that ACP-urea significantly slowed urea release compared with free urea, whereas HAP-urea exhibited a release profile similar to that of free urea. Greenhouse experiments on corn (<i>Zea mays</i>) showed that ACP-urea treatment enhanced the dry biomass and relative chlorophyll content compared to treatments with free urea combined with either ACP or monocalcium phosphate. Microbiome analyses indicated that the improved plant performance with ACP-urea was primarily due to the material's physicochemical properties rather than significant shifts in the rhizosphere bacterial communities. These findings highlight the potential of ACP nanoparticles as effective nanofertilizers for controlled phosphorus and nitrogen release, contributing to more sustainable agricultural practices.