Citrate-Stabilized Amorphous Calcium Phosphate Nanoparticles Doped with Micronutrients as a Highly Efficient Nanofertilizer for Environmental Sustainability

The increase in the global use of phosphorus (P) fertilizers for crop production has generated a series of unintended negative consequences. In response, there is growing interest in developing new fertilizers that curb adverse effects. Among them, amorphous calcium phosphate (ACP) is a viable alternative because of its tunable solubility for P release, high specific surface area, and ability to be doped with vital microelements essential for crops. Herein, we prepared a series of citrate-stabilized ACP nanoparticles (ACPc) doped with micronutrients (B, Cu, Mg, and Zn) and analyzed their dissolution and nutrient release characteristics. Comparative analysis of undissolved ACPc, released ions, and pH of eluted buffer showed a strong positive correlation between the P release rate and the corresponding change in buffer pH. The competitive advantage of ACPc against a monocalcium phosphate (MCP), a conventional commercial fertilizer, for providing P nutrition to plants was tested in lettuce (Lactuca sativa) plants in a greenhouse study. The results showed that undoped ACPc stimulated a 20% higher lettuce crop yield than that of MCP, and the doping with multimicronutrients increased the yield by 22%. More importantly, P resource use efficiency (RUE), calculated based on crop yield and P lost in leachate, was significantly higher in all ACPc than MCP and was about an order of magnitude higher in undoped and multimicronutrient doped ACPc. These results demonstrate that multimicronutrient doping in ACPc is a more efficient and sustainable approach for the dual delivery of P and micronutrients and thus contributes toward meeting the global food demands while minimizing the negative environmental impacts of agriculture.