Engineered Phosphate Fertilizers with Dual-Release Properties

A new strategy to produce phosphate (P) fertilizers with both fast and slowly soluble P by the compaction method to produce composite products is presented. This unique composition is created by combining monoammonium phosphate (MAP) as a highly soluble P nutrient source, with a commercially available slow-release P such as struvite (Str) or P-loaded graphene oxide (GO). Graphene oxide-loaded P was synthesized by in situ oxidation of GO and ferrous ion (GO-Fe) mixtures with hydrogen peroxide and further loading of P onto the GO-Fe composite. The nutrient release in water was studied for dual-release MAP-Str and MAP-GO-Fe-P and compared to their corresponding slow- and fast-release sources. Column perfusion experiments showed a biphasic dissolution behavior with no significant difference between MAP-GO-Fe-P and MAP-Str. Visualization of P diffusion and chemical analysis of the soil after diffusion were used to assess the diffusion of P from different P fertilizers in various types of soil. Runoff and leaching simulations were performed to investigate the effects of the prepared fertilizer formulations on the environment. Overall, the diffusion of the dual-release fertilizers and the P loss in runoff and leaching experiments were less than for MAP. The better environmental performance of the dual-release fertilizers compared to MAP was related to the specific properties of the GO-based materials such as their two-dimensional structure and to the low solubility of the Str in the case of Str-based fertilizers.