【Objective】The increase in global food demand and the consumption of phosphorus (P) fertilizer in modern agriculture have caused P accumulation in extensively managed croplands. Most of the accumulated P deposits exist in sparingly soluble or insoluble species, leading to their low availability, which is almost impossible to use directly by plants or microorganisms. Therefore, improving the utilization of soil accumulated P is not only one of the effective ways to enhance the utilization efficiency of P fertilizers but also relieves the increasing tension of P resources. At present, a large number of macroscopic field experiments have revealed the synergistic promoting effect of nitrogen (N) on P activation and uptake. However, in the N and P interaction, in-situ observation of dissolved N interacting with precipitated P has been lacking. 【Method】Herein, Ca-P precipitates with different solubilities, namely sparingly soluble (DCPD) and insoluble (HAP), were selected as test materials. Taking aqueous solution as control, five NH4Cl concentrations (0.5, 5, 50, 500, 1,000 mmol?L-1) were set as N sources. The in-situ dissolution kinetics of DCPD and HAP at different N levels were directly observed by atomic force microscopy (AFM). AFM-based dynamic force spectroscopy (DFS) technique was employed to characterize the interaction between ammonium cations and DCPD/HAP surfaces at the molecular scale. 【Result】The result showed that the surface dissolved immediately, accompanied by the formation of triangular etch pits, following the addition of NH4Cl. When increasing the NH4Cl concentration, the surface dissolution rate of DCPD was significantly promoted. The quantitative results further exhibited the dissolved P mass was significantly increased from 27.00 mg?kg-1 to 145.0 mg?kg-1 with the increase of NH4Cl concentration from 0.5 mmol?L-1 to 1 000 mmol?L-1. By contrast, the surface morphology of HAP almost remained constant without obvious dissolution even if the NH4Cl concentration was up to 1 000 mmol?L-1. The dissolved P mass was 5.00 mg?kg-1, which was not significant compared with the dissolved P mass of 3.00 mg?kg-1 in aqueous solution. AFM-based DFS results showed that the interaction force between ammonium cations and DCPD (230.6 pN) was significantly greater than that between ammonium cations and HAP (154.0 pN). Due to the difference in binding strength of ammonium cations on Ca-P surfaces at the molecular level, the hydration layer of mineral surfaces is destroyed at different degrees. As a result, the surface dissolution kinetics of DCPD and HAP were significantly different when regulated by ammonium cations. 【Conclusion】This research provides method guidance for in-situ observation of nanoscale dissolution kinetics of different Ca-P minerals. It also illustrates the enhanced interface dissolution on negatively charged DCPD induced by ammonium cation to release available P, thus improving the continuous P supply capacity in soils.