<p>Although ZnO nanoparticles (ZnO-NPs) are promising controlled-release Zn sources, the influence of synthesis route and precursor chemistry on Zn dissolution, leaching, and bioavailability in different soils remains unclear. This study compared five laboratory-synthesised ZnO formulations to determine how formulation design affects Zn mobility and availability in sand and soils. ZnO-NPs (C-NIT-1, C-SUL, C-NIT-2, S-ACE, and S-SUL) were synthesised via co-precipitation or sol–gel routes using different precursors and hydroxide sources, yielding distinct physicochemical properties. Dissolution was assessed in aqueous media, and leaching was evaluated through column experiments with sand, acidic soil (pH 5.8), and calcareous soil (pH 8.3). Zinc in leachates was periodically quantified, and bioavailable Zn was determined using low-molecular-weight organic acids. The formulations showed marked differences in structural and surface properties, with hydrodynamic diameters of 183–603 nm and zeta potentials from − 7.4 to + 16.5 mV. SEM revealed variable aggregation, with C-NIT-2 forming aggregates up to 10 μm. Elemental analysis confirmed precursor-dependent variation in S and Zn contents. These differences resulted in contrasting Zn release patterns: in sand, C-SUL and S-ACE released Zn rapidly, whereas C-NIT-1 and S-SUL showed slower kinetics. In acidic soil, C-SUL leached 1.4 mg Zn (&gt; 80% of available Zn), while in calcareous soil total leaching remained below 0.2 mg. Overall, the results demonstrated that Zn release and mobility are not determined solely by particle size, but by the combined influence of other key parameters, such as porosity, surface charge, solubility, synthesis conditions, as well as soil properties.</p>