This study investigates the leaching behaviour of nitrate and ammonium in three types of soils from Debrecen, Hungary, i.e., agricultural (Pallag), industrial (WWTP), and urban (VKI) soils—through soil leachate experiments, soil column tests using ammonium nitrate treatments at 1 g L-1, 5 g L-1, and 10 g L-1 concentrations, and long-term predictive modeling. Particle size distribution analyses revealed the texture of agricultural soil as sandy loam with a high proportion of silt and fine sand, while industrial and urban soils are richer in clay and silt, highlighting higher water retention capacity and lower permeability. Therefore, soil columns (0–40 cm) were prepared with upper and lower layers representing real field conditions, and further HYDRUS model is used to simulate leaching behaviour over 8 years of precipitation data. Results confirmed the high mobility of nitrate. In agricultural soil, nitrate migrated almost entirely to lower layers at high doses, whereas urban soils retained more nitrate in the top horizon. WWTP soils exhibited substantial surface accumulation but also notable subsoil enrichment, suggesting sensitivity to loading and potential groundwater risks. Leachate experiments showed the impact of super-absorbent polymers on soil pH and nitrate leaching. Unexpectedly, additions of bentonite, Zeba, and Stockosorb did not restrict nitrate leaching. The study calls for serious implications to be drawn for sustainable nitrogen management in agricultural, industrial, and urban soils to prevent long-term environmental impacts and conserve groundwater resources.