This paper describes the application of the Italian chabazite-rich tuff of Sorano (Grosseto) as a soil conditioner and slow nutrient fertilizer to a silty-clay soil and a sandy soil. The study was developed by means of batch and column experiments. The objectives of the study were: (1) to evaluate and compare the physical and hydraulic properties of mixtures of soil and natural zeolitite (95:5% v/v) with those of unamended soils, (2) to determine the effects of applying NH4+-enriched zeolitites on soils and (3) to model water and solutes movement in two different scenarios, with and without amendment incorporation. Results of column experiments were then modelled to obtain the physical–chemical and hydraulic parameters representative of the soils amended with the NH4+-enriched zeolitites. Using synthetic rainwater as eluent, NH4+ was never detected in the water phase of batches and columns; NO3− and PO43 − were both present at high concentrations in batch tests and were leached in column elution tests. NO3− displayed very high concentrations at the beginning of the elution whereas PO43 − showed low concentrations and retarded peaks in both amended soil columns. The rationale of the study lies in the belief that inorganic amendments, which improve the physical and hydraulic properties of soils, can lead to minimized leaching of nutrients.