The binding of trace metals to organic soils in the presence of common competing ions such as Al³⁺ and Fe³⁺ is still not well understood. In this study we studied the pH-dependent binding of Cd²⁺, Co²⁺, Ni²⁺ and VO²⁺ to a Swedish mor layer (Risbergshöjden Oe) in the absence or presence of different background concentrations of Al³⁺ and Fe³⁺ as nitrate salts. At pH 4, the order of binding for the four selected trace metals was: VO²⁺ >> Ni²⁺ > Cd²⁺ » Co²⁺. Additions of Al³⁺ and Fe³⁺ to the mor layer suspensions caused competition effects, although they were relatively modest in the case of VO²⁺. We used a geochemical model, Visual MINTEQ with the Stockholm Humic Model (SHM), to derive complexation constants for the trace metals in this system. The modelling relied mainly on complexation reactions that have been used in previous work with the SHM and WHAM models. However, because the complexation mode for Fe³⁺ in organic soils is poorly known, we conducted Fe K-edge EXAFS spectroscopy on the mor layer to constrain the Fe³⁺ complexation reaction in the model. The resulting model was capable of correctly accounting for the pH-dependent competition effects of Fe³⁺ and Al³⁺. These results will help to simulate trace metal binding in polluted organic soils.