The adsorption of natural organic matter (NOM) onto minerals is a major protection mechanism of carbon from degradation and influences the distribution of nutrients and pollutants in environment. However, due to the heterogeneous nature of NOM and the variation of soil conditions, it is so far unclear which mechanisms are regulating the preferential adsorption of NOM to metal (hydr)oxides. With carefully designed lab experiments and advanced surface complexation modeling, we aim to gain insights into the competitive adsorption of organic matter molecules with different sizes and sites. In the approach, the complexity of the adsorption systems will be stepwise increased to collect a comprehensive data set that can be used to constrain the model and gain a deeper knowledge of the binding characteristics of NOM under a wide range of conditions.