This study confirms that both interactions between organic matter and soil minerals and the chemical composition of soil organic matter can influence sorption of non-ionic organic compounds such as diuron. HF-treatment is a useful tool for investigating these two effects separately, although care should be taken in interpreting results for soils where organic matter recovery is low. The strong influence of organic matter–mineral interactions on KOC was evidenced by the large increase in KOC on HF-treatment. The lack of correlations between whole soil KOC and NMR-derived measures of C chemistry also provides evidence of the importance of these interactions on whole soil KOC. However, it should also be noted that HF-treatment did not reduce the variability in KOC between the soils – in fact the coefficient of variation (standard deviation divided by the mean) was almost the same for the HF-treated soils (65%) as for the whole soils (63%) ( Table 2). This indicates that the nature of soil organic matter is also an important contributor to KOC variability. Correlations of broadly-defined C types with KOC of the HF-treated soils goes some way toward understanding the influence of the nature of soil organic matter on KOC. In particular, the proportion of aryl C accounted for 40% of KOC variability. Importantly, this study demonstrates a consistent effect of the nature of soil organic matter on KOC can be detected across a diverse range of soils, even though this effect is diminished when compared to studies involving less diverse soils (e.g. Ahangar et al. (2008a, b)).