The other factor that is believed to influence soil KOC is the nature of the organic matter ( Wauchope et al., 2002). Solid-state 13C NMR analysis of the soils (following HF-treatment) indicated that there was considerable variability in organic matter chemistry amongst this set of soils, as shown by variations in the relative proportions of signal assigned to different C types ( Table 3). From Fig. 2 and Fig. 3, it is clear that the proportion of most C types is more closely correlated with KOC for the HF-treated soil than with KOC for the whole soil. This is consistent with whole soil KOC values being influenced by interactions between organic matter and soil minerals ( Ahangar et al., 2008b). By far the strongest correlation is between the proportion of aryl-C and KOC for the HF-treated soils; Table 4 shows that variation in aryl C accounts for 40% (R2 = 0.40) of the variability in KOC for the HF-treated soils. This is again consistent with the findings of Ahangar et al. (2008b) and also Ahmad et al. (2001), who reported strong correlations between aryl C and KOC for two non-ionic pesticides.