Role of the chemistry of soil organic matter on the sorption of diuron

The influence of organic matter chemistry on the sorption of diuron to soils collected from a small (2 ha) field was investigated.Organic carbon-normalized sorption coefficients (K OC ), determined by batch sorption, varied between 405 and 598 Lkg -1 amongst 10 A11 horizons, and between 547 and 975 Lkg -1 amongst 10 matching A12 horizons.In all cases K OC was greater for the A12 horizon than the corresponding A11 horizon by 27-81%.Organic matter chemistry of the A11 and A12 horizons was determined using solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy.K OC was positively correlated with aryl C (r 2 = 0.61, significance level 0.001) and negatively correlated with O-alkyl C (r 2 = 0.88, significance level <0.001) as a single factor and as a combination of both we also propose A index (r 2 = 0.65, significance level 0.001).Little change in soil mineralogy across a very small field led to diminished organic matter and clay mineral interactions, allowing the effect of organic matter chemistry on K OC to be clearly seen.