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 (KOC), determined by batch sorption, varied between 405 and 598 Lkg amongst 10 A11 horizons, and between 547 and 975 Lkg amongst 10 matching A12 horizons. In all cases KOC 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 C nuclear magnetic resonance (NMR) spectroscopy. KOC was positively correlated with aryl C (r = 0.61, significance level 0.001) and negatively correlated with O-alkyl C (r = 0.88, significance level <0.001) as a single factor and as a combination of both we also propose A index (r = 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 KOC to be clearly seen.