The nature of soil organic matter affects sorption of pesticides. 1. Relationships with carbon chemistry as determined by C-13 CPMAS NMR spectroscopy

The structural composition of soil organic matter (SOM) was determined in t wenty-seven soils with different vegetation from several ecological zones o f Australia and Pakistan using solid-state CPMAS C-13 NMR. The SOM was char acterized using carbon types derived from the NMR spectra. Relationships we re determined between K-oc (sorption per unit organic C) of carbaryl (1-nap hthyl methylcarbamate) and phosalone (S-6-chloro-2,3-dihydro-2-oxobenzoxazo l-3-ylmethyl O,O-diethyl phosphorodithioate) and the nature of organic matt er in the soils. Substantial variations were revealed in the structural com position of organic matter in the soils studied. The Variations in K-oc val ues of the pesticides observed for the soils-could be explained only when V ariations in the aromatic components of SOM were taken; into consideration. The highly significant positive correlations of aromaticity of SOM and K-o c values of carbaryl and phosalone revealed that the aromatic component; of SOM is a good predictor of a soil's ability to bind such nonionic pesticid es.