The important characteristics of soil organic matter affecting 2,4-dichlorophenoxyacetic acid sorption along a catenary sequence.

Variations in the characteristics of soil organic matter (SOM) at the field-scale are largely unknown, particularly in relation to observed variations in herbicide sorption. For the herbicide 2,4-D [2,4-dichlorophenoxyacetic acid], we found that its organic carbon-normalized sorption coefficient, Koc, varied by four-fold, from 76 to 315 L kg(-1), in the Ap-horizon along a slope transect in an undulating agricultural field in Manitoba, Canada. In order to explain the relatively large in-field variation in 2,4-D Koc values, techniques ranging from conventional chemical fractionation methods to solid state Cross Polarization and Magic-Angle Spinning (13)C-Nuclear Magnetic Resonance applied on whole soils, were used to derive SOM chemical, physical and structural parameters for correlation analyses with the measured 2,4-D Koc values on whole soils.