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TECHNICAL REPORTS

Vadose Zone Processes and Chemical Transport

Small-Scale Spatial Variability of Atrazine and Dinoseb Adsorption Parameters in an Alluvial Soil

^a Inst. of Environmental Science and Technology, Swiss Federal Inst. of Technology, EPFL, ENAC, ISTE, HYDRAM, Station 2, 1015 Lausanne, Switzerland
^b Université Grenoble 1, Lab. d'études des Transferts en Hydrologie et Environnement (LTHE), BP 53, F-38041 Grenoble Cedex 9; CNRS
^c State Key Lab. of Hydrology-Water Resources and Hydraulic Engineering, Hohai Univ., Nanjing, China
^d INRS, Centre Eau, Terre et Environnement, Université du Québec, 2800 rue Einstein, CP 7500, Ste-Foy, QC, G1V 4C7, Canada

^* Corresponding author (andre.mermoud{at}epfl.ch).

Received for publication June 7, 2007. Soil sorption processes largely control the environmental fate of herbicides. Therefore, accuracy of sorption parameters is crucial for accurate prediction of herbicide mobility in agricultural soils. A combined experimental and statistical study was performed to investigate the small-scale spatial variability of sorption parameters for atrazine and dinoseb in soils and to establish the number of samples needed to provide a value of the distribution coefficient (K_d) next to the mean, with a given precision. The study explored sorption properties of the two herbicides in subsurface samples collected from four pits distributed along a transect of an alluvial soil; two to four samples were taken at about 30 cm apart at each sampling location. When considering all the data, the distribution coefficients were found to be normally and log-normally distributed for atrazine and dinoseb, respectively; the CVs were relatively high (close to 50% for dinoseb and 40% for atrazine). When analyzed horizon by horizon, the data revealed distribution coefficients normally distributed for both herbicides, whatever the soil layer, with lower CVs. The K_d values were shown to vary considerably between samples collected at very short distance (a few centimeters), suggesting that taking a single soil sample to determine sorption properties through batch experiments can lead to highly unrepresentative results and to poor sorption/mobility predictions.

Abbreviations: CEC, cation exchange capacity • K_d, distribution coefficient • K_oc, carbon distribution coefficient • OC, organic carbon content • OM, organic matter content • SC, skewness coefficient