Sorption of herbicide butachlor, thiobencarb and chlomethoxyfen in soils

Hann-Chyuan Chiang¹ Yuh-Lin Chen² and Yei-Shung Wang^*2

 ¹ Department of Chemical Enginerring, National I-Lan Institute of Agriculture and   Mechanic, I-Lan, Taiwan

 ² Department of Agricultural Chemistry, National Taiwan University, Taipei, Taiwan

Abstract

      Sorption isotherms of three herbicides butachlor [N-(Butoxymethyl)-2-chloro-2’,6’-diethylacetanilide], thiobencarb [S-(4-Chlorobenzyl)-N,N-diethylthiol carbamate] and chlomethoxyfen (2,4-Dichlorophenyl-3-methoxy-4-nitrophenyl ether) in nine cultivated soils collected from paddy field around Taiwan were examined.  The orders of sorption strength are chlomethoxyfen > thiobencarb > butachlor for all soils.  Experimental results indicated that sorption of the herbicides on soils can be adequately described by a linear and Freundlich equation, but not with Langmuir isotherm. Soil properties such as clay content, pH and cation exchange capacity show a poor correlation to the sorption coefficient (K_d); however, organic matter content has a good correlation.  Soil minerals apparently show only slight attribution to sorption of the three herbicides.  Based on the water solubility of the herbicides, soil organic matter - water partition coefficients (K_om) could be estimated.  This evidence would suggested that the sorption of the three herbicides in soil in this experiment might be a partitioning process.