ABSTRACT
Herbicides are one of the major pesticide inputs in agriculture. In 2002, atrazine, acetochlor, and S-metolachlor were applied to the soil on 62, 25, and 15 percent of the treated hectares, respectively (Anonymous, 2003). The activity and fate of soil-applied herbicides are affected by multiple factors including soil organic matter (OM), pH, cation exchange capacity, and texture (Blackshaw et al., 1994). These factors are spatially variable, and herbicide adsorption to soil can differ considerably within elds (Koskinen et al., 1994). The soil adsorption of herbicides determines the bioavailability of the chemical to both weeds and microbes. Liu et al. (2002) found that the efcacy and mineralization of atrazine and alachlor varied across a eld depending on soil properties, and weed control was poor where the herbicides dissipated rapidly.
