ADSORPTION OF CHLORIDAZON BY SOILS AND THEIR COMPONENTS

The effect of soil composition on adsorption of chloridazon by 18 samples of natural soils, with different chemical and textural characteristics, obtained from west-central Spain, was investigated. The effect of removal of organic matter on adsorption and adsorption of the herbicide by the active components of the soils (montmorillonite and humic acid) was also studied. A highly significant correlation was found between the distribution coefficient (Kd) and organic matter content when all the soils or the soils with organic matter content > 2% were considered. According to the determination coefficients (r2), organic matter content accounted for 72% of the variance in adsorption in the former case and 92% in the latter. In soils with an organic matter content < 2%, there was no correlation between Kd and organic matter content. A significant correlation was observed between Kd and smectite content for soils containing smectite in their clay fraction. Both simple and multiple correlations showed that clay content, excluding the smectite fraction, had a relatively small effect on adsorption of the herbicide. Adsorption of chloridazon by oxidized soils, montmorillonite, and humic acid confirms the effect of organic matter and smectite on adsorption in natural soils.