Sorption of ametryn and imazethapyr in twenty-five soils from Pakistan and Australia.

Sorption of ametryn and imazethapyr in 25 soils from Pakistan and Australia was investigated using the batch method. The soils varied widely in their intrinsic capacities to sorb these herbicides as shown by the sorption coefficients, Kd, which ranged from 0.59 to 47.6 for ametryn and 0.02 to 6.94 for imazethapyr. Generally the alkaline soils of Pakistan had much lower Kd values of both herbicides than the soils of Australia. Both soil pH and soil organic carbon (SOC) were correlated significantly with the sorption of ametryn, whereas only soil pH was strongly correlated with imazethapyr sorption. No correlation was found between Kd values of the herbicides and the clay contents of the soils. Multiple regression analysis showed that Kd values were better correlated (r2=0.94 and 0.89 for ametryn and imazethapyr, respectively) if SOC and pH were simultaneously taken into account. The study indicated that sorption of these herbicides in the alkaline soils of Pakistan was low and consequently there is considerable risk of groundwater contamination.