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

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 coef ficients, K-d, 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 K- d values of both herbicides than the soils of Australia. Both soil pH and s oil organic carbon (SOC) were correlated significantly with the sorption of ametryn, whereas only soil pH was strongly correlated with imazethapyr sor ption. No correlation was found between K-d values of the herbicides and th e clay contents of the soils. Multiple regression analysis showed that K-d values were better correlated (r(2)=0.94 and 0.89 for ametryn and imazethap yr, 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 groundwate r contamination.