Fig. 2. Sorption–desorption isotherms of herbicides ([a] metolachlor, [b] atrazine, [c] 2,4-D, [d] picloram) on natural and PAM-treated soils. Each data point is the mean of three replicates and the error bar is its standard deviation. The solid line is the sorption isotherm and the dashed line is the desorption isotherm. The PAM application rate was 80 mg kg^-1.