Miscible displacement techniques were used to study the movement of a solution containing 4‐amino‐3, 5, 6‐trichloropicolinic acid (picloram) through an initially herbicide‐free Norge loam soil. Picloram mobility was reduced significantly by decreasing the average pore‐water velocity from 5.8 to 0.59 cm/hr. A variation in herbicide adsorption with pore‐water velocity was observed at each bulk density (1.55 and 1.65 g/cm 3 ) and aggregate size (<2.0 and <0.42 mm) studied. For a specific bulk density, picloram adsorption was greater when the largest soil aggregate size was <0.42 mm than when the soil contained <2.0‐mm aggregates. Differences in the effluent concentration distribution owing to variations in aggregate size were more evident at the lower bulk density. The average pore‐water velocity influenced picloram movement more significantly than variations in bulk density or largest aggregate size at a given flow rate.
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Davidson et al. (1972) studied this question.