Measured and simulated behaviour of fluometuron, aldoxycarb and chloride ion in a fallow structured soil

The distribution with depth of fluometuron, aldoxycarb and chloride anion was measured in the field during winter in a well‐structured fallow soil. Distribution patterns measured at monthly intervals over 4 months were compared with those simulated by two different models: that of Leistra, which is representative of models using Darcy's Law to describe water movement in soil; and a modified version of that originally developed by Addiscott to describe nitrate movement, which uses the concept of mobile and immobile water categories. Both models correctly predicted the general pattern of movement but underestimated the movement of chloride ion whilst overestimating the movement of aldoxycarb and fluometuron after the first month. The model of Addiscott was encouragingly accurate in predicting the small quantities of fluometuron which penetrated to depths between 25 and 40 cm.