Trifluralin behaviour in soil : a microlysimeter study

The fate of 14C-ring-labelled technical trifluralin was followed in the first 5 centimeters of soil in a microlysimeter experiment under outdoor conditions. The level of water extractable residues from soil was low (less than 1 % of applied radioactivity), but amounts of residues extracted with methanol were high (respectively 66.6, 39.0 and 30.0 % of applied radioactivity after 6, 12 and 18 months). Trifluralin proportion in methanolic extracts was over 80 % and led to high persistance of the product in soil. Seven degradation product were detected, none of them exceeded 2 % of the applied radioactivity. Non-extractable residues increased with time, reached 11.4 % of initial radioactivity after one year, and were stable afterwards. A second year microlysimeter experiment showed that the use of formulated trifluralin had no influence on availability and degradation.