TRIAZINE DISPERSION AND DISTRIBUTION IN THE UNSATURATED ZONE OF DRAINED SOILS IN THE BRIE (FRANCE)

The purpose of this study was to investigate the fate of triazines and their metabolites in the unsaturated zone in the field conditions dur ing a period from the spring sowings to the autumn tillages. The study was performed upon two soils treated for corn culture during the year 1992. The investigations were presented after the wet weather by subs urface drainage and surface runoff. Throughout the 6 months survey, th e relative importance of the triazines is by decreasing order: atrazin e > simazine > desethylatrazine (DEA). After the application, the herb icides were only found in the first 40 cm of the soil during the dry p eriod of the cultivation. They were dragged towards the depth by perco lation water mainly during the first water infiltrations when the drai ns were set in again in autumn or winter. The losses of herbicides aft er the cultivation cycle (october) expressed as a ratio of the initial input ranged from 40 to 73% for the atrazine and from 40 to 44% for t he simazine and depended on the importance of the application amount. In autumn and winter, the losses originating in percolation were highe r than those due to volatilization and/or degradation (abiotic and bio degradation), as the soil conditions were unpropicious to the formatio n of non-extractable residues.