MOBILITY AND PERSISTENCE OF THE HERBICIDES ATRAZINE, METOLACHLOR AND TERBUTHYLAZINE IN PLAINFIELD SAND DETERMINED USING FIELD LYSIMETERS

Field lysimeters (75 × 15 cm) packed with 18 kg (dry weight) Plainfield sand were used to study the mobility and persistence of commercial formulations of the herbicides atrazine, metolachlor and terbuthylazine under two precipitation regimes: rainfall, and rainfall with supplementary watering. Leachate from the 70-cm soil cores was monitored daily for each herbicide. Pairs of soil cores for each herbicide and each moisture regime were sectioned (7 × 10 cm) after 1, 2, 4, 8, 12 and 21 weeks to obtain both mobility and persistence data. After 21 weeks under rainfall, the maximum movements of atrazine, terbuthylazine and metolachlor were, respectively, 30, 20 and 10 cm, and under supplementary watering, were, respectively, 70, 50 and 40 cm. Only a single trace of atrazine appeared in the effluent of rainfall cores. Both atrazine and terbuthylazine appeared in the effluent following a 50-mm water application on day 2. Atrazine also appeared in the effluent on several occasions after week 12 under supplementary watering.