The leaching of metribuzin, oxadiazon and bromacil in two soils and simulated rainfalls of 60 and 120 mm of water was studied in columns. Columns with 10 cm diameter and 21 cm height, divided in sections of 3 cm were used. After the water percolated through the sections were separated and Lactuca sativa was sown in those with metribuzin and bromacil and Echinochloa cruzgalli in those with oxadiazon. Dead plants were counted every two days after emergence during two weeks and during ten days after a second sowing. An expression relating dead and living plants and the time plants took to die was used to estimate the concentration of the herbicides in each section of the columns, for each counting. Oxadiazon remained in the first 3 cm of the column for any condition studied. Metribuzin reached 9 cm in clay soil with 60 mm of water and 18 cm with 120 mm. In the loam soil it reached 21 cm with both precipitations. Bromacil showed more intense leaching than metribuzin in any conditions with lower retention in the upper sections with 60 mm. The differences of leaching between the two soils seem to be due more to the content and type of clay and less to the content of organic matter.
Leaching; metribuzin; oxadiazon; bromacil