LEACHING OF ATRAZINE FROM SUGARCANE IN SOUTHERN LOUISIANA

Atrazine was applied to sugarcane at 4.48 (earlier, 1989-1990, study) or 2.24 kg/ha (later, 1990-1991, investigation), and leaching into subsurface drains 1 m deep was measured for 3 months. Atrazine flow into the drains was characterized by maximum concentrations in the earlier study of 82-403-mu-g/L within 11 days after application; the concentrations averaged below 3-mu-g/L (the lifetime health advisory for drinking water) after day 20. The later study produced highs of 82-165-mu-g/L within 7 days of application; after day 30, concentrations averaged less than 3-mu-g/L. Total losses were 1.6-2.6% of the application in the earlier study and 0.6-1.8% of the application for the later investigation. Essentially all (97-98%) of the losses into the drains for 1989-1990 occurred within the first 21 days during a period of 203 mm of rainfall. In the 1990-1991 study a similar proportion of total leaching (91-95%) did not occur until 48 days after application; in this study 42 days passed before 209 mm of rain had fallen on the plots.