DISSIPATION OF CYANAZINE AND METOLACHLOR ON A CLAY LOAM SOIL, ONTARIO, CANADA, 1987-1990

Dissipation of cyanazine and metolachlor was determined following two and three applications, respectively, to a clay loam soil at the Animal Research Centre Farm, Ottawa between 1987 and 1990. Residue decline, leachability into the soil profile, movement into tile drainage water, and contamination of the groundwater of the two herbicides were measured. The amount of each herbicide applied to the soil surface was accounted for in the upper layer during the first week following treatment. Cyanazine disappeared from the upper 15 cm of the soil in 181 days in 1987 and 90 days in 1988, with a calculated half-life disappearance of 27 and 12 days respectively. Residues of cyanazine were not detected in the soil profile below 15 cm or in tile drainage water. A single residue was detected in a sample of groundwater in 1988 at the detection level of 0.01-mu-g/L. The decline of metolachlor was followed in the upper 15 cm of the soil for 332, 364 and 370 days respectively in 1987, 1988 and 1989 and the half-life disappearance of 80, 99 and 142 days were calculated. Residues of metolachlor were detected between 15 and 30 cm but not below 30 cm in the soil profile. Metolachlor was detected in some tile drainage waters throughout the study period 1987-90. Between 0.003 and 0.01% of the metolachlor applied to the surface appeared in tile drainage water following each of three applications. Metolachlor was present in groundwaters 1.2 to 4.6 m deep between the fall of 1988 to the summer of 1989. It was estimated that by the end of the season between 0.06 and 0.19% of the metolachlor moved into the shallow groundwater between the depths of 1.2 and 4.6 m.