Formulation and Adjuvant Effects on Leaching of Atrazine and Metolachlor

Atrazine (6-chloro-N-ethyl-N'-(methyethyl)-1,3,5-triazine-2,4-diamine) and metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide) levels in pan lysimeter leachates, collected 1.2 m deep in a Hagerstown silt loam (fine, mixed, mesic Typic Hapludalf), were used to evaluate leaching of these chemicals applied in combination (1.7 + 1.7; 3.4 + 3.4 kg a.i. ha -1 ) as a commercial formulation (CF) or adjuvant (polyacrylate polymer)-amended (AA)-CF and as a microencapsulated (ME) or starch-encapsulated (SE) formulation in conventional tillage (CT) and no-tillage (NT) planted corn (Zea mays L.). Atrazine leached more under NT than CT conditions. Areal losses of atrazine in 1992 from NT at the low rate were 4, 66, and 277 μg m -2 for the treatment sequence (CF, SE, and AA-CF); at the high rate, losses were 887, 488, and 334 μg m -2 . These amounts represented losses of <0.01 to 0.16% and 0.26 to 0.10%, respectively, of applied rates. In 1993, areal losses for the treatment succession (lesser rate) were 888, 253, and 497 μg m -1 of atrazine (0.52, 0.15, and 0.29%); these treatments (greater rate) yielded 5440, 1220, and 1600 μg m -2 of applied chemical (1.60, 0.36, and 0.47%). Application of ME (polyurea polymer) and AA-metolachlor reduced mobility of this chemical at both rates in 1993, but their effect was especially exemplified at the greater rate where a loss of 2.29% (CF) was reduced to 0.83% (ME) and 0.54% (AA). Where herbicide leaching was reduced, greater concentrations, particularly atrazine, were detected in the surface 15 cm of soil in late-season and in leachates, 6 to 12 mo following application.