TILE EFFLUENT QUALITY AND CHEMICAL LOSSES UNDER CONVENTIONAL AND NO-TILLAGE .2. ATRAZINE AND METOLACHLOR

The long-term effect of no-tillage (NT) and conventional tillage (CT) on the concentration and loss of the atrazine, deethylatrazine and met olachlor in tile effluent was studied over a 40-month period in four l oam soil, corn (Zea mays L.) fields of approximately 3 ha each. Atrazi ne and deethylatrazine were detected at low concentrations in most of the 773 samples collected between January 1991 and early May 1994. Und er both tillage treatments, atrazine concentrations were mostly below the USEPA advisory of 3 mu g/L while concentrations of atrazine plus d eethylatrazine were generally below 5 mu g/L, the Canadian Interim Max imum Acceptable Concentration (IMAC) for the sum of atrazine and its m etabolites. Concentrations exceeding these limits were mainly observed during rainfall-induced flow events within a few days or weeks follow ing herbicide application. The flow-weighted average concentrations of atrazine during flow events were significantly (p < 0.05) higher unde r NT than CT. Metolachlor was also detected at low concentrations, and in relatively few flow events. Concentrations were always well below the USEPA advisory of 100 mu g/L or the Canadian IMAC of 50 mu g/L. An nual loss of herbicides in tile effluent ranged from 0.02% to 0.34% of the amount applied. Most loss occurred during spring flow events when rile flow was the highest. Atrazine and deethylatrazine losses under the NT treatment were significantly (p < 0.05) higher than those under the CT treatment.