The Influence of Water Tables on Herbicide Losses

by R. L. Bengtson, Louisiana State Univ, United States,
L. M. Southwick, Louisiana State Univ, United States,
G. H. Willis, Louisiana State Univ, United States,
C. E. Carter, Louisiana State Univ, United States,



Document Type: Proceeding Paper

Part of: National Water Conference

Abstract: Atrazine and metolachlor were applied preemergent on April 22, 1987, to silage corn on high watertable fields which were either subsurface drained (104 mm drain tubes 1 m deep) or surface drained only. Surface runoff and subsurface outflow were sampled and analyzed for atrazine and metolachlor from April 22 to August 31, 1987. Lowering the watertables reduced atrazine and metolachlor losses by 55 and 51%, respectively. Two-thirds of the losses occurred within 30 days after the application of the herbicides and most of the losses were in the surface runoff. The atrazine concentrations, 12.5 and 9.0 ug/l, for the high watertable and drained fields, respectively, were 4 and 3 times greater than the U.S. Environmental Protection Agency advisory of 3 ug/l for drinking water. The metolachlor concentrations were near the U.S. EPA advisory of 10 ug/l.

Subject Headings: Runoff | Pesticides | Water table | Subsurface drainage | Soil water | Crops

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