Effect of subsurface drains on runoff losses of metolachlor and trifluralin from Mississippi River alluvial soil.

Subsurface drains reduced runoff losses of metolachlor and trifluralin from plots on Mississippi River alluvial soil planted with soybean. The drains reduced metolachlor runoff losses by 90% and trifluralin losses by 57%. Concomitantly, runoff volume was reduced 24% and soil erosional losses by 75%. The large reduction of metolachlor losses in runoff was due to a first event from the nondrained plot that was characterized by high chemical concentration, a characteristic that was not duplicated in the corresponding events from the drained plots. Due to low sediment concentrations in runoff and to low water solubility,trifluralin loss in runoff, even from the nondrained treatment, was less than 0.2% of the application.