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. T he drains reduced metolachlor runoff losses by 90% and trifluralin los ses by 57%. Concomitantly, runoff volume was reduced 24% and soil eros ional losses by 75%. The large reduction of metolachlor losses in runo ff was due to a first event from the nondrained plot that was characte rized by high chemical concentration, a characteristic that was not du plicated in the corresponding events from the drained plots. Due to lo w sediment concentrations in runoff and to low water solubility, trifl uralin loss in runoff, even from the nondrained treatment, was less th an 0.2% of the application.