HERBICIDE RETENTION BY VEGETATIVE BUFFER STRIPS FROM RUNOFF UNDER NATURAL RAINFALL

Effectiveness of vegetative buffer strips for herbicide retention from agricultural runoff was evaluated in a two-year natural rainfall stud y. A source area of 0.41 ha (mainly Canisteo silty clay loan soil), ha ving an average slope of 3%, was fall chisel-plowed, spring disked, an d planted to corn. Three herbicides (atrazine, metolachlor; and cyanaz ine) were applied to the source area in each spring. Six vegetative bu ffer strips, 1.52 m widex20.12 m long, were isolated with metal border s downslope of the source area in a well established bromegrass (Bromu s inermis) waterway These strips provided for three replications of tw o drainage to buffer area ratio treatments of 15:1 and 30:1. Herbicide retention was dependent on the antecedent moisture conditions of the strips. These retentions ranged from 11 to 100% for atrazine, 16 to 10 0% for metolachlor; and 8 to 100% for cyanazine. Herbicide retention b y the buffer strips for the two treatments were not significantly diff erent for the observed storm events. Herbicide concentrations in solut ion in outflow from the strips were less than the inflow concentration s for all the three herbicides. Infiltration was the key process for h erbicide retention by the buffer strips, although there war some adsor ption to in-place soil and/or vegetation. Metolachlor concentrations i n sediment increased in outflow for the two treatments; however the op posite was true for atrazine and cyanazine. Herbicide retention by sed iment deposition in the strip represented about 5% of the total herbic ide retention by the buffer strips. The buffer strips were found to ha ve high percent sediment retention, ranging from 40 to 100%; thus, the strips would be more effective for retaining strongly adsorbed herbic ides.