Erosional Losses of s-Triazine Herbicides

Erosional losses of two chloro-s-triazines, atrazine and GS13529, were evaluated in 1970 and 1971 from field runoff plots planted to corn (Zea mays L.) and situated on an Hagerstown silty clay loam of 14% slope. Losses of a methoxy-s-triazine, GS14254, were assayed in 1971 and 1972 from an alfalfa (Medicago sativa L.) stand. Herbicides were applied preemergent to corn and to dormant alfalfa only once during the initial growing season or initial season of evaluation at two rates, 2.2 and 4.5 kg/ha. Total losses of atrazine during the first and most critical season at the respective rates were 5.0 and 4.8% of that applied and 87 to 93% of this loss resulted within the first month following application. Total losses of the related chloro-s-triazine were comparable at each of the rates. Both of these compounds dissipated at a moderate rate over the growing season with GS13529 showing a higher level of recalcitrance, particularly early in the season. Soil core analysis revealed that one month after application an average of 35.3% of the applied atrazine was recovered; five months later an average level of 11.8% was residual. Recovery of GS13529 ranged from 62.5 to 9.8% for the same time period. Runoff losses of GS14254 from alfalfa were inconsequential. Little runoff was obtained from this cropping system, no sediment was ever collected and runoff concentrations of the herbicide were extremely small. Total losses of this herbicide for the year were 0.02 and 0.03% for the respective application rates. Actual losses of water and soil to runoff in 1970 appeared to be of a more critical nature than chemical losses. Runoff losses during one particular erosion event ranged from 17% of the incident rainfall for the check plot to 68% at the low rate of atrazine. Moreover, 9800 kg/ha (4.4 tons/a) of soil were lost at the low rate. These kinds of results speak strongly for sound soil and crop management practices and conservation measures on sloping cropland.