Metolachlor Dissipation In Eroded and Restored Landscapes.

In hilly landforms subject to long-term cultivation, erosion has denuded upper slope positions of topsoil and accumulated topsoil in lower slope positions. Landscape restoration is one approach to remediate these eroded landforms by moving soil from areas of topsoil accumulation to areas of topsoil depletion. Six replicate plots were established that extended from the summit to the toeslope of the test area. Half the plots were restored by moving 15 cm of soil from the lower slope to the upper slope. No soil movement occurred in the remaining (unrestored) plots. Restoration resulted in large changes in surface soil properties that were expected to impact herbicide dissipation. For example, surface soil organic carbon contents in upper slope positions averaged 14 g kg^-1 in unrestored plots and 35 g kg^-1 in restored plots. We conducted herbicide dissipation studies to evaluate the effects of landscape position and soil properties on the rate of metolachlor dissipation in the northern Corn Belt. Separate plots were treated with s-metolachlor according to label instructions in the fall and in the spring (preemergence) at a rate of 1.67 pints per acre. Potassium bromide, a non-sorbed, non-degraded tracer, was applied to each plot at 60 kg per ha. Soil cores were collected after application and throughout the growing season to a depth of 1 m and sectioned into 0-10, 10-20, 20-40, 40-60, and 60-100 cm increments.  Bromide and herbicide concentrations were measured in replicate samples at each depth at each sampling time. Metolachlor concentrations in the top 10 cm of showed significant decreases at most landscape positions in the first sampling 1 to 2 weeks after application. Samples are currently being analyzed, but preliminary results suggest that metolachlor dissipation was not drastically different in restored and unrestored plots despite large differences in surface soil properties.