Wednesday, November 7, 2007 - 2:40 PM
253-6
Spatial Variability of Atrazine and Metolachlor Dissipation on Dryland No-Tillage Crop Fields.
An area of interest in precision farming is variable rate application of herbicides to optimize herbicide use efficiency and minimize negative off-site and non-target effects. Two commonly used soil applied herbicides in dryland corn production are atrazine (6-chloro-4-(ethylamino)-6-isopropylamino)-s-triazine) and metolachlor (2-chloro-N-(6-ethyl-o-tolyl)-N-(2-methyloxy-1-methylethyl) acetamide). Variable rate application could help alleviate the problem of frequently finding both of these herbicides in surface and shallow ground waters. However, accelerated dissipation of atrazine has been discovered recently in irrigated corn fields in eastern Colorado . The objectives of this study were to i) compare the rates of dissipation of atrazine and metolachlor across different soil zones from three dryland no-tillage fields under laboratory incubation conditions, and ii) determine if rapid dissipation of atrazine and/or metolachlor occurred in dryland soils. Herbicide dissipation was evaluated at time points between 0 and 35 days after soil treatment using a toluene extraction with GC/MS analysis. Differential rates of atrazine and metolachlor dissipation occurred between two soil zones on two of three fields evaluated. In addition, accelerated atrazine dissipation occurred in soil from all fields of this study with half-lives ranging from 1.8 to 3.2 days in the laboratory. A history of atrazine use on all fields likely contributed to the rapid atrazine dissipation rates.
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