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Title: Rapid assay for detecting enhanced atrazine degradation in soil

Author
item Shaner, Dale
item Henry, William
item Krutz, Larry
item Hanson, Bradley

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2007
Publication Date: 9/5/2007
Citation: Shaner, D.L., Henry, W.B., Krutz, L.J., Hanson, B.D. 2007. Rapid assay for detecting enhanced atrazine degradation in soil. Weed Science.Volume 55:528-535

Interpretive Summary: Atrazine is a herbicide that is widely used for weed management in corn, often in combination with glyphosate, to provide residual control. Colorado farmers have complained about the lack of residual weed control with atrazine, particularly if it is applied year after year in continuous corn. Farmers originally thought that weeds were developing resistance to atrazine. However, recent reports suggest that continuous use of atrazine can lead to enhanced degradation of the herbicide by soil microorganisms. We have developed a rapid assay that can be used to screen soils from farmer’s fields for enhanced degradation of atrazine. The use of this simple assay will allow farmers to determine if they should apply atrazine or not.

Technical Abstract: Atrazine is widely used to control broadleaf weeds and grasses in corn, sorghum and sugarcane. Atrazine is reported to have an average half-life of 6 days and farmers expect to achieve full season weed control with a single application. However, reports of enhanced atrazine degradation in soil from fields that have a history of atrazine applications are increasing. A rapid laboratory assay was developed to screen soils for enhanced atrazine degradation. Soil (50 g) is placed in a 250 mL glass jar and treated with 7.5 mL of water containing atrazine (5 micrograms ai per mL) and capped with a Teflon-lined lid. The assay is conducted at room temperature (25 degree C). Soil subsamples (1.5-3 g) are removed at 0, 1, 2, 4, 8 and 16 d after treatment and extracted with an equal weight of water (v/w). The atrazine in the water extract is assayed on an HPLC. The half-life of atrazine in soils with a history of use is < 1.5 d, whereas the half-life in soils with no history of atrazine use is >8 d. The advantages of this assay are 1) the ease of set up; 2) the rapidity of extraction and 3) the simplicity of the quantification of the atrazine.