Principal Investigator: Gyles Randall
Co-Investigator(s): Jeffrey Vetsch
Organization(s): University of Minnesota Southern Research and Outreach Center
Award Amount: $30,000
Start Date: 7/1/2008 | End Date: 12/31/2010
Project Manager: Ron Struss
FINAL REPORT: Evaluation of Reduced Application Rates of Acetochlor to Reduce Concentration in Tile Drainage Water (PDF)
Background and Introduction
Two Minnesota water bodies, the Le Sueur River and Little Beauford Ditch, are included in Minnesota Pollution Control Agency's 2008 303(d) list of impaired waters due to concentrations of the corn herbicide acetochlor. This is the first time that a water body in Minnesota has been listed because of the detection of an herbicide. Acetochlor losses can occur by both surface runoff and leaching through the soil profile. This project will characterize leaching losses of acetochlor to drainage tile lines.
Leaching, the loss of water-soluble products through the soil profile, has been proposed as a mechanism transporting acetochlor in poorly drained soils. This study was initiated in the spring of 2008 and continued in 2009 and 2010 at the University of Minnesota Southern Research and Outreach Center at Waseca to determine if reduced application rates would result in reduced concentration and losses of acetochlor (and associated breakdown products) in tile drainage water from a corn-corn-soybean rotation.
Research Experiment
Nine small plots located on a Canisteo-Webster clay loam soil complex were used to conduct the acetochlor study. These nine plots are part of a 36-plot tile drainage facility located at the University of Minnesota's experimental research station in Waseca. These soils are representative of the area and benefit from tile drainage to maximize productivity.
- All plots were planted to corn. Five of these plots followed corn as the previous crop and four plots followed soybeans.
- The nine small plots were categorized according to the history of water flow. They either had a high flow history, medium flow history or low flow history. Each treatment (1.5 or 2.5 pt/acre of acetochlor) was evaluated in plots with each of the flow histories.
- Each plot measured 20' by 30' long and had a plastic perforated tile placed 3.5 ft. deep.
- Each plot was isolate to a depth of 6' by a 12-mil plastic sheet placed in a backfilled trench around each plot.
- Drainage from each of the nine plots was monitored separately.
- Measurements were made prior to and after acetochlor application.
For more details about the experimental design, please refer to the Final Report (PDF).
Climate Considerations
2008 and 2009 were relatively dry years; it was difficult to measure tile drainage losses because there was little to no water being drained.
2010 was considered a banner year to determine acetochlor losses in tile drainage, especially since flow was abundant both prior to and after acetochlor application.
2010 Results
- Tile discharge for each of the plots averaged 22.1 inches with 37.6 inches of precipitation for the March - October drainage season.
- Tile discharge for each of the plots averaged 16.1 inches for the acetochlor post application period (5/17/10 - 10/15/10).
- Average total post-application flow ranged from 14.2 inches to 17.2 inches, which is considered to be very uniform for field drainage research.
- 4 of the 39 samples collected prior to acetochlor application contained detectable levels of acetochlor ranging from 0.03 to 0.07 parts per billion (ppb). All detects were found in snow melt samples collected in March. Researchers suggest this may have been carried over from the previous year.
- No detections of acetochlor were recorded in water collected more than six weeks after the acetochlor application.
- Acetochlor was detected in 13 of the 182 (7.1%) water samples collected during 2010.
- Acetochlor was detected in 8 of the 143 (5.6%) samples collected after the acetochlor application in 2010.
- 1 of 47 samples (2.1%) from the 0.0 pt/acre treatment (control) showed a detectable level of acetochlor.
- 3 of 59 samples (5.1%) from the 1.5 pt/acre treatment contained acetochlor.
- 4 of 37 samples (10.8%) from the 2.5 pt/acre contained acetochlor.
For result from the 2008 and 2009 growing seasons and a discussion of acetochlor breakdown products, please refer to the following progress reports: Progress Report 1 (7/1/08-7/31/08), Progress Report 3 (1/1/09 - 6/30/09), Progress Report 4 (7/1/09 - 12/31/09) and Progress Report 5 (1/1/10 - 6/30/10).
