Abstract
Problem statement: The low organic soils of the Cumberland Plateau, as well as the karst geology of the region, may promote increased transport of herbicides outside of application sites. We have studied the fates of imazapyr and metsulfuron-methyl applied to a privately owned tract on the Cumberland Plateau in Tennessee and compared the field results with herbicide fate predicted by the computer model GLEAMS. Approach: The fate of the two herbicides, applied for pine release at a site on the Cumberland Plateau, was monitored over a sixteen month period. Concentrations in soil water were monitored using vacuum soil lysimeters. Grab samples were taken of water in ephemeral streams draining the clearcut area and of a perennial stream which receives water from the study area. Uncut streamside management zones of about 50 m bordered the streams. The field results were compared with those obtained using the GLEAMS computer model. Results: Concentrations of both herbicides in soil water dropped significantly within the first two months after application, imazapyr to less than 50 µg L-1 and metsulfuron-methyl to less than 3 µg L-1 and decreased more gradually in the following months. The maximum concentrations observed in soil water were 252 µg L-1 (imazapyr) and 13 µg L-1 (metsulfuron-methyl). Except on two dates occurring 5 months after application, the herbicides were not detected in the stream samples. GLEAMS predicted that very little herbicide should have been lost from the site in runoff or erosion sediment. The model predicted greater retention of the herbicides by the soil than was found through the field measurements. Conclusion/Recommendation: The rapid transport of imazapyr and metsulfuron we observed indicates that further study is justified at other locations on the Cumberland Plateau. Streamside management zones effectively prohibited contamination of receiving streams by herbicides at the study site.
Highlights
Imazapyr and metsulfuron-methyl are herbicides which are used worldwide in a variety of applications
We found imazapyr concentration dropped below 1 μg L−1 about 14 months after application and metsulfuron-methyl dropped to this covered with grass and other low vegetation, which could have caused some delay in transport of herbicide into the soil; the other two lysimeters were placed in an level about 5 months after application
While the soils around all three lysimeters were similar, the layering and detailed characteristics of the soils around the individual lysimeters varied, which may have caused some variation in retention of the Recommendations: The rapid transport of imazapyr and metsulfuron through the Cumberland Plateau soil which we observed in our study indicates that further study is justified
Summary
Imazapyr and metsulfuron-methyl are herbicides which are used worldwide in a variety of applications. Though belonging to different pesticide families (imazapyr is classified as an imidazolinone, while metsulfuron-methyl is classified as a sulfonylurea herbicide), they share many characteristics (Cox, 1996; Oregon State University, 1993) Both are ionic and water soluble, making them potentially mobile in soil and both are found to be generally non-toxic to animals, fish and insects. Lys 1 and Lys 2 were detection limits, determined as three times the standard positioned adjacent to one another, 1.5 m apart, in a portion of the clearcut free of any residual vegetation; Lys 3 was placed about 4 m from these two, in an area deviation of baseline noise of water “blank” sample, for the herbicides were: imazapyr-0.05 μg L−1 and metsulfuron-methyl -0.12 μg L−1. Spiked samples were prepared on-site by adding sample to aliquots of stock herbicide solutions
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