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United States Department of Agriculture

Agricultural Research Service

Title: Sorption and Leaching Potential of Herbicides in Brazilian Soils

Authors
item Oliveira Jr, R - UNIV. ESTADUAL DE MARINGA
item Koskinen, William
item Ferreira, F - UNIV. FEDERAL DE VICOSA

Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: February 8, 1999
Publication Date: N/A

Technical Abstract: Sorption of the herbicides alachlor, atrazine, dicamba, hexazinone, imazethapyr, metsulfuron-methyl, nicosulfuron, simazine, and sulfometuron-methyl were characterized on six Brazilian soils using the batch equilibration method. In general, weak acid herbicides (dicamba, imazethapyr, metsulfuron-methyl, nicosulfuron and sulfometuron-methyl) were ethe least sorbed, whereas weak bases such as triazines and non-polar, non-ionic herbicides (alachlor) were the most sorbed. The Kd values found showed a significant correlation with soil organic carbon content and CEC for most herbicides. Koc values showed a smaller variation among soils than Kd. For sulfonylureas, sorption was inversely correlated to the pKa values. To estimate the leaching potential, Koc and the Groundwater Ubiquity Score (GUS) were used to calculate half-lifes that would rank these herbicides as leachers. Evaluation of leaching potential demonstrated dthat sulfonylureas and hexazinone are leachers (calculated half-lives < observed half-lives) in all soils, and alachlor, atrazine and hexazinone are leachers or transitional (calculated half-lives > observed half- lives) depending on soil type. Results discussed in this paper provide background to prioritize herbicides or chemical groups that should be evaluated in field conditions with regard to their leaching potential to groundwater.

Last Modified: 12/19/2014
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