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ARS Home » Southeast Area » Stoneville, Mississippi » Crop Production Systems Research » Research » Publications at this Location » Publication #241486

Title: Picloram and Aminopyralid Sorption to Soil and Clay Minerals

Author
item Fast, Brandon - University Of Florida
item Ferrell, Jason - University Of Florida
item Macdonald, Gregory - University Of Florida
item Krutz, Larry
item Kline, William - Dow Agrosciences

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2010
Publication Date: 11/1/2010
Citation: Fast, B.J., Ferrell, J.A., Macdonald, G.E., Krutz, L.J., Kline, W.N. 2010. Picloram and Aminopyralid Sorption to Soil and Clay Minerals. Weed Science 58:484-489.

Interpretive Summary: Aminopyralid sorption data are needed to help predict off-target transport and plant available herbicide in soil solution. The objective of this research was to determine the sorption of picloram and aminopyralid to five soils and three clay minerals and determine if the potential for off-target movement of aminopyralid in soil is less than that of picloram. Regardless of soil type or clay mineral, aminopyralid sorption was typically greater than that of picloram. It was concluded that soil sorption of aminopyralid was greater than that of picloram, and that the potential for off-target movement of aminopyralid is less than that of picloram.

Technical Abstract: Aminopyralid sorption data are lacking, and these data are needed to predict off-target transport and plant available herbicide in soil solution. The objective of this research was to determine the sorption of picloram and aminopyralid to five soils and three clay minerals and determine if the potential for off-target movement of aminopyralid in soil is less than that of picloram. Picloram and aminopyralid sorption increased rapidly during an initial phase from 0 to 1 h and then increased very little from 1 to 48 h. The maximum theoretical sorption of picloram and aminopyralid were 10.3 and 15.2%, respectively. Freundlich distribution coefficients (Kf) for picloram ranged from 0.12 in a Cecil sandy loam to 0.81 in an Arredondo fine sand, while Kf values for aminopyralid ranged from 0.35 in a Cecil sandy loam to 0.96 in an Arredondo fine sand. Furthermore, Kf values of aminopyralid were higher than those of picloram regardless of soil type. Kf values of picloram in clay minerals were 0.25 (kaolinite), 1.17 (bentonite), and 1016.4 (montmorillonite), and those of aminopyralid were 5.63 (kaolinite), 2.29 (bentonite), and 608.90 (montmorillonite). Electrostatic potential models revealed that picloram and aminopyralid molecules in the dissociated form are highly electronegative; therefore, it is unlikely that these molecules would be soil sorbed because they would be repelled by the net negative charge of soil surfaces. It was concluded that soil sorption of aminopyralid was greater than that of picloram and that the potential for off-target movement of aminopyralid is less than that of picloram.