Picloram Sorption by Soils
1974
Farmer, W. J. | Aochi, Y.
Picloram (4-amino-3,5,6-trichloropicolinic acid) adsorption-desorption isotherms were derermined on six western USA soils. Adsorption isotherms were determined as a function of temperature, soil/solution ratio, and solution ionic strength. Special attention was given to the effects of pH and organic matter content in the analysis of the result. Adsorption increased with increasing organic matter with soils varying in organic matter content from 0.94% to 4.2%. Variations in adsorption between soils were not correlated with clay content or soil pH in the pH range 5.6 to 7.4, but increased adsorption resulted with decreasing solution pH of any individual soil. Sorption was described by the Freundlich isotherm at equilibrium concentrations less than 20 µg/ml. Temperature had only a slight effect on adsorption by the three soils examined. Increasing temperature from 10 to 20 to 30C generally resulted in decreased adsorption. Increasing the soil/solution ratio from 1:5 to 1:2 increased the Freundlich k value for the five soils tested. Freundlich k values were higher for the desorption isotherms than for the adsorption isotherms for all six soils. Increased adsorption with increasing ionic strength was predictable from associated pH changes and the dissociation constant for picloram.
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