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Soil Science Society of America Journal Abstract - SOIL PHYSICS

Kinetics of Glyphosate Desorption from Mobilized Soil Particles


This article in SSSAJ

  1. Vol. 75 No. 2, p. 434-443
    Received: May 12, 2010

    * Corresponding author(s): cpe@life.ku.dk
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  1. B. Gjettermanna,
  2. C. T. Petersen *a,
  3. S. Hansena,
  4. C. Bender Kocha and
  5. M. Styczena
  1.  aFaculty of Life Sciences, Dep. of Basic Sciences and Environment, Univ. of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg, Denmark


Desorption kinetics of chemical compounds can be important both for their mobility in soil and for the significance of particle-facilitated transport. We studied desorption of glyphosate [N-(phosphonomethyl)glycine] on mobilized particles from two soil columns (50-cm height, 30-cm diameter), i.e., particles leached by free drainage from the bottom and particles mobilized by splash erosion and collected next to the top of the column. Leaching and splash erosion were driven by three, 30-mm irrigation events following surface application of 14C-labeled glyphosate. Fresh leachate samples were investigated within 30 min of sampling, and desorption from splash-eroded particles in suspension (100 mg solid L−1) was followed for 48 h (starting 2.0 min after immersion). Glyphosate concentrations were determined by measuring the 14C activity using liquid scintillation counting. Similar fractional amounts of glyphosate (on average, 10–20% in 20 min) desorbed from leached and from splash-eroded particles (>20 nm) shortly after leaching or immersion, respectively, indicating that the processes of desorption from the different sources of particles were similar. In leachate, about 45 to 79% remained particle bound after 20 min, while calculated values at equilibrium were 20% or less. Equilibrium was established after about 5 to 10 h in suspensions with splash-eroded particles, except for one sample. These direct observations, supported by estimated values of the Damköhler number, lead to the conclusion that desorption kinetics are important for evaluating the significance of dissolved and particle-facilitated transport of glyphosate. To quantify particle-facilitated glyphosate transport, the water and solid phases in the leachate should consequently be separated within a few minutes after leaching.

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