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This article in JEQ

  1. Vol. 29 No. 2, p. 484-493
     
    Received: Feb 22, 1999
    Published: Mar, 2000


    * Corresponding author(s): qafoku@arches.uga.edu
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doi:10.2134/jeq2000.00472425002900020017x

Anion Transport in Columns of Variable Charge Subsoils: Nitrate and Chloride

  1. Nikolla P. Qafoku *,
  2. Malcolm E. Sumner and
  3. David E. Radcliffe
  1. Dep. of Crop and Soil Sciences, The Univ. of Georgia, Athens GA 30602-7272.

Abstract

Abstract

Acid variable charge subsoils exhibit a positive charge, which retards the passage of anions through the soil profile. The objective was to study the NO3 adsorption isotherms and the effect of changing the subsoil positive charge on NO3 and Cl retention, estimate NO3 and Cl retardation in different subsoils, and quantify relationships between transport and adsorption parameters. Subsoils from different subtropical and tropical areas were used in column experiments. Four lime treatments and four leaching solutions were used to create different anion exchange capacities (AECs) in subsoils. In the Cecil subsoil (Fine, kaolinitic, thermic Typic Kanhapludult), NO3 isotherms were linear between 5 and 30 mmol NO3 L−1. When forced through the origin, an L-curve NO3 isotherm was observed at native and low soil pH. The NO3 adsorption was largely affected by the changes in both pH and concentration of the leaching solution. Other variable charge subsoils have varying capacities to retard anions, which is reduced when either soil pH or leaching solution concentration is increased. Both parameters equally reduce the distribution coefficient Kd and the retardation coefficient R. The AEC correlates closely with R and Kd. As a result, AEC can be successfully used in the solute transport models to estimate Kd or R without measuring it to correct for the NO3 retardation.

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