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Anion Transport in Columns of Variable Charge Subsoils: Nitrate and Chloride
Author(s) -
Qafoku Nikolla P.,
Sumner Malcolm E.,
Radcliffe David E.
Publication year - 2000
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2000.00472425002900020017x
Subject(s) - subsoil , nitrate , leaching (pedology) , chemistry , adsorption , chloride , cation exchange capacity , lime , ion exchange , environmental chemistry , soil science , ion , soil water , environmental science , geology , paleontology , organic chemistry
Acid variable charge subsoils exhibit a positive charge, which retards the passage of anions through the soil profile. The objective was to study the NO − 3 adsorption isotherms and the effect of changing the subsoil positive charge on NO − 3 and Cl − retention, estimate NO − 3 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), NO − 3 isotherms were linear between 5 and 30 mmol NO − 3 L −1 . When forced through the origin, an L‐curve NO − 3 isotherm was observed at native and low soil pH. The NO − 3 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 K d and the retardation coefficient R . The AEC correlates closely with R and K d . As a result, AEC can be successfully used in the solute transport models to estimate K d or R without measuring it to correct for the NO − 3 retardation.