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Critical Coagulation Concentration of Paddy Soil Clays in Sodium–Ferrous Iron Electrolyte
Author(s) -
Saejiew Atinut,
Grunberger Olivier,
Arunin Somsri,
Favre Fabienne,
Tessier Daniel,
Boivin Pascal
Publication year - 2004
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2004.7890
Subject(s) - kaolinite , chemistry , electrolyte , flocculation , dispersion (optics) , dissolution , sodium adsorption ratio , sodium , soil water , clay minerals , cation exchange capacity , environmental chemistry , inorganic chemistry , mineralogy , geology , soil science , irrigation , agronomy , physics , organic chemistry , electrode , drip irrigation , optics , biology
Sodium affected rice ( Oryza sativa L.)‐cropped fields are very common. Due to their high exchangeable Na percentage, clay dispersion is one of the major risks for these soils when they are flooded. During flooding, Fe 2+ may become a major cation due to reductive dissolution of Fe oxides, but the flocculation effect of Fe 2+ is not known. In this paper, the effect of Fe 2+ on clay flocculation is studied by establishing critical coagulation concentration (CCC) curves of clays extracted from a paddy soil of Northeast Thailand. The effect of Na‐Fe 2+ and Na‐Ca electrolytes on the CCC values is compared for sodium adsorption ratio (SAR) values ranging from 0 to 40 and total electrolyte concentration (TEC) ranging from 0.5 to 10 mmol L −1 The extracted clay is a mixture of kaolinite and smectite but only the smectite and some poorly ordered kaolinite could be dispersed. The CCC values largely reflected the behavior of smectite, in agreement with previous studies. The CCC values were equal for electrolytes with Fe 2+ or Ca 2+ cations, suggesting that Fe 2+ strongly adsorbs on smectite exchange sites and behaves similarly to Ca 2+ The Fe 2+ concentration needed to flocculate the clays was at maximum 0.6 mmol L −1 for the most dispersive electrolytes, which is a common concentration in flooded rice fields. Reductive dissolution of Fe can protect sodic soils from clay dispersion upon flooded rice cropping.