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Cation-exchange properties of soil organic matter

1975; Taylor & Francis; Volume: 21; Issue: 4 Linguagem: Inglês

10.1080/00380768.1975.10432651

1747-0765

Yasuo Harada, Akio Inoko,

Clay minerals and soil interactions

Abstract The CEC was determined for humic acid preparations by changing the conditions for the CEC procedure and the CEC values obtained were compared with those of clay minerals. Humic acid was extracted from Kodonbaru and Kuriyagawa surface soils, Iwanuma peat, and straw with 0.1 M Na4P2O7-0.l M NaOH. The CEC was measured by a method which eliminates washing for the removal of excess saturating salt. The CEC of humic acid became larger as humification progressed, and increased in the order: Straw<Iwanuma<Kuriyagawa<Kodonbaru. An equilibrium of cation exchange for the humic acid preparations was attained in a short time in contrast with that for allophane. No effect of salt concentration on the CEC of the humic acid preparations was recognized. The CEC of humic acid was also determine using the procedure in which tbe excess salt was removed by washing with water. Practically no decrease of CEC with decreasing salt concentration was found. When the pH of the salt solution WBB reduced, the em: of the humic acid decreased, though the extent of the decrease was smaller than that of allophane. The CEC of halloysite and montmorillonite did not decrease through reduction of the pH of the salt solution. It was considered that humic acid is a stronger acid than allophane and a weaker acid than halloysite and montmorillonite. The difference between the CEC of humic add measured with Ca2+ and Ba2+ was small. Little temperature effect was observed for humic acid.