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DIFFUSE DOUBLE LAYER THEORY APPLIED TO Na‐Ca EXCHANGE EQUILIBRIA IN TEMPERATE AND SEMI‐ARID TROPICAL SOILS
Author(s) -
POONIA S. R.,
PAL RAJ,
TALIBUDEEN O.
Publication year - 1979
Publication title -
journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 0022-4588
DOI - 10.1111/j.1365-2389.1979.tb01018.x
Subject(s) - soil water , chemistry , temperate climate , analytical chemistry (journal) , arid , cation exchange capacity , surface charge , mineralogy , soil science , environmental chemistry , geology , botany , paleontology , biology
Summary A cation exchange equation based on diffuse double layer (DDL) theory was tested on 26 surface and sub‐surface soils from 6 field experiments in temperate and semi‐arid tropical regions. Sodification (the fraction of total charge on the surface neutralised by the excess of Na + plus the deficit of Cl − ), or the exchangeable Na percentage, ESP, of these soils in relation to SAR, the molar ratio (Na]/[Ca + Mg] 1/2 , was evaluated from the observed data on Na:Ca exchange in two ways, using the DDL equation: (1) by multiplying the surface charge density of the soil with a mean correction factor f (based on the whole isotherm) assuming no interaction between adjacent clay platelets; this predicted the sodification of the soils satisfactorily between 0–30 ESP, though at the highest SAR values ( i.e. > 60), predicted ESP values were significantly smaller than the experimental values for 23 of the 26 soils; (2) by assigning values to the extent of interaction Y d (directly related to the electric potential Ψ d midway between adjacent clay platelets) over the whole isotherm; Y d was found to increase by varying degrees in different soils with SAR and ESP. Also in 12 of the 15 pairs of soils compared, the mean value, d , over the whole Ca‐Na exchange isotherm was appreciably larger for surface soils (which had higher surface charge densities) than for the subsoils from the same sites. The suggestion that the Y d parameter provides a better criterion than the f parameter for characterising and comparing Na:Ca exchange equilibria in contrasting soils is discussed in relation to the effects of soil components.