Cation Exchange in Soils Through the Moisture Range, Saturation to the Wilting Percentage1
- D. A. Brown2
Data are reported to show the effect of soil moisture upon cation exchange in soils through the moisture range, saturation to wilting percentage, for seven soil series, including Lakeland, Ruston, Richland, Crowley, Sharkey, Houston, and Gila. Cation exchange resin membranes of known exchange capacity were saturated with the hydrogen ion and buried in 100-gram aliquots of each of the above soil series. These aliquots of soil were moistened to cover the range, saturation to the wilting percentage, in a systematic manner. The membranes were allowed to remain in the soil for 96 hours, then removed, and the amounts of Ca, Mg, Na, and K exchanged to them from the soil measured quantitatively.
The amounts of cations exchanged increased sharply as the soil moisture increased. The increase in cation exchange at saturation when based upon that exchanged at the moisture equivalent was 7 fold for Lakeland, 5 for Ruston, 2 for Richland, 3 for Crowley, but only a 0.2-fold increase for Sharkey, Houston, and Gila series. The percentage decrease in cation exchange at the wilting percentage, when based upon the exchange at the moisture equivalent was 50, 65, 85, and 72 for Lakeland, Ruston, Richland, and Crowley, respectively, but only 14, 19, and 25% for Sharkey, Houston, and Gila, respectively. The suite of exchanged cations were significantly altered with increases in moisture.
The percentage of Ca and Mg increased in the suite of cations, while that of K and Na decreased correspondingly as the soil moisture increased. The Ca:K ratio increased from 60 to 266 over the moisture range, wilting percentage to saturation, for the Houston series, 10 to 60 for the Richland series, but only 7 to 10 for the Lakeland series. The cation exchange-moisture relationships are explained on the basis of the relative abundance and continuity of the water films within the pore system of the soil that may effectively serve as a medium for the diffusion of cations through the soil.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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