EFFECT OF SODICITY, pH, ORGANIC MATTER, AND-CALCIUM CARBONATE ON THE DISPERSION BEHAVIOR OF SOILS
1984
Gupta, R. K. | BHUMBLA, D. K. | Abrol, I. P.
Excess exchangeable sodium is known to adversely affect soilʼs physical properties. Sodium adsorption ratio (SAR), which takes into account only the cations, ignoring the alkali-causing anionic species, has been widely used as an index of sodicity and related physical phenomena of clay dispersion, etc. In the presence of CaCO3, excess exchangeable sodium results in high pH of sodic soils. The effect of high pH accompanying high soil sodicity on the physical behavior of soil has generally been overlooked. The objective of the present study was to evaluate the relative role of sodicity and pH on the dispersion behavior of a representative soil in relation to CaCO3 and organic matter. For this study homoionic sodium-saturated soils were used to study dispersion in salt-concentration solutions of various alkalinity (pH 6.0 to 10.8) and SAR (5 to 100). The study revealed that increasing alkalinity (pH) or SAR increased the clay dispersion. Calcium carbonate and high electrolyte concentration were found to be very effective against dispersion. An alkalinity buildup in the presence of humic substances sharply enhanced the clay dispersion. Additions of organic matter at SAR more than 15 to 20 also increased dispersion. We discuss the results for their practical implications under the natural conditions of alkali soils having both high sodicity and high pH.
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