Na+-(Ca2+ + Mg2+) EXCHANGE EQUILIBRIA UNDER SUBMERGED SOIL CONDITIONS
1977
PASRICHA, N. S. | Ponnamperuma, F. N.
The sodium quantity/intensity (Q/I) relationship, which relates the changes in exchangeable Na content (Q) to the changes in activity ratio [I = Na (Ca + Mg)] were measured in the equilibrium soil solutions from alkali treatments at various periods of submergence. Alkalinity markedly increased the Na-intensity values. The Q/I curves for different alkali treatments were superimposable on each other and on the curve relating change in percent sodium saturation and sodium activity ratio for the untreated soil. The intercept of the Q/I curve with the Q-axis at activity ratio AR = 0 has been taken as a measure of the amount of labile Na. Comparison of the intercept values of exchangeable sodium saturation with that observed at zero-time submergence showed that with submergence an additional 22 percent of sodium comes in the labile form. The exchange isotherms for the submerged Maahas clay showed smaller buffering capacity, ΔQ/ΔI, for Na than for K despite less percent exchangeable Na than K, showing thereby that Na is held on the soil complex much less strongly than is K. Submergence decreased the intensity of K from 20.21 x 10 to 3.51 x 10 M after 10 weeks of submergence, but the intensity of Na during the same period increased from 101 x 10 to 184 x 10 M.
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