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Effect of Sodium Ion on Synthetic Water-stable Aggregates¹

ABSTRACT

Particles of diameter <0.15µ were separated from Hesperia sandy loam (micaceous soil) and electrodialyzed. Proper quantities of 0.1 N NaOH were added to the electrodialzed suspensions so that the symmetry-concentrations, S, of Na⁺ were 0.0625, 0.125, 0.25, 0.50, 1.0, and 2.0. Each suspension was dried to induce aggregation. The dry synthetic aggregates were then analyzed for their water-stability by shaking them in water for 2-, 20-, 200-, and 2,000-minutes. After each shaking period a size distribution of aggregates was obtained.

The cumulative weight percentage curves for aggregates with Na⁺ showed two distinct types of size distribution. Those for aggregates formed with electrodialyzed particles and with Na⁺ of 0.25-S and less showed a sigmoid type of size distribution, while those for aggregates formed with Na⁺ of 0.50-, 1.0-, and 2.0-S showed a bimodal type. The aggregates formed with electrodialyzed particles were more stable in water than any of the aggregates with Na⁺. The order of water-stability of aggregates for each of the four shaking periods, as shown by the geometric mean diameters, was: electrodialyzed particles > 0.0625-S Na⁺ > 0.125-S Na⁺ > 0.25-S Na⁺ > 0.50-S Na⁺ > 1.0-S Na⁺ > 2.0-S Na⁺.

The effect of Na⁺ on the values of geometric mean diameter of water-stable aggregates was not a linear function, but rather some power function.

¹ Experimental work was done in the laboratories of the Division of Soils at the Calfiornia Agricultural Experiment Station, Berkeley 4, Calif. Presented before Section I, Soil Science Society of America, State College, Pa., August 28, 1951.

² Associate Professor of Agronomy, University of Nebraska, Lincoln 1, Nebr.