The comparative effects of exchangeable calcium, magnesium, and sodium on some physical properties of red-brown earth subsoils. III. The permeability of Shepparton soil and comparison of methods

Abstract

Beds of aggregates of Shepparton soil were leached with calcium chloride or magnesium chloride or with chloride solutions of given SAR with either calcium or magnesium as the complementary cation to bring the aggregates to a known ESP within the range 2.6-5.2. The last solution was 1 mM in the divalent cation. Water was then allowed to flow slowly through and the decrease in the flow rate measured. The permeability of aggregate beds washed with calcium or magnesium showed only a negligible decrease with time. With sodium present, the rate of decrease for a given ESP was faster the greater the initial flow rate of the water and also for smallersized aggregates. The ESP required to produce a given decrease in flow rate was reduced when magnesium was the complementary cation rather than calcium. The flow patterns are explained in terms of the rate of dispersion of clay from the aggregates in sympathy with the rate of loss of soluble salts, rather than detachment due to viscous drag. Four methods of measuring aggregate stability in water have been described in this series of papers. Their possible use to predict whether sodium in conjunction with magnesium will reduce water transmission through subsoils compared with similar calcium soils is discussed.