The effect of sodium and calcium on physical properties and micromorphology of two red‐brown earth soils

Abstract

SUMMARY The effect of treatment with either gypsum or sodium chloride on the saturated hydraulic conductivity ( K s ) of repacked soil columns and modulus of rupture (MOR) was studied on surface samples of two red‐brown earth soils from SE wheat belt in Australia. When the exchangeable sodium percentage (ESP) of the two soils was increased to >80, K S was substantially reduced and MOR increased relative to the untreated soil; the values of the parameters were nearly equal for these pairs of high ESP soils. However, after treatment with gypsum the Raywood soil had a K s twice, and a MOR less than half, the corresponding values for the Glenloth soil. Micromorphological and scanning electron microscope (SEM) observations suggest that the increase in K s following gypsum treatment is associated with an increase in visible macropores and reduced clay dispersion; Na treatment increased dispersion at the soil surface, with the clay particles forming an impermeable surface seal and illuviation argillans.