Original Articles

Effect of exchangeable sodium and phosphogypsum on the hydraulic properties of several South African soils


The susceptibility of soils to the deleterious effects of sodicity was assessed for samples which varied with respect to physical, mineralogical and other properties. For this purpose soil samples were collected from different locations in South Africa. The effect of electrolyte concentration and sodium adsorption ratio (SAR) on hydraulic conductivity (HC) was determined with permeameters, while the combined effects of raindrop impact energy and low electrolyte concentration of rain on infiltration rate (IR) were assessed using a rainfall simulator. Soils proved to be either stable or susceptible to the effects of sodicity as indicated by modulus of rupture, air-water permeability ratio, HC and IR measurements. Sesquioxides and organic matter promoted stability. Final IR was always less than HC due to crust formation even at low exchangeable sodium percentage (ESP) levels as a result of the dispersive effects of both mechanical impact (physical disruption) of rain drops and low electrolyte concentration (chemical dispersion). When the chemical effect was reduced (ESP>1 or higher electrolyte concentration as a result of surface gypsum application), final IR was higher.

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