Effects of salinity on solute and ion transport in quasi-structural unstable sodic soil in a semi-arid environment in botswana: Simulations using mixed ions of sodium(Na+) and calcium(Ca2+)

Otlogetswe Totolo, Oagile Dikinya

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Sodium (Na) and calcium (Ca) ions are the most common ions on the exchange complex in arid and semi-arid soils. The paper examines the effects of the composition of mixed Ca and Na ions in solution on the Na-Ca exchange behaviour and solute transport of an agricultural sodic soil. Permeability index (K/Ko) was used a measure of solute transport. Generally K/Ko was found to decrease with increasing sodium adsorption ratio (SAR) and decreasing electrolyte concentration attributed to mechanisms of swelling and dispersion. In the exchange behviour a strong preference for Ca2+ ions than Na+ ions in the exchange complex was observed. Combined with breakthrough curves obtained for the various solutions these measurements provide insights into the progressive passage of the exchange front and associated structural changes through the soil columns. Measured pHs of the solution were found to remain essentially constant during leaching while the electrical conductivity decreased with decreasing electrolyte concentration. Further elucidation of SAR effects of K/Ko were evaluated at the critical threshold concentration and turbidity concentration at SAR 15. However the results revealed structural breakdown of the pore matrix system as evidenced by decreased permeability during leaching with decreasing solution concentration at SAR 15. The reductions in K/Ko were likely to be caused by partial blocking of pores by dispersed clay particles, as evidenced by the appearance of suspended clay particles in the effluent during leaching.

Original languageEnglish
Pages (from-to)215-226
Number of pages12
JournalInternational Journal of Applied Environmental Sciences
Issue number2
Publication statusPublished - 2010


All Science Journal Classification (ASJC) codes

  • Environmental Science(all)

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