Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


The extensive occurrence of soils with high levels of exchangeable Na and especially those with acid sola in humid subtropical regions has not been widely recognized. This study was initiated to (1) study the physical, chemical and mineralogical characteristics, and relationships with associated soils toposequences with low, intermediate and high levels of exchangeable Na, and (2) to evaluate the effectiveness of different strength CaSO(,4)(.)2H(,2)O solutions to displace Na from the exchange complex by a sequential leaching process. A total of six soils were included in the study. Total soil analysis indicated that Bonn, Groom, and Mollicy soils have total Ca, Na, and K contents that decrease in the order named. The total Ca, Na, and K contents in the other three soils studied decreased in the order Deerford, Gilbert, and Gigger. The soil parent materials significantly influenced the pattern of distribution and quantity of cations released. Soils that contain high level of exchangeable Na have high Na concentration in their saturated paste extracts and equilibrated soil suspensions. Correlation analysis on Na in the saturated soil paste extract(SSPE) and in the equilibrium soil suspension(ESS) indicate a strong relationship (r > .94) in soils with intermediate and high levels of exchangeable Na. The Na to Ca ratios in the SSPE from Bonn, Groom and Mollicy were narrower than those measured in the ESS. The opposite was true for the Deerford, Gilbert and Gigger soils. With a finite volume of liquid, many of the cations displaced, especially Na, from the upper soil sola were redistributed into the lower few horizons. The quantity of cation and depth where readsorption began to occur were directly related to the CaSO(,4)(.)2H(,2)O composition and volume of the liquid that passed through that particular horizon. The electrical conductivity(EC) and activity of Na in leachates had showed a positive linear relationship to Ca activity in the leaching solutions in each horizon and soil. The amount of Na displaced increased linearly with strength of Ca in the leaching solutions introduced.