MISCIBLE DISPLACEMENT OF REACTIVE SOLUTES IN SALINE-SODIC SOILS UNDER VARYING FLOW CONDITIONS

Abstract

A laboratory study was made on miscible displacement of reactive solutes during leaching a highly saline-sodic soil rich in soluble Na2CO3 with solutions of calcium chloride. The effect of varying flow velocities, initial soil moisture content and concentration of Ca in the leaching water on the extent of carbonate precipitation and replacement of Na by Ca from the exchange positions was studied in soil columns. Precipitation of soluble carbonates in the soil increased with increasing flow velocity, initial soil moisture content and concentration of Ca in the leaching solution. The Ca exchange capacity of the soil was reduced significantly and nearly proportionally with decrease in the degree of water saturation as a consequence of decreased water application rate and initial soil moisture content. A simple model to describe Ca-Na exchange under unsaturated flow conditions in saline-sodic soils under consideration is proposed. Possible implications of the results in actual field situations is discussed.