SODIUM MOVEMENT IN SOIL-MINESPOIL PROFILES: DIFFUSION AND CONVECTION

Abstract

We studied the movement of sodium and other ions in sodic strip-mine spoils reclaimed by soil spreading. In columns containing two different soils placed over minespoil, both model calculations and measurements indicated that considerably more Na migrated upward by salt diffusion than by convective flow generated by soil-water evaporation. More Na movement occurred in columns without evaporation than in columns with evaporation: reduced water contents reduced diffusion, and very low minespoil hydraulic conductivity severely restricted convective flow. Application of column results and model calculations to field observations of salt movements in topsoil-covered minespoils under semiarid, continental climatic conditions indicated that salt diffusion is a significant mechanism for Na accumulation in soil, provided the spoil is highly dispersed and the necessary chemical gradient is present. However, these calculations and data both indicate that significant quantities of Na would diffuse only 10 to 15 cm upward in materials of this nature.