Relationships between electrical conductivity (EC) and sodium adsorption ratio (SAR) in reconstructed soils at surface coal mining operations are poorly documented in the literature. Research has focused primarily on agricultural and range soils. Chemical and physical properties of reconstructed soils are unique and quite different from natural soils formed over hundreds of years through pedogenic processes. These differences largely occur because relatively unweathered overburden is exposed during mining processes and subsequently used as a lower root-zone medium (minesoil) during soil reconstruction. Some of these materials are classified as sodic and therefore are considered unsuitable rooting media for establishment of native vegetation. Weatherable minerals (i.e., pyrite, calcite, gypsum, and other geologic substrates) present in minesoils can effectively remediate or mitigate an elevated SAR condition by maintaining EC levels in the soil solution to promote clay particle stability and by providing sources of exchangeable calcium and magnesium. Coversoil (e.g., topsoil) enhances remediation through physical and chemical buffering between sodic root-zone material and the reconstructed soil surface. A laboratory core-study was used to evaluate weathering potential of 10 minesoil materials from three mining operations in the Southwestern United States. Cores were prepared with 15 cm of coversoil over 30 cm of minesoil and subjected to simulated precipitation. Chemical evaluations of weathered materials show significant reductions in EC and SAR and overall improvement of minesoil quality. Chemistry of drainage water from three coversoils shows these materials behave as a chemical buffer above the underlying sodic materials. Coversoils provide a source of calcium and other electrolytes that promote physical stability and enhance remediation of sodic minesoil materials.

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Evolving relationships between electrical conductivity (EC) and sodium adsorption ratio (SAR) in reconstructed soils at surface mines have been insufficiently documented in the literature. Some minesoils (i.e., rootzone material) are classified as saline, sodic, or saline-sodic and are considered unsuitable for revegetation. Weatherable minerals such as calcite and gypsum are common in alkaline minesoils and on dissolution tend to mitigate elevated SAR levels by maintaining or increasing electrolytes in the soil and providing sources of exchangeable calcium and magnesium. Topsoils (i.e., coversoils) contribute to mitigation of sodic conditions when soluble cations are translocated from coversoils into the underlying minesoils. This study evaluated the weathering characteristics of minesoils sites from three surface coal mines in northwestern New Mexico and northeastern Arizona. Minesoils were grouped into 11 classes based on EC and SAR. After 6 to 14 yr, differences between upper and lower halves of the coversoils suggest general increases occurred with EC, SAR, chloride (Cl(-)), and sulfate (SO(4)(2-)) with depth. Within the reclaimed minesoils, there were several significant (P < 0.05 or < 0.10) relationships among EC and SAR that related to Minesoil Class. Lower SAR levels with corresponding increases in EC compared to baseline minesoils were more apparent in upper minesoil depths (0-5 and 5-15 cm). Minesoil anion concentrations suggested coversoil leachates and gypsum dissolution influenced EC and SAR chemistry. Over time, chemical changes have increased the apparent stability of the saline and sodic reclaimed minesoils studied thereby reducing risks associated with potential aggregate slaking and clay particle dispersion.

Abstract. Relationships between electrical conductivity (EC) and sodium adsorption ratio (SAR) changes over time in reconstructed soils at surface coal mining operations are insufficiently documented in the literature. Some minesoils (i.e., rootzone material) are classified as saline, sodic, or saline-sodic and have been considered unsuitable rooting media for establishment of native vegetation. Weatherable minerals (e.g., pyrite, calcite, gypsum, and other geologic substrates) commonly present in minesoils can mitigate the effects of elevated SAR levels by maintaining or increasing electrolytes in the soil and provide sources of exchangeable calcium and magnesium. Coversoil (i.e., topsoil) enhances this mitigation through physical and chemical buffering of minesoils. Weathering characteristics of minesoils and rooting patterns of key reclamation species were evaluated at sites from three surface coal mines in northwestern New Mexico and northeastern Arizona.Unweathered minesoils were grouped into 11 classifications based on EC and SAR. Comparison of saturated paste extracts from unweathered and weathered (6 to 14 years after reclamation) minesoils show significant (p < 0.05) reductions in SAR levels and increased EC. Weathering increased the apparent stability of saline and sodic minesoils thereby reducing risks of aggregate slaking and clay particle dispersion. Root density of fourwing saltbush (Atriplex canescens), alkali sacaton (Sporobolus airoides), and Russian wildrye (Psathyrostachys junceus) were generally unaffected by increasing minesoil EC and SAR levels. Saline and sodic minesoils can be successfully reclaimed when covered with topsoil and seeded with salt tolerant plant species.

Weathering characteristics of minesoils and rooting patterns of key shrub and grass species were evaluated at sites reclaimed for 6 to 14 years from three surface coal mine operations in northwestern New Mexico and northeastern Arizona. Non-weathered minesoils were grouped into 11 classifications based on electrical conductivity (EC) and sodium adsorption ratio (SAR). Comparisons of saturated paste extracts, from non-weathered and weathered minesoils show significant (p < 0.05) reductions in SAR levels and increased EC. Weathering increased the apparent stability of saline and sodic minesoils thereby reducing concerns of aggregate slaking and clay particle dispersion. Root density of fourwing saltbush (Atriplex canascens), alkali sacaton (Sporobolus airoides), and Russian wildrye (Psathyrostachys junceus) were nominally affected by increasing EC and SAR levels in minesoil.