Physical reconstruction of mine tailings after surface mining mineral sands from prime agricultural land

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Minable quantities of heavy minerals occur in prime agricultural lands of the Atlantic Coastal Plain. We evaluated the use of yard waste compost to reclaim tailings mined from these lands. A 30 × 60-m area was excavated to a depth of 5 m to establish a reclamation study site. Soils were removed, treated in a manner simulating the separation of the mineral sands, and returned in a slurry form. Undisturbed natural soils, Hapludults and Paleudults, have sand and loamy sand surface horizons. Mining these soils and redistributing the tailings as a slurry resulted in sandy loam and sandy clay loam textures. Treatments established in the tailings were: unamended tailings; tailings amended with 23 to 270 t/ha compost; and tailings capped with 45 cm of topsoil. Selected treatments were sampled and analyzed to test for differences in the physical properties related to treatment. Gravimetric water contents of tailings amended with 135 t/ha compost were significantly higher (at the 0.05 level) than unamended tailings, tailings capped with top soil, or the natural soil. Mechanical resistance values recorded in the Fall for tailings amended with 135 t/ha of compost were lower than the unamended tailings and tailings capped with topsoil. Mean hydraulic conductivity (Ksat) and porosity values for tailings amended with 135 t/ha compost were higher than the natural soil surface horizons. Tailings amended with as little as 45 t/ha compost had higher porosity (48%) and lower bulk density (1.38 g/cm3) values than the natural soil surface (45% and 1.43 g/cm3). Tailings capped with topsoil had the highest bulk density (1.64 g/cm3) and lowest porosity (38%) and Ksat (0.13 cm/hr), suggesting that this reclamation approach may not be the best way to try to reclaim the tailings. Average corn yields for tailings amended with compost were higher than those for tailings capped with topsoil or unamended tailings. Results suggest that mine soils can be constructed with excellent physical properties with regard to plant growth by amending tailings with yardwaste compost.

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Soil Science