Topsoil and Subsoil Thickness Requirements for Reclamation of Nonsodic Mined‐land

Abstract Eight trenches were excavated to a depth of 4.6 m and filled with one of three different textures of spoil to evaluate topsoil and subsoil thickness requirements for crop production on nonsaline, nonsodic spoil material. Yields of wheat ( Triticum aestivum L.) in 1979 and 1982, barley ( Hordeum vulgare L.) in 1980, and corn ( Zea mays L.) in 1981 and 1983 were compared on plots with 0.23, 0.46, or 0.69 m of topsoil replaced over loamy sand spoil with and without subsoil, over clay loam spoil, or over silty clay loam spoil. Crop yields increased with increasing thickness of replaced topsoil, especially on trenches filled with loamy sand spoil. Crop yields were greater when subsoil was replaced than when no subsoil was replaced on loamy sand spoil at a given topsoil thickness. Average yields from the trenches were equal to or better than average yields from undisturbed plots in 1979 and 1983. On irrigated plots in 1983, response of silage and corn grain to subsoil/spoil treatments was similar to the nonirrigated plots. Wheat grown on irrigated plots in 1982 did not respond significantly to topsoil thickness or subsoil/spoil treatments. At least 0.69 m of topsoil plus subsoil was required to achieve highest yields on nonsodic, nonsaline, loamy sand spoil, but 0.46 to 0.69 m of topsoil was sufficient for highest yields on clay loam and silty clay loam nonsaline, nonsodic spoil. Crop yields were not increased by broadcast applications of N and P fertilizer.