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Soil Depth <br />Several studies have evaluated the effects of varying depths of topsoil (growth <br />medium) on vegetation success. Barth (1980) established sixteen topsoil depth <br />studies in 1977 at 14 active coal mines in the Northern Great Plains using mixed <br />A and B horizon materials. Topsoil varied from 0 to 60 inches and the plots were <br />seeded with both native and introduced grasses. Biomass production generally <br />increased as topsoil thickness increased from 0 to 28 inches. However, between <br />28 and 60 inches, biomass production showed inconsistent and minimal response to <br />incremental increases in topsoil thickness. <br />Greenhouse studies conducted in Colorado by McGinnies and Nicholas (1980) demon- <br />strated that the root system of most species tested was confined to the topsoil. <br />They found however, that there was significant variation between species. Aver- <br />age above ground biomass production for native and introduced species were simi- <br />lar, but the introduced species had greater average root production, especially <br />in spoil material. They further concluded that plant stand and above ground bio- <br />mass production of intermediate wheatgrass and wheat increased with increasing <br />topsoil thickness up to a depth of 18 inches. <br />Another topsoil depth study in Montana by McCormack (1974) indicated that 17 to <br />28 inches of topsoil was optimum for good plant growth. <br />A number of researchers have shown that both plant productivity and soil moisture <br />storage are affected by retopsoiling. Shuman et al (1978) completed a study in <br />Wyoming using 0 to 24 inches of good quality A and B horizon material, mixed and <br />spread over mine spoils. Using barley (Hordeum vulgare) to provide a stubble - <br />mulch and then seeding green needlegrass (Stipa viridula), western wheatgrass <br />(Agropyron smithii), slender wheatgrass (A. trachycalum) and thickspike wheat - <br />grass (A. dasystachyum) they found that barley production increased significantly <br />with the first 8 and 16 inches of topsoil. A lesser increase in production was <br />noted when soil depths were increased to 24 inches. Production of native grasses <br />increased with increased soil thickness, with maximum production at the 24 inch <br />soil thickness. Water infiltration into the soil also increased with increased <br />• 3-52 <br />