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( Bouteloua gracilis) and sideoats grama (Bouteloua curtipendula). Spring wheat plots were re- <br />seeded with smooth brome after completion of this study as well. Results for all topsoil depths <br />examined during this study showed that alfalfa yields were highest on 20 cm of topsoil and 71 <br />cm subsoil (where total soil depth was equal to 92 cm). Crested wheatgrass yields were highest <br />on 71 to 92 cm of subsoil only. The native grass mixture yields showed no difference between <br />the 20 cm and 60 cm topsoil plots, but had the highest yields on 51 to 71 cm subsoil. Spring <br />wheat yields showed no difference between 20 and 60 cm of topsoil, but had highest yields on 71 <br />to 92 cm of subsoil. Yields of all vegetation types were generally higher on 20 cm topsoil plots <br />with total soil depths of 92 to 132 cm than on mixed, 0 and 60 cm topsoil depth plots. <br />1235 <br />Figure 1. Schematic diagram of Zap, ND Double Soil Wedge (Doll et al., 1984). There were <br />four subplots for each subsoil type in the diagram. Each subplot was approximately 4 <br />m wide. Single species of vegetation were seeded in each subplot. <br />After completion of the ZSW and SSW studies in 1981, Doll et al. (1984) suggested that <br />long -term studies of soil wedges are necessary for understanding plant community development <br />through time over various soil depths on reclaimed mine lands. Objectives of this study were; <br />(1) to examine long -term changes in plant communities in relation to variable soil depths and soil <br />characteristics for the ZSW and SSW and (2) to examine plant community, variable soil depth <br />and soil property relationships on the ZSW and SSW in 2003. <br />Hypotheses for this study were; (1) production and diversity are significantly influenced <br />through time by total soil depth (topsoil and subsoil) and soil characteristics (EC and pH), (2) <br />production and diversity are significantly influenced through time by slope position (toe -, mid - <br />and shoulder -slope positions) on the soil wedge and (3) production and diversity are significantly <br />influenced by different subsoil types on the ZSW. <br />