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• restricted the upward movement of water. These findings are consistent with <br /> the resuRs reported for the Northern Great Plains by Merrill et. al. 1983 a and <br /> b). <br /> In another study on processed oil shale, Redente and Ruzzo (1979) <br /> reported that after two growing seasons the topsoil treatments yielding the <br /> highest biomass were between 61 and 92 cm of respread topsoil. Third year <br /> results (Redente and Mount 1982) revealed that percent plant cover was <br /> highest on the 90 and 60 cxrt gravel barrier treatments. Total plant biomass <br /> was consistently highest on the 90 cm topsoil Veatment. Fourth growing <br /> season response data reported by Biondini and Redente (1986), established <br /> that the regulatory goals of high diversity and production were mutually <br /> exGusive, and that both could not be simultaneously obtained. Highest <br /> production but lowest diversity was obtained on the thicker layers of respread <br /> topsoil. They recommended that in order to increase the diversity of the <br /> reclaimed community, thinner layers of topsoil would need to be reapplied. <br /> F'rfth year plant response data from this study presented by Biondini and <br /> Redente (1985) showed that the thickness of respread topsoil over retorted <br /> shale had a signficant effect on plats species composition, with fortis <br /> reaching greatest growth on the shallowest soils and grasses greatest growth <br /> on the thicker soils. Eighth year results from this study (Redente et. al. 1985) <br /> documented that overall production between the three thicknesses of <br /> respread topsoil was not different, however, forb growth was signfcantly <br />• higher on the 30 cm Veatment. Shrub biomass was significantly higher on <br />the 60 cm Veatment compared to the 30 and 90 cm treatments. They <br /> concluded that the benefits of deeper soil was becoming less apparent over <br /> time, a finding that was previously discussed. <br /> The results of sodium movement in respread topsoil over retorted sodic <br /> oil shale were reported by Redente and Cook (1984). For plots established <br /> in 1977, the non topsoiled shale treatment was reported to have a maximum <br /> SAR of approximately 7, the 30 crr- topsoil treatment a maximum SAR of <br /> approximately 12, the 60 cm topsoil treatment a maximum SAR of <br /> approximately 8, and the 90 cm topsoil treatment a maximum SAR of <br /> approximately 13. These data appear to be consistent with the upward <br /> migration of sodium reported by Barth and Martin (1982) and follow the <br /> trends suggested by Merrill et. al. (1980) wherein they calculated that the <br /> upward extent of sodium migration would increase as the thickness of <br /> respread topsoil was increased. <br /> The interaction of various soil properties and species diversity on <br /> disturbed native soils in the Piceance Basin of Colorado were evaluated by <br /> Stark and Redente (1985). They reported highly significant and positive <br /> correlations between species diversity and all measures of sodium and salt <br /> content. Increased diversity was attributed to increases in environmental <br /> heterogeneity caused by high SAR values (average 23.8). They also reported <br /> that there were signficant and negative correlations between seeded species <br /> richness and the depth to bedrock. They recommended that reducing inputs <br /> of fertilizers and topsoil thickness were viable options towards achieving the <br />• regulatory goals of adequate production and diversity. <br />13 <br />