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Enzyme Activities in Revegetated Surface Soil Overlying Spent Paraho Process Oil Shale¹

ABSTRACT

Techniques for covering Paraho retorted oil shale with surface soil to allow more efficient revegetation have been evaluated for 2 years in the Piceance Basin of Colorado. In this study, several key microbiological parameters related to soil development and biogeochemical cycling processes have been monitored to evaluate possible relationships between surface soil management and soil microbiological responses.

Surface soil of 30-, 61-, and 91-cm depths placed directly over Paraho processed oil shale showed appreciable reduction in nitrogenase (acetylene reduction), dehydrogenase, and phosphatase activities as compared with surface soil not in contact with processed shale. The decreased nitrogenase and dehydrogenase activities in these soils placed directly over the processed shale at the various depths were not significantly different (P 0.05). With a 30-cm coarse rock capillary barrier between 61 cm of soil and the processed shale, the soil had nitrogenase and phosphatase activities which were not significantly lower (P 0.05) than the control soil. Interactive effects of seeding mixtures and fertilization on nitrogen fixation potential were also suggested, with introduced species plot soils not showing decreased nitrogen fixation potentials that were observed with the native species plots. These field results suggest that a capillary barrier may allow better maintenance of microbial processes in soils placed over Paraho retorted shale during revegetation.

Key Words: nitrogen fixation • reclamation • capillary barriers • seeding • fertilization • dehydrogenase • phosphatase

¹ Research supported by the Department of Energy under contract no. EY-76-S-02-4018, with Colorado State Univ., Dep. of Range Sci.

² Research Assistant and Professor, Dep. of Microbiol.; Research Assistant, Dep. of Range Sci.; and Research Associate, Dep. of Microbiol.; respectively, Colorado State Univ., Fort Collins, CO 80523.

Received for publication June 6, 1980.