Evaluation of Soil Resources for Sustained Vegetative Cover of Cut-Slopes Along I-70 near Straight Creek

Revegetation of high elevation decomposed granite cut-slopes often requires repeated applications of soil amendments to attain sustained vegetative cover. Plant transects from slopes west of the Eisenhower Tunnel from 2007 to 2012 showed that cover was generally stable during this period. Soil fertility tests indicated that nutrients are generally low but still comparable to disturbed-but-revegetated reference plots. Soil organic matter and slow-release forms of nitrogen (N) may be a potential limiting factor. The N release rates of several common Colorado Department of Transportation (CDOT) soil amendments were evaluated in a multi-year, field incubation experiment. Test results indicate a wide range of N release availability from nearly immediate to fairly slow release rates. Of the slow-release materials, about 74% of total N content was released the first growing season, another 7% in the following two years, while about 19% was still retained in a more stable organic matter form at the end of the experiment. The study suggests that after several applications of slow-release amendments, vegetative cover on these cut-slopes is stabilizing. Slopes that show signs of vegetation thinning should be re-amended promptly with modest amounts of slowly available N. Established stands or sites with more moderate growth conditions may be able to take up much of the available N from larger applications of these slow-release amendments. But on newly seeded sites in high elevation conditions with slow growth potential, the plants may not be large enough to capture N as it is released. An amendment with high carbon such as wood chips or shreds may immobilize excess N by incorporating it into microbial biomass as the mulch degrades. This mulch layer would also help retain organic duff to rebuild the soil. Combinations of existing organic amendments may provide slower, more long-lasting N release. Development of a soil test to specifically measure slowly releasing organic N would improve monitoring and management of erosive slopes.


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Media Info

  • Media Type: Digital/other
  • Edition: Final Report
  • Features: Appendices; Figures; Photos; References; Tables;
  • Pagination: 46p

Subject/Index Terms

Filing Info

  • Accession Number: 01491283
  • Record Type: Publication
  • Report/Paper Numbers: CDOT-2013-14
  • Contract Numbers: 30.02
  • Created Date: Jul 30 2013 4:07PM